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Habitat, population and leaf characteristics of Zostera marina L. on Roberts Bank, British Columbia Moody, Robert 1978

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HABITAT, POPULATION AND LEAF. CHARACTERISTICS OF Zostera marina L. ON ROBERTS BANK, BRITISH COLUMBIA by ROBERT MOODY B.Sc, University of British Columbia, 1975 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Plant Science We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May, 19 78 ©ROBERT MOODY, 1978 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 representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Plant Science The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date May 1. 1978 5 ii ABSTRACT The sand and mud flats of the Fraser River fore shore support extensive meadows of the seagrass Zostera marina L. (eelgrass). Industrial, residential and recreational developments threaten these valuable foreshore areas. A study was undertaken into the habitat requirements and population and morphological characteristics of eelgrass on southern Roberts Bank, British Columbia to provide information which would help minimize the potentially deleterious effects of such developments on the eelgrass resource. Watecr temperatures and salinities and wave motion on southern Roberts Bank all approach the world-wide optima for eelgrass. The upper distributional limit of eelgrass was lower than those of other Pacific Coast eelgrass populations. The sandy nature of the substrate influences "desiccation" which, in turn, controls the intertidal limit of eelgrass growth. Light availability determines the lower distribu tional limit of eelgrass in other areas. These two factors, the sandy substrate and reduced light availability in the turbid estuarine waters of the Fraser River foreshore, appear to be responsible for the narrow depth range of eelgrass on southern Roberts Bank. A stratified random sampling technique was used to determine seasonal changes in eelgrass standing crop, turion density and leaf dimensions at five elevations, located at 0.5 m depth intervals, from the upper to the lower limits of eelgrass growth. A pronounced decline in both turion density and leaf standing crop occurred in late summer. Throughout the study period, leaf standing crops and turion densities were greatest'at the three intermediate study elevations. Reduced leaf standing crops were found near the upper and lower edges of the eelgrass bed; no significant difference in standing crops was found for these two elevations. Turion densities were also lower near the upper and lower depth limits of eelgrass and a significant difference in turion densities was found between these two elevations, with the lowest turion density recorded near the lower limit of eel grass. Near the upper edge of the eelgrass bed, turion weights and mean leaf lengths were one-half those of the lower elevations. " A synthesis of the available information indicates that depth-related factors strongly influence certain morphological and population characteristics of eelgrass on southern Roberts Bank. iv TABLE OF CONTENTS Page 1. INTRODUCTION 1 1.1. Purpose of the Study 1 1.2. Previous Research 2 1.3. Objectives of the Study 9 2. THE STUDY AREA 10 3. ENVIRONMENTAL FACTORS IN RELATION TO EELGRASS HABITAT 7 3.1. Materials and Methods 13.2. Habitat Factors 21 3.2.1. Salinity3.2.1.1. Seasonal Changes 21 3.2.1.2. Diurnal Changes 4 3.2.2. Temperature 23.2.2.1. Seasonal Changes 24 3.2.2.2. Diurnal Changes 7 3.2.3. Light 2 7 3.2.3.1. Seasonal Changes 27 3.2.3.2. Diurnal Changes  7 3.2.4. Tidal Range and Percentage Exposure 32 3.2.5. Substrate  3 3.2.5.1. Surface Level Changes 33 3.2.5.2. Physical and Chemical Characteristics 33.2.6. Waves and Currents 9 3.3. Discussion 34. STANDING CROP, TURION DENSITY, BIOMASS AND LEAF MEASUREMENT STUDIES 45 4.1. Materials and Methods4.2. Standing Crop 4 8 4.2.1. Temporal Changes 50 4.2.2. Influence of Depth 2 V Page 4.3. Turion Density 56 4.3.1. Influence of Time and Elevation on Total Turion Density 56 4.3.2. Influence of Time and Elevation on Reproductive Turion Density ... 64 4.4. The Influence of Depth on Organic Weight per Turion 4.5. Biomass 4.6. Leaf Measurements 4.7. Discussion 5. SUMMARY AND CONCLUSIONS 79 GLOSSARY BIBLIOGRAPHY APPENDICES .. 64 70 70 75 83 86 91 vi LIST OF TABLES Table Page 1. Particle size composition of sediments 36 2. Organic and carbonate carbon contents of sediments 40 3. Comparisons of habitat factors affecting eel grass growth (modified from Stout 1976, and Phillips 1972) 1 4. Analysis of variance summary table for mean leaf standing crop (organic dry weight in grams per 0.25 square meter quadrat) 51 5. Newman-Keuls Multiple Range Test for mean leaf standing stocks (organic dry weight in grams per 0.2 5 square meter quadrat) at five elevations 5 6. Analysis of variance summary table for mean total turion density (turions per 0.25 square meter quadrat 58 7. Newman-Keuls Multiple Range Test for total turion density (turions per 0.25 square meter quadrat) means at five elevations 59 8. Total turion densities (turions per 0.25 square meter quadrat) for fourteen sampling sessions, May to December 1976 61 9. Analysis of variance summary table for mean reproductive turion density (turions per square meter) 65 10. Linear regression equations of organic dry weight (g) on turion numbers per quadrat for five elevations 66 11. Analysis of covariance summary testing for significant differences between slopes of linear regression lines of organic dry weight on turion numbers for five elevations 6 8 12. Newman-Keuls Multiple Range Test for differ ences between slopes of linear regressions of organic dry weight on turion numbers for five elevations 69 vii Table Page 13. Percentages of above-substrate (leaf) and below-substrate (roots and rhizomes) standing crops, April 1976 to January 1977 ... 71 14. Leaf measurements for five elevations, August 1976 to January 1977 72 15. Leaf and rhizome measurements for samples collected at 0.8 meters (in relation to Chart Datum), August 19 76 to January 19 77. Number of observations in brackets 74 viii LIST OF FIGURES Figure Page 1. Aerial photo mosaic of the Fraser River Delta showing location of the study area 11,12 2. Diagram of the study site showing transect locations 13,14 3. Schematic profile of the study site showing transect elevations in relation to Chart Datum 18,19 4. Surface and 1.5 m salinities and temperatures at the study site and mean monthly air temper ature at Vancouver International Airport (Monthly Record, Meteorological Observations in Canada, Atmospheric Environment, Fisheries and Environment Canada, April 19 76 to^January 19 77). Mean monthly air temperature plotted at the midpoint of each month 22,23 5. Diurnal surface and 1.5 m salinities. May 2, July 2 8 and October 4, 19 76. January 18, 1977 : 25,26 6. Diurnal air temperatures and surface and 1.5 m water temperatures. May 2, July 2 8 and October 4, 1976. January 18, 1977 28,29 7. Secchi depth (meters) at the study site and maximum daily discharge (thousands of cubic meters per second) of the Fraser River at Hope, B.C. for each month from March 19 76 to January 1977 30,31 8. Net oscillations of sediment surface levels, July 1976 to January 1977. Mean + Standard Error 34,35 9. Sediment samples taken at 10-meter intervals from the upper to the lower limits of eelgrass growth: a. Percentage of fines b. Percentages of organic and carbonate carbon 37,38 10. Mean leaf standing crop (grams per square meter) for five elevations (in relation to Chart Datum), April 1976 to January 1977 53,54 ix Figure Page 11. Mean total turion numbers