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Predation by juvenile salmonids on harpacticoid copepods in a shallow subtidal seagrass bed : effects… Webb, Donald G. 1989

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PREDATION B Y JUVENILE SALMONIDS O N HARPACTICOID COPEPODS IN A S H A L L O W SUBTIDAL SEAGRASS BED: EFFECTS O N COPEPOD C O M M U N I T Y J STRUCTURE A N D D Y N A M I C S By D O N A L D G. WEBB B.Sc. (Hons.), McGi l l University, 1983 A THESIS SUBMITTED IN P A R T I A L F U L F I L L M E N T OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE F A C U L T Y OF G R A D U A T E STUDIES (Department of Oceanography) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH C O L U M B I A August 1989 © Donald G. Webb, 1989 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of QC£ArQ QGrRAPHY The University of British Columbia Vancouver, Canada DE-6 (2/88) - i i -ABSTRACT The hypothesis that predation by juvenile chum {Oncorhynchus keta (Walbaum)) and pink {Oncorhynchus gorbuscha (Walbaum)) salmon controls the abundance of harpacticoid copepods inhabiting a shallow subtidal seagrass {Zostera marina L.) bed on Roberts Bank, British Columbia, was tested. Previous studies of the impact of juvenile salmonid predation on harpacticoid communities have yielded contradictory results and have been based on indirect and weak evidence. The hypothesis was tested in two ways: by comparison of patterns of harpacticoid mortality with patterns of salmonid consumption and by the response of the harpacticoid community in controlled field experiments in which epibenthic predators/disturbers were excluded from portions of the seagrass bed. Samples of Zostera leaves and underlying sediment were collected at approximately biweekly intervals from late January to early July in 1986 and 1987 for the estimation of harpacticoid copepod abundance at the study site. Collections for estimation of juvenile salmonid abundance and gut contents during their period of residence in the area were made concurrently at a low tide refuge adjacent to the seagrass bed. Juvenile chum and pink salmon were found mainly to consume three harpacticoid copepod species (>75% by number in gut contents in both years): Harpacticus uniremis Kroyer, Tisbe cf. furcata (Baird) and Zaus aurelii Poppe. These copepod species were found primarily as epiphytes on Zostera leaves and demonstrated distinct periods of abundance in this habitat. Using a simple and robust deterministic, compartmental population dynamic model, mortality of adults and potential adults of these three species between sampling dates was estimated. In comparison with an index of consumption estimated for the salmonid population, temporal patterns of copepod mortality generally did not correspond to temporal patterns of salmonid consumption. This lack of correspondence indicates salmonid consumption did not cause the observed declines in Harpacticus uniremis, Tisbe cf. furcata - i i i -and Zaus aurelii abundance during the sampling season in either year. Controlled exclusion cage (7 mm mesh) experiments were conducted within the Zostera marina bed from late March-early April to mid June in both 1986 and 1987, the period of major juvenile salmonid occurrence in the study area in both years. Exclusion of large epibenthic predators/disturbers appeared to have little effect on the harpacticoid copepod community inhabiting either seagrass leaves or the sediment. Treatment controls were adequate in design. Abundance of Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii generally did not increase in the exclusion treatment relative to the control and shifts in species abundance and composition of the harpacticoid community did not occur. It appears that juvenile salmonids and large epibenthic predators/disturbers in general, have little impact on the dynamics of harpacticoid copepod populations at this study site. -iv-T A B L E OF C O N T E N T S A B S T R A C T i i T A B L E OF CONTENTS iv LIST OF T A B L E S .vi LIST OF FIGURES . . vii P R E F A C E xxi A C K N O W L E D G E M E N T S xxii 1. G E N E R A L INTRODUCTION ; 1 1.1 INTRODUCTION 1 1.2 STUDY SITE 6 2. STRUCTURE OF THE HARPACTICOID COPEPOD C O M M U N I T Y 9 2.1 INTRODUCTION 9 2.2 METHODS . 11 2.3 RESULTS 14 2.4 DISCUSSION ,48 3. M O R T A L I T Y PATTERNS OF SELECTED EPIPHYTIC HARPACTICOID COPEPODS: COMPARISON WITH PATTERNS OF SALMONID CONSUMPTION 57 3.1 INTRODUCTION 57 - V -3.2 METHODS . . . . 59 3.2.1 Harpacticoid Mortality 59 3.2.2 Salmonid Abundance and Consumption 64 3.3 RESULTS 69 3.3.1 Harpacticoid Mortality 69 3.3.2 Salmonid Abundance and Consumption 95 3.4 DISCUSSION I l l 4. RESPONSE OF T H E HARPACTICOID COPEPOD C O M M U N I T Y TO T H E E X C L U S I O N OF EPIBENTHIC PREDATORS 115 4.1 INTRODUCTION 115 4.2 METHODS 118 4.3 RESULTS 122 4.4 DISCUSSION 174 5. G E N E R A L DISCUSSION . 179 REFERENCES 183 APPENDIX 1. SPECIES LIST OF HARPACTICOID COPEPODS FOUND IN B I W E E K L Y ZOSTERA MARINA L E A F SAMPLES AND/OR SEDIMENT CORES A T STATION H : J A N U A R Y 22-J U L Y 9,1986 A N D J A N U A R Y 24-JULY 9,1987 192 -vi-APPENDIX 2. ESTIMATING THE A B U N D A N C E OF L E A F - D W E L L I N G HARPACTICOID COPEPODS O N THE SEAGRASS ZOSTERA MARINA L . : THE USE OF INTRASHOOT DISTRIBUTIONS 194 APPENDIX 3. SHOOT DENSITY, INTRASHOOT L E A F S U R F A C E A R E A PATTERNS A N D INTRASHOOT DISTRIBUTIONS OF SELECTED HARPACTICOID COPEPOD SPECIES A N D D E V E L O P M E N T A L STAGES N E A R STATION H , 1986 A N D 1987 210 APPENDIX 4. EMPIRICAL ANALYSIS OF THE EFFECT OF T E M P E R A T U R E O N M A R I N E HARPACTICOID COPEPOD D E V E L O P M E N T TIME 219 APPENDIX 5. DIURNAL PATTERNS IN FEEDING ACTIVITY A N D D A I L Y RATION OF JUVENILE C H U M A N D PINK S A L M O N IN A S H A L L O W SUB TIDAL SEAGRASS BED 237 -vii-L IST O F T A B L E S Table 3.1. Estimates of percentage of total copepodite development time spent in individual stages for male and female harpacticoid copepods, male copepodite development time as a percentage of female (both after Bergmans (1981) for Tisbe furcata at 18°C) and estimated juvenile copepodite (C1-C3) sex ratio for Harpacticus uniremis (H), Tisbe cf. furcata (T) and Zaus aurelii (Z). C1-C5 = Copepodites 1 to 5 63 Table 3.2. Number of estimated negative mortality rates of adults and potential adults (deaths-cm-2-d-l) for male and female Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii at the mean and 95% Confidence Limits (C.L.) of the predicted copepodite development time in 1986 and 1987. Mortality was estimated for 12 periods in each year 93 Table 3.3. Numbers and proportions of Harpacticus uniremis (H), Tisbe cf. furcata (T), Zaus aurelii (Z) and other harpacticoid copepod species found in the gut contents of sampled juvenile chum and/or pink salmon in 1986 and 1987. Total = total number of harpacticoids in all sampled fish 102 Table 3.4. Percent composition of adult females, males and individual juvenile copepodite stages of Harpacticus uniremis (H), Tisbe cf. furcata (T) and Zaus aurelii (Z) in gut contents of sampled juvenile chum and/or pink salmon in 1986 and 1987. Values are the mean and Standard Error of the percent composition of each stage in the fish samples on each sampling date where the copepod species was found in the gut contents, n = sample size; C6F = adult female; C 6 M = adult male; C1-C5 = Copepodites 1 to 5 103 -vi i i -L IST OF F I G U R E S Figure 1.1. Station locations on Roberts Bank, British Columbia, Canada. Station F indicates the location of fish sampling and Station H is the location of harpacticoid copepod sample collection. Hatched area indicates extent of Zostera marina bed (after Harrison 1987). Dotted line shows seaward limit of shallow subtidal flat 8 Figure 2.1. Abundance (number-cm-2 sediment) of total harpacticoid copepods in 1986 at Station H on Zostera marina leaves (a) and in the sediment (b), along with copepod vertical distribution in the sediment (c). Plotted values are the mean ± 1 Standard Error, n = 6 15 Figure 2.2. Abundance (number-cm-2 sediment) of total harpacticoid copepods in 1987 at Station H on Zostera marina leaves (a) and in the sediment (b), along with copepod vertical distribution in the sediment (c). Plotted values are the mean ± 1 Standard Error, n = 6 16 Figure 2.3. Abundance (number-cm-2 sediment) of Harpacticus uniremis in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 18 Figure 2.4. Abundance (number-cm-2 sediment) of Harpacticus uniremis in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 19 Figure 2.5. Abundance (number-cm-2 sediment) of Tisbe cf. furcata in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 20 Figure 2.6. Abundance (number-cm-2 sediment) of Tisbe ctfurcata in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean + 1 Standard Error, n = 6 21 -ix-Figure 2.7. Abundance (number-cm-2 sediment) of Zaus aurelii in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 22 Figure 2.8. Abundance (number-cm-2 sediment) of Zaus aurelii in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 23 Figure 2.9. Abundance (number-cm-2 sediment) of Amonardia normani in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 25 Figure 2.10. Abundance (number-cm-2 sediment) of Amonardia normani in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 26 Figure 2.11. Abundance (number-cm-2 sediment) of Amphiascus undosus in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 27 Figure 2.12. Abundance (number-cm-2 sediment) of Amphiascus undosus in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 28 Figure 2.13. Abundance (number-cm-2 sediment) of Dactylopodia crassipes in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 . 30 -X-Figure 2.14. Abundance (number-cm-2 sediment) of Dactylopodia crassipes in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error,n = 6 31 Figure 2.15. Abundance (number-cm-2 sediment) of Ectinosoma melaniceps in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 32 Figure 2.16. Abundance (number-cm-2 sediment) of Ectinosoma melaniceps in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 33 Figure 2.17. Abundance (number-cm-2 sediment) of Heterolaophonte variabilis in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 34 Figure 2.18. Abundance (number-cm-2 sediment) of Heterolaophonte variabilis in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 35 Figure 2.19. Abundance (number-cm-2 sediment) of Mesochra pygmaea in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 37 Figure 2.20. Abundance (number-cm-2 sediment) of Mesochra pygmaea in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean i 1 Standard Error, n = 6 38 -xi-Figure 2.21. Abundance (number-cm-2 sediment) of Amphiascus minutus sp. 1 in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6.. . 39 Figure 2.22. Abundance (number-cm-2 sediment) of Amphiascus minutus sp. 1 in 1987 at Station H in the sediment (total abundance (a) and juvenile copepodite, male and female abundance (b)). Plotted values are the mean ± 1 Standard Error, n = 6 40 Figure 2.23. Abundance (number-cm-2 sediment) of Danielssenia typica in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 .42 Figure 2.24. Abundance (number-cm-2 sediment) of Danielssenia typica in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 43 Figure 2.25. Abundance (number-cm-2 sediment) of Halectinosoma sp. 1 in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 44 Figure 2.26. Abundance (number-cm-2 sediment) of Halectinosoma sp. 1 in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 . 45 Figure 2.27. Abundance (number-cm-2 sediment) of Pseudobradya lanceta in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 46 - X l l -Figure 2.28. Abundance (number-cm-2 sediment) of Pseudobradya lanceta in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 Figure 2.29. Abundance (number-cm-2 sediment) of Robertsonia propinqua in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6 Figure 2.30. Abundance (number-cm-2 sediment) of Robertsonia propinqua in 1987 at Station H in the sediment (total abundance (a) and juvenile copepodite, male and female abundance (b)). Plotted values are the mean ± 1 Standard Error, n = 6 Figure 2.31. Abundance (number-cm-2 sediment) of Stenhelia (D.) latioperculata in 1986 at Station H in the sediment (total abundance (a) and juvenile copepodite, male and female abundance (b)). Plotted values are the mean ± 1 Standard Error, n = 6 Figure 2.32. Abundance (number-cm-2 sediment) of Stenhelia (D.) latioperculata in 1987 at Station H in the sediment (total abundance (a) and juvenile copepodite, male and female abundance (b)). Plotted values are the mean ± 1 Standard Error, n = 6 Figure 3.1. Mean sediment surface temperature (°C) between harpacticoid copepod sampling dates at Station H in 1986 (a) and 1987 (b) Figure 3.2. Relationships between dry weight and wet weight for juvenile chum and pink salmon (a) (Dry weight = 0.004 + 0.21-(Wet weight), r2 = 0.99, n = 21, P<0.001) and salmon gut contents (b) (Dry weight = -2.3 + 0.14-(Wet weight), r2 = 0.97, n = 18, P<0.001) Figure 3.3. Abundance (number-cm-2 sediment) of Harpacticus uniremis eggs and copepodite stages on Zostera marina leaves and in the sediment at Station H in 1986. Individual plots are for eggs (a), CI (b), C2 (c), C3 (d), C4 Male (e), C4 Female (f), C5 Male (g), C5 Female (h), C6 Male (i) and C6 Female (j). Values are the mean ± 1 Standard Error, n = 6, .70 Figure 3.3. Continued. .71 Figure 3.3. Continued. 72 -xii i-Figure 3.4. Abundance (number-cm-2 sediment) of Harpacticus uniremis eggs and copepodite stages on Zostera marina leaves and in the sediment at Station H in 1987. Individual plots are for eggs (a), CI (b), C2 (c), C3 (d), C4 Male (e), C4 Female (f), C5 Male (g), C5 Female (h), C6 Male (i) and C6 Female (j). Values are the mean ± 1 Standard Error, n = 6. 73 Figure 3.4. Continued 74 Figure 3.4. Continued . 7 5 Figure 3.5. Abundance (number-cm-2 sediment) of Tisbe cf. furcata eggs and copepodite stages on Zostera marina leaves and in the sediment at Station H in 1986. Individual plots are for eggs (a), CI (b), C2 (c), C3 (d), C4 Male (e), C4 Female (f), C5 Male (g), C5 Female (h), C6 Male (i) and C6 Female (j). Values are the mean ± 1 Standard Error, n = 6 76 Figure 3.5. Continued 77 Figure 3.5. Continued 78 Figure 3.6. Abundance (number-cm-2 sediment) of Tisbe• cf. furcata eggs and copepodite stages on Zostera marina leaves and in the sediment at Station H in 1987. Individual plots are for eggs (a), CI (b), C2 (c), C3 (d), C4 Male (e), C4 Female (f), C5 Male (g), C5 Female (h), C6 Male (i) and C6 Female (j). Values are the mean ± 1 Standard Error, n = 6 80 Figure 3.6. Continued 81 Figure 3.6. Continued 82 Figure 3.7. Abundance (number-cm-2 sediment) of Zaus aurelii eggs and copepodite stages on Zostera marina leaves and in the sediment at Station H in 1986. Individual plots are for eggs (a), CI (b), C2 (c), C3 (d), C4 Male (e), C4 Female (f), C5 Male (g), C5 Female (h), C6 Male (i) and C6 Female (j). Values are the mean ± 1 Standard Error, n = 6 83 Figure 3.7. Continued 84 Figure 3.7. Continued 85 Figure 3.8. Abundance (number-cm-2 sediment) of Zaus aurelii eggs and copepodite stages on Zostera marina leaves and in the sediment at Station H in 1987. Individual plots are for eggs (a), CI (b), C2 (c), C3 (d), C4 Male (e), C4 Female (f), C5 Male (g), C5 Female (h), C6 Male (i) and C6 Female (j). Values are the mean ± 1 Standard Error, n = 6 86 Figure 3.8. Continued.. 87 -xiv-Figure 3.8. Continued 88 Figure 3.9. Numbers of eggs-female-1 for Harpacticus uniremis on Zostera marina leaves and in the sediment at Station H in 1986 (a) and 1987 (b). Values are the mean ± 1 Standard Error. Numerals above or below error bars indicate, from top to bottom, the sample size for leaf and sediment estimates, respectively 89 Figure 3.10. Numbers of eggs-female-1 for Tisbe cf. furcata on Zostera marina leaves and in the sediment at Station H in 1986 (a) and 1987 (b). Values are the mean ± 1 Standard Error. Numerals above or below error bars indicate, from top to bottom, the sample size for leaf and sediment estimates, respectively .91 Figure 3.11. Numbers of eggs-female-1 for Zaus aurelii on Zostera marina leaves and in the sediment at Station H in 1986 (a) and 1987 (b). Values are the mean ± 1 Standard Error. Numerals above or below error bars indicate, from top to bottom, the sample size for leaf and sediment estimates, respectively 92 Figure 3.12. Adult and potential adult mortality (deaths-cm-2-d-l) calculated both with and without developmental assumptions for male and female Harpacticus uniremis at Station H in 1986 (a) and in 1987 (b) . 94 Figure 3.13. Adult and potential adult mortality (deaths-cm-2-d-l) calculated both with and without developmental assumptions for male and female Tisbe cf. furcata at Station H in 1986 including the female mortality estimates for the first interval (a) and excluding the first interval female mortality estimates (b) 96 Figure 3.14. Adult and potential adult mortality (deaths-cm-2-d-l) calculated both with and without developmental assumptions for male and female Tisbe cf. furcata at Station H in 1987. 97 Figure 3.15. Adult and potential adult mortality (deaths-cm-2-d-l) calculated both with and without developmental assumptions for male and female Zaus aurelii at Station H in 1986 (a) and in 1987 (b) 98 Figure 3.16. Catch per Unit Effort (number in 3 beach seine sets) at Station F of juvenile chum and pink salmon in 1986 (a) and juvenile chum salmon in 1987 (b) 99 Figure 3.17. Food weight as a percentage of body weight at Station F for juvenile chum and pink salmon in 1986 (a) and juvenile chum salmon in 1987 (b). Values are the mean ± 1 Standard Error, n = 20, except for (a): March 19, n = 3; July 10, n = 4; and (b): March 5, n = 1; April 2, n = 15 101 -XV-Figure 3.18. Consumption index (number consumed-h-1) of male and female adult and potential adult Harpacticus uniremis by juvenile chum and pink salmon in 1986 (a) and male and female adult and potential adult mortality (deaths-cm-2-d-l) of Harpacticus uniremis in 1986 (b). Error bars in (a) are approximate 95% Confidence Limits 104 Figure 3.19. Consumption index (number consumed-h-1) of male and female adult and potential adult Harpacticus uniremis by juvenile chum salmon in 1987 (a) and male and female adult and potential adult mortality (deaths-cm-2-d-1) of Harpacticus uniremis in 1987 (b). Error bars in (a) are approximate 95% Confidence Limits 106 Figure 3.20. Consumption index (number consumed-h-1) of male and female adult and potential adult Tisbe cf. furcata by juvenile chum and pink salmon in 1986 (a) and male and female adult and potential adult mortality (deaths-cm-2-d-l) of Tisbe cf. furcata in 1986 (b). Error bars in (a) are approximate 95% Confidence Limits 107 Figure 3.21. Consumption index (number consumed-h-1) of male and female adult and potential adult Tisbe cf. furcata by juvenile chum salmon in 1987 (a) and male and female adult and potential adult mortality (deaths-cm-2-d-l) of Tisbe cf. furcata in 1987 (b). Error bars in (a) are approximate 95% Confidence Limits. . 108 Figure 3.22. Consumption index (number consumed-h-1) of male and female adult and potential adult Zaus aurelii by juvenile chum and pink salmon in 1986 (a) and male and female adult and potential adult mortality (deaths-cm-2-d-l) of Zaus aurelii in 1986 (b). Error bars in (a) are approximate 95% Confidence Limits 109 Figure 3.23. Consumption index (number consumed-h-1) of male and female adult and potential adult Zaus aurelii by juvenile chum salmon in 1987 (a) and male and female adult and potential adult mortality (deaths-cm-2-d-l) of Zaus aurelii in 1987 (b). Error bars in (a) are approximate 95% Confidence Limits 110 Figure 4.1. Sediment grain size characteristics in the Control and Exclusion treatments on March 31,1986 (a) and June 25,1986 (b). Values are the mean i 1 Standard Error, n = 3 .123 Figure 4.2. Sediment grain size characteristics in the Control and Exclusion treatments on April 2,1987 (a) and June 11,1987 (b). Values are the mean ± 1 Standard Error, n = 3 . .124 Figure 4.3. Abundance of total harpacticoid copepods on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 126 -xvi-Figure 4.4. Abundance of total harpacticoid copepods on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean i 1 Standard Error, n = 3 127 Figure 4.5. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Harpacticus uniremis on Zostera marina leaves (number-cm-2 leaf) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3.. 128 Figure 4.5. Continued. 129 Figure 4.6. Total abundance (a) and juvenile copepodite (b), adult male(c) and adult female (d) abundance of Harpacticus uniremis in the sediment (number-cm-2 sediment) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 130 Figure 4.6. Continued 131 Figure 4.7. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Harpacticus uniremis on Zostera marina leaves (number-cm-2 leaf) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 132 Figure 4.7. Continued .133 Figure 4.8. Total abundance (a) and juvenile copepodite (b) and adult female (c) abundance of Harpacticus uniremis in the sediment (number-cm-2 sediment) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 134 Figure 4.8. Continued ,135 Figure 4.9. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Tisbe cf. furcata on Zostera marina leaves (number-cm-2 leaf) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 137 Figure 4.9. Continued 138 •Figure 4.10. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Tisbe cf. furcata in the sediment (number-cm-2 sediment) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 139 Figure 4.10. Continued 140 -xvii-Figure 4.11. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Tisbe cf. furcata on Zostera marina leaves (number-cm-2 leaf) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 141 Figure 4.11. Continued 142 Figure 4.12. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Tisbe cf. furcata in the sediment (number-cm-2 sediment) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 143 Figure 4.12. Continued 144 Figure 4.13. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Zaus aurelii on Zostera marina leaves (number-cm-2 leaf) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 145 Figure 4.13. Continued. 146 Figure 4.14. Total abundance (a) and juvenile copepodite (b) abundance of Zaus aurelii in the sediment (number-cm-2 sediment) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 147 Figure 4.14. Continued . .148 Figure 4.15. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Zaus aurelii on Zostera marina leaves (number-cm-2 leaf) in the Control and Exclusion treatments in 1987. Values are the mean + 1 Standard Error, n = 3 149 Figure 4.15. Continued 150 Figure 4.16. Abundance of Amonardia normani on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 152 Figure 4.17. Abundance of Amonardia normani on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 153 -XV111-Figure 4.18. Abundance of Amphiascus undosus on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 Figure 4.19. Abundance of Amphiascus undosus on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 Figure 4.20. Abundance of Dactylopodia crassipes on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 Figure 4.21. Abundance of Dactylopodia crassipes on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 Figure 4.22. Abundance of Ectinosoma melaniceps on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 Figure 4.23. Abundance of Ectinosoma melaniceps on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean + 1 Standard Error, n = 3 Figure 4.24. Abundance of Heterolaophonte variabilis on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 Figure 4.25. Abundance of Heterolaophonte variabilis on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 Figure 4.26. Abundance of Mesochra pygmaea on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 Figure 4.27. Abundance of Mesochra pygmaea on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 -xix-Figure 4.28. Abundance of Amphiascus minutus sp. 1 on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 165 Figure 4.29. Abundance of Danielssenia typica on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 166 Figure 4.30. Abundance of Danielssenia typica on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean + 1 Standard Error, n = 3 167 Figure 4.31. Abundance of Halectinosoma sp. 1 on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 168 Figure 4.32. Abundance of Halectinosoma sp. 1 on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 169 Figure 4.33. Abundance of Pseudobradya lanceta on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 170 Figure 4.34. Abundance of Pseudobradya lanceta on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 171 Figure 4.35. Abundance of Robertsonia propinqua in the sediment (number-cm-2 sediment) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 172 Figure 4.36. Abundance of Robertsonia propinqua on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 173 Figure 4.37. Abundance of Stenhelia (D.) latioperculata on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3 175 -XX-Figure 4.38. Abundance of Stenhelia (D.) latioperculata in the sediment (number-cm-2 sediment) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3 176 -xxi-P R E F A C E This thesis consists of a main body of 5 chapters and 5 additional appendices. In order to provide a concise account of my work, the main body of the thesis has not been diluted with the information presently residing in the appendices. However, the appendices (especially Appendices 2, 4 and 5) contain data, analyses and discussion directly relevant to the main body of the thesis and are substantial aspects of the presented research. Therefore, the appendices should be regarded as part of the thesis in toto but separated from the main body of text solely for purposes of lucidity. Portions of Appendix 4 have been previously published (Webb, D.G., and Parsons, T.R. 1988. Empirical analysis of the effect of temperature on marine harpacticoid copepod development time. Can. J. Zool. 66: 1376-1381.). -xxii-A C K N O W L E D G E M E N T S I would like to thank my supervisor, Dr. T.R. Parsons, and the other members of my research committee (Drs. P.G. Harrison, P.J. Harrison, T.F. Pedersen and N.J. Wilimovsky) for their advice and support throughout the course of this research. I am indebted to Dr. D. D'Amours, M . St. John and M . Gollner for their assistance with the field sampling. Mr. J. Stalzer of Westshore Terminals Ltd. kindly provided access to company property for beach seining. Dr. D. D'Amours allowed use of his 1986 temperature data and Dr. M.C. Healey supplied me with his unpublished data on juvenile salmon gut evacuation. J. Acreman identified samples of epiphytic diatoms. Dr. B.C. Coull made me aware of the description of Stenhelia (£>.) latioperculata. I especially thank Dr. D. D'Amours and A . Metaxas for their numerous criticisms, insights and often animated discussions of this research. Dr. D. D'Amours, M . Levasseur, A . Metaxas, Dr. S.M.C. Robinson, and M . St. John all provided criticisms of various drafts and manuscripts arising from the thesis. W.P. Cochlan applied his artistry to Fig. 1.1. A special thanks to Anna for her encouragement and smiles. Logistical support for this study was provided by NSERC Operating Grants to T.R. Parsons. Personal support was provided by a NSERC Postgraduate Scholarship, Fonds F C A C (Quebec), the Kit Malkin Scholarship, a Summer University of British Columbia Graduate Fellowship and the Capt. T.H. Byrne Scholarship to the author and NSERC Operating Grants to T.R. Parsons. -1-1. GENERAL INTRODUCTION 1.1 INTRODUCTION Benthic, epibenthic and epiphytic marine harpacticoid copepods (Class Crustacea, Subclass Copepoda, Order Harpacticoida) are commonly encountered in the gut contents of a variety of fish species from a number of different habitats. Harpacticoids are especially common and often dominant, by numbers or volume, as the prey of juvenile fishes inhabiting soft sediment or vegetated marine areas. In unvegetated marine soft sediment habitats, harpacticoid copepods are considered to be a primary prey source for newly settled flatfish (Pleuronectidae) (Bregnballe 1961; Evans 1983; De Morais and Bodiou 1984; Hicks 1984; Gee 1987), small gobies (Gobiidae) (Bodiou and Villiers 1978/79; Zander and Hartwig 1982; Evans and Tallmark 1985), grunts (Pomadasyidae) (Alheit and Scheibel 1982) and larval sculpins (Cottidae) (Laroche 1982). In vegetated areas (e.g. kelp and seagrass beds), harpacticoids are eaten in large numbers by clingfish (Gobiesocidae) (Roland 1978), dragonets (Callionymidae) (Sogard 1984), kelpfish (Clinidae) (Gibbons 1988), porgies (Sparidae) (Stoner 1980; Stoner and Livingston 1984), and pipefish and seahorses (Syngnathidae) (Tipton and Bell 1988). On the Pacific coast of North America, the gut contents of juvenile Pacific salmon (Oncorhynchus spp.) indicate intense predation on harpacticoid copepods. Kaczynski et al. (1973) were the first researchers to document feeding on harpacticoids by juvenile salmon during their nearshore residence period (see Healey 1980). They found that juvenile chum (Oncorhynchus keta (Walbaum)) and pink (Oncorhynchus gorbuscha (Walbaum)) salmon <60 mm in length, foraging epibenthically in the littoral zone of Puget Sound, Washington, had consumed by numbers, 57% and 36% harpacticoid copepods, respectively. Previous studies had suggested that juvenile chum and pink salmon were planktivorous but these conclusions were based on the analysis of gut contents of older, larger fish that had already -2-adopted an open water lifestyle (e.g. Manzer 1969). The use of harpacticoid copepods as a major food source for juvenile chum and pink salmon foraging nearshore, was confirmed in later studies. Mason (1974) indicated that juvenile chum salmon fed on harpacticoids in the saline portion of a small estuary. Another study conducted in Puget Sound showed that harpacticoids accounted for >80% by numbers of the prey of juvenile chum feeding on epibenthos (Feller and Kaczynski 1975). A similar result (>80% by numbers) was obtained by Healey (1979) for juvenile chum in the Nanaimo River estuary, British Columbia. Juvenile pink salmon in British Columbia coastal waters also feed heavily on harpacticoids (Godin 1981 (38-47% by numbers); see also Healey 1980; 1982a). Harpacticoid copepods are also commonly observed prey in the guts of juvenile pink and chum salmon from nearshore habitats in Alaska (Cordell 1986). Therefore, it has become apparent that marine harpacticoid copepods are a favoured prey resource for juvenile salmonids during nearshore residence and before the fish start feeding planktonically further offshore at a size of 60-80 mm (Healey 1980; Simenstad et al. 1982). Since fishes have been observed to eat large numbers of harpacticoid copepods, research has been directed towards estimating the impact of fish predation on the harpacticoid community. The results have been equivocal. Bregnballe (1961) suggested that if harpacticoid copepods undergo a reproductive "stagnation", juvenile flatfish predation may have a severe impact on prey standing stock. Dethier (1980) proposed that the rocky intertidal splashpool harpacticoid Tigriopus californicus Baker is limited to this habitat by fish predation in the lower intertidal. Her conclusion is based on the high survival of copepods transplanted to lower levels in the absence of fish predation. Alheit and Scheibel (1982) observed that 90% by numbers of all harpacticoids eaten by grunts in a Bermudan lagoon were one species, Longipedia helgolandica Klie. However, when they estimated predator impact on this species by assessing fish abundance, number of copepods per fish, gut evacuation rates and Longipedia density, only 0.1% of the copepod population was estimated to be removed per day. The harpacticoid Amphiascus lobatus Hicks is selectively -3-preyed upon by a blennioid fish in mid to high intertidal rock pools in New Zealand but the habitat complexity of tufted coralline algae provides this epiphytic copepod with a refuge from fish predators (Coull and Wells 1983). Juvenile flatfish in the western Mediterranean may consume most of the estimated production of their harpacticoid prey (mainly Longipedia scotti Sars, Halectinosoma caniculatum (Por) and Pseudobradya beduina Monard) but the sediment cores used to estimate copepod density may have underestimated species abundances, especially that of the epibenthic Longipedia (De Morais and Bodiou 1984). Hicks (1985a), using a similar approach to that of Alheit and Scheibel (1982), estimated only 0.38% of the population of the harpacticoid Parastenhelia megarostrum Wells, Hicks and Coull was consumed per day by newly settled flatfish in New Zealand. Predator cage inclusion experiments with gobies on an English mudflat yielded little observable effect on total harpacticoid numbers in the sediment but indicated shifts in species dominance (Gee et al. 1985). However, these experiments were pseudoreplicated (sensu Hurlbert 1984) and interpretation of the results is difficult. Gee (1987), by estimating consumption of the surficial harpacticoid Asellopsis intermedia (T. Scott) by flatfish and gobies and comparing estimated values to reductions in copepod population density, found that the effect of fish predation was small compared to that of other predators (e.g. shrimp). It is clear from these studies that the overall impact of fish predation on harpacticoid copepod populations in the field is low. The effect of predation by juvenile chum and pink salmon on harpacticoid copepods has been estimated in two studies. Healey (1979) analyzed the feeding and production of juvenile chum preying on harpacticoids in the Nanaimo estuary, British Columbia and Cordell (1986) worked on the impact of chum and pink salmon on epibenthic harpacticoids at Spuhn Island, Alaska. Healey (1979), on the basis of a bioenergetic analysis of salmonid consumption and an estimate of harpacticoid prey densities in the estuary by Sibert (1979), concluded that juvenile chum salmon have a severe impact on the densities of selected copepod species and that the fish may be food-limited in the estuary through reliance on rare -4 -harpacticoid species as prey. Cordell (1986), however, found no evidence that juvenile chum and pink salmon in Alaskan waters were food-limited by reliance on certain harpacticoids and he suggested that the salmon have little effect on copepod populations from analysis of estimates of harpacticoid densities in the study area. Healey's and Cordell's conclusions, however, are weak since both studies contain flaws in design, especially in the assessment of harpacticoid copepod densities at their respective study sites. Healey (1979) observed that the major harpacticoid prey for juvenile chum salmon in the Nanaimo estuary was Harpacticus uniremis Kroyer, a relatively large (2 mm) and rare component of the sediment copepod community (Sibert 1979). Copepods of the genus Harpacticus, however, are typically epiphytic (Hicks 1985b). Healey (1979) states that the salmonids were seined at low tide while the fish inhabited tidal channels which contained eelgrass (Zostera marina L.), which is common in the lower reaches of the estuary (Naiman and Sibert 1979). Sibert's (1979) cores were obtained throughout the estuary in unvegetated sediments. It is unclear, therefore, whether the gut contents of the chum reflected feeding in the estuary proper and whether Sibert's measurements of copepod density accurately estimated true population abundance. Therefore, any discussion regarding food limitation of fish and effects on harpacticoid populations based on these results is speculative. Cordell (1986) concluded that juvenile chum and pink salmon foraging on harpacticoid copepods near Spuhn Island, Alaska, were not food-limited by copepod abundance and that predation had little effect on the prey species. He found that the copepods most commonly preyed upon were Harpacticus uniremis and Tisbe spp.. The genus Tisbe is generally also epiphytic (Hicks 1985b). Cordell observed no trend in a "fullness index" of the salmon over his study period. Also, based on selection for specific life history stages by the fish and the presence of peaks in copepod density under high predation pressure, he suggested that predation by salmon was unimportant to the harpacticoid populations. Cordell based his estimates of copepod density on epibenthic pump samples in an area of "macrophyte" cover on the assumption that this technique would better sample the - 5 -harpacticoid community "available" to salmon. While this technique may efficiently sample epibenthic and migrating (see Palmer 1988) copepods, it may underestimate the abundance of epiphytic species. Also, active entry into the water column by epiphytic and sediment-dwelling harpacticoids may be confined to certain species and life history stages within species (e.g. Bell et al. 1988; D'Amours 1988a; Walters 1988). Therefore, epibenthic pump sampling may give an inaccurate indication of harpacticoid densities and population structure for the purpose of estimating the impact of predation. Cordell's (1986) suggestions are as much based on speculation as Healey's (1979). No firm conclusion can be reached from either study as to the effect of juvenile salmon predation on harpacticoid copepods. However, this information is not only of academic but possible commercial importance since mortality, of juvenile salmon nearshore may be size-selective, with higher mortality on smaller fish (Healey 1982b; Hargreaves and LeBrasseur 1986). Therefore, factors affecting growth rate, such as food availability, may influence the number of adult salmon returning to the fishery. This thesis will test the hypothesis that predation by juvenile salmonids controls the abundance of harpacticoid copepod populations. This hypothesis will be tested in two complementary ways. First, patterns of mortality imposed by juvenile salmon on harpacticoids will be compared to actual patterns of mortality in the copepod populations. Secondly, the response of the harpacticoid community will be monitored when epibenthic predators in general are excluded from portions of the study site by cages. The thesis is divided into three major sections. The first section deals with the structure of the harpacticoid copepod community at the study site (Chapter 2). The second compares patterns of mortality of selected copepod species with patterns of mortality imposed by juvenile salmon (Chapter 3). The third describes the response of the harpacticoid community when epibenthic predators are excluded (Chapter 4). -6-1.2 S T U D Y SITE This study was conducted on Roberts Bank, British Columbia, Canada (49°N, 123°W). Sampling stations were located between the Westshore Terminals Ltd. causeway and the Tsawwassen Ferry Terminal causeway (Fig. 1.1). This area is vegetated with the seagrasses Zostera marina L . seaward and Zostera japonica Aschers. and Graebn. along its landward extent (see Harrison 1987 for a detailed description of vegetation patterns). This section of Roberts Bank was chosen for this study because it is a known foraging area for large numbers of juvenile salmonids (Gordon and Levings 1984) and because the fish feed heavily on harpacticoid copepods during their period of residence in this area (79.8% and 79.7% of total prey by number in 1985 and 1986, respectively) (D'Amours 1987). Dominant harpacticoids in salmonid gut contents were Harpacticus uniremis, Tisbe spp. and Zaus aurelii Poppe (D'Amours 1987). Separate stations were sampled for harpacticoid copepods and juvenile salmon on Roberts Bank. Sampling stations were identical to those of D'Amours (1987). Harpacticoid copepods were sampled at Station H (Fig. 1.1). This station is located within the main body of the Zostera marina bed and is in a shallow subtidal area. Approximately 5 cm of water covers the sediment surface at low tide (D'Amours 1987; Harrison 1987; personal observation). Maximum water depth at high tide is -3.2 m. Station H is 1.6 m above chart datum at the Port of Reference (Point Atkinson, British Columbia) (D'Amours 1987). Sediments are fine sands at this location (Swinbanks and Luternauer 1987). Since the purpose of the harpacticoid copepod sampling was to establish temporal rather than spatial patterns in copepod abundance, only this one station was occupied throughout the duration of the study allowing a large number of replicate samples to be collected on each date. Sampling for juvenile salmon was conducted at a low tide refuge adjacent to the Westshore Terminals Ltd. causeway (Station F) (Fig. 1.1). This station was selected for estimation of juvenile salmonid abundance and sampling of gut contents after the fish are forced out of the main seagrass beds by the ebbing tide. Abundance could then be estimated -7-while the fish are spatially concentrated and gut content composition should reflect the feeding occurring within the seagrass beds. Attempts were made to sample fish in the seagrass beds at high tide using a small purse seine but sets were unsuccessful (D. D'Amours and D.G. Webb, unpublished data). Therefore, Station F was used for fishing purposes. While this section of Roberts Bank is in close proximity to the Fraser River, salinity at Station H indicates a strong marine influence. Although variable, in biweekly samples over the period of January 22-July 10, 1986 and January 24-July 9, 1987, salinity ranged from 19.5-30.3%o. Salinity was generally above 25%o. It is possible that the presence of the Westshore Terminals Ltd. causeway deflects fresh water from the Fraser River away from the study area. Temperature data will be described in detail in Chapter 3. -8-49° 3' N 49° I'N 123° 9 'W 123° 7 'W Figure 1.1. Station locations on Roberts Bank, British Columbia, Canada. Station F indicates the location of fish sampling and Station H is the location of harpacticoid copepod sample collection. Hatched area indicates extent of Zostera marina bed (after Harrison 1987). Dotted line shows seaward limit of shallow subtidal flat. -9-2. STRUCTURE OF THE HARPACTICOID COPEPOD COMMUNITY 2.1 INTRODUCTION Harpacticoid copepods are usually the numerically dominant meiofaunal group inhabiting the surfaces of marine intertidal and subtidal macroalgae (e.g. Colman 1940; Wieser 1952; Mukai 1971; Pallares and Hall 1974; Beckley and McClachlan 1980; Hicks 1980; Johnson and Scheibling 1987). High algal sediment loads, however, may favour the dominance of other meiofaunal groups such as nematodes (see Hicks 1985b). In the northern hemisphere, representative families of epiphytic harpacticoids are the Harpacticidae, Tisbidae, and Thalestridae (Hicks 1980; 1985b). The family Porcellidiidae is abundant in the southern hemisphere (e.g. Hicks 1977). Species in the above mentioned families generally all possess morphological adaptations to the phytal habitat. These include prehensile maxillipeds and first swimming legs for grasping the substrate, and dorso-ventral compression which is suggested to be an adaptation to decrease drag (Hicks 1985b; Bell et al. 1987). However, relatively little information is available on the structure of harpacticoid copepod communities inhabiting aquatic angiosperms such as seagrasses, especially at the species level. There are three subhabitats potentially available for use by harpacticoid copepods in seagrass beds: seagrass leaves, the sediment matrix and the water column (Bell et al. 1984). Initial reports of harpacticoid populations inhabiting seagrass leaves were simple records of presence and correlation with obvious characteristics of the leaves (e.g. epiphytic algal biomass (Nagle 1968; Lewis and Hollingsworth 1982) and distance along individual leaves (Caine 1980; Novak 1982)). Bell et al. (1984) made the first attempt to integrate data on harpacticoids on seagrass leaves with information from the other subhabitats and provided a review of the literature on seagrass meiofauna to that time. The first comparative data of harpacticoid abundances on seagrass leaves and in underlying sediments were provided by -10-Bell et al. (1986) who demonstrated that leaves, on a per unit sediment area basis, have harpacticoid densities equal to or greater than the sediments. In temporally sporadic samples from a Zostera bed in New Zealand, Hicks (1986) determined species abundances on leaves, in sediments and in emergence traps (used to capture individuals entering the water column from leaves and the sediment). He clearly showed that leaf and sediment samples contained different species with typical algal fauna predominating on the leaves. He also observed that some species had shared abundances between these two subhabitats and that these "itinerant" species were often collected in the emergence traps. In comparison with samples from an adjacent unvegetated area, the overall conclusion from his study was that harpacticoid communities in the seagrass bed were denser and had a higher species richness. More recent studies on the harpacticoid fauna on seagrass leaves have expanded our knowledge of leaf communities to Indian waters (Arunachalam and Nair 1988), as well as described the feeding selectivity of fishes for rare species in the leaf fauna (Tipton and Bell 1988), the generally positive numerical response of harpacticoids to the increased habitat complexity afforded by epiphytic algae on the leaves (Hall and Bell 1988) and the abundance of copepods in relation to leaf inflorescences (Hellwig-Armonies 1988). Studies on sediment-dwelling harpacticoids in seagrass beds are rare. Kikuchi (1966) made collections once within a Zostera marina bed in Japan but did not analyze the samples to the species level. Tietjen (1969) examined a one-year series of monthly samples from Zostera marina beds but also did not identify to the species level. Decho etal. (1985) studied the harpacticoid community of calcareous sediments in a Thalassia bed in Florida. They observed higher copepod abundance in areas outside the bed than within it. As mentioned earlier, Hicks (1986) found the opposite result from sediment samples inside and outside a New Zealand Zostera meadow. Recently, Castel et al. (1989) have substantiated Hicks' result by observing higher copepod abundances inside than outside Zostera beds in France. Patterns of abundance of harpacticoid copepods in the water overlying seagrass beds is an area of current research activity. In Thalassia beds in Florida, as measured by -11-emergence traps (which did not enclose seagrass shoots), extremely large numbers of harpacticoids migrate from the sediment into the water column (>50% by number of total sediment-dwelling copepods) (Walters and Bell 1986; Walters 1988), with greater migration observed in vegetated areas compared to bare sand (Walters 1988). Behaviour of this type was also recorded in New Zealand by Hicks (1986). This phenomenon appears to have a diurnal cycle in the subtidal Thalassia beds with increased migration occurring at night (Walters 1988), whereas migration seems to be linked to tidal inundation in the intertidal New Zealand Zostera bed (Hicks 1986). Harpacticoid migrations appear to be related to precopulatory association of males and juvenile females (Bell et al 1988). To adequately describe the harpacticoid copepod prey community for juvenile salmonids using the Zostera marina bed on Roberts Bank, it was necessary to undertake a rigorous sampling program for both leaf and sediment-dwelling harpacticoids during the period of salmon residence. Samples could be taken at low tide to obviate the need for water column sampling. The epiphytic community was considered to be of the greatest importance since previous work has shown typical epiphytic genera {Harpacticus, Tisbe, Zaus) are primarily preyed upon (D'Amours 1987). Since there is little information, especially of temporal patterns of abundance at the species level, on seagrass bed harpacticoid communities, a detailed analysis of the observed community will be presented in this chapter. 2.2 M E T H O D S Samples of Zostera marina leaves and underlying sediments were collected at Station H on Roberts Bank, B.C., Canada (see Fig. 1.1). Collections were made at low tide at approximately biweekly intervals from January 22 to July 9, 1986 and January 24 to July 9, 1987. This period bracketed the time of occurrence of juvenile chum (Oncorhynchus keta) and/or pink (0. gorbuscha) salmon in the study area in both years (see Chapter 3). -12-Six Zostera leaves were sampled at randomly determined locations within 20 m of Station H on each sampling date. Locations were determined through random selection of a map coordinate (e.g. North, South, East, West) using a die and by taking a randomly chosen (using a random number table) number of steps (0-9) from the station marker in that direction. The first encountered shoot was selected for sampling and the longest leaf on the shoot was enclosed within a 30 cm long, 4 cm internal diameter P V C tube with a screw cap of 63 Jim Nitex mesh at one end. Any portion of the leaf protruding from the tube (if present) was cut off and the sampler capped. The sampler was retrieved and its contents rinsed into a jar using 40 u,m filtered seawater. The sample was then preserved by addition of a 4% Formaldehyde/40 |i.m filtered seawater solution. Relative age of the sampled leaf within the shoot was determined morphologically by observing the point of leaf insertion in the sheath in relation to the oldest (basal) leaf and the alternating pattern of leaf emergence. This procedure was repeated for the remaining five samples. To sample sediment-dwelling copepods, six cores were taken at Station H on each sampling date. Cores were taken at random coordinates within a 0.25 m2 quadrat divided into 100 squares of equal area. The quadrat was placed 1 m south of the station marker. Coordinates were picked randomly using a random number table. The cores were 5.3 cm2 in area and 5 cm in depth. This depth generally exceeded that of the redox potential discontinuity as determined by changes in sediment colour. Cores were extruded, separated into 0-1 and 1-5 cm depth fractions, placed into jars and preserved with a 4% Formaldehyde/40 \Lm filtered seawater solution. In the laboratory, leaf samples were processed as follows. The leaf was shaken 5 times in the sample jar to remove any attached copepods. Using samples from May 14, 1987, this procedure is 99.4 ± 0.17% (mean ± S.E., n=6) efficient in retrieving copepods. The leaf was removed, divided into, at most, 20 cm long segments and length and width measurements made to the nearest 0.5 mm. Surface area was estimated arithmetically for each segment and then segment areas were summed to obtain sample area. The solution -13-remaining in the sample jar was concentrated onto a 63 u,m sieve and rinsed with filtered seawater into a counting tray. For each sample, all copepodites of Harpacticus uniremis Kroyer, Tisbe cf. furcata (Baird) and Zaus aurelii Poppe were counted. Fifty individuals of each species were removed and identified to copepodite stage and gender. A l l remaining copepodites of other species were enumerated and 50 removed and identified to species and gross developmental stage (juvenile, adult male or female). Abundance of each species and stage in the sample was then estimated as a proportion of the total number of copepods. Nauplii were not enumerated. To obtain copepods from the core samples, filtered seawater was added to the jars, the samples were swirled, the sediment allowed to settle for 5 s and the supernatant water decanted through a 63 u,m sieve. This procedure was repeated 5 times and, based on sorting through remaining sediment in the January 22, 1986 samples, resulted in a 99.4 ± 0.36% (mean ± S.E., n=6) recovery of copepods in the 0-1 cm fraction and 100% (n=6) recovery in the 1-5 cm fraction. The concentrated sample on the sieve was rinsed with filtered seawater into a counting tray and analysis proceeded identically as with the leaf samples. To allow comparison of harpacticoid densities between seagrass and sediment samples, abundances in each sample (leaf and sediment) were converted to number-cm-2 sediment area. This was accomplished for seagrass-dwelling harpacticoids using collected data on abundances in samples, relative leaf age of samples, intrashoot copepod distributions and shoot density and leaf areas (see Appendix 2 for a detailed discussion of this methodology and Appendix 3 for the data on shoot density, leaf surface area patterns within shoots and intrashoot distributions of the copepods throughout the study period in both 1986 and 1987). A step-by-step outline of the procedure is presented in Appendix 3, Table 3. Since core area was known, sediment harpacticoid densities were directly determined for both depth fractions. -14-2.3 RESULTS A total of 55 harpacticoid species in 13 families were observed, in either leaf or sediment samples during one or both years of this study. The family Diosaccidae with 16 species observed was dominant in terms of number of species. A complete family and species listing is available in Appendix 1. Because of the large number of species found, only species with densities at their abundance peak of >10% of the total harpacticoid numbers on that sampling date in either subhabitat in either year are discussed further. Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii were exempt from this decision. The results concerning total harpacticoids, the above three species plus the others meeting the cutoff criterion, will be considered further on an individual basis. Total Harpacticoids (Figs. 2.1,2.2) In 1986, seagrass-dwelling harpacticoids had their highest mean density on January 22, when over 3500-cm-2 sediment were found. A secondary peak was observed on March 4 with numbers tapering off towards July. Maximal sediment densities were two orders of magnitude lower and peak mean density was observed on June 10, after which numbers declined to late winter levels. The vast majority of sediment-dwelling harpacticoids were observed in the top 1 cm of sediment. Maximum mean density of seagrass copepods was much lower in 1987 (under 70-cm-2 sediment on May 28) with low numbers observed until April 30. Numbers declined after the peak but remained higher than pre-April 30 values. Peak mean sediment-dwelling copepod abundance was observed on May 14 at a similar density to 1986. Densities in late January-early February were higher than in 1986 and a serious decline after the May peak was not observed. Similar to their vertical distribution in 1986, sediment-dwelling harpacticoids were mainly confined to the upper 1 cm of sediment. -15-a Sj 4500-E TO in 1 9 8 6 Figure 2.1. Abundance (number-cm"^ sediment) of total harpacticoid copepods in 1986 at Station H on Zostera marina leaves (a) and in the sediment (b), along with copepod vertical distribution in the sediment (c). Plotted values are the mean ± 1 Standard Error, n = 6. -16-a i i — i i i — i — i — i i — i — i i i 24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April May June July 1 9 8 7 b c o o 0—1 em 24 07 20 07 19 02 16 30 14 28 11 25 09 24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April May June July Jan Feb March April May June July 1 9 8 7 1 9 8 7 Figure 2.2. Abundance (number-cm"z sediment) of total harpacticoid copepods in 1987 at Station H on Zostera marina leaves (a) and in the sediment (b), along with copepod vertical distribution in the sediment (c). Plotted values are the mean ± 1 Standard Error, n = 6. -17-Harpacticus uniremis Kroyer (Figs. 2.3,2.4) In 1986, peak mean density of Harpacticus uniremis on leaves was just under 5-cm-2 sediment on April 28. Peaks in adult density in late April and May were preceded by large numbers of juvenile copepodites. Abundance of H. uniremis in the sediment was considerably lower (<0.5-cm-2 sediment) and was mainly composed of adult females which were most numerous after the peak in female abundance on the seagrass leaves. The temporal distribution of seagrass-dwelling H. uniremis was much tighter in 1987 with a maximum just slightly less than that in 1986 on May 14. Peaks in juveniles, males and females coincided. Sediment densities were also low in 1987 compared to those on the leaves and the peak in females in the sediment after the leaf peak was noted as in 1986. Tisbe cf. furcata (Baird) (Figs. 2.5,2.6) Tisbe cf. furcata mean densities in 1986 on Zostera leaves were maximal on January 22 at >750-cm-2 sediment. A smaller secondary peak was seen on March 18. These peaks were mainly caused by elevated juvenile abundances. Sediment densities were comparatively low. Abundance was much lower and temporally more discrete on leaves in 1987, with a maximum of just over 20-cm-2 sediment on May 14. Peaks in juveniles, males and females coincided. Small numbers were again observed in the sediment as in 1986. Zaus aurelii Poppe (Figs. 2.7,2.8) In 1986, Zaus aurelii mean abundance on leaves was unimodal with a peak of over 200 copepods-cm-2 sediment on April 14. Maxima of juveniles and females were on April 14 with the male maximum on the next sampling date. This species was extremely rare in the sediments. -18-c <u E '•6 0) m CM I E L) C v XI E 3 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1 9 8 6 -o Females - » Males -a Juveniles 22 06 19 04 18 31 14 28 12 26 10 24 0? April May June July 1 9 8 6 Jon Feb March Figure 2.3. Abundance (number-cm"^ sediment) of Harpacticus uniremis in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -19-c <D E '•o in v XI E D 2 2-24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April May June July 1 9 8 7 24 07 20 07 19 02 16 30 Jon Feb March April 1 9 8 7 14 28 11 25 09 May June July - 3-2-o o Females » » Males o — o Juveniles 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 Females -» Males - ° Juveniles 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 Figure 2.4. Abundance (number-cm'^ sediment) of Harpacticus uniremis in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -20-1000-750-500-250-22 06 19 04 18 31 14 28 12 26 10 24 09 Jgn Feb Morch April May June July 1 9 8 6 22 06 19 04 18 31 14 28 12 26 10 24 09 Jon Feb Morch April May June July 1 9 8 6 c me 1000 "D V at 750 CM 1 cm" 500 ^_ a> _o E 250 Z - ° Femaies - * Males - • Juveniles 22 06 19 Jan Feb 04 18 31 March 14 28 12 26 10 24 09 April May June July 1 9 8 6 1000-750-500-250--o Females - » Males -a Juveniles 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1 9 8 6 Figure 2.5. Abundance (number-cm - 2 sediment) of Tisbe cf. furcata in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -21-a c 24 07 20 07 19 02 16 30 14 28 11 25 09 24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April May June July Jan Feb March April May June July 1 9 8 7 1 9 8 7 b 201 15-10-5--« Females Males -o Juveniles 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 20 is-le-s' o—» Females » — » Males a a Juveniles 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May / June July 1 9 8 7 Figure 2.6. Abundance (number-cm"2 sediment) of Tisbe cf. furcata in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the seciiment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -22-300-200-100-22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1 9 8 6 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1 9 8 6 225-150-75-o o Females * — * Males o — o juveniles 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April Moy June July 1 9 8 6 225 150-75-° o Females * — • Males a o Juveniles 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1 9 8 6 Figure 2.7. Abundance (number-cm"2 sediment) of Zaus aurelii in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -23-c <v E XI IV in CM I E o I-<u . o E 3 60 -i 40-20-24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April May June July 60-40-20 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 1 9 8 7 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 30-20 10-o — • Females » — » Males a — ° Juveniles 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 Figure 2.8. Abundance (number-cm"2 sediment) of Zaus aurelii in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -24-Abundance was also unimodal on leaves in 1987, with a maximum mean density of just over 40-cm-2 sediment on May 28. Coincidental peaks in males and females were observed with a juvenile peak preceding. Sediment densities were extremely low, as in 1986. Amonardia normani (Brady) (Figs. 2.9,2.10) In 1986, Amonardia normani mean density on the leaves peaked on July 9, the last sampling date, at just under 7 individuals-cm-2 sediment. This maximum was composed mainly of juvenile copepodites. Densities in the sediment were low. This species had a unimodal peak on the leaves on May 28 in 1987 at just under 5-cm-2 sediment. Similar to 1986, this peak was composed of juveniles. Sediment densities were also low as in 1986. Amphiascus undosus Lang (Figs. 2.11,2.12) On the seagrass leaves, mean density of this species had a maximum on March 4 in 1986 of over 15-cm-2 sediment followed by a sharp decline with a secondary increase occurring after April 28. The March 4 peak was of juveniles which was followed by an increase in adults. The second increase was initially composed of females followed by juveniles. The sediment harboured small numbers, mainly females, throughout the sampling period. In 1987, the leaf population of this species did not increase until late April and reached a maximum of just under 10 copepods-cm-2 sediment on May 14. The leaf population was composed mainly of females with juvenile numbers highest after June 11. The sediment population in 1987 was more dense with a maximum of just under 15-cm-2 sediment on February 7 which declined towards summer. The sediment population was also composed mainly of females. -25-c 9-6- 6-3-22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1 9 8 6 22 06 19 04 18 31 Jan Feb March 14 28 April 12 26 10 24 09 May June July 1 9 8 6 b o ° Females » — » Males a — o Juveniles 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1 9 8 6 6--o Females - • Males -a Juveniles 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1 9 8 6 Figure 2.9. Abundance (number-cm"2 sediment) of Amonardia normani in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -26-c E V in E o E 2 24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb Morch April May June July 1 9 8 7 6-24 07 20 Jan Feb 07 19 02 16 30 14 28 11 25 09 March April May June July 1 9 8 7 » o Females • • Femoles « — • Males • — • Males o • Juveniles 8- o — 3 Juveniles 6-4-2-— » . 0-24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April Moy June July 1 9 8 7 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April Moy June July 1 9 8 7 Figure 2.10. Abundance (number-cm - 2 sediment) of Amonardia normani in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -27-a c CD E ~o <D in CM I E o XI E 3 401 30-20-10-401 30-20 10-22 06 19 04 18 31 Jon Feb March 14 28 April 12 26 10 24 09 May June July 22 06 19 04 18 31 Jan Feb March 1 9 8 6 14 28 12 26 April May 1 9 8 6 10 24 09 June July c IV E x> V in CM I E u c 0) XI E 3 2 40 i 30-20-10-• — o Females « » Males d—o Juveniles 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 40-, 30-20 10 -o Females -» Moles -a Juveniles 1 9 8 6 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1 9 8 6 Figure 2.11. Abundance (number-cm"2 sediment) of Amphiascus undosus in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -28-a 20 n c <u 1 9 8 7 c 20-, 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 20-, 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 20 n 15 10 ° 0 Females » — * Males ° — ° Juveniles 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 Figure 2.12. Abundance (number-cm -2 sediment) of Amphiascus undosus in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -29-Dactylopodia crassipes Lang (Figs. 2.13,2.14) In 1986, this species on the leaves exhibited sporadic density maxima of between 10 and 20-cm_2 sediment during the period from March 4 to May 26. These sporadic maxima were generally because of increases in males with an underlying long term increase in juveniles and females. The long term pattern without the sporadic increases in males was observed at lower densities in the sediment. On the leaves in 1987, a peak of just over 5 copepods-cm-2 sediment was observed on June 11. This peak was mainly because of an increase in juveniles. In the sediments, a smaller peak of juveniles, males and females together was seen on June 25. Juveniles were present in the sediments during late winter-early spring when leaf populations were extremely low. Ectinosoma melaniceps Boeck (Figs. 2.15,2.16) A maximum mean abundance of just under 9-cm-2 sediment was observed on the leaves on March 18 in 1986. This maximum was composed of juveniles and females. Sediment densities were similar to leaf densities after March 18. No obvious pattern was apparent. Mean leaf densities in 1987 were <l*cm-2 sediment throughout the sampling period. Leaf samples contained chiefly juveniles and males. Sediment densities were higher than leaf densities on most sampling dates in 1987 with the sediment population composed mainly of females. Female density in the sediment generally declined throughout the study period. Heterolaophonte variabilis Lang (Figs. 2.17,2.18) In 1986, this species showed a maximum on the leaves of just over 12-cm-2 sediment on July 9, which was composed mainly of juveniles. Sediment densities were extremely low. -30-Figure 2.13. Abundance (number-cm"2 sediment) of Dactylopodia crassipes in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -31-c E XI ID to CM I E u l l 0) -O E 3 o o Females » — • Males • a Juveniles 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 3-2-o—o Females » — » Males a — a Juveniles 24 07 20 07 19 02 16 30 Jan Feb March April 1 9 8 7 14 28 11 25 09 Moy June July Figure 2.14. Abundance (number-cm"2 sediment) of Dactylopodia crassipes in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -32-c E <D VI CN I E u u. m 15-, id-s' 22 06 19 04 18 31 Jon Feb March 14 28 12 26 10 24 09 April May June July 1 9 8 6 22 06 19 04 18 31 14 28 12 26 10 24 09 Jon Feb March April May June July 1 9 8 6 o » Females « — « Males o o Juveniles 22 06 19 04 18 31 14 28 12 26 10 24 0? Jan Feb March April Moy June July 1 9 8 6 15 10 5-• — • Females « — » Males o — a Juveniles 22 06 19 04 18 31 Jan Feb Morch 14 28 12 26 10 24 09 April Moy June July 1 9 8 6 Figure 2.15. Abundance (number-cm"2 sediment) of Ectinosoma melaniceps in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -33-a c — » 1 ' I T I T I T I 1 1 1 1 U I 1 1 1 1 • 1 1 1 1 1 1 1 1 24 07 20 07 19 02 16 30 14 28 11 25 09 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April Moy June July Jon Feb Morch April May June July 1 9 8 7 1 9 8 7 Figure 2.16. Abundance (number-cm"2 sediment) of Ectinosoma melaniceps in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -34-15- 15-10- 10-5- 5-S1 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1 9 8 6 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1 9 8 6 o o Females « — » Males a — o Juveniles ID-S' 22 06 19 04 18 31 14 28 12 26 10 24 09 Jon Feb March April Moy June July 1 9 8 6 10-5-o o Females • — « Males o — a Juveniles 22 06 19 04 18 31 14 28 12 26 10 24 09 Jon Feb March April May June July 1 9 8 6 Figure 2.17. Abundance (number-cm"2 sediment) of Heterolaophonte variabilis in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -35-c E '-5 <u in CM I E o .0 E D 12-9-24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April May . June July 12 9-6-24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April May June July 1 9 8 7 1 9 8 7 . b 24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April May June July 1 9 8 7 o — o Females » — » Males o — = Juveniles 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 Figure 2.18. Abundance (number-cm - 2 sediment) of Heterolaophonte variabilis in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -36-The 1987 maximum on the leaves was slightly lower (just under 10-cm-2 sediment) and the increase started earlier than in 1986 (May 14 in 1987 versus June 24 in 1986). The 1987 increase was composed of a greater proportion of females than in 1986. Sediment densities were low. Mesochra pygmaea (Claus) (Figs. 2.19,2.20) This species was the main contributor to the density maximum of total harpacticoid copepods on the leaves on January 22 in 1986. A peak of just over 2700-cm-2 sediment was observed, composed almost entirely of females. A secondary peak on March 4 was also composed of females. Sediment densities were comparatively low. Mean densities in 1987 were much lower on leaves, with a maximum of just under 3.5-cm-2 sediment on June 11. Females predominated until April 30 after which juveniles and males became proportionately more abundant. Sediment densities were maximal on January 24 at a similar level to the leaf maximum after which numbers declined throughout the sampling period. Sediment samples contained mostly females. Amphiascus minutus (Claus) sp. 1 Lang (Figs. 2.21,2.22) This second member of the genus Amphiascus had low leaf densities in 1986. In the sediment, a maximum mean density of just under 2-cm-2 was observed on January 22 composed chiefly of females. Densities declined after this date reaching low levels by March 18. In 1987, this species (primarily females) occurred sporadically throughout the study period in the sediment at low densities (<0.05-cm-2). it was not found in leaf samples in 1987. -37-^ 4000-c E in CM I E u 2000-- | 1000-D 2 4000 3000 2000-1000-22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 22 06 19 04 18 31 Jan Feb March 1 9 8 6 14 28 12 26 10 24 09 April May June July 1 9 8 6 b 4000-c aj E 'I 3000 T1 in CM I E o 2000-- | 1000-3 » — o Females » — » Males o — • Juveniles 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 4000 3000 2000-1000 o — o Females » — » Males • — a Juveniles 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1 9 8 6 1 9 8 6 Figure 2.19. Abundance (number-cm - 2 sediment) of Mesochra pygmaea in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean i 1 Standard Error, n = 6. -38-Figure 2.20. Abundance (number-cm"2 sediment) of Mesochra pygmaea in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -39-c CD E W CN I E u <D E 22 06 19 04 18 31. 14 28 12 26 10 24 09 Jon Feb March April Moy June July 1 9 8 6 22 06 19 04 18 31 Jon Feb Morch 14 28 12 26 April Moy 1 9 8 6 10 24 09 June July c E V U) CM I E o CD .D E 1 • o o Females » — » Males o — • juveniles 2 n 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1 9 8 6 o — o Females • — » Moles o — o Juveniles 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1 9 8 6 Figure 2.21. Abundance (number-cm"z sediment) of Amphiascus minutus sp. 1 in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -40-Figure 2.22. Abundance (number-cm"2 sediment) of Amphiascus minutus sp. 1 in 1987 at Station H in the sediment (total abundance (a) and juvenile copepodite, male and female abundance (b)). Plotted values are the mean ± 1 Standard Error, n = 6. -41-Danielssenia typica Boeck (Figs. 2.23,2.24) In 1986 samples, this species was rarely observed on leaves. Sediment samples showed a maximum of just under 3-cm-2 on March 31. This maximum was composed of juveniles, males and females. This species was also rare in leaf samples in 1987. It showed a similar temporal pattern of abundance to that of 1986 in the sediment in 1987 but a lower peak abundance was observed (<0.75-cm-2). Halectinosoma sp. 1 (Figs. 2.25,2.26) This species was the most abundant sediment-dwelling harpacticoid in both years and it defined the pattern of total harpacticoid abundance in the sediment. It was comparatively rare in leaf samples in both years. Peak abundance in the sediment was chiefly because of large numbers of females in both years. The period of maximum density in 1987 occurred earlier than in 1986. No evidence of a decline in abundance was evident near the end of the 1987 sampling period as in 1986. Pseudobradya lanceta Coull (Figs. 2.27,2.28) This species was rare in leaf samples in both years. In 1986, mean sediment densities increased steadily from January 22 to a mid-May maximum of just under 4-cm-2. The population rapidly declined during the next month. Juveniles, males and females were usually found in all samples with juveniles generally more abundant. In 1987, the sediment population increased to a peak of just under 2.5-cm-2 on April 2 after which a slower decline than observed in 1986 occurred. A secondary peak was observed on May 14. Juveniles were not as predominant in 1987. -42-b d 22 06 19 04 18 31 14 28 12 26 10 24 09 22 06 19 04 18 31 14 28 12 26 10 24 09 Jon Feb March April May June July Jan Feb March April May June July 1986 1986 Figure 2.23. Abundance (number-cm"2 sediment) of Danielssenia typica in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -43-<D E 1.0-x> CD in CN I 1 E u 0.5-CD XI E 3 2 0.0-24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April May June July 1.0 0.5 0.0 24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April May June July 1 9 8 7 1 9 8 7 0.501 c E <D in C N I E o CD XI E 3 -•> Females Males - ° Juveniles 0.50 0.25-0.00-1 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 0.25-24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 Figure 2.24. Abundance (number-cm - 2 sediment) of Danielssenia typica in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -44-c <D E •o 0> in CM I ID E 3 451 30-15-22 06 19 04 18 31 Jon Feb March 14 28 12 26 10 24 09 April May June July 45 30 15-22 06 19 04 18 31 Jan Feb March 1986 14 28 12 26 10 24 09 April May June July 1986 c E TJ 01 in CM I E u w 01 _o E z b 30 H 20-10-• — ° Females » — » Males • a Juveniles 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April Moy June July 1986 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb Morch April May June July 1986 Figure 2.25. Abundance (number-cm - 2 sediment) of Halectinosoma sp. 1 in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -45-c o E TJ OJ CM I E u OJ -O E 40-30-20-10-24 07 20 07 19 Jan Feb March 02 16 30 14 28 11 25 09 April May June July 1 9 8 7 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 30-20-1 0 -- ° Females -» Males -o Juveniies 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April May June July 1 9 8 7 Figure 2.26. Abundance (number-cm - 2 sediment) of Halectinosoma sp. 1 in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -46-2- 2-22 06 19 04 18 31 14 28 12 26 10 24 09 Jon Feb March April May June July 1986 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1986 o — o Females » — « Moles o • Juveniles 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1986 o — ° Females » » Males • — • Juveniles 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1986 ure 2.27. Abundance (number-cm"z sediment) of Pseudobradya lanceta in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -47-c E T3 O J in CN I E o k_ O J X I E 1 • 24 07 20 07 19 02 16 30 Jon Feb March April 1 9 8 7 14 28 11 25 09 Moy June July 24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April Moy June July 1987 Figure 2.28. Abundance (number-cm"2 sediment) of Pseudobradya lanceta in 1987 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -48-Robertsonia propinqua (T. Scott) (Figs. 2.29,2.30) In 1986, this species was rarely found on leaves and exhibited a small maximum of just over 1.2-cm-2 in the sediment on March 4. This peak was composed of males and females with a few juveniles. The pattern of abundance was different in 1987. A peak of just over 3-cm-2 was seen on January 24 with a smaller secondary peak on March 19. Maxima were composed of mainly males and females. This species was not collected in leaf samples in 1987. Stenhelia (Delavatta) latioperculata l td (Figs. 2.31,2.32) This species was not found in leaf samples in either year. In the sediment in 1986, a maximum of just over l-cm-2 was observed on January 22 after which the population steadily declined. Juveniles and males were rare after March 18. In 1987, the maximum mean sediment density was halved compared to 1986 and no obvious pattern was apparent in the population. This species generally maintained a stable density throughout the study period. 2.4 DISCUSSION Of the 55 harpacticoid copepod species encountered over both sampling years, 15 species were considered for detailed analysis. Amonardia normani, Amphiascus undosus, Dactylopodia crassipes, Harpacticus uniremis, Heterolaophonte variabilis, Mesochra pygmaea, Tisbe cf. furcata and Zaus aurelii are considered to be epiphytic since they were found to be more abundant on seagrass leaves than in the underlying sediment or to undergo their majority of pre-adult development (as evidenced by juvenile numbers) in this subhabitat (e.g. Amphiascus undosus, Mesochra pygmaea). This harpacticoid fauna is similar in the composition of families and genera to other epiphytic faunas in temperate waters of the northern hemisphere (e.g. Hicks 1980; Hicks 1985b; Johnson and Scheibling 1987). -49-2.0 1.5-1.0-c <v E X) 0) 1/1 CM I E u X i 0.5 -E D 0.0-i 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1986 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April Moy June July 1986 c OJ E T> OJ U) CM I E o iL OJ X I E 3 i.o-0.5-o ° Females » — « Males a — a juveniles 0.0-22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July o Females • Males o Juveniles 1986 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1986 Figure 2.29. Abundance (number-cm"2 sediment) of Robertsonia propinqua in 1986 at Station H on Zostera marina leaves (total abundance (a) and juvenile copepodite, male and female abundance (b)) and in the sediment (total abundance (c) and juvenile copepodite, male and female abundance (d)). Plotted values are the mean ± 1 Standard Error, n = 6. -50-c CD CD 00 CN E O 24 07 20 07 19 02 16 30 14 28 1 1 25 09 Jan Feb March April May June July 1 9 8 7 c CD E '-o CD CO C M I E o i l CD E ° ° Females * * Males c • Juveniles 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 Figure 2.30. Abundance (number-cm"z se(ument) of Robertsonia propinqua in 1987 at Station H in the sediment (total abundance (a) and juvenile copepodite, male and female abundance (b)). Plotted values are the mean ± 1 Standard Error, n = 6. -51-c E '"O OJ cn CNJ I E o \L OJ E 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1 9 8 6 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1 9 8 6 Figure 2.31. Abundance (number-cm"z sediment) of Stenhelia (D.) latioperculata in 1986 at Station H in the sediment (total abundance (a) and juvenile copepodite, male and female abundance (b)). Plotted values are the mean ± 1 Standard Error, n = 6. -52-0.75 c CD X> CD CO CN E U i l CD 0.50 0 .25 -0.00 07 19 March 02 16 April 1 9 8 7 14 28 May 11 25 09 June July c CD XI CD CO CN 0.50 I 0.25-I E o CD E 0.00 / o -• -•° Females * Males ° Juveniles 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April 1 9 8 7 May June July Figure 2.32. Abundance (number-cm - 2 sediment) of Stenhelia (£>.) latioperculata in 1987 at Station H in the sediment (total abundance (a) and juvenile copepodite, male and female abundance (b)). Plotted values are the mean ± 1 Standard Error, n = 6. -53-Harpacticoid species that can be considered sediment-dwellers since they were abundant in the sediment but not on the seagrass leaves are Amphiascus minutus sp. 1, Danielssenia typica, Halectinosoma sp. 1, Pseudobradya lanceta, Robertsonia propinqua and Stenhelia (D.) latioperculata. In both years, the sediment community was dominated in numbers by the Ectinosomid Halectinosoma sp. 1. Community dominance by the Ectinosomatidae is not uncommon in shallow soft-sediment habitats (see Hicks and Coull 1983). Ectinosoma melaniceps appears to have a shared abundance between the leaf and sediment subhabitats with juveniles present in both. This is also the case for populations of this species inhabiting New Zealand Zostera beds (Hicks 1986), where it was designated an "itinerant" species. In 1986, the highest total leaf copepod densities occurred before March 18. These abundances were extremely high, especially on the first sampling date. This peak was mainly caused by high numbers of Mesochra pygmaea and Tisbe cf. furcata, but may be artificial since only a few individuals of each species were found in the samples. The high calculated density was due to these individuals being found in samples of leaves from the areal midpoint of shoots, where there should have been none according to the March intrashoot distribution data (see Appendix 3). The January 22,1986 sampling date was notable for large numbers of ducks feeding on Zostera shoots in the vicinity of Station H during sampling. Numerous feeding pits were noticed in the sediment. It is possible that the high copepod densities calculated are artifacts of this disturbance. The copepods may have been redistributed within shoots by the feeding activity of the birds, thus leading to calculation of artificially high densities. The abundance pattern and densities observed in 1987 for Tisbe and Mesochra, and in turn total harpacticoids, may be more realistic and typical. Since the leaf epiphyte community is the primary subhabitat for the harpacticoid species previously identified as being the major prey for juvenile salmonids at the study site (Harpacticus uniremis, Tisbe and Zaus aurelii) (D'Amours 1987), further detailed discussion -54-of species abundance patterns on the leaves throughout the study period is warranted. Excluding the possibly artifactual density maxima of Tisbe and Mesochra in 1986, the epiphytic community present from late January to early July in both years is characterized by two major harpacticoid species groups: 1) early to mid sampling period group and 2) late sampling period group. Leaf-dwelling harpacticoid species with their abundance maxima in the early to mid sampling period are Dactylopodia crassipes, Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii. These 4 species start to increase in abundance in mid-March to mid-April and have generally declined to low densities by mid-June. A detailed analysis of the abundance patterns of Harpacticus, Tisbe and Zaus will be presented in Chapter 3. Late period species are Amonardia normani, Amphiascus undosus and Heterolaophonte variabilis. These 3 species generally start to increase in abundance in mid-May, with persistent high densities or evidence of further possible increases (i.e. large numbers of juveniles) on the last sampling date in early July. While the details of this pattern vary somewhat between the two years studied, the basic structure is similar, as has been found for seasonal patterns in multi-year harpacticoid data sets (e.g. Coull and Dudley 1985). Ectinosoma melaniceps and Mesochra pygmaea were found in reasonable numbers throughout the study period in both years. The leaf harpacticoid community, excluding the January 22, 1986 sampling date, exhibits a general increase in abundance starting in early to mid-March in 1986 and in early to mid-April in 1987. A similar increase in the spring is also seen in the sediment community. A spring "bloom" of harpacticoid copepods is commonly observed in epiphytic and sediment communities (e.g. Hagerman 1966; Kito 1977; Rudnick et al. 1985; Bell et al. 1986; Johnson and Scheibling 1987). This pattern may be related to increases in temperature and light levels during the spring leading to enhanced bacterial and microalgal production. These two groups are considered to be the major food source for marine harpacticoid copepods (see Hicks and Coull 1983). At this study site, the spring harpacticoid "bloom" -55-may be predictably triggered by shifts in tidal pattern which lead to increased light levels and temperature (D'Amours 1988b). Some of the epiphytic species populations on the leaves appear to be seeded from females in the sediment earlier in the sampling season. However, reproduction (as deduced from increases in the number of juveniles) seems to take place primarily on the leaves. This appears to be the case for Amphiascus undosus, Dactylopodia crassipes and Mesochra pygmaea and is especially obvious in the 1987 data. For A. undosus and M. pygmaea, the leaf population appears to be initiated from females present in the sediment in late January and February which have presumably overwintered there. Females appear on the leaves without juveniles being present beforehand which implies immigration, with the sediment females being a likely source. The D. crassipes leaf population is also probably seeded from the sediment. However, juveniles are present in the sediment in January and February. The juveniles are male and female fifth stage copepodites (the adult is the sixth copepodite) which are encysted in a manner similar to that described by Coull and Grant (1981) for Heteropsyllus. The Dactylopodia within the cysts have a bent urosome like the description for Heteropsyllus and droplets (presumably lipid) can be seen within the copepods. If these copepods are truly encysted, then I believe this is the first record of encystment in marine harpacticoids after that of Coull and Grant (1981). Overall, the distribution of these three species implies that individuals of epiphytic species may commonly spend portions of the year in the sediments, perhaps as a mechanism to avoid stress. One record of habitat switching of this kind is found for the harpacticoid Thalestris longimana Claus in England where females overwinter subtidally but reproductive activity occurs only in the summer on intertidal macroalgae (Hicks 1979). In summary, from leaf and sediment samples taken from late January to early July in 1986 and 1987, both the seagrass Zostera marina and the underlying sediment harbour a diverse and abundant harpacticoid copepod community. The seagrass leaf community has two major groups which are abundant at different times. The leaf community generally -56-differs from the sediment community in species composition but some epiphytic species are common in the sediment in winter, presumably as overwintering individuals. -57-3. MORTALITY PATTERNS OF SELECTED EPIPHYTIC HARPACTICOID COPEPODS: COMPARISON WITH PATTERNS OF SALMONID CONSUMPTION 3.1 INTRODUCTION As discussed in the general introduction to this thesis, marine harpacticoid copepods have been observed to be eaten in large quantities by non-salmonid fishes. However, the effect of this predation on the copepod community appears to be minimal. The evidence regarding the effect of juvenile salmonid predation is more controversial. Healey (1979) states there is a strong effect on one harpacticoid species while Cordell (1986) suggests that the same species is not affected. Both studies are based on indirect and weak evidence. Ignoring aforementioned problems with adequately sampling the target harpacticoid community, Healey's (1979) estimate of predatory mortality is based on a crude bioenergetic model of fish feeding parameters and ration over the entire sampling season while Cordell's (1986) estimate of predator impact is based on changes in the specific composition of gut contents with no regard for changes in fish abundance and consumption rates. To resolve the question of the impact of juvenile salmonids on harpacticoid communities, direct comparisons of mortality rates of the harpacticoid prey assemblage to rate of mortality imposed by the fish in the field are required. Estimates of mortality imposed by fishes on harpacticoid copepod populations in the field are few. Alheit and Scheibel (1982) probably accurately described the predatory impact of grunts on the harpacticoid Longipedia in Bermuda (0.1% of population-d-! consumed) using assessments of fish density by divers, numbers of the copepod in guts, an estimated gut turnover rate and density estimates for the harpacticoid in the area. Hicks (1985a) used a similar method of obtaining consumption rates but he based his estimate on a seasonal average of copepod abundance. Healey (1979), De Morais and Bodiou (1984) and Gee -58-(1987) also used long-term averages of predator and prey abundance to estimate harpacticoid copepod mortality. No discrete estimates of predatory mortality performed serially over a long period (i.e. months) are available. Estimations of total mortality rates for field populations of harpacticoid copepods are also uncommon in the literature. The general method used is to estimate the coefficient r (the parameter of the intrinsic rate of increase in the exponential model for population growth) from population abundance data. Birth rate (b) of the population is estimated using a modification of the "egg-ratio" method adapted for sexual populations (e.g. Van Dolah et al. 1975). The instantaneous mortality rate (d) is then calculated from the relation r = b- d. This methodology has been used by Fleeger (1979), Feller (1980) and Palmer (1980). However, the birth rate in these studies probably has been severely overestimated since no corrections for egg mortality were used. Unless egg mortality is zero or a correction based on substaging the embryonic population employed to estimate egg mortality (e.g. Dorazio 1986), population mortality rates are probably in error and therefore inadequate. Since Harpacticus uniremis, Tisbe spp. (actually mostly Tisbe cf. furcata) and Zaus aurelii were previously identified as the most important harpacticoid prey species for juvenile salmonids at this study site (D'Amours 1987), determination of copepod mortality rates and salmonid feeding rates were confined to these three species. The abundance of eggs and individual copepodite stages and genders were estimated. The number of eggs per adult female was calculated on each sampling date as an index of the reproductive activity of the population. Using a simple and robust deterministic compartmental model, copepod mortality rates were estimated between consecutive sampling dates. Predation rate by juvenile chum and pink salmon was also estimated between sampling dates using fish abundance data, copepod abundance in gut contents and gut evacuation rates. This was done throughout the time of presence of juvenile salmon in the study area in both years and is the first discrete-interval, long-term study of harpacticoid mortality in relation to fish predation. -59-3.2 M E T H O D S 3.2.1 Harpacticoid Mortality General sampling methodology and protocol for estimating abundance for copepods at Station H is as described in the Chapter 2 Methods section. In each sample, as described, all copepodites of Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii were counted. In addition, all adult females were counted and the number of gravid (i.e. carrying an egg sac on the urosome) females was noted. Fifty copepodites of each species were removed and identified to one of the six copepodite stages (copepodite 1 (CI) to copepodite 6 (C6), where C6 is the adult) and gender, i f possible. Total abundance of each stage and gender was estimated as a proportion of the total number of copepodites of that species in the sample. The first 5 gravid females of each species encountered in the sorting process were removed, the egg sacs teased apart with fine needles and the number of eggs recorded. Estimation of the number of eggs-cm-2 sediment in each sample was based on the number of females-cm-2 sediment, the proportion of gravid females present and the mean number of eggs in the 5 counted sacs. Number of eggs-female-1 in each sample was calculated by dividing number of eggs-cm-2 sediment by number of females-cm-2 sediment. To estimate the mortality of each species between sampling dates, a simple deterministic compartmental model, based on that of Argentisi et al. (1974), was used. The form is: [1] N a , t + l = N a , t + N r - M , where Na is the number of adults, N r is the number of juveniles that could potentially develop into adults during the interval between samples (t to t+1), M is the number of adults and potential adults dying during the interval and t is the sampling date. As long as the number of adults at each sampling date and the number of potential recruits to the adult -60-population in the interval between sampling dates can be estimated, mortality can be determined. This model was run for each gender in both years. To determine mortality between sampling dates, the mean abundances of adults (summing leaf and sediment densities) on each sampling date were used and recruitment was estimated from juvenile copepodite abundance on the first sampling date and by determining copepodite development time at the mean temperature during the interval between samples. Development times were estimated from predictive equations formed from literature data, with temperature as the independent variable (see Appendix 4 for details). Mortality of each gender in the interval between samples was simply calculated as predicted potential minus actual adult number. Assumptions inherent in the model are that there is a uniform age distribution in each juvenile stage and that immigration and emigration are equal or zero. This model does not provide stage-specific mortality rates for juveniles over the sampling season since standard methods for this (e.g. Southwood's graphical method (see Southwood 1978)) are inaccurate unless the pattern and relative amount of mortality within a stage is known (Sawyer and Haynes 1984; Hairston and Twombly 1985). Therefore calculated species mortality rates using the model are restricted to the gross category of adults and potential adults. Since dependence of copepodite development time on temperature was the method used to estimate the number of potential adults between sampling dates, accurate measurement of this parameter was required at Station H . Temperature was measured using a Peabody-Ryan recording thermograph emplaced at Station H for the majority of the sampling season in both 1986 and 1987. The thermograph was encased in a perforated P V C tube and buried, probe upward, in the sediment within 5 m of the station. The thermograph probe tip was 1 cm below the sediment surface in 1986 and level with the surface in 1987. Temperature records were obtained from February 19 to July 9 in 1986 and February 20 to July 9 in 1987. Data were manually digitized from the thermograph chart paper to the nearest 0.5°C at 4 h intervals. The average of all temperature values extracted between sampling dates was used as the average temperature between sampling dates. Resulting temperature -61-records for both years are presented in Fig. 3.1. In both years, temperature for the two intervals preceding thermograph emplacement was assumed to be equal to that of the first measured interval. These measured intersampling temperatures are assumed to be the temperature experienced by both seagrass and sediment-dwelling harpacticoids since temperatures obtained with a hand-held thermometer in the ~5 cm of water overlying the sediment on each date did not differ significantly from those measured by the thermograph in both years (regression of water temperature on thermograph temperature, Ho: slope not different from 1, P>0.05). Using these average intersampling temperatures, mean copepodite development times (along with 95% Confidence Limits of the predictions) between sampling dates were obtained (see Appendix 4). Three values of copepodite development time (mean and associated 95% Confidence Limits) were calculated for each intersampling interval. These values are for females only and if used to estimate individual copepodite stage durations, isochronal development (equal stage duration) must be assumed (see Appendix 4). Therefore, they are not as yet applicable to estimating the development times of potential males since males may develop faster than females (see Bergmans 1981). Also, the assumption of isochronal development for copepods may be invalid since there is evidence that a large proportion of the copepodite development may be spent in the later (e.g. C4, C5) copepodite stages (Bergmans 1981; Landry 1983). To alleviate these application problems, male copepodite development time and differential stage durations were calculated and applied to all three species using Bergmans' (1981) extremely precise observational data for Tisbe furcata (see Table 3.1). Table 3.1 also includes estimated sex ratios for the first 3 copepodite stages of each copepod species, which cannot be assigned to gender on the basis of secondary sexual characteristics. Sex ratios were calculated by surnming the abundances of each gender in the C4 stage throughout the sampling season in each year and then dividing the two sums to get a ratio. This approach assumes no gender differential mortality in the C4 stage. -62-a 1 i ~ i i — i — i — i — i — i — i — i — , — i — 22 06 19 04 18 31 14 28 12 26 10 2 4 09 J a n Feb March April May June July 1 9 8 6 b 24 0 7 20 0 7 1 9 0 2 16 3 0 14 2 8 11 25 09 J a n Feb March April May June July 1 9 8 7 Figure 3.1. Mean sediment surface temperature (°C) between harpacticoid copepod sampling dates at Station H in 1986 (a) and 1987 (b). -63-Table 3.1. Estimates of percentage of total copepodite development time spent in individual stages for male and female harpacticoid copepods, male copepodite development time as a percentage of female (both after Bergmans (1981) for Tisbe furcata at 18°C) and estimated juvenile copepodite (C1-C3) sex ratio for Harpacticus uniremis (H), Tisbe cf. furcata (T) and Zaus aurelii (Z). C1-C5 = Copepodites 1 to 5. % of Total Sex Ratio (femalermale) Female Male H T Z CI 15.2 18.5 1986 2.8:1 5.4:1 1.5:1 C2 15.2 18.5 1987 2.4:1 1.1:1 1.5:1 C3 18.2 18.5 C4 21.2 18.5 C5 30.3 25.9 Male development time = 81.8% of female -64-Using the abundance and development time calculations described above, adult and potential adult mortality for both males and females was calculated for each interval between sampling dates in 1986 and 1987 for Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii. To test the robustness of the model to the assumptions regarding non-isochronal development, unequal gender stage durations and juvenile sex ratios, an empirical sensitivity analysis was performed. Using the best development time estimate (i.e. the one value of the mean prediction and associated 95% Confidence Limits that gave the least number of negative mortality estimates during both sampling seasons), the model was rerun with isochronal development, equal development times for each gender and a 1:1 sex ratio for the C1-C3 stages. Two assumptions which could not be assessed were uniform age distributions within each juvenile stage and the standard one of immigration and emigration being equal or zero. The uniform age distribution assumption is probably not a severe problem due to the long interval (i.e. 14 d) between samplings compared to the stage development times. 3.2.2 Salmonid Abundance and Consumption Estimates of juvenile chum and pink salmon abundance in 1986 and juvenile chum alone in 1987 were made from samples collected at Station F on Roberts Bank (see Fig. 1.1). Samples were collected at approximately biweekly intervals from early March to early July in both years. Collections were made at the daytime low tide on the day after sampling Station H in 1986 and on the same day, prior to sampling at Station H , in 1987. Fish were collected with a 15 m long (3 m bunt), 1.85 m high beach seine with a stretched mesh size of 1 cm in the wings and 3 mm in the bunt. The seine was placed parallel to the shore and retrieved using lines from the shore. In 1986, the seine was set by boat approximately 10 m from shore. In 1987, due to logistical difficulties, the seine was set manually approximately 5 m from shore. The seine was set 3 times on each sampling date. Catch Per Unit Effort (CPUE, the number of fish in 3 seine sets) was used as an index of abundance of juvenile salmon. CPUE is a valid index of abundance over time if the "catchability" of the target -65-population does not vary (see Ricker 1975). This seems to be valid for juvenile salmon nearshore since juvenile chum of different size are equally vulnerable to beach seines in the range of 35-80 mm (Bax 1983), which is generally the size range of fish nearshore at Station F (see D'Amours 1987). At least twenty juvenile chum and/or pink salmon, if present, were taken randomly from the first seine catch by pulling the seine completely onto the shore and collecting the first twenty fish from the left edge of the bunt to the sampler on each sampling date. The fish were preserved in a 4% Formaldehyde/ seawater solution. No regurgitation of stomach contents was observed. Samples of other fish species (e.g. juvenile chinook salmon (Oncorhynchus tshawytscha (Walbaum))) were often taken concurrently. In 1986, both juvenile chum and pink were often caught together. It was difficult to differentiate these two species in the field so identification occurred after preservation. Therefore, in 1986, individual species abundances were based on proportions in the preserved samples. Pink salmon were not found in any 1987 seine sets. Fish samples were analyzed in the laboratory at least six months after preservation. Individual fish were removed from sample containers, blotted dry, and weighed to the nearest 10 mg on a Mettler P1210 top-loading balance. To analyze gut contents, the fish was cut open and the digestive tract severed anteriorly just behind the gill arches and posteriorly at the anus. The gut along with its contents was blotted dry and weighed to die nearest 50 u,g on a Mettler H16 balance. The gut was then sliced open, its contents removed and the gut wall reweighed. Food weight was then measured by subtraction. To estimate dry weight of both fish body weight and food weight, predictive equations relating dry weight to wet weight were formulated. Each sample usually had extra salmonids not used for gut content analysis. One fish chosen randomly from each sampling date in 1986 and 1987 plus the smallest and largest fish present were blotted dry, weighed, rinsed with 10 ml of distilled water, placed in an aluminium weighing boat, dried at 60°C for 24 h and reweighed. One randomly selected premeasured gut content from each sampling date in 1986 and 1987 plus -66-the smallest and largest wet weight gut contents found were filtered at a vacuum pressure of -1.1 arm onto predried (60°C, 24 h), preweighed Whatman GF/C filters. Filters were rinsed with 10 ml of distilled water to remove salts. The filters were placed into aluminium weigh boats, dried at 60°C for 24 h and weighed. Dry food weight was estimated by subtraction of filter weight. Dry weight was regressed against wet weight for both fish and food (Fig. 3.2). Wet weights throughout the study were then converted to dry weight using these predictive equations (Fig. 3.2). Salmonid gut contents were analyzed in a counting tray. A l l copepodites of Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii were enumerated. At least 50 copepodites of each species were identified to stage and gender, where possible. In some cases (i.e. only adult males and females in gut contents), all the copepodites were staged. A l l copepodites of other species were counted and 50 removed and identified to species and gross development stage (juvenile, male or female). In 1986 samples, to test whether chum salmon were feeding on similar numbers of harpacticoids as pink salmon, abundances of the three studied copepods-mg-1 dry food weight in the fish were compared between salmon species starting with the April 29 data. Comparisons were made using Student's Mest on the untransformed data. Variances were checked for homogeneity using Bartlett's test at the 0.05 level of significance. If heteroscedascity was found, the data were loge(x-fl) transformed. The log transformation was successful in removing heteroscedascity in all cases when applied. The 0.05 level of significance was observed. A l l analyses were performed using the M G L H module of SYSTAT (Wilkinson 1985) on an I B M PC/XT microcomputer. Using the youngest copepodite stage that was a potential adult for either gender (determined from the copepodite development time predictions (see above)), the number of adults and potential adults of each gender consumed-h-1-fish-1 within the intersampling interval was calculated. Unsexable juveniles were considered to be all of the gender for which mortality was to be calculated. Estimation of consumption-h-l-fish-1 required a knowledge of copepod abundance in gut contents and gut turnover rate. Number of adults -67-and potential adults-mg-1 dry food weight was estimated for each fish. Food evacuation rate (% dry body weight-h-1), depending on mean intersampling interval temperature, was calculated (see Appendix 5). Assuming the maintenance of a constant food weight in the fish guts, dry food weight consumed-h-1 was estimated for each date for each fish on the basis of its body weight. Since number of adults and potential adults consumed-mg-1 dry food weight was known, number of adults and potential adults consumed-h-1-fish-1 was calculated for each sampling date. The number consumed over the interval was calculated by averaging values from consecutive sampling dates. Averages were made for the mean number consumed and the 95% Confidence Limits, since sample size sometimes varied between consecutive sampling dates. If these averages are multiplied by the average number of fish obtained from numbers on the two consecutive sampling dates, a mean and an error for number of adults and potential adults consumed-h-1 by the salmonid population is obtained. Note that this value is solely an index of consumption and does not represent harpacticoid consumption on an areal basis (since fish density could not be assessed areally). Patterns of mortality of adults and potential adults at Station H (Deaths-cm-2-d-l) for each gender of the three harpacticoid species were compared to patterns in the number of adults and potential adults consumed-h-1 by the salmonid population sampled at Station F. Fish data were collected one day after the copepods in 1986. For comparative purposes these values were assumed to be the same as on the previous day. In 1987, collections of salmonids were performed on the same day as copepod sampling. If patterns of mortality and consumption are dissimilar, then it is likely that juvenile salmonid predation alone does not control the abundance of these harpacticoid copepod species. This comparison is only valid if the fish gut contents in the sampled fish population reflect feeding in the seagrass bed and there are no dramatic changes in fish feeding rate during the day. These suppositions are supported by relationships of the abundance of Harpacticus, Tisbe and Zaus in gut contents with tidal height and high resolution determination of fish food weight diurnally (see Appendix 5). -68-1.0 0.5 CD O 0.0 0 1 2 3 Wet we igh t (g ) CT) J Z CD 'CD 100 200 300 Wet we igh t ( m g ) 400 Figure 3.2. Relationships between dry weight and wet weight for juvenile chum and pink salmon (a) (Dry weight = 0.004 + 0.21-(Wet weight), r2 = 0.99, n = 21, P<0.001) and salmon gut contents (b) (Dry weight = -2.3 + 0.14-(Wet weight), r2 = 0.97, n = 18, P<0.001). 3.3 RESULTS -69-3.3.1 Harpacticoid Mortality The egg and copepodite stage abundances for the three harpacticoid copepod species described are presented for 1986 and 1987 in Figs. 3.3 to 3.8 (Figs. 3.3, 3.4: Harpacticus uniremis; Figs. 3.5, 3.6: Tisbe cf. furcata; Figs. 3.7, 3.8: Zaus aurelii). For all three species gender could be determined morphologically only at the fourth copepodite stage (C4). In 1986, Harpacticus uniremis adult females (C6 female) were first observed in leaf samples on March 4 (Fig. 3.3). The peak abundance on the leaves was on April 28 with a decline to zero by June 10. In the sediment, females were the only commonly observed stage and were first seen on April 14 with a peak abundance on May 26 dropping to zero on June 24. Egg numbers were highest on March 4 and then declined gradually to zero by June 10. The C I , C2, C3, C4, C5, and adult male stages all first appeared on March 18. The CI and C2 stages peaked on March 18 and both had disappeared by May 12. The C3, C4 and C5 stages had a maximum density on April 28 and disappeared by May 26. The adult male population peaked on May 26 and declined to zero by June 24. The Harpacticus uniremis population in 1987 generally first appeared in April (Fig. 3.4). A few C6 males and C4 females were present on March 7. The temporal pattern was much sharper in 1987 than in 1986 with all copepodite stages peaking in abundance on May 14. However, adult females in the sediment did not reach a maximum density until June 11. Egg density had two almost equal peaks on April 16 and May 14 but eggs disappeared by May 28. A l l the juvenile copepodite stages and leaf-dwelling adult females were gone by June 11. Adult males and females in the sediment disappeared on July 9. The Tisbe cf. furcata population had a prolonged temporal distribution relative to Harpacticus in 1986 (Fig. 3.5). Adult males and females, eggs, C3, and C4 and C5 females were all first seen on January 22. The C4 female and C5 female stages were extremely abundant and peaked on this date. The CI and C2 stages were first observed on February 6 -70 -T3 V in CN I £ o <D E 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1986 22 06 19 04 18 31 Jon Feb March 14 28 12 26 10 24 09 April May June July 1986 c CD E x> <u in CN I E u <D E 3 0.75 0.50-0.25-0.00 C3 o—o Leaves » — » Sediment 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1986 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1986 Figure 3.3. Abundance (number-cm -2 sediment) of Harpacticus uniremis eggs and copepodite stages on Zostera marina leaves and in the sediment at Station H in 1986. Individual plots are for eggs (a), CI (b), C2 (c), C3 (d), C4 Male (e), C4 Female (f), C5 Male (g), C5 Female (h), C6 Male (i) and C6 Female (j)- Values are the mean ± 1 Standard Error, n = 6. - 7 1 -Figure 3.3. Continued. -72-C6 Male c CD CD CO CM I E u CD E o -A -• o Leaves Sediment 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1 9 8 6 C6 Female c CD x> CD CO CM I E CJ CD E 1.0 0.5-^ 0.0 •° Leaves Sediment 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1 9 8 6 Figure 3 . 3 . Continued. -73-c d 24 07 20 07 19 02 16 30 14 28 11 25 09 24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April Moy June July Jon Feb March April May June July 1 9 8 7 1 9 8 7 Figure 3.4. Abundance (number-cm"z sediment) of Harpacticus uniremis eggs and copepodite stages on Zostera marina leaves and in the sediment at Station H in 1987. Individual plots are for eggs (a), CI (b), C2 (c), C3 (d), C4 Male (e), C4 Female (f), C5 Male (g), C5 Female (h), C6 Male (i) and C6 Female (j)- Values are the mean ± 1 Standard Error, n = 6. -74-24 07 20 07 19 02 16 30 14 28 11 25 09 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb Morch April May June July Jan Feb Morch April May June July 1 9 8 7 1 9 8 7 Figure 3.4. Continued. -75-C6 Male 24 07 20 07 19 02 16 30 14 28 1 1 25 09 Jan Feb March April May June July 1 9 8 7 1.0 c CD CD CO CN I E o iL CD - Q E J C6 Female •° Leaves Sediment 0.5' 0.0 24 07 20 07 19 02 16 30 14 28 1 1 25 09 Jan Feb March April May June July 1 9 8 7 Figure 3.4. Continued. -76-Figure 3.5. Abundance (number-cm - 2 sediment) of Tisbe cf. furcata eggs and copepodite stages on Zostera marina leaves and in the sediment at Station H in 1986. Individual plots are for eggs (a), C I (b), C2 (c), C3 (d), C4 Male (e), C4 Female (f), C5 Male (g), C5 Female (h), C6 Male (i) and C6 Female 0)- Values are the mean ± 1 Standard Error, n = 6. -77-c E TJ CD in CM I E o l l <D X> E 3 C 5 Mole o — o Leaves » — » Sediment 600-400-200 C5 Female « » Leaves » » Sediment 22 06 19 04 18 31 Jon Feb March 14 28 12 26 10 24 09 April May June July 1986 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1986 Figure 3.5. Continued. -78-C6 Male 1 9 8 6 C6 Female ° ° Leaves a * Sediment 1 9 8 6 Figure 3.5. Continued. -79-and the C4 and C5 males on March 4. A l l copepodite stages and eggs were abundant on March 18. The CI , C2 and C3 stages declined after this. Eggs and the C4 stages had another peak on April 28. Adult male and female abundance peaked on May 12. The female maximum on May 12 was similar to that of March 18. Eggs and all copepodites except the adult female had disappeared by June 10. Adult females were not seen on or after June 24. In 1987, eggs and a number of the copepodite stages including the adults of Tisbe cf. furcata were seen on January 24 (Fig. 3.6). However, population densities were low until at least mid-April. Eggs and the CI , C4 female, C5 and C6 male and female all had maxima on May 14. The peak of the C2, C3 and C4 male stages was on May 28. A l l copepodites and eggs had disappeared by June 25. Zaus aurelii C I , C2 and C3 stages first appeared on February 19 in 1986 (Fig. 3.7). A few C4 females were present on February 6 but were not seen again until March 4. The C6 female stage and eggs were first observed on February 6. The C5 of both genders first appeared on March 4 while the C4 male and adult male did not appear until March 18. A l l stages and egg densities reached a maximum on April 14, except for the C5 stages and adult males, which peaked on April 28. The population had generally declined to zero by June 10. In 1987, Zaus aurelii appeared later in the sampling season than in 1986 (Fig. 3.8). A few C2 and C3 stages were found in March. A l l copepodite stages and eggs were seen on April 16. The C I stage peaked on April 30 and was still abundant on May 14. The C2 was abundant on April 30 but was maximal on May 14. The C3 and C5 males also peaked on May 14 while the C4 male had already peaked on April 30. Adults and the C4 and C5 female stages were maximal on May 28, along with egg numbers. Most copepodite stages disappeared by June 11. Adults, eggs and C5 females were still present on June 11 but were gone on June 25. Numbers of eggs-female-1 for Harpacticus uniremis in 1986 were maximal on March 4 and decreased to March 31, after which this value stayed fairly constant (Fig. 3.9a). In 1987, this parameter peaked on April 2 and steadily declined thereafter (Fig. 3.9b). For Tisbe -80-Figure 3.6. Abundance (number-cm"z sediment) of Tisbe cf. furcata eggs and copepodite stages on Zostera marina leaves and in the sediment at Station H in 1987. Individual plots are for eggs (a), CI (b), C2 (c), C3 (d), C4 Male (e), C4 Female (f), C5 Male (g), C5 Female (h), C6 Male (i) and C6 Female (j)- Values are the mean ± 1 Standard Error, n = 6. -81-C5 Male 0.75 0.50-0.25-0.00 C5 Female o o Leaves » » Sediment 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April Moy June July 1 9 8 7 24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April May June July 1 9 8 7 Figure 3.6. Continued. -82-C6 Male •° Leaves * Sediment » ~ » — » — ~ y ~ — o + ^ — I — ^ $ 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 C6 Female 1.0 ° ° Leaves * * Sediment 0.5 A 0.0 $ 3—- ^ ——^  ^ 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April 1 9 8 7 May June July Figure 3.6. Continued. -83-o o o T3 E u E 3 12- Eggs o — o Leaves ai * — * Sediment C. •6 v in E <j ti v J3 E D 22 Jan 06 19 Feb 04 18 31 March 14 28 April 986 12 26 Moy 10 24 09 June July 12 26 10 24 09 May June July 1986 Figure 3.7. Abundance (number-cm"2 sediment) of Zaus aurelii eggs and copepodite stages on Zostera marina leaves and in the sediment at Station H in 1986. Individual plots are for eggs (a), CI (b), C2 (c), C3 (d), C4 Male (e), C4 Female (f), C5 Male (g), C5 Female (h), C6 Male (i) and C6 Female (j). Values are the mean ± 1 Standard Error, n = 6. -84-f c OJ E T> OJ CO C N I E u hi OJ X I E 3 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1986 3 2 C4 Female o — o Leaves » » Sediment 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1986 C5 Male o » Leaves »——» Sediment C5 Female 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb Morch April Moy June July 1986 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1986 Figure 3.7. Continued. -85-c OJ E OJ U) CM I E u i l OJ - Q E C6 Male ° — o Leaves A * Sediment 40 2 0 -0 22 06 19 04 18 31 Jan Feb March -* * p * o * * — 14 28 12 26 10 24 09 April May June July 1 9 8 6 C6 Female c OJ E x> OJ 00 OJ I E u l l OJ - Q E 225 150-75 0 Leaves A Sediment 0 22 06 19 04 18 31 Jan Feb March 14 28 12 26 10 24 09 April May June July 1 9 8 6 Figure 3.7. Continued. -86-Figure 3.8. Abundance (number-cm"2 seciiment) of Zaus aurelii eggs and copepodite stages on Zostera marina leaves and in the sediment at Station H in 1987. mcUvidual plots are for eggs (a), C I (b), C2 (c), C3 (d), C4 Male (e), C4 Female (f), C5 Male (g), C5 Female (h), C6 Male (i) and C6 Female (j). Values are the mean ± 1 Standard Error, n = 6. -87-f 0.75 C4 Female 0.00 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 g h 24 07 20 07 19 02 16 30 14 28 11 25 09 24 07 20 07 19 02 16 30 14 28 11 25 09 Jon Feb March April May June July Jan Feb March April May June July 1 9 8 7 1 9 8 7 Figure 3.8. Continued. -88-c OJ CD 00 CM C6 Male -o Leaves Sediment 2 0 4 E o CD E ZJ 1(H 0 P * * * « » * ? * 9 9 2 4 0 7 20 07 19 02 16 30 14 28 11 2 5 09 J a n Feb March April May June July 1 9 8 7 c CD E CD 00 CN I E u C CD E • J 3 0 2 0 J 1 ( H C6 Female ° — ° Leaves A A Sediment 0 2 4 0 7 20 07 19 02 16 30 14 28 1 1 2 5 09 J a n Feb March April May June July 1 9 8 7 Figure 3.8. Continued. -89-a 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1 9 8 6 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 Figure 3.9. Numbers of eggs-female"1 for Harpacticus uniremis on Zostera marina leaves and in the sediment at Station H in 1986 (a) and 1987 (b). Values are the mean ± 1 Standard Error. Numerals above or below error bars indicate, from top to bottom, the sample size for leaf and sediment estimates, respectively. -90-cf. furcata, number of eggs-female-1 in 1986 increased from January 22 to a maximum value on March 4 after which a steady decline was observed (Fig. 3.10a). No obvious pattern was observed over time for this parameter for Tisbe in 1987 (Fig. 3.10b). For Zaus aurelii in 1986, number of eggs-female-1 was fairly constant from February 6 to April 14 but declined on April 28 (Fig. 3.11a). In 1987, a peak was seen on April 30 after which a decrease was observed (Fig. 3.11b). In running the harpacticoid mortality model, it was found that using the copepodite development time from the lower 95% Confidence Limit of the prediction (i.e. fastest development time at the specified temperature) gave the least number of negative mortality rates for all three copepod species (Table 3.2). Therefore, these development times were used in further analysis. Calculated adult and potential adult mortality rates along with the results of the sensitivity analyses of the developmental and sex ratio assumptions for all three copepod species in 1986 and 1987 are presented in Figs. 3.12 to 3.15 (Fig. 3.12: Harpacticus uniremis; Figs. 3.13, 3.14: Tisbe cf. furcata; Fig. 3.15: Zaus aurelii). Running the model without the assumptions regarding non-isochronal development, differential development times for males and females and different juvenile sex ratios resulted in little change in mortality estimates in all cases and mortality patterns were conserved. The model appears to be robust and, therefore, mortality estimates with the discussed assumptions will be described further. In 1986, Harpacticus uniremis adult and potential adult female mortality was maximal between April 28 and May 12 (0.16 deaths-cm-2.d-l) and then declined toward July (Fig. 3.12a). Adult and potential adult male mortality was highest between May 26 and June 10 (0.19 deaths-cm-2-d-l) and sharply dropped at the next interval. In 1987, adult and potential adult female mortality was largest between May 14 and May 28 (0.18 deaths-cm-2-d -l) and then sharply decreased after this period (Fig. 3.12b). Adult and potential adult -91-_CD o E CD 00 cr> en CD CD -Q 13 100 75 5 0 -25 0-6 6 5 6 0 0 0 0 ° Leaves a Sediment 0 0 0 0 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1 9 8 6 OJ CD 00 cn cn CD CD E 3 •° Leaves A Sediment 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 Figure 3.10. Numbers of eggs-female"1 for Tisbe cf. furcata on Zostera marina leaves and in the sediment at Station H in 1986 (a) and 1987 (b). Values are the mean ± 1 Standard Error. Numerals above or below error bars indicate, from top to bottom, the sample size for leaf and sediment estimates, respectively. -92-30 n _CD D E OJ H— 00 CP cn CD CD 20 •o Leaves - A Sediment 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 Figure 3.11. Numbers of eggs-female"1 for Zaus aurelii on Zostera marina leaves and in the sediment at Station H in 1986 (a) and 1987 (b). Values are the mean ± 1 Standard Error. Numerals above or below error bars indicate, from top to bottom, the sample size for leaf and sediment estimates, respectively. -93-Table 3.2. Number of estimated negative mortality rates of adults and potential adults (deaths-cm-2-d-l) for male and female Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii at the mean and 95% Confidence Limits (C.L.) of the predicted copepodite development time in 1986 and 1987. Mortality was estimated for 12 periods in each year. 1986 1987 Female Male Female Male H. uniremis -Upper C L . 4 5 4 5 -Mean 4 5 4 5 -Lower C L . 4 5 3 5 T. cf. furcata -Upper C.L. 1 5 5 3 -Mean 1 5 5 3 -Lower C.L. 0 5 3 3 Z. aurelii -Upper C.L. 4 5 5 5 -Mean 4 5 4 3 -Lower C.L. 2 5 4 2 u CO JZ -t—' o CD Q 0.2 0.1 0.0 -94-i i F e m a l e s MM F e m a l e s - n o a s s u m p t i o n s E S M a l e s M a l e s - n o a s s u m p t i o n s Dim 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1 9 8 6 OJ I E u ob _C •+-> O CD Q 0.2 0.1 -0.0 i i F e m a l e s • i F e m a l e s — n o a s s u m p t i o n s M a l e s V/A M a l e s — n o a s s u m p t i o n s Inn 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 Figure 3.12. Adult and potential adult mortality (deaths-cm'^-d"1) calculated both with and without developmental assumptions for male and female Harpacticus uniremis at Station H in 1986 (a) and in 1987 (b). -95-male mortality was also highest during this period (0.13 deaths-cm-2-d-l) and showed a similar drop after. Tisbe cf. furcata adult and potential adult female mortality was highest between January 22 and February 6 in 1986 (41 deaths-cm-2-d-l) (Fig. 3.13a). Adult and potential adult male mortality was largest between March 18 and March 31 (1.1 deaths-cm-2-d-l) which was also the period of a second peak in female mortality (Fig. 3.13b). In 1987, Tisbe adult and potential adult female mortality was maximal between May 14 and May 28 (0.75 deaths-cm-2-d-l), which was the same period as the peak in adult and potential adult male mortality (0.76 deaths-cm-2-d-1) (Fig. 3.14). In 1986, Zaus aurelii adult and potential adult female mortality was largest between April 14 and April 28 (9.6 deaths-cm-2-d-l) and dropped after this period (Fig. 3.15a). Adult and potential adult male mortality was highest between April 28 and May 12 (2.8 deaths-cnr 2-d-l). In 1987, mortality of adults and potential adults of both genders was maximal between May 28 and June 11 (females, 1.6 deaths-cm-2-d-l; males, 1.4 deaths'Cm-2-d-l) (Fig. 3.15b). In a few periods between sampling dates, the temporal interval exceeded copepodite development time. This may have led to underestimates of potential adult mortality since uncounted nauplii may have recruited to the adult population. Periods when mortality may have been underestimated are, for females, after May 26 in 1986 and after June 11 in 1987. For males, underestimates may have occurred after May 26 in 1986 and May 14 in 1987. However, for all three harpacticoid species, egg numbers were rapidly declining and/or early copepodite stages were not present after these dates indicating that the bulk of adult recruitment was over. Therefore, this problem is not considered to be severe. 3.3.2 Salmonid Abundance and Consumption In 1986, juvenile chum and pink salmon abundance was maximal on May 27 with a CPUE of 1575 fish (Fig. 3.16a). A small number of fish were present in April with peak -96-C N I E o ob sz o cu o a 4 0 -20 I I F e m a l e s • 1 F e m a l e s — n o a s s u m p t i o n s E S M a l e s y/A M a l e s - n o a s s u m p t i o n s JL - i 1 1 """" i i r -1 1 1 1 22 06 19 04 18 31 14 28 12 26 10 24 09 J a n Feb March April May June July 1 9 8 6 C N I E ( J ob _c D OJ a 4- , 3-0 I I F e m a l e s H i F e m a l e s — n o a s s u m p t i o n s E S S M a l e s ZZ2 M a l e s — n o a s s u m p t i o n s L- i l l runn , 22 06 19 04 18 31 14 28 12 26 10 24 09 J a n Feb March April May June July 1 9 8 6 Figure 3.13. Adult and potential adult mortality (deaths-cm'^-d-1) calculated both with and without developmental assumptions for male and female Tisbe cf. furcata at Station H in 1986 including the female mortality estimates for the first interval (a) and excluding the first interval female mortality estimates (b). -97-0.8 c\i' I u 00 0.6 0.4 S 0.2 0.0 [ I F e m a l e s • • F e m a l e s — n o a s s u m p t i o n s E S I M a l e s (ZZ2 M a l e s - n o a s s u m p t i o n s JUL 24 07 20 07 19 02 16 30 14 28 1 1 25 09 Jan Feb March April May June July 1 9 8 7 Figure 3.14. Adult and potential adult mortality (deaths-cm"2-d_1) calculated both with and without developmental assumptions for male and female Tisbe cf. furcata at Station H in 1987. -98-" D I E u 00 J Z o OJ Q 1... I Females • • Females -no assumptions ESS Males v/A Males—no assumptions 0 n 1 j r 22 06 19 04 18 31 14 28 12 26 10 24 09 Jan Feb March April May June July 1 9 8 6 CNJ U 00 J Z o OJ Q 1.5 1.0-0.5 0.0 i i Females • • Females—no assumptions Males V/A Ma les -no assumptions — i 1 1 r Inn . 24 07 20 07 19 02 16 30 14 28 11 25 09 Jan Feb March April May June July 1 9 8 7 Figure 3.15. Adult and potential adult mortality (deaths-cm"2-d_1) calculated both with and without developmental assumptions for male and female Zaus aurelii at Station H in 1986 (a) and in 1987(b). -99-1 9 8 7 ure 3.16. Catch per Unit Effort (number in 3 beach seine sets) at Station F of juvenile chum and pink salmon in 1986 (a) and juvenile chum salmon in 1987 (b). -100-densities in May dropping to low levels in June. Chum salmon were more abundant than pink during April and June samples while pink formed a greater proportion of the May samples. Chum were found to consume similar numbers of the three target harpacticoid species as pink salmon except on June 11, when chum consumed significantly (Student's Mest, F<0.05) more Zaus aurelii than pink salmon. Since the diets were so similar, the two species were considered one unit. In 1987, juvenile chum abundance also peaked in May (Fig 3.16b). Low numbers were captured in June, 1987, similar to 1986, but abundance in April, 1987, was proportionately higher than in 1986. In both years , food weight expressed as a percentage of body weight of the fish varied over the sampling season but high values were always observed during the period of peak fish abundance (Fig. 3.17). The vast majority of harpacticoid prey consumed in 1986 and 1987 by the juvenile salmon were Harpacticus uniremis, Tisbe cf. furcata, and Zaus aurelii (>75% by numbers in both years) (Table 3.3). Adult males and especially females of all three species were the dominant copepodite stages observed in gut contents on all sampling dates in both years (Table 3.4). Qualitative analysis of gut contents of juvenile chinook salmon (Oncorhynchus tshawytscha), the only other juvenile salmonid captured throughout the sampling period, indicated little feeding on harpacticoids. The estimated indices of consumption rate of the juvenile salmonids on the three harpacticoid species for 1986 and 1987 are presented in Figs. 3.18 to 3.23 (Figs. 3.18, 3.19: Harpacticus uniremis; Figs. 3.20, 3.21: Tisbe cf. furcata; Figs. 3.22, 3.23: Zaus aurelii). The adult and potential adult mortality rates for the period of salmonid presence are also included in these figures for comparative purposes. In 1986, consumption of adults and potential adults (both genders) of Harpacticus uniremis was high from April 28 to June 10 (Fig. 3.18a). Comparison of 95% Confidence Limits indicates the three measurements are not different. Adult and potential adult male consumption was significantly lower than that of adult and potential adult females after May 26. Copepod mortality rates, however, were highest for adult and potential adult females -101-o J o 1 9 8 6 Figure 3.17. Food weight as a percentage of body weight at Station F for juvenile chum and pink salmon in 1986 (a) and juvenile chum salmon in 1987 (b). Values are the mean ± 1 Standard Error, n = 20, except for (a): March 19, n = 3; July 10, n = 4; and (b): March 5, n = 1; Apri l 2, n = 15. Table 3.3. Numbers and proportions of Harpacticus uniremis (H), Tisbe cf. furcata (T), Zaus aurelii (Z) and other harpacticoid copepod species found in the gut contents of sampled juvenile chum and/or pink salmon in 1986 and 1987. Total = total number of harpacticoids in all sampled fish. Year Fish Total H T Z Others 1986 127 30,407 7,720 (25.4%) 5,980 (19.7%) 9,538 (31.4%) 7,169 (23.6%) 1987 136 35,924 15,838 (44.1%) 8,866 (24.7%) 4,557 (12.7%) 6,663 (18.5%) Table 3.4. Percent composition of adult females, males and individual juvenile copepodite stages of Harpacticus uniremis (H), Tisbe cf. furcata (T) and Zaus aurelii (Z) in gut contents of sampled juvenile chum and/or pink salmon in 1986 and 1987. Values are the mean and Standard Error of the percent composition of each stage in the fish samples on each sampling date where the copepod species was found in the gut contents, n = sample size; C6F = adult female; C6M = adult male; C1-C5 = Copepodites 1 to 5. C6F C6M Stage C5 C4 C3 C2 CI 1986 H (n=8) 55.919.30 26.915.61 11.014.49 4.9012.08 <1 <1 <1 T (n=7) 94.9±3.59 5.0513.59 0 0 0 0 0 Z (n=7) 98.3±0.728 1.6310.701 <1 <1 0 <1 0 1987 H (n=8) 55.6±8.72 33.515.29 3.5711.76 4.6812.57 1.8710.760 <1 <1 T (n=7) 94.1+1.56 5.1511.29 <1 <1 0 0 0 Z (n=7) 99.210.422 <1 <1 0 <1 0 0 -104-5000 H J Z 4000 -" 6 CD E D 3000 -CO c o u 2000 -_^ CD _ Q E 1000-D z 0 a | | Females Males 04 18 31 March 14 28 12 26 April May 1 9 8 6 A 10 24 09 June July 0.2 0.1 -0.0 I I Females W Males n 0 4 18 31 March 14 28 12 26 April May 1 9 8 6 10 24 June 09 July Figure 3.18. Consumption index (number consumed-h"1) of male and female adult and potential adult Harpacticus uniremis by juvenile chum and pink salmon in 1986 (a) and male and female adult and potential adult mortality (deaths-cm-2-d-l) of Harpacticus uniremis in 1986 (b). Error bars in (a) are approximate 95% Confidence Limits. -105-between April 28 and May 12 and then declined (Fig. 3.18b). Adult and potential adult male mortality rates were only high between May 26 and June 10 and were higher than those for females. In 1987, consumption rate of adult and potential adult females and males by the fish were elevated, fairly constant and not different between genders from April 2 to June 11 (Fig. 3.19a). However, high mortality of both genders was limited to the period from May 14 to May 28 (Fig. 3.19b). Tisbe cf. furcata adult and potential adult consumption by juvenile salmon in 1986 was highest from April 28 to May 26, with female consumption significantly greater than male consumption (Fig. 3.20a). Adult and potential adult copepod mortality during this period was also high, but lower than a previous peak from March 18 to 31 (Fig. 3.20b). Adult and potential adult male mortality appeared to be larger than female between May 12 and May 26. In 1987, Tisbe consumption was high between April 30 and June 11 (Fig. 3.21a). Adult and potential adult female consumption was significantly greater between May 14 and May 28 than in the preceding and following intervals. Adult and potential adult female consumption was significantly greater than male consumption during this period. Mortality of adults and potential adults was only high between May 14 and June 11 with male mortality slightly higher than female (Fig. 3.21b). For Zaus aurelii in 1986, consumption rates were highest and equal for adults and potential adults of both genders between May 12 and June 10 (Fig. 3.22a). Female consumption was much greater than male. However, mortality rates were only high for adult and potential adult females between April 14 and May 12 while male mortality was high between April 28 and May 12 (Fig. 3.22b). In 1987, consumption rates were largest and not different between the two periods for either gender of adults and potential adults between May 14 and June 11 (Fig. 3.23a). Female consumption was significantly larger than male. Mortality rates were high only between May 28 and June 11 with adult and potential adult female mortality just slightly greater than male (Fig. 3.23b). -106-3 0 0 0 -CD E Z5 00 c; 2000 -O C J i_ CD _Q 1000-E 2 0 Females & Males 07 19 March 02 16 April 30 14 28 May 1 9 8 7 1 1 25 June 09 July TO CN* C J ob o CD Q 0 . 2 n 0.1 0.0 i i Females Males n 1X1 , r - i 07 19 02 16 30 14 28 March April May 1 9 8 7 11 25 June 09 July Figure 3.19. Consumption index (number consumed-h"1) of male and female adult and potential adult Harpacticus uniremis by juvenile chum salmon in 1987 (a) and male and female adult and potential adult mortality (deaths-cm-2-d-l) of Harpacticus uniremis in 1987 (b). Error bars in (a) are approximate 95% Confidence Limits. -107-3, 1 , .1 Females Males J Z 6000 xj CD <— C oo 4000 c o CJ CD J D 2000 0-04 18 31 March I 14 28 April 1 9 8 6 12 26 May 10 24 June 09 July T J CM' I E u 00 - C D CD Q 3n 0 n i i Females Males L E L 04 18 31 March 14 28 12 26 April May 1 9 8 6 10 24 June 09 July Figure 3.20. Consumption index (number consumed-h"1) of male and female adult and potential adult Tisbe cf. furcata by juvenile chum and pink salmon in 1986 (a) and male and female adult and potential adult mortality (deaths-cm-2-d-l) of Tisbe cf. furcata in 1986 (b). Error bars in (a) are approximate 95% Confidence Limits. -108-9000 6000 3000 0 I i Females 3, Males I 07 19 March 02 16 April 30 14 28 May 11 25 June 09 July 1 9 8 7 0.8-, 0.6 E 0.4 u § 0.2 Q 0.0 Females gS3 Males 07 19 02 16 30 14 28 March April May 1 9 8 7 11 25 June 09 July Figure 3.21. Consumption index (number consumed-h"1) of male and female adult and potential adult Tisbe cf. furcata by juvenile chum salmon in 1987 (a) and male and female adult and potential adult mortality (deaths-cm-2.d-l) of Tisbe cf. furcata in 1987 (b). Error bars in (a) are approximate 95% Confidence Limits. - 1 0 9 -o o o T J CD D CO c o CJ L_ CD £ 15 10 5 -0-I I Females Males ISI_ 04 18 31 March 14 28 12 26 April May 1 9 8 6 10 24 June 09 July T J CN I E CJ CO o CD Q 9 -0 I I Females ESS Males 04 18 31 March 14 28 12 26 April May 1 9 8 6 10 24 June 09 July Figure 3.22. Consumption index (number consumed-h"1) of male and female adult and potential adult Zaus aurelii by juvenile chum and pink salmon in 1986 (a) and male and female adult and potential adult mortality (deaths-cm-2-d-l) of Zaus aurelii in 1986 (b). Error bars in (a) are approximate 95% Confidence Limits. -110-6 0 0 0 -" D CD E 4 0 0 0 =3 CO c o u o3 2 0 0 0 JD 0 I I Females Si Males I 07 19 02 16 30 14 28 March April May 1 9 8 7 11 25 June 09 July 1.5-1.0 o 0.5 CD Q 0.0 i i Females 13 ESS Males I l r 07 19 March 02 16 30 14 28 April May 1 9 8 7 11 25 09 . June July Figure 3.23. Consumption index (number consumed-h"1) of male and female adult and potential adult Zaus aurelii by juvenile chum salmon in 1987 (a) and male and female adult and potential adult mortality (deaths-cm-2.d-l) of Zaus aurelii in 1987 (b). Error bars in (a) are approximate 95% Confidence Limits. -111-3.4 DISCUSSION Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii all appeared to have discrete periods of abundance within the sampling season in both 1986 and 1987. Harpacticus and Zaus had one density maximum throughout the sampling period in both years while Tisbe in 1986 may have had as many as three maxima (including January 22). In 1987, however, only one Tisbe density peak was observed. In 1986, a single Harpacticus uniremis cohort seems to have resulted from the sole presence of adult females and high egg numbers occurring in early March. This cohort matured and disappeared by late June. In 1987, adult females and eggs first appeared in early April with the resulting cohort of offspring maturing and disappearing by July 9. Reproductive activity as evidenced by number of eggs-female-1 was highest in both years when females were initially observed, and declined thereafter. The large numbers of female offspring produced early in the sampling season seem to have undergone little reproductive activity as adults in late April and May. Also, since few juveniles were present in the sediment, the peak in female numbers there, while the leaf population is declining, suggests movement of females from seagrass to sediment. In previous studies which have enumerated H. uniremis in the spring and early summer, a similar single density peak was observed (Ito 1971; Jewett and Feder 1977; Kito 1977; Sibert 1979; Cordell 1986), with data to support production of a single cohort (Jewett and Feder 1977; Cordell 1986). A decline in reproductive activity of the population with time has also been described (Ito 1971; Jewett and Feder 1977). The Tisbe cf. furcata population in 1986 had two main peaks in adult female density: March 18 and May 12. The March 18 female peak was probably due to recruitment in January and before sampling commenced. The May 12 peak appears to be a result of high reproductive activity (number of eggs-female-1) occurring before the end of March. Reproductive activity after March declined steadily. In 1987, a single sharp cohort was observed in May with reproductive activity lower than in 1986 and with no obvious pattern. -112-Juvenile copepodites (C2, C3) were observed in high numbers after the female peak on May 14 but adults were not. Tisbe furcata generally is abundant in the spring or early summer (e.g. Hagerman 1966; Marcotte 1977; Bergmans and Janssens 1988) but is often present in low numbers throughout the year (e.g. Huys et al. 1986). Zaus aurelii in both years showed a sharply defined single population maximum. This peak was in April in 1986 and May in 1987. Reproductive activity (number of eggs-female-1) was highest before the end of March in 1986, whereas a sharp pulse was observed in late April in 1987. To my knowledge, data on the temporal distribution of this species does not exist. However, species of Zaus are often common in late spring (e.g. Kito 1977). As has been previously documented at this study site (D'Amours 1987), juvenile salmonids consume large numbers of harpacticoid copepods, especially the primarily epiphytic species Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii. Juvenile chum salmon gut contents generally did not differ from those of juvenile pink in 1986 with respect to these three species. Also, food weight as a percentage of body weight was high at periods of maximal fish density. This is contradictory to the results of Healey (1979) for juvenile chum in the Nanaimo estuary but supports the analyses of a juvenile chum and pink "fullness index" in Alaska (Cordell 1986). The finding of no decrease in relative food weight with juvenile salmonid density suggests that fish density did not affect food intake. The adult and potential adult copepod mortality model used here appears to be robust and is unhindered in application by avoiding detailed analysis of stage-specific mortality of juveniles (e.g. Ohman 1986). Coupled with the accurate estimates of harpacticoid density obtained using intrashoot distributions (Appendix 2), valid estimates of mortality of Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii, especially in temporal pattern, were obtained. Estimation of juvenile salmonid abundance, analysis of gut contents, diurnal feeding patterns and gut evacuation rates (Appendix 5) allowed calculation of an index of gender-specific consumption rates of the three harpacticoid species. While estimation of consumption rates on an areal basis were logistically impossible in this study (mark--113-recapture experiments would have required enormous numbers of marked fish given previous results from this area (Levings et al. 1983)), temporal patterns in consumption are deemed valid. Therefore, a comparison of patterns of harpacticoid mortality and salmonid consumption provides a true assessment of the impact of salmonid predation on the populations of Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii. Juvenile chum and pink salmon predation does not appear to control the abundance cycles of Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii. Consumption was out of phase with the major period of mortality for H. uniremis, T. cf. furcata and Z. aurelii in both years. Also, relative male and female mortality did not correspond to relative consumption rates. In 1986, female H. uniremis mortality was declining while salmonid consumption was at its highest. Male mortality was highest while consumption was decreasing. In 1987, salmonid consumption of both genders was high and fairly constant for two months while the major mortality occurred in a two week period. The major period of T. cf. furcata mortality occurred in March in 1986 whereas consumption levels did not rise until after late April. Also, male mortality was higher than female in mid-May but male consumption was low. In 1987, consumption started to rise in mid-April but mortality did not markedly increase until mid-May. Male mortality appeared higher than female but male consumption was significantly lower than female. For Z. aurelii in 1986, high mortality preceded high consumption by a month for both males and females while in 1987 high mortality occurred later than the consumption maximum. Also, in 1987 mainly female consumption was observed while male mortality was nearly as high as female. Even considering potential underestimates of recruitment later in the sampling season, mortality and consumption patterns of the copepod species would not converge. Therefore, it appears unlikely that juvenile salmonid predation caused the decline in these three copepod species. Since it has been demonstrated that there is little correspondence between juvenile salmonid consumption and harpacticoid mortality but sharp copepod population cycles still occur, Healey's (1979) suggestion that chum predation caused a decline in Harpacticus -114-uniremis appears to be a coincidence of timing and also perhaps due to an underestimate of Harpacticus abundance. Indeed, although maximum densities obtained from sediment cores were 6.6-cm-2 at one station in the Nanaimo estuary (Sibert 1979), at 6 other stations maximum H. uniremis abundance was <2-cm-2, which, on average, would lead to lower densities than obtained in this study (see Chapter 2). The results of this study are the first real test of the impact of juvenile salmonid predation on selected harpacticoid copepod species and supports the suggestion of Cordell (1986) that this predation does not structure the community. To this point, the thesis has dealt with the analysis of descriptive, observational data. While the conclusions reached in this chapter seem valid, it is impossible to attach any statistical significance to the differences in patterns of fish consumption and copepod mortality based on the generated analysis. The next chapter will present the results of a manipulative field experiment carried out in 1986 and 1987 to determine the response of the harpacticoid community when large epibenthic predators, such as juvenile salmon, are excluded from portions of the seagrass bed. -115-4. R E S P O N S E OF T H E H A R P A C T I C O I D C O P E P O D C O M M U N I T Y T O T H E E X C L U S I O N OF E P I B E N T H I C P R E D A T O R S 4.1 I N T R O D U C T I O N Marine harpacticoid copepods have been implicated to be a potentially significant food source for juvenile fish (see Chapter 1) and other epibenthic predators (e.g. mysids (Neomysis mercedis, Johnston and Lasenby 1982) and shrimp (e.g. Crangon crangon, Jensen and Jensen 1985)). Attempts have been made to assess the importance of this predation in controlling copepod density using experiments manipulating potential predator numbers in the field. The first serious effort to determine the effect of epibenthic predators on harpacticoid copepods in a field experiment was undertaken by Bell (1980) in a salt marsh. Using 2 mm mesh cages placed over the sediment to exclude epibenthic predators and repetitively sampling the sediment-dwelling harpacticoid copepod community with cores, she observed that harpacticoids initially increased in abundance inside cages compared to unmanipulated "control" areas but returned to "control" densities in 2 to 3 months. No difference in age class structure (i.e. proportion of juveniles to adults) was observed inside the cages compared to "control" areas. Unfortunately, this experiment had either no replicates of the cage treatment or cores from replicate cages were pooled (thus eliminating a treatment error term). This lack of true replication undermined the statistical analysis of the results through the use of an inappropriate error term (pseudoreplication sensu Hurlbert 1984). Fleeger et al. (1982), also in a salt marsh, used 3 mm2 mesh cages to exclude potential epibenthic predators. This experiment was properly replicated and the results indicated that caging had no effect on the total number of harpacticoids in the sediment. However, community diversity (number of species present) rose. Fitzhugh and Fleeger (1985) used inclusion of gobies (Gobiidae) in 1.1 mm diameter mesh cages to determine the -116-effect of these fish on the sediment meiofaunal community of a brackish pond. They observed that in short (40 h) experiments, gobies ate mostly nematodes and no effect on the harpacticoid community was seen^ In this study, treatments were not replicated in individual experiments but experiments were, leading to temporal pseudoreplication (Hurlbert 1984) and invalid statistical analyses. Fleeger (1985) also used 3 mm.2 mesh cages to exclude macroepifauna in a salt marsh, both in tidal marsh creeks and subtidally, during two summers. He only observed a change in sediment harpacticoid numbers subtidally and suggested that this was a response to increased predator foraging time in that habitat. He also found that the epibenthic harpacticoid Cletocamptus deitersi (Richard) increased in exclusion cages while the inbenthic, tube dwelling Pseudostenhelia wellsi Coull and Fleeger decreased. He interpreted this change as a response to a decrease in visual predation on Cletocamptus allowing it to outcompete the presumably less visually vulnerable Pseudostenhelia. This experiment, however, was also pseudoreplicated in that data from cage "controls" and unmanipulated areas were pooled. Bell and Woodin (1984), in an elegantly designed experiment, assessed the response of harpacticoid copepods to epibenthic predator/disturber exclusion on an intertidal sandflat at various densities of polychaete tubes. Exclusion cages of 6.2 mm mesh were used and significant increases in total sediment-dwelling harpacticoids and dominant copepod species within exclusion cages were observed in short-term (2 or 4 week) experiments. Gee et al. (1985) used the inclusion of a number of different potential predators (adult and juvenile gobies, adult and juvenile crabs) in 2 mm mesh cages to assess their influence on the composition of a mudflat community. For sediment-dwelling harpacticoid copepods, an effect was only observed in juvenile crab cages in one of the three experiments described where total harpacticoid numbers decreased. These authors found that, even if total copepod numbers did not change, shifts in species composition were observed with inbenthic harpacticoids decreasing in crab inclusions, while epibenthic species increased. The opposite pattern was observed in fish inclusions. These changes would appear to be related to the -117-predator's foraging behaviour. Unfortunately, there are statistical problems in this study also, since either cage "controls" were unreplicated or multiple cores from individual cages were used as replicates, thus artificially increasing sample size in the subsequent analysis. In a properly replicated and analyzed experiment, Hunt et al. (1987) demonstrated that in inclusion experiments, the presence of the gastropod mollusc Ilyanassa significantly decreased sediment harpacticoid copepod abundance compared to controls while enhanced densities of the bivalve Mercenaria had no effect. Three factors become apparent in consideration of the above field studies on the influence of invertebrate macrofauna and fish on harpacticoid copepods. The first is that with the exceptions of the studies by Fleeger et al. (1982), Bell and Woodin (1984) and Hunt et al. (1987), all have problems with experimental design and/or subsequent statistical analysis. This makes interpretation of the results difficult. The second factor to consider is that in none of the predator inclusion studies is any differentiation made between predation and disturbance being the factor causing declines in harpacticoid abundance or species composition shifts. Sediment disturbance may have a significant impact on harpacticoid densities (e.g. Chandler and Fleeger 1983). Third, although some of the above studies have been conducted in vegetated habitats such as salt marshes, no caging manipulations have been conducted where the response of both epiphytic and sediment-dwelling harpacticoid copepod communities has been measured and no studies have been conducted within seagrass beds. A number of manipulation experiments assessing the response of macrofauna (e.g. polychaetes, decapod Crustacea) to predator exclusion or inclusion in seagrass beds have been performed. Higher densities of both macroinfauna and macroepifauna are generally found within seagrass beds than in adjacent unvegetated areas (see Summerson and Peterson 1984). In predator exclusion cages, Summerson and Peterson (1984) found increased abundance of infauna in a bare area but no change was observed in the seagrass sediment infauna. It appears that the high level of structure present in seagrass beds may provide a -118-refuge from predation (Orth et al. 1984). Leber (1985) found in predator (shrimp) inclusion experiments that the seagrass structure decreases predation rate on some epifauna by inhibiting predator effectiveness. Further studies have also indicated that the presence of seagrasses increases survival (Peterson 1986, Wilson et al. 1987). However, there is evidence to suggest that high animal densities in seagrass beds may simply be functions of active habitat preference (Bell and Westoby 1986) or passive deposition of planktonic larval stages because of decreased current speeds within seagrass beds (Eckman 1987). In any case, there has been no research done on the response of harpacticoid copepods to predator/disturber manipulation in seagrass habitats. This chapter reports the results of predator exclusion experiments using cages conducted in both 1986 and 1987 near Station H on Roberts Bank. The response of both the seagrass and sediment harpacticoid community to macroepifauna exclusion was monitored over time in both years. The primary goal was to exclude juvenile salmonids (although other potential epibenthic predators would also be excluded) from portions of the seagrass bed and, using appropriate experimental design and statistical analysis, provide statistical corroboration for the conclusion regarding the impact of salmonid predation reached in Chapter 3. 4.2 M E T H O D S Predator exclusion experiments were conducted from March 31 to June 10 in 1986 and April 2 to June 11 in 1987. These periods bracketed the time of major abundance of juvenile chum and/or pink salmon in the study area in both years (see Chapter 3). Circular aluminium cages (1 m diameter, 0.5 m high, 7 mm square mesh; 0.8 m2 enclosed area) were placed within the seagrass bed 4 m southeast of Station H . Cages were designed to minimize potential artifacts of cage introduction. The circular design was selected to permit drift algae (e.g. Ulva) in the study area to roll around the cages rather than block the mesh (after Leber 1985). The large diameter of the cages was chosen to -119-allow the enclosure of a number of entire Zostera marina shoots and to allow them to lie normally within the shallow water present at low tide. This was found to be the case upon observation during repeated sampling. The extended height of the cages was to allow typical upright posture of the seagrass shoots during high tide. Repeated observations by divers indicated that normal behaviour of the shoots within cages was observed at high tide (e.g. upright, swaying in wave surge). The large mesh size employed (7 mm) was determined to be sufficiently small for excluding large epibenthic predators (e.g. juvenile salmon) but large enough to allow water flow through the cages when fouled. Observations made during sampling indicated that although fouling was observed, the majority of the intermesh space was unblocked. Coupled with the fact that flow within seagrass beds is turbulent due to the leaves acting as a "mesh" (Nowell and Jumars 1984), artifacts within the cages due to impeded flow (e.g. siltation (Virnstein 1978; Hulberg and Oliver 1980)) should be small. Full exclusion cages and cage "controls" were used in this experiment in both years. Cage "controls" were of the same design as the full exclusion cages except that two opposing 50 cm x 50 cm segments of mesh were removed on the sides. These "controls" were used to mimic any effects of the cage structure (e.g. shading, reduced flow) while still allowing access by potential epibenthic predators. Observations by divers at high tide indicated that cage "controls" did not act as "reefs" attracting large numbers of fish and macroinvertebrates. Cages were placed within the seagrass bed at low tide 4 days before they were first sampled to allow any effect of disturbance on the harpacticoid copepod community caused by emplacement to subside. After disturbance (e.g. raking the sediment), harpacticoid copepod abundance and species composition attain pre-disturbance values after a maximum of about 2 days (e.g. Sherman and CouU 1980; Thistle 1980; Chandler and Fleeger 1983). Three replicate cages of each treatment (exclusion cages (hereafter referred to as the exclusion treatment) and cage "controls" (hereafter referred to as the control)) were used. The six cages were placed 1 m apart in a line perpendicular to the incoming tidal flow. The controls were oriented so that the areas with mesh were also perpendicular to the tidal flow. -120-The two treatments were alternated in a systematic design to ensure adequate interspersion of treatments. The skirt of each cage was pushed approximately 3 cm into the sediment and each cage was anchored with nylon cable ties to 3 aluminium posts hammered 50 cm into the sediment. Sampling was performed through a hinged port on the top of the exclusion cages and through the holes in the sides of the controls. To determine i f the sediment grain size in the cages differed between treatments, two 19.6 c m 2 cores were taken to a depth of 1 cm in each cage at the beginning and at the termination of the experiment in each year. Cores were obtained on March 31 and June 25 (two weeks after the last copepod samples) in 1986 and April 2 and June 11 in 1987. Cores were taken using randomly determined compass orientations (North, South, East, West) at a distance of y-5 cm (where y is a random number from 1 to 9) from the center of the cage. In this way, random samples were taken but none was closer than 5 cm to the cage edge. Cores were transported back to the laboratory, spread out in glass dishes and air-dried for one week. After drying, the sediment was divided into size fractions on a graded sieve series (595 |im, 355 |im, 180 urn, 75 u,m and 53 urn) using an Endecotts EVS1 sieve shaker set at 65 Hz for 10 min. The amount of sediment trapped by each sieve was weighed on a Mettier P1210 top-loading balance and converted to a percentage of the total sediment weight on all the sieves. The average value of the percentage on each sieve from the two cores per cage was taken. The percentages in each size class were compared between treatments using Student's r-test. Harpacticoid copepod sampling was conducted within the cages at approximately biweekly intervals, from March 31 to June 10 in 1986 and April 2 to June 11 in 1987. Four leaf samples and three cores were taken for harpacticoid copepods in each cage on each sampling date. Both leaf and core samples were taken using randomly determined compass orientations (North, South, East, West) at a distance of y-5 cm (where y is a random number from 1 to 9) from the center of the cage. In this way, random samples were taken but none was closer than 5 cm to the cage edge. For leaves, the oldest leaf on the shoot present at the -121-picked location was sampled. This was done instead of choosing the longest leaf since estimating abundance using intrashoot distributions was impractical because this would entail lifting the shoot from the water to calculate relative leaf age. This was deemed to be too much disturbance to the shoots within cages and could influence copepod numbers in following samples. Leaves were sampled using the tube sampler in an identical manner to that described in Chapter 2. Core samples for harpacticoids were taken to a depth of 1 cm as the majority of copepods were found to be in this stratum at Station H (see Chapter 2). Core sampler size and sample collection was identical to the methodology described in Chapter 2. At the conclusion of sampling on each date, the exterior of the cages were brushed free of fouling organisms. Leaf and core sample processing in the laboratory was similar to that described in Chapter 2. Differences in processing the leaf samples were that the 50 copepodites of Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii were only identified to gross developmental stage (juvenile, male and female) while the 50 other copepodites were simply identified to species, and that since intrashoot distributions to estimate abundance were not used, abundances are expressed as number-cm-2 leaf area. Since samples were all taken from the oldest leaves on shoots, abundances can better be considered an index of abundance for comparison between treatments rather than absolute values. For core samples, H. uniremis, T. cf. furcata and Z. aurelii were also only identified to gross developmental stage and the other copepodites only to species, as above. Averages of the 4 leaf samples and 3 cores per cage were obtained, thus giving one value for each in each cage. Leaf and core harpacticoid densities were compared between the two treatments on each sampling date using Student's r-test. For all statistical comparisons between treatments, homogeneity of variance was assessed using Bartlett's test at the 0.05 level of significance. If heteroscedascity was observed, the data were subjected to arcsine square root and both loge(x+l) and square root transformations for sediment grain size and harpacticoid abundance, respectively. If -122-transformation did not alleviate heteroscedascity, the non-parametric Mann-Whitney £/-test was used to compare values between treatments. The 0.05 level of significance was observed. A l l statistical analyses described in this section were conducted using the M G L H and NPAR modules of SYSTAT (Wilkinson 1985) on an I B M PC/XT microcomputer. 4.3 RESULTS From observations at each sampling date in both years of the experiment, caging seemed to have little effect on the enclosed environment. Invertebrates which could travel through the mesh (e.g. amphipods, shrimp) did not appear to have larger populations inside the cages than in the surrounding area. The appearance of the sediment surface inside the cages did not appear to be different from that in the general vicinity. Surficial manifestations of increased biological activity (e.g. increased number of polychaete burrows) were not evident inside the cages. One noticable difference, however, was that leaf epiphytic growth (e.g. diatoms) seemed lower on seagrass shoots inside the cages than outside. However, this decrease appeared to be similar in both the exclusion treatment and the control. In 1986, sediment grain size characteristics in the cages at the start of the experiment (March 31) showed no significant difference between treatments in any size category (Student's r-test, P>0.10) (Fig. 4.1a). On June 25, however, both grain size categories <75 |0.m were significantly higher in the exclusion treatment cages (Student's f-test, F<0.01 in both cases) (Fig. 4.1b). However, differences between treatments were small. The 53-74 u,m category consisted of a mean of 1.9% of the total sediment in the exclusion treatment compared to 1.2% in the control while the <53 | im size class had a mean of 4.9% of the total sediment in the exclusions and 3.4% in the control. In 1987, at the start of the experiment (April 2), the percentage of sediment in the 355-594 u,m size class was significantly higher in the control relative to the exclusion treatment (Mann-Whitney (/-test, P<0.05) and the percentage of total sediment in the 75-179 Jim size class was significantly greater in the exclusion treatment (Mann-Whitney (/-test, P=0.05) (Fig. 4.2a). However, differences -123-c OJ o CD Q _ 60 W Control i l Exclusion 40-20-0 60 n >595 3 5 5 -594 180-354 7 5 -.179 5 3 -74 G r a i n s i z e ( / x m ) a <53 c CD O i_ CD CL 40 20 0 Control Exclusion >595 J L KA3 . I I 3 5 5 -594 180-354 7 5 -179 5 3 -74 G r a i n s i z e ( ^ m ) n <53 Figure 4.1. Sediment grain size characteristics in the Control and Exclusion treatments on March 31, 1986 (a) and June 25,1986 (b). Values are the mean ± 1 Standard Error, n = 3. -124-c CD U i _ CD 0_ C CD U i _ CD CL 60 4 40 4 20 0 60 4 40 4 20 4 0 Control Exclusion _E2_ >595 3 5 5 -5 9 4 1 8 0 -3 5 4 7 5 -179 5 3 -7 4 G r a i n s i z e ( / im) Control Exclusion _CS2_ >595 3 5 5 -5 9 4 1 8 0 -3 5 4 7 5 -179 5 3 -7 4 G r a i n s i z e ( / im) n <53 <53 Figure 4.2. Sediment grain size characteristics in the Control and Exclusion treatments on Apri l 2, 1987 (a) and June 11, 1987 (b). Values are the mean ± 1 Standard Error, n = 3. -125-between treatments were again small with the 355-594 (im size class consisting of 0.98% of the total sediment in the control versus 0.80% in the exclusion treatment and the 75-179 (im size class composed of 69.5% of the sediment in the exclusion treatment compared to 66.3% in the control. At the end of the experiment (June 11), however, no significant differences were observed between treatments in any sediment grain size class (Student's Mest, />>0.30 in all cases) (Fig 4.2b). The 15 harpacticoid species found to be abundant on seagrass leaves and in the sediment in Chapter 2 were tested for differences in abundance between the exclusion treatment and control on each sampling date in each year of the experiment. No species other than those included in the original descriptive analysis in Chapter 2 was found to compose >10% by number of the harpacticoid community in either subhabitat on any sampling date in either year in the exclusion experiment. The overall result for the analysis of harpacticoid densities between the exclusion treatment and control on each sampling date in both years was that very little difference in the community was observed. The results concerning total harpacticoids, Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii plus the other 12 species will be considered further on an individual basis. Total Harpacticoids (Figs. 4.3,4.4) Total harpacticoid numbers in leaf samples did not differ significantly between treatments on any date in either year. In the sediment, total harpacticoid densities were not different between treatments on any date in 1986 while in 1987, total copepod density was significantly higher in the control treatment on April 16 (Student's Mest, P<0.05). Harpacticus uniremis Kroyer (Figs. 4.5,4.6,4.7,4.8) In 1986, H. uniremis densities on leaves were not different in either treatment on any date for total numbers, juveniles and females. Numbers of males were significantly higher in the control on March 31 (Student's Mest, iM).05). In the sediment in 1986, total numbers -126-Figure 4.3. Abundance of total harpacticoid copepods on Zostera marina leaves (number-cm" 2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -127-21 • • Control 0 T 1 1 1 1 1 1 0 2 16 30 14 28 11 A p r i l M a y J u n e 1 9 8 7 Figure 4.4. Abundance of total harpacticoid copepods on Zostera marina leaves (number-cm" 2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -128-Figure 4.5. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Harpacticus uniremis on Zostera marina leaves (number-cm-2 leaf) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -129-1 9 8 6 Females • • Control ° ° Exclusion 1 9 8 6 Figure 4.5. Continued. -130-0.0 Juveniles 31 14 28 12 26 M a r c h A p r i l M a y 1 9 8 6 • Control ° Exclusion 10 J u n e Figure 4.6. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Harpacticus uniremis in the secliment (number-cm-2 sediment) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -131-c CD E CD CO C M I E u c CD 0.10 0.05 0.00 Males • — • Control ° ° Exclusion 1 • f — . 3 1 14 28 12 March April May 1 9 8 6 / —t— 26 10 June Figure 4.6. Continued. -132-0 2 16 30 14 28 1 1 A p r i l M a y J u n e 1 9 8 7 Figure 4.7. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Harpacticus uniremis on Zostera marina leaves (number-cm-2 leaf) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -133-0.4 Males o C\l I E o i i a> • • Control ° 0 Exclusion 16 Apri l 14 28 May 11 J u n e 1 9 8 7 0 . 2 ! o CM I E O c E ZJ 0.0 02 16 30 14 28 Apri l May • 1 9 8 7 Figure 4 . 7 . Continued. -134-Figure 4.8. Total abundance (a) and juvenile copepodite (b) and adult female (c) abundance of Harpacticus uniremis in the sediment (number-cm-2 sediment) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -135-0.4 c OJ E T J OJ CO OJ I E o i l OJ - Q Females • • Control ° ° Exclusion 0 . 2 J 0 . 0 1 9 8 7 Figure 4.8. Continued. -136-were significantly higher in the control on May 12 (Student's f-test, P<0.05) and in the exclusion treatment on June 10 (Student's f-test, P<0.05). The increase in total numbers in the controls on May 12 was mainly due to a significant increase in female abundance (Student's f-test, P<0.05). The increase in the exclusion treatment on June 10 appeared to be general since, individually, juvenile, male and female densities were not significantly higher. In 1987, Harpacticus uniremis total numbers on the leaves were higher in the exclusion treatment on April 2 (Student's f-test, P<0.05) and in the control on May 14 (Student's f-test, F<0.05). Individually juveniles, males and females were not higher in the exclusion treatment on April 2 but all three groups were significantly more abundant in the control on May 14 (Student's f-test, P<0.05 in all cases). Sediment densities were not different between treatments for total numbers and juvenile or female abundance. Tisbe cf. furcata (Baird) (Figs. 4.9,4.10,4.11,4.12) Tisbe cf. furcata total numbers on leaves in either year were not different between treatments. In 1986, juvenile and male densities were not different between treatments on any date but female numbers were significantly larger on leaves in the exclusion treatment on April 28 (Student's f-test, P=0.05) and May 26 (Mann-Whitney [/-test, /><0.05). No groups were different between treatments in 1987. Total numbers and juvenile, male or female densities were not different between treatments in the sediment on any date in either year. Zaus aurelii Poppe (Figs. 4.13,4.14,4.15) Zaus aurelii total numbers and juvenile, male or female abundance did not differ between treatments on any date on leaves in 1986 and 1987 or in the sediment in 1986. This species was not found in sediment samples in 1987. -137-• • Control T ° ° Exclusion ? 31 14 28 12 26 10 M a r c h A p r i l M a y J u n e 1 9 8 6 Figure 4.9. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Tisbe cf. furcata on Zostera marina leaves (number-cm-2 leaf) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -138-Figure 4.9. Continued. -139-c CD £ T J CD CO CN I E (J C CD _Q E • • Control ° ° Exclusion 31 M a r c h 14 28 12 26 A p r i l M a y 1 9 8 6 10 J u n e Juveniles c CD E T J CD CO o C aj - O E 0 . 2 -0.0 •• Control •o Exclusion 31 M a r c h 14 28 12 26 A p r i l M a y 1 9 8 6 10 J u n e Figure 4.10. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Tisbe cf. furcata in the sediment (number-cm-2 sediment) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -140-0.2 c CD CD CO CM I E u C CD jQ E 0.1 Males • • Control ° 0 Exclusion 31 M a r c h -9 14 28 12 26 A p r i l M a y 1 9 8 6 10 J u n e 0 .10 c CD CD CO C M U l l CD - Q E d 0 .05 J, 0 .00 Females • • Control ° ° Exclusion 31 M a r c h / —t-14 A p r i l M a y 1 9 8 6 10 J u n e Figure 4.10. Continued. -141-12 o CD C N I O 0 -Q Q • • Control o o Exclusion 0 2 16 30 14 28 A p r i l M a y 1 9 8 7 11 J u n e 0 2 16 30 14 28 11 A p r i l M a y J u n e 1 9 8 7 Figure 4.11. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Tisbe cf. furcata on Zostera marina leaves (number-cm-2 leaf) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -142-1 9 8 7 2 - , 0 Females — • Contro l — ° Exclusion 02 16 3 0 14 28 A p r i l M a y 1 9 8 7 11 June Figure 4.11. Continued. -143-c CD CD CO CN I E u LL CD _Q E 0.3 0.2 0.1 0.0 0 2 •• Control o Exclusion 16 A p r i l \ 30 14 28 M a y 11 J u n e 1 9 8 7 Juveni les c CD E XJ CD CO CNJ O C CD jQ E 0.0 1 9 8 7 Figure 4.12. Total abundance (a) and juvenile copepodite (b), adult male (cl and adult female (d) abundance of Tisbe cf. furcata in the sediment (number-cm-2 sediment) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -144-0.2 Males • — • Control ° 0 Exclusion 0.1 0 .0 0 2 16 A p r i l 30 14 28 M a y 1 9 8 7 11 J u n e Fema les • — • Control ° ° Exclusion o CD 1 9 8 7 c CD E TJ CD 00 CM 0 .05 Figure 4.12. Continued. -145-31 14 28 12 26 10 M a r c h A p r i l M a y J u n e 1 9 8 6 Figure 4.13. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Zaus aurelii on Zostera marina leaves (number-cm-2 leaf) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -146-1 9 8 6 Figure 4.13. Continued. -147-c CD E "O CD CO CN I E u si CD -Q E a — •• Control ° Exclusion 0 .04 J 0 .02 J 0 .00 31 M a r c h 14 28 12 26 A p r i l M a y 1 9 8 6 — t — 10 J u n e Figure 4.14. Total abundance (a) and juvenile copepodite (b) abundance of Zaus aurelii in the sediment (number-cm-2 sediment) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -148-Juveni les 0 .04 0 .02 J 0 .00 -• Control •° Exclusion — — — t • « 1 1— 31 14 28 12 26 10 M a r c h A p r i l M a y J u n e 1 9 8 6 Figure 4.14. Continued. -149-1 9 8 7 Figure 4.15. Total abundance (a) and juvenile copepodite (b), adult male (c) and adult female (d) abundance of Zaus aurelii on Zostera marina leaves (number-cm-2 leaf) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -150-1 9 8 7 Figure 4.15. Continued. -151-Amonardia normani (Brady) (Figs. 4.16,4.17) Amonardia normani density did not differ between treatments on any date on leaves or in the sediment in either year. Amphiascus undosus Lang (Figs. 4.18,4.19) Amphiascus undosus density on leaves did not differ between treatments on any date in either year. In the sediment, densities were not different between treatments during the 1986 experiment but this species was significantly more abundant in the exclusion treatment on May 14,1987 (Mann-Whitney tf-test, /><0.05). Dactylopodia crassipes Lang (Figs. 4.20,4.21) Abundances of leaf-dwelling Dactylopodia crassipes were significantly higher in the control on March 31, 1986 (Student's f-test, /MX01) and May 14, 1987 (Student's r-test, F<0.01). Sediment densities were not different between treatments during the experimental period in either year. Ectinosoma melaniceps Boeck (Figs. 4.22,4.23) Ectinosoma melaniceps density did not differ between treatments on any date on leaves or in the sediment in either year. Heterolaophonte variabilis Lang (Figs. 4.24,4.25) Heterolaphonte variabilis density did not differ between treatments on leaves or in the sediment in the 1986 experiment. In 1987, densities of this species were significandy higher in the control on the leaves on May 14 (Student's Mest, P<0.01) and in the sediments on June 11 (Mann-Whitney (/-test, P<0.05). -152-Figure 4.16. Abundance of Amonardia normani on Zostera marina leaves (number-cm"2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -153-Figure 4.17. Abundance of Amonardia normani on Zostera marina leaves (number-cm"2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -154-0.0-1 1 1 • , - , J — 31 14 28 12 26 10 M a r c h A p r i l M a y J u n e 1 9 8 6 Figure 4.18. Abundance of Amphiascus undosus on Zostera marina leaves (number-cm~z leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -155-1 9 8 7 o.o-I 1 . 1 1 , , — 0 2 16 30 14 28 11 A p r i l M a y J u n e 1 9 8 7 Figure 4.19. Abundance of Amphiascus undosus on Zostera marina leaves (number-cm"2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -156-0.75-, c CD CD 0.50 CO CN I E o c CD E 3 0.25 0.00 •• Control - o Exclus ion 31 14 28 12 26 10 M a r c h Apri l May June 1 9 8 6 Figure 4.20. Abundance of Dactylopodia crassipes on Zostera marina leaves (number-cm -2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -157-1 9 8 7 Figure 4.21. Abundance of Dactylopodia crassipes on Zostera marina leaves (number-cm"2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -158-• • Control o ° Exclusion 31 14 28 12 26 10 M a r c h Apri l May J u n e 1 9 8 6 Figure 4.22. Abundance of Ectinosoma melaniceps on Zostera marina leaves (number-cm - 2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -159-1.5 o CD C N O L. CD E 3 1.0 0.5-0.0 • • Control © ° Exclusion 16 Apri 30 14 28 May 1 9 8 7 11 June c CD E CD CO C N I E o CD. -O E 3 3 -2 -1 -0 • • Control ° o Exclusion \ T 02 16 30 14 28 April May 1 9 8 7 11 June Figure 4.23. Abundance of Ectinosoma melaniceps on Zostera marina leaves (number-cm"2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -160-0 .08 T J OJ 0 .06 £ 0 .04 <J 0 . 0 2 -0 .00 b r • • Control ° o Exclus ion < / \ 1 \ / / \ / / / / / \ / / f 1 \ / \ <f- c \ 1 * 1 31 M a r c h 14 28 12 26 A p r i l M a y 1 9 8 6 10 J u n e Figure 4.24. Abundance of Heterolaophonte variabilis on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) Q>) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -161-D JD C M I E u CD E Z5 -• Contro l •° Exclus ion 14 28 M a y 11 J u n e 1 9 8 7 1 9 8 7 Figure 4.25. Abundance of Heterolaophonte variabilis on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -162-Mesochra pygmaea (Claus) (Figs. 4.26,4.27) Mesochra pygmaea density did not differ between treatments on any date on leaves or in the sediment in either year. Amphiascus minutus (Claus) sp. 1 Lang (Fig. 4.28) Amphiascus minutus sp. 1 was not found in samples from the 1986 experiment. Density did not differ between treatments on any date on leaves or in the sediment in 1987. Danielssenia typica Boeck (Figs. 4.29,4.30) Danielssenia typica abundances did not differ between treatments on either leaves or in the sediment during the 1986 experiment. This species did not differ in abundance on leaf samples in 1987 but sediment densities were significantly higher in the control on April 16 (Student's f-test, P<0.05). Halectinosoma sp. 1 (Figs. 4.31,4.32) This species did not differ in abundance between treatments on leaves or in the sediment in 1986. Sediment densities were not different between treatments in 1987 but Halectinosoma sp. 1 was significantly more abundant on the leaves in the exclusion treatment on June 11 (Student's f-test, P<0.05). Pseudobradya lanceta Coull (Figs. 4.33,4.34) Pseudobradya lanceta density did not differ between treatments on any date on leaves or in the sediment in either year. Robertsonia propinqua (T. Scott) (Figs. 4.35,4.36) This species was not found in leaf samples in 1986 but was significantly more abundant in the sediment on April 28 in the control (Mann-Whitney t7-test, /MX05). -163-1 9 8 6 Figure 4.26. Abundance of Mesochra pygmaea on Zostera marina leaves (number-cm"2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -164-Figure 4.27. Abundance of Mesochra pygmaea on Zostera marina leaves (number-cm"2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -165-Figure 4.28. Abundance of Amphiascus minutus sp. 1 on Zostera marina leaves (number-cm" z leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -166-0.02 0.01 -0 .00 •• Contro l -o Exc lus ion / 31 M a r c h 14 28 12 26 10 A p r i l M a y J u n e 1 9 8 6 1 9 8 6 Figure 4.29. Abundance of Danielssenia typica on Zostera marina leaves (number-cm"2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. - 1 6 7 -O.OIOn •• Control •° Exclusion D CD CM o 0.005 CD jQ £ Z5 0.000 02 16 Apri l 30 14 28 May — • — 11 J u n e 1 9 8 7 1 9 8 7 Figure 4.30. Abundance of Danielssenia typica on Zostera marina leaves (number-cm"z leaf) (a) and in the secliment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -168-lr\ • • Control o o Exclusion 6-3 -0 31 14 28 12 26 10 M a r c h Apri l May J u n e 1 9 8 6 Figure 4.31. Abundance of Halectinosoma sp. 1 on Zostera marina leaves (number-cm"z leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -169-0.4 n •• Control -° Exclusion o _0J CM I E o C CD E 0.3 0.2 16 A p r i l 30 14 28 M a y 1 9 8 7 11 J u n e c CD £ T J OJ CO CM I E CJ si CD JD E zs 15 10-0 • • Control ° o Exclusion 0 2 16 A p r i l 30 14 28 M a y 11 J u n e 1 9 8 7 Figure 4.32. Abundance of Halectinosoma sp. 1 on Zostera marina leaves (number-cm"z leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -170-Figure 4.33. Abundance of Pseudobradya lanceta on Zostera marina leaves (number-cm"2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -171-0 . 0 1 0 n o OJ CM o 0.005 si OJ E 0.000 •• Control - o Exclusion 14 28 May 11 J u n e 1 9 8 7 Figure 4.34. Abundance of Pseudobradya lanceta on Zostera marina leaves (number-cm"2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -172-Figure 4.35. Abundance of Robertsonia propinqua in the sediment (number-cm"2 sediment) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -173-O.OIOn -• Control •° Exclusion o CD C N o 0 . 0 0 5 -CD E Z5 0 .000 30 14 28 M a y 1 9 8 7 — f — 11 June 1 9 8 7 Figure 4.36. Abundance of Robertsonia propinqua on Zostera marina leaves (number-cm" leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1987. Values are the mean ± 1 Standard Error, n = 3. -174-Robertsonia propinqua was not different between treatments in the two subhabitats during the 1987 experiment. Stenhelia (Delavalia) latioperculata l td (Figs. 4.37,4.38) Density of this species did not differ between treatments on any date on leaves or in the sediment in either year. It was not found in leaf samples during the 1987 experiment. 4.4 DISCUSSION The caging experiments conducted in both 1986 and 1987 were adequate in design and appropriately tested for an effect of epibenthic predation on the harpacticoid copepod community near Station H . General observational data indicated that conditions inside the cages were similar to those in the surrounding area (e.g. surficial sediment structure) and those that were not (e.g. seagrass epiphytic growth) were mimicked by the control cage treatment. Comparison of sediment grain sizes between treatments at the end of the experiments indicated a significant increase in the <75 u,m fraction in the exclusion treatment in 1986 and no difference in 1987. However, the increase in this size class was only a mean of 2.2% of the total sediment weight higher than the control. This is a small change in comparison to the minimum 19% increase in silt-clay (<62 nm) content compared to surrounding sediment observed by Virnstein (1977) in 12 mm mesh cages in Chesapeake Bay. Therefore, artifacts introduced by caging seem to be minor and the control treatment seems to be fairly adequate in. design. Therefore, comparison between the exclusion treatment and the control should provide a good test of the effect df large epibenthic predators on the harpacticoid community at the study site. Exclusion of large epibenthic predators (e.g. juvenile salmonids, crabs) seems to have little effect on the abundance and species structure of the harpacticoid copepod community living on the seagrass or in the sediment in either year. Overall, species abundances were either not different between treatments or densities were higher in the controls. Species -175-D CM I E CJ 0 .06 0 .04 OJ E 0 .02 0 . 0 0 -• • Control ° ° Exclusion 31 14 28 12 26 10 M a r c h A p r i l M a y J u n e 1 9 8 6 Figure 4.37. Abundance of Stenhelia (D.) latioperculata on Zostera marina leaves (number-cm-2 leaf) (a) and in the sediment (number-cm-2 sediment) (b) in the Control and Exclusion treatments in 1986. Values are the mean ± 1 Standard Error, n = 3. -176-c CD E CD CO CNJ I E o CD _ Q E 3 • • Control 0 0 Exclusion 16 30 14 28 A p r i l M a y 1 9 8 7 11 J u n e Figure 4.38. Abundance of Stenhelia (£>.) latioperculata in the sediment (number-cm -2 sediment) in the Control and Exclusion treatments in 1987. Values are the mean i 1 Standard Error, n = 3. -177-abundances generally did not increase in the exclusion treatment as would be expected i f consumption by large epibenthic predators was causing declines in population densities. Also, changes in species dominance (see Gee et al. 1985) in either subhabitat did not occur. Tisbe cf. furcata female densities in leaf samples were higher in the exclusion treatment on two dates in 1986. No difference was seen in 1987. However, no sustained population of this species was observed in the exclusion treatment in 1986 and juvenile numbers did not increase relative to the control. An increase in juvenile numbers would be expected if predation on females was controlling the Tisbe population through removal of reproductive individuals. The Harpacticus uniremis and Zaus aurelii populations did not increase in the exclusion treatment relative to the control in either year. It appears that exclusion of large epibenthic predators does little to halt the population declines of Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii in the late spring and early summer and therefore these declines, at least at this study site, are not related to predation by juvenile salmonids. This conclusion confirms the suggestion of Cordell (1986) and is contradictory to the analysis of Healey (1979). A possible criticism of an experiment like this one is that although the cage mesh size was sufficient to exclude the target predator populations, the harpacticoid copepods were not enclosed and therefore dilution of any increases in the exclusion treatment could occur. This could lead to no significant increases being detected between treatments. This is possible considering that harpacticoids are commonly found to enter the water column (e.g. Walters 1988). Therefore, dilution of cage populations could occur solely through tidal current transport at high tide. However, D'Amours (1988a), based on a sled sampler study conducted at high tide at the study site in 1986, calculated that almost no Harpacticus uniremis, Tisbe spp. or Zaus aurelii would be expected above 50 cm from the sediment. This is the height of the cages used in this study. Therefore, although lateral transport could occur throughout the seagrass bed, these copepods would not be found above the cages. Thus, any swimming activity within the cage area may not lead to a loss. Also, given that mainly adult males and -178-late-stage female copepodites are generally found in the water column (Bell et al. 1988), adult female and total juvenile copepodite abundance should still exhibit a treatment effect if large epibenthic predators are controlling the populations of Harpacticus, Tisbe and Zaus. Sustained increases of females and juveniles in the exclusion treatment were not observed for any species. The conclusion of little effect of large epibenthic predators on these three species is, therefore, supported. These experiments demonstrate that juvenile chum and/or pink salmon, as one predator group tested, exert little control on the population cycles of Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii. This supports the results regarding the comparison of copepod mortality and salmonid consumption patterns presented in Chapter 3. Exclusion of large (those that cannot enter a 7 mm square mesh) epibenthic predators has no obvious effect on the harpacticoid copepod community on the seagrass or in the sediment near Station H . Predation and/or disturbance by these animals appears to have little negative impact on harpacticoid copepods. -179-5. G E N E R A L DISCUSSION The harpacticoid copepod community in the seagrass bed, at this sampling site, appears to be affected litde by large epibenthic organisms either through direct consumption or disturbance-related mechanisms. A group of predators suggested to have an effect on harpacticoid copepod densities were juvenile Pacific salmon (Healey 1979). Harpacticus uniremis, Tisbe cf. furcata andZaus aurelii were the harpacticoid species consumed the most by juvenile chum and pink salmon using the seagrass bed as a foraging area. These three species were common as epiphytes on seagrass leaves in the spring and early summer. From comparisons of patterns of their mortality to patterns of an estimated consumption index of juvenile chum and pink salmon, little correspondence was observed. This lack of correspondence suggests that predation by juvenile salmon does not control the pattern of H. uniremis, T. cf. furcata and Z. aurelii abundance at the study site. This conclusion was statistically corroborated and extended to large epibenthic predators/disturbers in general through controlled predator/disturber exclusion experiments conducted within the seagrass bed. These exclusion experiments also demonstrated that the harpacticoid copepod community as a whole, both on seagrass leaves and in the sediment, does not respond to exclusion of large epibenthos, either in density changes or species composition shifts. During the study period, seagrass-dwelling Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii start to increase in abundance during mid-March to mid-April. However, these three species have generally disappeared by mid-June. A similar pattern is observed for the epiphyte Dactylopodia crassipes. A possible explanation for this pattern is predation by animals small enough to pass in and out of the 7 mm mesh used in the exclusion "experiments in this study. The significance of small potential predators was not tested in this thesis. However, leaf samples from Station H and the cages in qualitative examination contained only small numbers of other meiofauna (e.g. nematodes, mites) and organisms such as -180-amphipods, juvenile polychaetes and gastropod molluscs were also uncommon in comparison to the dominant harpacticoid copepods. Amphipods are not abundant at this study site until later in the summer than sampled here (Miller 1985). Given the rapid population declines observed for the aforementioned copepod species, it is hard to ascribe a significant role to predation by other small invertebrates. An intriguing possibility, however, is the interaction of the epiphytic copepods with the structure of the primary epiphyte community (e.g. diatoms) on the seagrass leaves. The reproductive activity of the Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii populations (as indicated by number of eggs.female-1) generally decreases with time during the duration of this study in both years. Reproductive activity is at a maximum in the early spring. It would appear that conditions for population growth of these species on the leaves becomes worse as summer approaches. This supposition is supported by a perceived movement of Harpacticus uniremis females from the seagrass leaves to the sediment in both years studied. An interesting observation that was noted in both years of this study was that the epiphytic diatom community changes in early June. Macroalgal epiphytes on seagrass leaves were not commonly observed either during sampling or on preserved leaf samples during this study. Analysis of qualitative scrapings of seagrass leaf surfaces throughout the sampling period in both years by normal transmitted light and epifluorescence microscopy indicated that the primary epiphytic community was composed chiefly of bacteria and diatoms. Until early June, the diatom flora was dominated by the genera Cocconeis and Isthmia and little vertical relief was observed on the leaves. However, after this time, the diatom community was dominated by a tube-building Navicula, along with species of Synedra and Rhoicosphenia. The leaf epiphyton in June had a vertical, filamentous appearance due to the tube-building Navicula. Dorso-ventrally flattened epiphytic harpacticoids, such as Zaus, have been found to be more abundant on macroalgal surfaces or seagrass leaves with low primary epiphytism compared to surfaces with high epiphyte loads (Caine 1980, Hall and Bell 1988, this study -181-(intrashoot distributions of Zaus aurelii, Appendix 3)). The genus Tisbe is typically found in high numbers in disturbed, polluted and/or unpredictable environments and can adapt to these conditions (e.g. Marcotte and Coull 1974; Lopez 1982; Webb and Marcotte 1984; Alongi 1985; Gee et al. 1985). Tisbe furcata feeds raptorially by creating spherical masses of flocculant material and gleaning food from the surface while the sphere is rotated by the mouthparts (Marcotte 1977). Species in the genus Dactylopodia apparently feed by sweeping broad, planar surfaces (Marcotte 1977). Perhaps the decline in Tisbe cf. furcata, Zaus aurelii and Dactylopodia crassipes is related to a reduced feeding rate for Tisbe and Dactylopodia on the more structurally complex leaf surface, found later in the sampling season, coupled with the high epiphyte loads being inhospitable for Zaus. Unfortunately, no information on feeding mechanisms is available for Harpacticus uniremis. Interestingly, species of the genus .Heterolaophonte appear to have an almost obligate requirement to feed off of cylindrical objects (Marcotte 1977). The H. variabilis increase, observed late in the sampling season in both years, may be linked to an appropriate habitat such as the tube-building Navicula becoming common. These questions require further research. One further point requires discussion. Based on the results generated from the Nanaimo River estuary study, Sibert et al. (1977) suggested that juvenile salmonid production in the estuary is linked to a detritus-based food web. This conclusion was based on higher assimilation rates of heterotrophic bacterial carbon compared to autotrophic microalgal carbon by Harpacticus uniremis and Tisbe furcata in radiotracer experiments, the presence of the copepods in the sediment and feeding on the copepods by the fish. However, if the salmon are feeding on the epiphytic harpacticoid community on Zostera marina, as is possible given their sampling design, this is not neccessarily a detrital food web. While not disputing the preferential assimilation of bacterial carbon by the copepods, excretion of D O C (dissolved organic carbon) by living Zostera leaves has been demonstrated to be almost sufficient to support epiphytic bacterial activity (Kirchman et al. 1984). Assuming the copepods are feeding on epiphytic bacteria, it may be premature to invoke the detrital -182-pathway as the link to juvenile salmon production, although the importance of detritus has been established elsewhere (see Mann 1988). Attention should also be given to the spatial and temporal patterns of "primary" production in nearshore, vegetated marine areas as a possible contributing factor to the recruitment success of individual salmonid year-classes. -183-R E F E R E N C E S Alheit, J., and Scheibel, W. 1982. 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Meeresunters. 35: 47-63. -192-APPENDIX 1 SPECIES LIST OF HARPACTICOID COPEPODS FOUND IN BIWEEKLY ZOSTERA MARINA LEAF SAMPLES AND/OR SEDIMENT CORES AT STATION H: JANUARY 22-JULY 9,1986 AND JANUARY 24-JULY 9,1987 Family Longipediidae Sars, Lang Longipedia americana Wells Family Ectinosomatidae Sars, Olofsson Ectinosoma melaniceps Boeck Ectinosoma sp. 1 Halectinosoma sp. 1 Halectinosoma sp. 2 Pseudobradya lanceta Coull Family Tachidiidae Sars, Lang Danielssenia reducta Gee Danielssenia typica Boeck Tachidius (Neotachidius) triangularis Shen and Tai Family Harpacticidae Sars Harpacticus compressus Frost Harpacticus spinulosus Lang Harpacticus uniremis Kroyer Harpacticus sp. 1 Zaus aurelii Poppe Zaus sp. 1 Family Tisbidae Stebbing, Lang Scutellidium arthuri Poppe Scutellidium hippolytes Kroyer Tisbe cf. furcata (Baird) Tisbe sp. 1 Family Tegastidae Sars Tegastes sp. 1 Family Thalestridae Sars, Lang Dactylopodia crassipes Lang Dactylopodia tisboides (Claus) -193-Family Thalestridae Sars, Lang Dactylopodia vulgaris f. inornata Lang Diarthrodes sp. 1 Parathalestris californica Lang Family Diosaccidae Sars Amonardia normani (Brady) Amonardia perturbata Lang Amphiascoides petkovskii Lang Amphiascoides sp. 1 Amphiascopsis cinctus (Claus) Amphiascus minutus (Claus) sp. 1 Lang Amphiascus undosus Lang Bulbamphiascus imus (Brady) Diosaccus spinatus Campbell Paramphiascopsis ekmani Lang Robertsonia propinqua (T. Scott) Schizopera knabeni Lang Stenhelia (Delavalia) latioperculata Ito Stenhelia (Stenhelia) asetosa Thisde and Coull Stenhelia (Stenhelia) peniculata Lang Typhlamphiascus pectinifer Lang Family Ameiridae Monard, Lang Ameira longipes Boeck Ameira minuta Boeck Nitocra spinipes armata Lang Nitocra typica Boeck Family Canthocamptidae Sars, Monard, Lang Mesochra pygmaea (Claus) Mesochra sp. 1 Orthopsyllus illgi (Chappuis) Family Cylindropsyllidae Sars, Lang Paraleptastacus spinicauda (T. and A . Scott) Family Cletodidae T. Scott Enhydrosoma sp. 1 Huntemannia jadensis Poppe Leimia vaga Willey Limnocletodes behningi Borutzky Family Laophontidae T. Scott Heterolaophonte variabilis Lang Paralaophonte congenera (Sars) -194-A P P E N D I X 2 E S T I M A T I N G T H E A B U N D A N C E OF L E A F - D W E L L I N G H A R P A C T I C O I D C O P E P O D S O N T H E S E A G R A S S Z O S T E R A M A R I N A L . : T H E USE OF I N T R A S H O O T DISTRIBUTIONS I N T R O D U C T I O N Marine harpacticoid copepods exhibit patchy distributions in sediments on a variety of spatial scales (see Hicks and Coull 1983 for review). Little is known of spatial patterns in other habitats (e.g. phytal, but see Hicks 1980). Recendy, harpacticoid copepods inhabiting seagrass leaves have become the focus of intensive study (see Bell et al. 1984 for review; Bell et al. 1986; Hicks 1986; Hall and Bell 1988). The methodology of sampling leaf dwelling harpacticoids consists of either using small quadrats and sampling all leaves within the contained area or enclosing individual, randomly selected leaves in a hollow tube, cutting the leaf and retrieving the contained copepods (Bell et al. 1986; Hicks 1986). Estimates of harpacticoid abundance as a function of sediment area can then be calculated using quadrat area (Hicks 1986) or data on the number of leaves*m-2 (Bell et al. 1986). The high abundance of harpacticoids on seagrasses (e.g. up to 11.9-cm-2 leaf area, present study) makes the sampling of individual leaves preferable to quadrat sampling since sample sorting time will be lower for individual leaves than quadrats containing many leaves. Therefore, the number of replicate leaves taken can be increased leading to more accurate and precise density estimates for the same sorting time. Seagrass shoots grow vegetatively by the apical addition of new leaves (Den Hartog 1970). Thus within shoots, leaves are of different ages. Epiphyte (e.g. diatoms and bacteria) biomass is positively correlated with leaf age (Novak 1984; Borum 1987). Hicks (1986) found no relationship between the surface area of seagrass leaves and the abundance of associated harpacticoids, which is surprising in comparison with studies of copepod abundance on macroalgae (Hicks 1980). If harpacticoids are selecting for a leaf characteristic -195-other than surface area (e.g. leaves with high epiphyte biomass (Hall and Bell 1988)), this would result in a non-uniform distribution of copepods within shoots. Therefore, randomly sampling leaves would obscure any relationship between leaf surface area and harpacticoid abundance. Also, small sample numbers may lead to low accuracy and precision of estimates of copepod density. The hypothesis that harpacticoid copepods are non-uniformly distributed among leaves of individual shoots of the seagrass Zostera marina L . was tested. The significance of surface area-copepod abundance relationships in seagrasses is discussed and an accurate method for determining the abundance of seagrass dwelling harpacticoid copepods is described. M E T H O D S Sampling was conducted in a shallow subtidal Zostera marina bed on Roberts Bank, British Columbia, Canada (49° 2'N;123° 8'W) (for a detailed description of the study site see Harrison, 1987). Mean Z. marina shoot density for the sampling dates at the reference station (Station H) was 88.6 ± 3.81 shoots-m"z (mean ± S.E., n=4). On four occasions (June 10, 1986, March 19, May 14 and July 9, 1987), 3 seagrass shoots were selected at random within 20 m of the station. Samples were collected at low tide when approximately 5 cm of water covered the shoots. Neighbouring shoots were gently pushed away from the area of the shoot to be sampled. Each leaf of the selected shoot, commencing with the oldest, was gently enclosed in a 30 cm long, 4 cm diameter P V C tube with a screw cap of 63 urn Nitex mesh at one end. Relative leaf age was determined morphologically by observing the point of leaf insertion in the sheath in relation to the oldest (basal) leaf and the alternating pattern of leaf emergence. When the entire leaf was within the tube sampler, the leaf was cut at its base and the other end of the sampler capped. The sampler was retrieved and its contents rinsed into a jar with 40 p.m filtered seawater. The sample was then preserved by addition of a 4% Formaldehyde/40 \im filtered seawater solution. -196-In the laboratory, the leaf was shaken 5 times in the sample jar to remove any attached copepods. This procedure has been found to be 99.4 ± 0.17% (mean ± S.E., n=6) efficient in retrieving copepods (D.G. Webb, unpublished data). The leaf was divided into, at most, 20 cm long segments and length and width measurements made to the nearest 0.5 mm. Surface area was estimated arithmetically for each segment and then segment areas were summed to obtain leaf surface area. For each sample, all copepodites of Harpacticus uniremis Kroyer, Tisbe cf. furcata (Baird) and Zaus aurelii Poppe were counted. Fifty of each species were removed and identified to copepodite stage and gender. A l l remaining copepodites were enumerated and fifty removed and identified to species. Abundance of each species per leaf was then estimated as a proportion of the total number of copepods in the sample. Numbers of copepods of each species-leaf-1 were summed for all the leaves in a shoot to obtain numbers-shoot-1. Numbers-leaf-1 were then expressed as a percentage of numbers-shoot-1. Starting with the youngest leaf on the shoot, leaf surface areas were transformed to a cumulative percentage of shoot area. These transformations of copepod abundance and leaf area were used to normalize for variations in the number and relative surface area of leaves for each shoot. Surface areas of individual leaves were summed to obtain surface area-shoot-1. Leaf area was then expressed as a cumulative percentage of shoot area, starting with the youngest leaf. Empirical relationships with number of copepods-leaf-1 as a percentage of number-shoot-1 regressed against cumulative percentage of shoot area were fitted to determine if there was a relationship between copepod abundance and position within shoots. Only harpacticoid species making up a minimum of 5% of the total number of copepods in 2 of the 3 replicate shoots were selected for analysis. Curves were fitted for total harpacticoids and each species separately. Leaf area as a percentage of shoot area was also regressed -197-against cumulative percentage of shoot area to determine leaf surface area patterns within shoots. A l l curves were fitted using the M G L H module of SYSTAT (Wilkinson 1985) on an I B M PC/XT microcomputer. Percentage data were arcsine transformed to remove heteroscedacity (Sokal and Rohlf 1981). Power, exponential or polynomial up to cubic fits, forced through the origin, were used. Maximization of the coefficient of determination (r2) and a lack of pattern in the residuals were used as criteria to select the best fit equation. The 0.05 level of significance was observed throughout. R E S U L T S Harpacticoid copepod abundance ranged from 0.1-cm-2 shoot area in March 1987 to 11.9-cm-2 shoot area in May 1987 (Table 1). A maximum of 5 species on any date had abundances above the selected criterion for analysis. The species selected comprised at least 70% of the leaf dwelling harpacticoid community on any date (Table 1). The relationship between number of copepods-leaf-1 as a percentage of number-shoof 1 and cumulative percentage of shoot area was not uniform (Figs. 1-4). A l l fitted regressions for total harpacticoids and for individual species had slopes significantly different from zero (Table 2). Relationships for most sampling dates were extremely strong, with r2 > 0.90, except for March 1987, which had coefficients of determination between 0.40 and 0.82. A l l regressions were nonlinear in form, with polynomial fits being the most common (Table 2). The relationship between leaf area as a percentage of shoot area and cumulative percentage of shoot area was extremely strong (r2 > 0.98) and similar on all sampling dates (Table 3) (Figs. 1-4 a). Best fit equations were cubic polynomials with the peak of the equation occurring at a cumulative percentage of shoot area of 50-75%, indicating that leaves with the largest surface area were in the middle of shoots. -198-Table 1. Harpacticoid copepod abundance.shoot-1, species selected for analysis and then-percentage of the leaf dwelling harpacticoid community for each sampling date, x + S.E. = mean ± 1 Standard Error; n = sample size. Date Copepods No-cm-2 x+SE,n=3 Species Percent x±SE,n=3 June 10,1986 1.7±0.38 Amonardia normani (Brady) Amphiascus undosus Lang Dactylopodia crassipes Lang 82.3±4.85 March 19,1987 0.1±0.03 Mesochra pygmaea (Claus) Tisbe cf. furcata (Baird) 69.6±7.72 May 14,1987 11.9±1.41 D. crassipes Harpacticus compressus Frost Heterolaophonte variabilis Lang M. pygmaea T. cf. furcata 83.6±2.29 July 9,1987 5.7±1.20 A. undosus Ectinosoma melaniceps Boeck H. variabilis M. pygmaea 93.0±1.59 -199-40-I 30-20-10-o o 6 o o 00 o o 8 Ld O o o o p 25 cP o o 8 ° o ° 1 25 50 75 100 0  50 75 100 CUMULATIVE PERCENTAGE OF SHOOT AREA Figure 1. Plots of leaf area as a percentage of shoot area against cumulative percentage of shoot area (a) and number of copepods-leaf-1 as a percentage of number-shoot-1 against cumulative percentage of shoot area for total harpacticoids (b); Amonardia normani (c); Amphiascus undosus (d) and Dactylopodia crassipes (e) for June 10, 1986. -200-o oq 50 75 ~9 100 CUMULATIVE PERCENTAGE OF SHOOT AREA Figure 2. Plots of leaf area as a percentage of shoot area against cumulative percentage of shoot area (a) and number of copepods-leaf-1 as a percentage of number-shoot-1 against cumulative percentage of shoot area for total harpacticoids (b); Mesochra pygmaea (c) and Tisbe cf. furcata (d) for March 19,1987. -201-30-i 2 0 -O cm o o o _Q_ O O 1 o T T O O o o o .o o 1 25 50 75 100 25 50 75 100 CUMULATIVE PERCENTAGE OF SHOOT AREA Figure 3. Plots of leaf area as a percentage of shoot area against cumulative percentage of shoot area (a) and number of copepods-leaf-1 as a percentage of number-shoot-1 against cumulative percentage of shoot area for total harpacticoids (b); Dactylopodia crassipes (c); Harpacticus compressus (d); Heterolaophonte variabilis (e); Mesochra pygmaea (f) and Tisbe cf. furcata (g) for May 14,1987. -202-bJ O o o o o o "i r o T T O 0 ~1 o 8 1 0 25 50 75 100 0 25 50 75 100 CUMULATIVE PERCENTAGE OF SHOOT AREA Figure 4. Plots of leaf area as a percentage of shoot area against cumulative percentage of shoot area (a) and number of copepods-leaf-1 as a percentage of number-shoot-1 against cumulative percentage of shoot area for total harpacticoids (b); Amphiascus undosus (c); Ectinosoma melaniceps (d); Heterolaophonte variabilis (e) and Mesochra pygmaea (f) for July 9,1987. -203-Table 2. Relationships between number of copepods-leaf-1 as a percentage of number-shoot-1 (y) and cumulative percentage of shoot area (x) for total harpacticoids and individual species on each sampling date. Both y and x are arcsine transformed (in radians). r2=coefficient of determination; n=sample size. Anorm = Amonardia normani; Aund = Amphiascus undosus; Dcrass = Dactylopodia crassipes; Emel = Ectinosoma melaniceps; Hcomp = Harpacticus compressus; Hvar = Heterolaophonte variabilis; Mpyg = Mesochra pygmaea; Tfurc = Tisbe cf. furcata. Date Species Relationship r2 n P June 10,1986 Total y=0.94x2-0.43x3 0.98 16 <0.001 Anorm y=0.79x2-0.33x3 0.90 16 <0.001 Aund y=0.87x2-0.38x3 0.95 16 <0.001 Dcrass y=1.05x2-0.52x3 0.94 16 <0.001 March 19,1987 Total y=e0.33x 0.81 16 <0.001 Mpyg y=0.24x3 0.82 16 <0.001 Tfurc y=e0.25x 0.40 11 0.027 May 14,1987 Total y=0.90x-0.37x2 0.97 15 <0.001 Dcrass y=0.81x-0.24x3 0.97 15 <0.001 Hcomp y=0.80x-0.23x3 0.92 15 <0.001 Hvar y=e0.36x 0.93 15 <0.001 Mpyg y=1.20x2-0.62x3 0.95 15 <0.001 Tfurc y=1.04x-0.50x2 0.93 15 <0.001 July 9,1987 Total y=0.63x-0.08x3 0.99 15 <0.001 Aund y=0.98x2-0.43x3 0.96 15 <0.001 Emel y=x0.59 0.98 15 <0.001 Hvar y=0.65x-0.10x3 0.99 15 <0.001 Mpyg y=0.66x-0.10x3 0.98 15 <0.001 -204-Table 3. Relationship between leaf area as a percentage of shoot area (y) and cumulative percentage of shoot area (x) for each sampling date. Both y and x are arcsine transformed (in radians). r2=coefficient of determination; n = sample size. Date Relationship r2 n P June 10,1986 y=1.43x-1.27x 2+0.34x3 0.99 16 <0.001 March 19,1987 y=1.47x-1.30x2+0.33x3 0.98 16 <0.001 May 14,1987 y=1.47x-1.33x2+0.37x3 0.98 15 <0.001 July 9,1987 y=1.35x-1.08x2+0.27x3 0.99 15 <0.001 -205-For the June 1986 and March and July 1987 samplings, there appeared to be little correspondence between leaf surface area and copepod numbers. Maximal harpacticoid abundances were observed on the older leaves of shoots (i.e. large cumulative percentage of shoot area) irrespective of leaf surface area (Figs. 1,2,4). The May 1987 data however, shows a better correlation between copepod abundance and leaf surface area except for Heterolaophonte variabilis. (Fig. 3). DISCUSSION Harpacticoid copepod abundance in phytal habitats has generally been considered to be directly correlated with habitable surface area and mediated by habitat complexity (see Hicks 1980). Hicks (1986) showed that copepod numbers on seagrass leaves did not correlate with surface area and suggested that harpacticoids are responding to some other characteristic of the leaves. Older leaves of seagrasses have a greater biomass of epiphyton (Novak 1984; Borum 1987). At this study site, diatoms and bacteria are the dominant epiphytes on Zostera marina leaves (D.G. Webb, personal observation). These two groups are considered to be the major food source for harpacticoid copepods (see Hicks and Coull 1983 for review). It has been demonstrated that copepod abundance within shoots increases with leaf age. It is therefore suggested that harpacticoid copepods are distributed as a function of higher food resource availability on older leaves, not as a function of leaf surface area. Recently, Hall and Bell (1988) showed that there was a significant positive relationship between epiphyte biomass and harpacticoid copepod density on leaves of the seagrass Thalassia testudinum in Florida. The dominant epiphyte at their study site was a filamentous brown alga. From experiments with abiotic simulations of the epiphyte, they suggested that this observed relationship of harpacticoid density was mostly due to the increased habitat complexity afforded by the epiphyte. At this study site, macroalgal epiphytes are rare and mbe-forming diatoms, which could increase the complexity of the leaf -206-surface, are only common after mid-June (D.G. Webb, personal observation). The presence of significant relationships between copepod abundance and leaf age on all the sampling dates indicates that increased habitat complexity is not the only operative factor determining intrashoot harpacticoid arrangement. Harpacticoid distributions within shoots rnirrored leaf surface area relations in May 1987 only. This was the date with the highest leaf dwelling copepod abundance. At high population densities, habitable surface area may become a limiting factor. In these cases, harpacticoid abundance becomes more directly related to leaf surface area. Therefore, intrashoot distributions of harpacticoid copepods in seagrass beds can not be considered static and probably depend on population size. Since significant patterns in copepod abundance within shoots have been demonstrated, random sampling of individual seagrass leaves may lead to imprecise and inaccurate estimates of harpacticoid density for a given sampling effort. To test this hypothesis, a method of estimating leaf dwelling copepod density as a function of sediment area using a knowledge of intrashoot distributions was developed. In this study the number of copepods on each of the 3 shoots per sampling date is known. Therefore, density estimates made from individual leaves can be compared to the number per shoot. Using the equations describing the intrashoot distribution of total harpacticoids, a percentage of the number of copepods on a shoot can be determined from the abundance on an individual leaf as long as the position of the leaf within the shoot is known from its relative age. This was done for the oldest leaf on each shoot for each sampling date. To simulate sampling blades randomly in the field, a leaf was selected at random from each shoot and number of copepods per shoot estimated using the mean number of leaves per shoot. Table 4 compares the results from each method with the true number on each shoot. It is obvious that density estimates from randomly selected leaves are much less accurate than those that use intrashoot distributions for a similar number of copepods sorted and counted. From these results an appropriate sampling strategy is that a leaf of known relative age on a -207-randomly selected shoot should be sampled and its relationship to total shoot area measured. Leaf dwelling harpacticoid abundance as a function of sediment area can then be estimated using data on shoot density and intrashoot distributions. Since abundance on shoots is quite variable, the precision of the density estimate can be increased by sampling more leaves. Intrashoot distributions should be checked periodically in leaf dwelling harpacticoid sampling programs. Although more tedious in the field than randomly sampling leaves, this methodology will allow an accurate estimation of harpacticoid copepod numbers on seagrasses. Table 4. Total harpacticoid abundance-shoot"1 and estimated abundance-shoot"1 using both random leaf sampling and intrashoot distributions. CPS = cumulative percentage of shoot area. Shoot abundances estimated by each method are underlined. Known Random Intrashoot Shoot No.-shoot-l Leaf No.-leaf-l Leaves-shoot-1 No.-shoot-l Leaf CPS No.-leaf-l % of shoot No.-shoot-l 1986 1 627 2 18 95 6 100 158 36.9 428 June 10 2 65 4 34 5.3 180 4 80.3 34 29.1 117 3 528 2 9 48 6 100 161 36.9 436 1987 1 7 3 2 11 5 84.9 1 20.8 4.81 March 19 2 19 4 1 5.3 53 5 84.9 15 20.8 72.1 3 37 1 0 0 6 100 23 39.8 57.8 1 2071 4 581 2900 4 74.4 581 26.1 2230 May 14 2 5425 2 361 5.0 1800 6 100 1545 23.1 6690 3 2136 1 35 170 5 91.5 349 27.0 1290 1 2008 4 624 3120 5 100 740 39.5 1870 July 9 2 558 3 101 5.0 500 5 100 238 39.5 602 3 1754 4 588 2940 5 100 639 39.5 1620 -209-R E F E R E N C E S Bell, S.S., Kern, J.C., and Walters, K . 1986. Sampling for meiofaunal taxa in seagrass systems: Lessons from studies of a subtropical Florida estuary, USA. In Biology of Benthic Marine Organisms. Techniques and Methods as applied to the Indian Ocean. Edited by M.-F. Thompson, R. Sarojini and R. Nagabhushanam. A . A . Balkema, Rotterdam, pp. 239-245. Bell, S.S., Walters, K. , and Kern, J.C. 1984. Meiofauna from seagrass habitats: A review and prospectus for future research. Estuaries, 7: 331-338. Borum, J. 1987. Dynamics of epiphyton on eelgrass (Zostera marina L.) leaves: Relative roles of algal growth, herbivory and substratum turnover. Limnol. Oceanogr. 32:986-992. Den Hartog, C , 1970. The seagrasses of the world. Verh. K . Ned. Akad. Wet. Afd. Natuurkd., Sect. 2. 59: 1-275. Hall, M.O., and Bell, S.S. 1988. Response of small motile epifauna to complexity of epiphytic algae on seagrass blades. J. Mar. Res. 46: 613-630. Harrison, P.G. 1987. Natural expansion and experimental manipulation of seagrass (Zostera spp.) abundance and the response of infaunal invertebrates. Estuar. Coast. Shelf Sci. 24:799-812. Hicks, G.R.F. 1980. Structure of phytal harpacticoid copepod assemblages and the influence of habitat complexity and turbidity. J. Exp. Mar. Biol . Ecol. 44: 157-192. Hicks, G.R.F. 1986. Distribution and behaviour of meiofaunal copepods inside and outside seagrass beds. Mar. Ecol. Prog. Ser. 31: 159-170. Hicks, G.R.F., and Coull, B.C. 1983. The ecology of marine meiobenthic harpacticoid copepods. Oceanogr. Mar. Biol . 21: 67-175. Novak, R. 1984. A study in ultra-ecology: Microorganisms on the seagrass Posidonia oceanica (L.) Delile. P.S.Z.N.I.: Mar. Ecol. 5: 143-190. Sokal, R.R., and Rohlf, F.J. 1981. Biometry. 2nd ed. W.H. Freeman and Co., San Francisco. Wilkinson, L . 1985. SYSTAT. The system for statistics. Version 2.1. Systatjnc, 1800 Sherman Ave., Evanston, IL 60201, U.S.A. -210-APPENDIX 3 SHOOT DENSITY, INTRASHOOT LEAF SURFACE AREA PATTERNS AND INTRASHOOT DISTRIBUTIONS OF SELECTED HARPACTICOID COPEPOD SPECIES AND DEVELOPMENTAL STAGES AT STATION H, 1986 AND 1987 To use intrashoot distributions of seagrass dwelling harpacticoid copepods to estimate abundance on a sediment area basis, data on seagrass shoot density, leaf surface area patterns within shoots and copepod intrashoot distributions on each sampling date are required. For this study, on each sampling date the number of Zostera marina shoots in three 0.25 m.2 quadrats was determined near Station H . Locations of quadrats were selected by using randomly determined (with a die) map coordinates (e.g. North, South, East, West) and a random number of steps (0-9, taken from a random number table) in the appropriate direction from the station marker. This procedure was repeated three times. In one of the three quadrats (chosen by rolling a die), a maximum of 10 Z. marina shoots were culled by cutting individual shoots at their point of emergence from the sediment starting with the nearest shoot to the observer. The shoots were placed in a plastic bag and returned to the laboratory. For each leaf on each shoot, the relative leaf age (i.e. leaf 1, 2, 3, etc.) was noted. The leaf was divided into, at most, 20 cm long segments and length and width measurements made to the nearest 0.5 mm. Segment areas were then summed to obtain leaf surface area. The average surface areas of leaves of different relative ages on each sampling date along with the average shoot density in the three quadrats are presented in Table 1. Since intrashoot distributions of harpacticoid copepods were not determined on each sampling date, the measured distributions on the four samplings were extrapolated to various sampling periods. Since intrashoot distributions were not estimated early in the sampling season in 1986, data from 1987 were used. The intrashoot distributions determined on March 19,1987 were used for the periods of January 22 to March 31,1986 and January 24 to April 2, 1987. The distributions from May 14, 1987 were applied to the periods April 14 to May -211-12,1986 and April 16 to May 28,1987. The June 10,1986 intrashoot distributions were used from May 26 to July 9, 1986 and the July 9,1987 distributions were applied to the period of June 11 to July 9,1987. For the species present in leaf samples of the 15 harpacticoid species analyzed in Chapter 2, intrashoot distributions are presented in Table 2. Separate relationships are presented for juvenile copepodites, adult males and adult females, when present. If the relationship between abundance and shoot area is not significant, abundance per shoot is simply estimated from the proportion of the mean shoot area (Table 1) sampled. A step-by-step outline of the procedure used in this study for estimating leaf-dwelling copepod abundance per unit sediment area is presented in Table 3. -212-Table 1. Average number of Zostera marina shoots-m-2 sediment area (n=3) near Station H and average surface area (cm2) of leaves of different relative ages on each sampling date in 1986 and 1987. Average shoot surface area is the sum of the average leaf areas on that date. #Z = number of Z. marina shoots-m-2; Shoot = average shoot surface area (cm2); n = sample size; 1 = youngest leaf, - = no data. Leaf Date #Z Shoot n 1 2 3 4 5 6 7 8 1986 22/01 124.0 133.9 10 4.4 13.9 25.2 35.0 36.0 8.5 10.9 -06/02 102.7 110.4 10 10.7 22.8 28.1 27.8 21.0 - - -19/02 100.0 154.5 10 13.0 31.4 45.4 44.6 20.1 - - -04/03 81.3 148.0 10 7.4 23.0 31.8 30.7 31.9 20.9 2.3 -18/03 102.7 137.5 10 12.7 22.7 34.8 26.4 19.4 10.5 11.0 -31/03 80.0 156.4 10 7.5 23.7 31.6 34.0 28.9 20.5 7.1 3.1 14/04 124.0 99.7 9 9.7 26.0 29.2 23.6 10.0 1.2 - -28/04 101.3 166.0 8 16.1 39.9 45.1 32.6 25.5 6.8 - -12/05 No Data (Average of April 28 and May 26 values used) 26/05 81.3 216.5 9 19.9 43.9 53.5 45.1 39.4 14.7 - -10/06 92.0 177.4 8 17.4 38.6 46.2 40.2 28.3 v 6.7 - -24/06 69.3 201.8 10 15.9 43.8 52.4 48.6 29.7 11.4 - -09/07 78.7 191.2 8 13.8 43.4 56.1 52.7 22.0 3.2 - -1987 24/01 53.3 193.6 5 18.7 35.0 51.2 49.6 34.5 4.6 - -07/02 97.3 177.2 11 10.9 29.9 46.0 43.0 30.9 16.5 - -20/02 106.7 127.4 9 6.0 18.2 29.9 26.7 26.6 14.8 5.2 -07/03 102.7 140.1 10 5.1 18.4 29.5 31.0 25.8 18.1 12.2 -19/03 92.0 209.9 10 14.5 32.2 49.3 48.2 34.0 31.7 - -02/04 121.3 243.0 9 11.0 34.3 50.8 53.9 45.5 24.9 12.7 9.9 16/04 100.0 177.2 10 13.8 35.3 45.9 38.0 25.1 13.1 6.0 --213-Table 1. Continued. Leaf Date #Z Shoot n 1 2 3 4 5 6 7 8 1987 30/04 85.3 296.9 10 24.1 54.9 65.6 59.4 55.3 31.2 6.4 -14/05 93.3 281.1 9 17.3 54.7 72.6 64.5 48.1 23.9 - -28/05 84.0 224.0 9 19.5 56.0 65.4 45.8 27.5 9.8 - -11/06 69.3 391.0 10 25.7 75.1 97.6 95.0 62.7 34.9 - -25/06 70.7 405.1 10 28.5 89.8 97.8 103 49.8 36.5 - -09/07 77.3 236.1 10 23.5 69.6 67.6 58.9 16.5 - - --214-Table 2. Relationships between number of copepods-leaf-1 as a percentage of number-shoot-1 (y) and cumulative percentage of shoot area (x) for copepodites of individual harpacticoid species and gross developmental stages on each sampling date. Both y and x are arcsine transformed (in radians). J = juveniles; M = adult male; F = adult female; r2 = coefficient of determination; n = sample size; NS = not significant at the 0.05 level. Amin = Amphiascus minutus sp. 1; Anorm = Amonardia normani; Aund = Amphiascus undosus; Dcrass = Dactylopodia crassipes; Emel = Ectinosoma melaniceps; Halec = Halectinosoma sp. 1; Huni = Harpacticus uniremis; Hvar = Heterolaophonte variabilis; Mpyg = Mesochra pygmaea; Plane = Pseudobradya lanceta; Rprop = Robertsonia propinqua; Slat = Stenhelia (£>.) latioperculata; Tfurc = Tisbe cf. furcata; Zaur = Zaus aurelii. Date Species/Stage Relationship r z n P 10/06/86 Anorm (J) y=0.23x3 0.59 16 <0.001 Anorm (M) y = e 0 . 3 0 x 0.77 12 <0.001 Anorm (F) y=1.8x2-l.l x3 0.53 10 NS Aund (J) y=0.26x3 0.69 12 <0.001 Aund(M) y = e 0 . 3 4 x 0.88 16 <0.001 Aund (F) y=0.95x2-0.44x3 0.95 16 <0.001 Dcrass (J) y= 1.2x2-0.65x3 0.92 16 <0.001 Dcrass (M) y=0.30x3 0.80 16 <0.001 Dcrass (F) y=0.34x2 0.85 16 <0.001 Emel (J) y=0.27x3 0.75 10 <0.01 • . . . Emel(F) y=x0.38 . . 0.42 10 <0.05 Halec (F) y=x0.29 0.18 4 NS Hvar (J) y=0.36x3 0.90 4 <0.05 Hvar (M) y = e 0 . 2 7 x 0.47 10 <0.05 Hvar (F) y=0.35x2 0.44 10 <0.05 Huni (M) y=0.25x3 0.68 12 <0.01 Mpyg (M) y=-1.2x2+l.l x3 0.94 6 <0.01 Mpyg (F) y=0.23x3 0.78 16 <0.001 Plane (F) y=x0.19 0.10 12 NS. -215-Table 2. Continued. Date Species/Stage Relationship r 2 n P 10/06/86 Zaur(M) y = x 0 . 2 9 0.18 4 NS 19/03/87 Amin (F) y = x 0 . 2 8 0.22 11 NS Aund (J) y=1.0x-2.8x2+1.8x3 0.98 11 <0.001 Dcrass (M) y=-1.0x2+1.0x3 0.98 5 <0.01 Emel (J) y=1.0x-2.8x2+1.8x3 0.98 11 <0.001 Emel (M) y=-1.0x2+1.0x3 0.98 5 <0.01 Emel(F) y = x 0 . 2 8 0.18 5 NS Mpyg (J) y=0.28x3 0.80 11 <0.001 Mpyg (F) y=0.24x3 0.82 16 <0.001 Rprop (F) y = x 0 . 1 6 0.075 6 NS Slat (F) y = x 0 . 2 8 0.22 5 NS Tfurc (J) y=0.25x3 0.82 6 <0.01 Tfurc (M) y = x 0 . 2 8 0.18 5 NS Tfurc (F) y=0.32x 0.24 6 NS Zaur (J) y = x 0 . 1 6 0.075 6 NS 14/05/87 Anorm (J) y=-1.0x2+1.0x3 0.96 6 <0.01 Anorm (M) y=x0.21 0.12 5 NS Aund (J) y = x 0 . 5 3 0.86 15 <0.001 Aund (M) y=x0.19 0.094 11 NS Aund (F) y=0.27x3 0.74 15 <0.001 Dcrass (J) y=0.80x-0.23x3 0.96 15 <0.001 Dcrass (M) y=X0.46 0.65 15 <0.001 Dcrass (F) y=1.2x-0.70x2 0.86 15 <0.001 Emel (J) y=0.82x2-0.34x3 0.86 15 <0.001 -216-Table 2. Continued. Date 14/05/87 09/07/87 Species/Stage Relationship r 2 n P Emel (F) y = x 0 . 2 9 0.30 6 NS Halec(J) y=-1.0x2+1.0x3 0.96 6 <0.01 Halec (F) y=-1.0x2+1.0x3 0.96 6 <0.01 Hvar (J) y=0.81x2-0.33x3 0.93 15 <0.001 Hvar (M) y=e0.35x 0.80 15 <0.001 Hvar(F) y=1.3x2-0.76x3 0.80 15 <0.001 Huni (J) y=l.lx-0.59x2 0.93 15 <0.001 Huni (M) y=X0.52 0.85 15 <0.001 Huni (F) y=-0.84x+2.4x2-1.0x3 0.94 15 <0.001 Mpyg (J) y=l.2x2-0.64x3 0.95 15 <0.001 Mpyg (M) y = x 0 . 4 3 0.57 15 <0.01 Mpyg (F) y = x 0 . 5 0 0.80 15 <0.001 Tfurc (J) y=1.0x-0.50x2 0.93 15 <0.001 Tfurc (M) y=x0.41 0.50 9 <0.05 Tfurc (F) y=l.lx-0.57x2 0.89 15 <0.001 Zaur (J) y=3.4x-5.1x2+1.9x3 0.90 15 <0.001 Zaur (M) y=3.7x-5.6x2+2.2x3 0.89 15 <0.001 Zaur(F) y=3.5x-5.2x2+1.9x3 0.86 15 <0.001 Anorm (J) y= x0.49 0.68 15 <0.001 Anorm (M) y=x0.22 0.12 15 NS Anorm (F) y=-1.1x2+1.1x3 0.97 5 <0.01 Aund (J) y=0.87x2-0.36x3 0.95 15 <0.001 Aund (M) y=x0.14 0.042 10 NS Aund (F) y=x0.36 0.38 15 <0.05 -217-Table 2. Continued. Date Species/Stage Relationship r2 n P 09/07/87 Dcrass (J) y=0.85x-0.27x3 0.78 15 <0.001 Dcrass (F) y=x0.24 0.13 10 NS Emel (J) y=x0.59 0.98 15 <0.001 Emel (M) y = x 0 . 2 8 0.18 5 NS Emel (F) y=-0.92x2+0.98x3 0.98 5 <0.01 Halec (J) y = x 0 .068 0.010 5 NS Halec (M) y = x 0 .068 0.010 5 NS Halec (F) y = x 0 . 3 1 0.22 10 NS Hvar (J) y=0.69x-0.12x3 0.98 15 <0.001 Hvar (M) y=0.75x-0.21x2 0.99 15 <0.001 Hvar(F) y = e 0 . 3 8 x 0.93 15 <0.001 Mpyg (J) y=l .6x2-0.94x3 0.87 15 <0.001 Mpyg (M) y=e0.36x 0.86 15 <0.001 Mpyg (F) y=l. 1x2-0.51x3 0.92 15 <0.001 Tfurc (J) y = x 0 .068 0.010 5 NS -218-Table 3. Steps used to estimate abundance of leaf-dwelling harpacticoid copepods on a per unit sediment area basis. 1. Estimate number of copepods-cm"2 leaf sample. 2. Knowing the relative leaf age of the sample, calculate number of copepods-leaf-1 using the average leaf area estimated for the specified relative leaf age on the specific sampling date. 3. Estimate the position of the sampled leaf within the calculated average shoot as a cumulative percentage of shoot area starting with the youngest average leaf. 4. Using the appropriate intrashoot relationship, estimate number of copepods-leaf-1 as a percentage of number-shoot-1. 5. Using number of copepods-leaf-1 calculated in 2. above, estimate number of copepods-shoot-1. 6. Using data on shoot abundance per unit sediment area, estimate number of copepods per unit sediment area. -219-APPENDIX 4 EMPIRICAL ANALYSIS OF THE EFFECT OF TEMPERATURE ON MARINE HARPACTICOID COPEPOD DEVELOPMENT TIME INTRODUCTION The population dynamics and production of field populations of marine harpacticoid copepods have elicited much recent interest (e.g. Fleeger 1979; Feller 1980; 1982; Fleeger and Palmer 1982; Herman et al. 1984; Herman and Heip 1985). This type of information is necessary to determine the role of harpacticoid copepods in marine ecosystems, such as the transfer of biomass to higher trophic levels, since harpacticoid copepods are often the most common prey taken by the juveniles of many fish species (e.g. Alheit and Scheibel 1982; Hicks 1985; Sibert 1979). Estimates of production (Crisp 1984), stage specific mortality rates for populations with recognizable cohorts (Southwood 1978; Lynch 1983) and total mortality rates for populations near steady state (e.g. Van Dolah et al. 1975) all require independently derived values of embryonic and/or juvenile development time. Development times can not be estimated from temporal patterns in field data, even for defined cohorts, unless mortality rates are known (Hairston and Twombly 1985). Therefore, harpacticoid copepod development times calculated from analysis of laboratory populations are generally extrapolated to field situations. Development times of harpacticoid copepod eggs, nauplii and copepodites may vary with a number of factors, especially temperature and food quantity and quality (see Hicks and Coull 1983 for review). While food quantity and quality should have little effect on egg development rates, they may be significant factors for nauplii and copepodites. However, food quantity and especially quality are hard to measure in the field because of the diversity of possible food types present (e.g. species of microalgae and bacteria) and the highly selective feeding of harpacticoids (e.g. Rieper 1985). This diversity of food types and the -220-selectivity of the copepods also makes the simulation of a natural feeding environment for laboratory populations difficult. Water temperature, however, is controllable in laboratory experiments and is usually measured in field sampling routines. Few laboratory studies have explored the relationship between temperature and developmental rates for the life history stages of harpacticoid copepods (e.g. Heip and Smol 1976; Palmer and Coull 1980), although there are more data for single temperatures which have been collected for other purposes (e.g. Bergmans 1981). These studies on the effect of temperature are limited to a few species of copepods, and their applicability to other species is questionable (Palmer and Coull 1980). One solution is to raise laboratory populations of the species under study at a range of temperatures that spans field conditions. This approach is tedious and a large number of replicate populations and measurements are required for precise estimation of development times. Also, the problem with a representative food environment is present. However, another approach is the statistical analysis of the relationship between development time and temperature for a variety of species. In this case, the effect of factors such as non-realistic food environments for individual species can be defined within the probability region around the predictive relationship. This paper describes the analysis of the relationship between development time and temperature for marine harpacticoid copepods. Using data extracted from the literature, predictive equations of development time based on temperature are constructed for eggs, nauplii, copepodites, and all juvenile stages, along with generation time. This study will allow prediction of development time within the range of temperatures used in each regression and will facilitate the study of the population dynamics and production of marine harpacticoid copepods. M E T H O D S Data on development time and temperature for laboratory populations of marine harpacticoids, including pelagic species, were extracted from the literature (Table 1). -221-Table 1. List of species, data type, and references for values used in regression analyses. E : egg development, N : naupliar development, C: copepodite development, J: total juvenile development, G: generation time. Species Data type Reference(s) Fam. Canuellidae Scottolana canadensis Fam. Ectinosomatidae Ectinosoma curticorne Fam. Tachidiidae Euterpina acutifrons Microarthridion littorale Tachidius discipes Fam. Harpacticidae Harpacticus littoralis Harpacticus sp. Tigriopus brevicornis Tigriopus californicus Tigriopus japonicus Fam. Tisbidae Tisbe carolinensis Tisbe clodiensis E,N,CJ ,G E,N,C,J,G E,N,C,J,G E,N,C,J,G E,N,C,J,G E,N,C,J E N,C,J,G N,C,J,G E J,G Harris 1977; Lonsdale 1981; Lonsdale and Levinton 1985a,b,1986 Muus 1967 Neunes and Pongolini 1965; Haq 1972; Zurlini et al. 1978; D'Apolito and Stancyk 1979 Palmer and Coull 1980 Muus 1967; Heip and Smol 1976 Raibaut 1967 in Rosenfield and Coull 1974;Castel 1976 Walker 1981 Comita and Comita 1966; Harris 1973 Huizinga 1971 in Rosenfield and Coull 1974; Vittor 1971 in Dethier 1980; Feldman 1986 Ito 1970 in Hicks and Coull 1983;Takano 1971a Lee et al. 1985 Lazzaretto-Colombera and Polo 1969 in Bergmans 1981; Volkmann-Rocco 1972; -222-Table 1. Continued. Species Data type Reference(s) Fam. Tisbidae Tisbe clodiensis Tisbe cucumariae Tisbe dilatata Tisbe dobzhanskii Tisbe furcata Tisbe holothuriae Tisbe pori Tisbe sp. Fam. Thalestridae Dactylopodia vulgaris Diarthrodes cystoceus Diarthrodes nobilis Fam. Parastenheliidae Parastenhelia megarostrum Fam. Diosaccidae Amonardia normani Amphiascoides sp. Paramphiascella fulvofasciata Volkmann-Rocco and Battaglia 1972 J,G Guidi 1984; Webb and Marcotte 1984 E,N,G Muus 1967 J,G Volkmann-Rocco 1972; Volkmann-Rocco and Battaglia 1972 E,N,C,J,G Johnson and Olson 1948; Bergmans 1981 E,N,C,J,G Parise and Lazzaretto 1966 in Gaudy and Guerin 1977;Volkmann -Rocco 1972; Hoppenheit 1976; Gaudy and Guerin 1977 ,1978; Rieper 1978, 1984; Gaudy et al. 1982 J Betouhim-El and Kahan 1972 N Takano 1971b E,N,C,J,G Rieper 1985 E,C Fahrenbach 1962 N,C Hicks unpubl. in Hicks and Coull 1983 N Hicks 1984 E,N,C,J,G Castel 1979 N,C,J Walker 1979 N,C,J,G Rosenfield and Coull 1974 -223-Table 1. Continued Species Data type Reference(s) Fam. Diosaccidae Paramphiascella vararensis Robertgurneya sp. Schizopera elatensis Fam. Ameiridae Nitocra lacustris Nitocra spinipes Nitocra spinipes var. orientalis Nitocra typica Fam. Canthocamptidae Mesochra lilljeborgi Fam. Cletodidae Cletocamptus confluens Cletocamptus retrogressus Cletodes pusillus Huntemannia jadensis Fam. Laophontidae Paronychocamptus nanus E,N,C,J,G Rieper 1978,1984 N,C,J,G Rosenfield 1967 in Rosenfield and Coull 1974 N,C,J,G Kahan 1981 in Hicks and Coull 1983 N,C,J Raibaut 1967 in Rosenfield and Coull 1974 E,N,J,G Muus 1967 N,C,J Abraham and Gopalan 1975 in Hicks and Coull 1983 E,N,C,J,G Heip and Smol 1976; Lee et al. 1976 E,N,C,J,G Castel 1984 E,N,C,J,G Castel 1984 N,C,J Raibaut 1967 in Rosenfield and Coull 1974 E,N,C,J Soyer 1980 E,N,C,J Feller 1980 E,N,C,J,G Heip and Smol 1976 -224-Separate data sets were created for egg development, naupliar development (first nauplius to first copepodite), copepodite development (first copepodite to adult female), total juvenile development (first nauplius to adult female) and generation time (gravid female to gravid female or first nauplius to first nauplius). If the temperature to which the cultures were exposed was expressed as a range, the mean of the range values was used. If the range was greater than 5°C, the data were discarded. If a range of development time at a certain temperature was given, the mean of the range was taken. In some cases, development time values were obtained by difference (e.g. copepodite development = total juvenile development - nauplius development). Some development time data were obtained from food quality experiments (e.g. Lee et al. 1976). In these cases, if different development times on different food sources were reported, the shortest time was included in the data set. If generation time was calculated from life table equations rather than direct observation, only values of mean generation time (sensu Pielou 1977) were included in the data set. The data were transformed to natural logs to meet the assumptions of linear regression and analysis of variance. Regressions of the form [1] l n D = lna + b l n T were performed on each of the five data sets, where D is development time in days and T is temperature in °C. Higher order equations of the form [2] In D = In a + b In T + c (In T)2 were also fitted as suggested by previous work on the relationship between development time and temperature (see Bottrell 1975), but second order coefficients were not significant for any data set (partial F-tests, P>0.05) and therefore the transformed power equation was used. Residuals from each regression were visually scanned for remaining patterns but none was obvious. Statistical outliers in the data sets were detected through the use of leverage coefficients and Studentized residuals according to criteria in Sokal and Rohlf (1981). The outliers were removed from the data set and the equation recalculated. Outliers detected were values of total juvenile development time at 33°C for Microarthridion littorale -225-(Palmer and Coull 1980) and at 10°C for Tisbe longicornis (Raibaut 1967 in Rosenfield and Coull 1974), along with values of generation time at 33°C for M. littorale (Palmer and Coull 1980) and at 8°C for Huntemannia jadensis (Feller 1980). Scatterplots of the values used in each regression are presented in Fig. 1. A l l regressions were performed using the M G L H module of SYSTAT software (Wilkinson 1985) on an I B M PC/XT computer. Significance levels of 0.05 were used. RESULTS The slopes of all five regressions were significantly different from zero (ANOVA, P<0.001). The regression statistics for each data set along with information to construct Confidence Limits for the regression coefficients and Confidence Limits for predictions made from each equation are presented in Table 2. Predictions of development time made from temperature are generally precise. Table 3 shows some predicted development times and their 95% Confidence Limits for each data set. Predictions were obtained at the temperature extremes and the temperature mean of each data set. Estimates are most imprecise at low temperatures (4-5°C) with the 95% Confidence Limits ranging from 39-65% of the predicted value (Table 3). However, 95% Confidence Limits will generally be less than 25% of the predicted value when estimates are made for spring and summer temperate zone field temperatures. For the purposes of this thesis, copepodite development time predictions (and 95% Confidence Limits) made at each intersampling interval are presented in Table 4. -226-Figure 1. Scatterplots of In development time (d) against In temperature (°C). (a) egg development; (b) naupliar development; (c) copepodite development; (d) total juvenile development; (e) generation time. Table 2. Statistics describing regressions of In development time (D, d) on In temperature (T,°C). Values are the intercept (In a) and its standard error, the slope (b) and its standard error, the means of the independent (In T) and dependent (In D) variables, the pooled mean square for deviations from the regression (S2D.T)> the sum of squares of In T (L In t 2), the coefficient of determination (r 2), the sample size (n) and the range of the independent variable, T (°C). Other symbols as in Table 1. Data set In a b InT InD SVT H n t 2 r 2 n Range E " 4.40+0.33 -1.10+0.11 2.87 1.24 0.21 15.75 0.49 99 4.0-40.0 N 5.86±0.44 -1.3710.15 2.88 1.92 0.29 12.56 0.52 80 5.0-33.0 C 6.34+0.55 -1.4010.19 2.90 2.29 0.28 7.84 0.46 66 5.0-33.0 J 6.99±0.36 -1.4210.12 2.96 2.78 0.16 10.58 0.53 122 5.0-30.0 G 6.54±0.36 -1.2210.12 2.89 3.00 0.10 6.34 0.58 73 5.0-28.0 -228-Table 3. Predicted values of development time (d) and 95% Confidence Limits from the equations. Values presented are at the extremes of the temperature range of each regression and at the mean temperature of each data set. Also given is the temperature ( ° Q and the upper confidence limit as a percentage of the prediction. Means have been corrected for bias after back transformation (see Bird and Prairie 1985). Symbols as in Table 1. Data Set Low Temperature Mean High E Temperature Prediction 95% C.L. Upper C.L.(%) 4.0 19.6 27.8-13.8 41.8 17.6 3.8 4.2-3.5 10.5 40.0 1.6 1.8-1.4 12.5 N Temperature Prediction 95% C.L. Upper C.L.(%) 5.0 44.8 66.8-30.0 49.1 17.8 7.9 8.9-7.0 12.7 33.0 3.4 4.2-2.7 23.5 C Temperature Prediction 95% C.L. Upper C.L.(%) 5.0 68.4 112.8-41.5 64.9 18.2 11.2 12.8-9.8 14.3 33.0 4.9 6.4-3.8 30.6 J Temperature Prediction 95% C.L. Upper C.L.(%) 5.0 119.2 167.5-84.8 40.5 19.3 17.5 18.8-16.3 7.4 30.0 9.4 10.7-8.3 13.8 G Temperature Prediction 95% C.L. Upper C.L.(%) 5.0 102.0 141.9-73.3 39.1 18.0 21.4 23.1-19.9 7.9 28.0 12.5 14.2-11.0 13.6 -229-Table 4. Temperature (°C) at Station H and predicted copepodite development time (d) and 95% Confidence Limits for each intersampling interval in 1986 and 1987. Temp = Temperature (°C). Copepodite Development Time Date Temp Lower C L . Mean Upper C.L. 1986 19/02-04/03 6.1 33.7 52.0 80.0 04/03-18/03 7.6 26.7 38.1 54.2 18/03-31/03 7.7 26.3 37.3 53.0 31/03-14/04 9.0 22.3 29.9 40.2 14/04-28/04 8.8 23.0 31.2 42.2 28/04-12/05 10.7 18.6 23.6 29.9 12/05-26/05 11.4 17.4 • 21.8 27.1 26/05-10/06 13.4 14.4 17.1 20.3 10/06-24/06 14.1 13.6 16.0 18.7 24/06-09/07 14.8 12.9 15.0 17.5 1987 20/02-07/03 7.5 27.4 39.2 56.2 07/03-19/03 8.8 23.0 31.2 42.2 19/03-02/04 9.6 21.0 27.7 36.4 02/04-16/04 10.8 18.4 23.3 29.5 16/04-30/04 11.2 17.6 22.0 27.5 30/04-14/05 12.6 15.6 18.9 22.9 14/05-28/05 13.8 14.0 16.6 19.6 28/05-11/06 13.8 14.0 16.6 19.6 11/06-25/06 15.2 12.5 14.4 16.7 25/06-09/07 16.6 11.2 12.8 14.6 -230-DISCUSSION Overall, approximately 50% of the variance in each data set was explained by temperature (Table 2). Some possible factors contributing to the remaining error are unnatural experimental conditions, including quantity and quality of food, and possible relationships between development time and body size and phylogeny (Peters 1983; Felsenstein 1985). However, predictions of development time are still precise enough for general use in estimating production and mortality rates of harpacticoid copepods (Table 3). There are a few caveats to note in the application of predictions derived from the regression equations. Phytal, epibenthic and pelagic harpacticoids overwhelmingly dominate the species in each data set (Table 1). Data for interstitial and true inbenthic, burrowing harpacticoid species are lacking because these groups are difficult to culture successfully in the laboratory (see Chandler 1986). Therefore, caution should be used in > applying predictions made from these equations to such groups. In estimating the duration of individual copepodite stages from the copepodite development time regression, isochronal development (i.e. equal stage durations) must be assumed. However, from the few studies giving detailed information on the duration of individual copepodite stages, it appears that a larger percentage of time is spent in the later copepodite stages (see Bergmans 1981). Another factor which may be a hindrance in the application of the equations is that the predictions derived may be conservative for male copepods since males may develop faster than females (Haq 1972; Zurlini et al. 1978; Bergmans 1981; Walker 1981; Castel 1984). This is the reason that the data sets for development to adult include females only. The predictive equations presented here allow the estimation of marine harpacticoid copepod development time in the field for various life history stages when temperature is known. Use of these predictive relationships will facilitate the study of harpacticoid copepod population dynamics, especially for phytal and epibenthic species. While these groups may be the most important for biomass transfer through visually foraging epibenthic predators, -231-more information on inbenthic harpacticoid developmental rates is required. This will allow the assessment of the generality of the equations with respect to these species of copepods. -232-R E F E R E N C E S Alheit, J., and Scheibel, W. 1982. Benthic harpacticoids as a food source for fish. Mar. Biol . (Berlin), 70: 141-147. Bergmans, M . 1981. A demographic study of the life cycle of Tisbe furcata (Baird, 1837) (Copepoda : Harpacticoida). J. Mar. Biol. Ass. U .K . 61: 691-705. Betouhim-El, T., and Kahan, D. 1972. Tisbe pori n.sp. (Copepoda: Harpacticoida) from the mediterranean coast of Israel and its cultivation in the laboratory. Mar. Biol . (Berlin), 16: 201-209. Bird, D.F., and Prairie, Y.T . 1985. 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Obtaining life table data from cohort analyses: a critique of current methods. Limnol. Oceanogr. 30: 886-893. Haq, S.M. 1972. Breeding of Euterpina acutifrons, a harpacticoid copepod, with special reference to dimorphic males. Mar. Biol . (Berlin), 15: 221-235. Harris, R.P. 1973. Feeding, growth, reproduction and nitrogen utilization by the harpacticoid copepod, Tigriopus brevicornis. J. Mar. Biol. Ass. U .K. 35:785-800. Harris, R.P. 1977. Some aspects of the biology of the harpacticoid copepod, Scottolana canadensis (Willey), maintained in laboratory culture. Chesapeake Sci. 18: 245-252. Heip, C , and Smol, N . 1976. Influence of temperature on the reproductive potential of two brackish - water harpacticoids (Crustacea: Copepoda). Mar. Biol. (Berlin), 35: 327-334. Herman, P.M.J., and Heip, C. 1985. Secondary production of the harpacticoid copepod Paronychocamptus nanus in a brackish water habitat. Limnol. Oceanogr. 30: 1060-1066. Herman, P.M.J., Heip, C , and Guillemijn, B . 1984. 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(Berlin), 46: 59-64. -237-APPENDIX 5 DIURNAL PATTERNS IN FEEDING ACTIVITY AND DAILY RATION OF JUVENILE CHUM AND PINK SALMON IN A SHALLOW SUBTIDAL SEAGRASS BED INTRODUCTION Mortality of juvenile Pacific salmon (Oncorhynchus spp.) in the ocean has been found to be size-selective, with higher mortality of smaller fish observed (e.g. Healey 1982; Hargreaves and LeBrasseur 1986). Quantification of food intake and daily ration of these fish in different marine habitats is therefore required to assess if some areas are better "nurseries" than others. Surprisingly, little work has been done on diurnal feeding patterns and daily ration estimation for juvenile chum (Oncorhynchus keta (Walbaum)) and pink salmon (0. gorbuscha (Walbaum)). Bailey et al. (1975) demonstrated that juvenile chum and pink salmon in Alaska are mainly diurnal feeders and that feeding does not occur during night hours. Healey (1979) roughly estimated a daily ration of -15% body weight-d'l for juvenile chum in the Nanaimo estuary. These fish were presumably feeding in the bare substrate area of the estuary but these fish may also have been feeding in seagrass (Zostera marina L.) beds at low tide. In two bays near the Nanaimo estuary, Godin (1981) showed that juvenile pink salmon fed less at night. He also observed a dusk peak in stomach contents in one bay but no clear diurnal pattern was found in the other. The fish were caught in intertidal areas with some macroalgae and seagrass cover. Daily ration was estimated to be 13.1% body weight-d-1 and 6.6% body weight-d-1 in the two areas. This thesis required an assessment of diurnal feeding patterns in juvenile salmon along with the estimation of gut evacuation rates at different temperatures. As a byproduct of this sampling, daily ration estimates were obtained and are the first for juvenile salmonids known to be using a large seagrass bed as a foraging area. -238-M E T H O D S Fish sampling was conducted at Station F on Roberts Bank, B.C. (see Chapter 1, Fig. 1.1). On three dates (May 15 and June 12,1985 and June 4,1986), samples of juvenile chum and/or pink salmon were collected at 3 h intervals for 21 h. The fish were caught by a boat-set beach seine as described in the Methods section of Chapter 3. Sets were made until 15 fish for gut content analysis were caught or to a maximum of 3 sets. Fish samples were preserved in a 4% Formaldehyde/ natural seawater solution. No regurgitation was observed. On each sampling date, fish were also caught by beach seine for estimation of gut evacuation rate. Approximately 100 juvenile chum and/or pink salmon were beach seined and gently transferred to large plastic buckets. The fish were then placed in a 200 urn SCOR plankton net floating off the end of a nearby wharf. Samples of 5 fish were removed at the time of emplacement in the net and at subsequent 2 h intervals. Fish were preserved as above. At each sampling of the enclosed fish, surface water temperature adjacent to the net was measured to the nearest 0.5°C with a hand-held thermometer. For all fish, dry body weight and dry gut content weight were estimated as in Chapter 3 and dry food weight was expressed as a percentage of dry body weight. The sum of number of the harpacticoid copepods Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii-mg-1 dry food weight was calculated for each fish in the diurnal series on all dates to allow examination of feeding periodicity on these seagrass-dwelling harpacticoids (see Chapter 2). If the fish caught at Station F are actually feeding within the seagrass bed, abundance of these copepod species in gut contents should peak at low tide when the fish are forced out of the seagrass bed. For the evacuation experiments, since the fish were mainly feeding on small, low energy food particles (e.g. harpacticoid copepods), the mean food weights expressed as a percentage of body weight of subsequent fish samples were fitted to an exponential decay model with time (Jobling 1986, 1987). Examination of residuals indicated the exponential model adequately described the data in all cases. Daily ration was calculated using the model -239-of Elliot and Persson (1978). This method assumes an exponential gut evacuation rate, which is supported for these fish, and a constant feeding rate between the 3 h sampling intervals. This second assumption is probably valid since juvenile pink salmon have been shown to initiate feeding after only a 15% decrease in stomach content weight (Godin 1979). To examine the relationship of gut evacuation rate with temperature, individual rates (h-1) were regressed against measured water temperature. To increase the sample size, unpublished data on evacuation rates of both wild and hatchery raised juvenile chum and pink salmon at different temperatures, provided by M.C. Healey (Dept. of Fisheries and Oceans, Pacific Biological Station, Nanaimo, B.C., Canada V9R 5K6), were also used. Only evacuation determinations on fish fed the calanoid copepod Neocalanus plumchrus, were used to approximate the prey size in this study. Healey's data were also fitted to exponential curves and examination of residuals showed an adequate fit in all cases. A l l curve fitting was performed using the M G L H module of SYSTAT (Wilkinson 1985) on an I B M PC/XT microcomputer. The 0.05 level of significance was observed. R E S U L T S A N D DISCUSSION Plots of food weight as a percentage of body weight against time of day are presented for all three determinations in Figs. 1 and 2. No striking pattern was seen during daylight hours and no evidence of a dusk peak (e.g. Godin 1981) was observed. For the May 15,1985 and June 4,1986 samplings, food weight declined at night and increased in the early morning coincident with reduced feeding during night hours (e.g. Bailey et al. 1985). However, mean food weight was highest at night in the June 12, 1985 sampling. This was caused by high light levels in the vicinity of the sampling area from tugboat lights. Observations indicated that the boat lights attracted swarms of amphipods and cumaceans which juvenile salmon were seen to exploit. The high food weights at night on this date appear to be an artifact of this luminescence. -240-o o >> 0 4 . 1 • « — 1700 2300 0500 1100 T i m e o f d a y ( h ) o o s 1 ->s 0 -I 1 1 1 1 3 1600 2100 0200 0700 T i m e o f d a y ( h ) Figure 1. Relationship between food weight as a percentage of body weight and time of day (Pacific Daylight Time) for juvenile chum salmon on (a) May 15, 1985 and (b) June 12,1985. Horizontal black lines indicate dark hours. Values are the mean ± 1 Standard Error, n = 15 except for (a) 2300h, n=13 and (b) 1515h, n=12; 0015h, n=8; 0915h, n=14. -241-Figure 2. Relationship between food weight as a percentage of body weight and time of day (Pacific Daylight Time) for juvenile chum and pink salmon on June 4, 1986. Horizontal black lines indicate dark hours. Values are the mean ± 1 Standard Error, n = 15 except for 2130h, n=l 1; 0030h, n=4; 0330h, n=l 1. -242-The results of the studies on the diurnal periodicity of feeding on seagrass dwelling harpacticoid copepods are presented in Table 1. Small numbers (<3-mg-l dry food weight) of the three species counted were observed in salmonid gut contents throughout the day. However, larger numbers were generally only observed near low tides, usually at tidal levels of 2 m or less. Note that the height of the harpacticoid sampling station in the seagrass bed (Station H) is 1.6 m (D'Amours 1987). This indicates that the fish caught at Station F are indeed feeding in the seagrass bed and that sampling fish at low tide will reflect this feeding in terms of prey species identity. A summary of the gut evacuation rate determinations is shown in Table 2. Surprisingly, the relationship between gut evacuation rate and temperature (11-15°C range) was not significant (y=0.16 - 0.007x, r2 = 0.17, n = 9).' Strong linear relationships between these two variables are common both for individual species and in multispecies data sets (e.g. Elliot 1972, Persson 1981, Durbin et al. 1983). A mean evacuation rate from the 9 estimates was then calculated (0.070 ± 0.011, mean ± S.E., n = 9) for use in estimating salmonid consumption rates in Chapter 3. Using the gut evacuation rates on the three sampling dates in this study, the diurnal pattern of food weights and the Elliot and Persson (1978) ration model, daily ration was calculated. Estimated values of daily ration were 10.1 and 5.1% body weight-d-1 on May 15 and June 4,1985, respectively, and 5.9% body weight-d-1 on June 4, 1986. These values are all lower than that estimated by Healey (1979) for juvenile chum. The ration estimate for May, 1985 is in the range reported by Godin (1981) for juvenile pink but the other two are lower. From these estimations, it appears that feeding in seagrass beds does not necessarily lead to an increased daily food intake for juvenile salmonids compared to other habitats. Table 1. Percent juvenile chum and/or pink salmon containing various numbers of the harpacticoid copepods Harpacticus uniremis, Tisbe cf. furcata and Zaus aurelii at each sampling interval for the three diurnal feeding studies. Tide levels (m) and times (h) are for Point Atkinson, the Port of Reference for this study area. Time = Pacific Daylight Savings Time; n = number of fish analyzed. Time n 0-3 Number-nig"* dry food weight 3-6 6-9 9-12 12-15 >15 Tide Level May 15,1985 1400 15 40 13 13 7 20 7 1700 15 67 0 7 13 0 13 2000 15 67 27 7 0 0 0 2300 13 62 15 0 0 0 23 0200 15 53 20 7 0 0 20 0500 7 57 14 29 0 0 0 0800 14 7 21 7 21 14 29 1100 15 33 47 13 7 0 0 12,1985 1215 15 93 7 0 0 0 0 1515 12 83 8 8 0 0 0 1815 14 86 7 7 0 0 0 2115 14 100 0 0 0 0 0 0015 7 100 0 0 0 0 0 0315 14 100 0 0 0 0 0 1025h 2.0m 1645h 3.5m 2150h 2.6m 0355h 4.3m 1050h 1.6m 0905h 2.0m 1525h 3.4m 2000h2.9m 0220h 4.3m Table 1. Continued. Time n 0-3 Number-mg"* dry food weight 3-6 6-9 9-12 12-15 >15 Tide Level June 12,1985 0615 15 47 13 7 0 0 33 0915 14 50 14 7 21 0 7 0940h 1.7m June 4,1986 0325h 4.2m 0930 15 93 7 0 0 0 0 1050h 1.2m 1230 15 87 0 0 13 0 0 1530 15 87 7 0 7 0 0 1810h4.1m 1830h 15 87 13 0 0 0 0 2130 10 80 20 0 0 0 0 2255h 3.4m 0030 1 100 0 0 0 0 0 0330 7 71 0 0 0 0 29 0350h4.1m 0630 15 67 13 7 0 0 13 1115h 0.9m Table 2. Gut evacuation rates of juvenile chum and/or pink salmon estimated in this study and by using data from M.C. Healey (unpublished). Temp = temperature (°C); r 2 = the coefficient of determination; n = sample size; P = probability level. In equations, y = dry food weight as a percentage of dry body weight and x = time (h). Species Date Temp Relationship r 2 n P Chum 15/05/85a 11.0 y=0.96e" 0- 1 5 x 0.97 4 <0.05 Chum 12/06/85a 14.5 y=0.40e-0.047x 0.85 6 <0.01 Mixed 04/06/86a 14.0 y=1.2e-0.077x 0.71 7 <0.05 Pink ?b 11.0 y=1.4e-0.053x 0.90 6 <0.01 Pink ?b 15.0 y=1.3e-0.050x 0.97 6 <0.001 Chum ?b 11.0 y=1.8e-0.063x 0.99 6 <0.001 Chum ?b 11.0 y=1.6e-0.066x 0.98 6 <0.001 Chum ?b 15.0 y=l.le-0.064x 0.97 7 <0.001 Chum ?b 15.0 y=1.4e-0.058x 0.92 6 <0.01 a this study b M.C . Healey, Dept. of Fisheries and Oceans, Pacific Biological Station, Nanaimo, B.C. , unpublished data -246-R E F E R E N C E S Bailey, J.E., Wing, B.L . , and Mattson, C R . 1975. Zooplankton abundance and feeding habits of fry of pink salmon, Oncorhynchus gorbuscha, and chum salmon, Oncorhynchus keta, in Traitors Cove, Alaska, with speculations on the carrying capacity of the area. Fish. Bull. 73: 846-861. D'Amours, D. 1987. Trophic phasing of juvenile chum salmon (Oncorhynchus keta Walbaum) and harpacticoid copepods in the Fraser river estuary, British Columbia. Ph.D. thesis, University of British Columbia, Vancouver. Durbin, E.G., Durbin, A .G . , Langton, R.W., and Bowman, R.E. 1983. Stomach contents of silver hake, Merluccius bilinearis, and Atlantic cod, Gadus morhua, and estimation of their daily rations. Fish. Bull. 81:437-454. Elliot, J .M. 1972. Rates of gastric evacuation in brown trout, Salmo trutta L . . Freshw. Biol . 2: 1-18. Elliot, J .M. , and Persson, L . 1978. The estimation of daily rates of food consumption for fish. J. Anim. Ecol. 47: 977-991. Godin, J.-G.J. 1979. Diel rhythms of behavior in juvenile pink salmon (Oncorhynchus gorbuscha Walbaum). Ph.D. thesis, University of British Columbia, Vancouver. Godin, J.-G.J. 1981. Daily patterns of feeding behavior, daily rations, and diets of juvenile pink salmon (Oncorhynchus gorbuscha) in two marine bays of British Columbia. Can. J. Fish. Aquat. Sci. 38: 10-15. Hargreaves, N.B. , and LeBrasseur, R.J. 1986. Size selectivity of coho (Oncorhynchus kisutch) preying on juvenile chum salmon (O. keta). Can. J. Fish. Aquat. Sci. 43: 581-586. Healey, M.C . 1979. Detritus and juvenile salmon production in the Nanaimo estuary: I. production and feeding rates of juvenile chum salmon (Oncorhynchus keta). J. Fish. Res. Board Can. 36: 488-496. Healey, M.C . 1982. Timing and relative intensity of size-selective mortality of juvenile chum salmon (Oncorhynchus keta) during early sea life. Can. J. Fish. Aquat. Sci. 39: 952-957. Jobling, M . 1986. Mythical models of gastric emptying and implication for food consumption studies. Env. Biol. Fish. 16: 35-50. Jobling, M . 1987. Influences of food particle size and dietary energy content on patterns of gastric evacuation in fish: test of a physiological model of gastric emptying. J. Fish Biol . 30: 299-314. Persson, L . 1981. The effects of temperature and meal size on the rate of gastric evacuation in perch (Perca fluviatilis) fed on fish larvae. Freshw. Biol. 11: 131-138. Wilkinson, L . 1985. SYSTAT. The system for statistics. Version 2.1. Systat, Inc., 1800 Sherman Ave., Evanston, Illinois, U.S.A. 60201. 

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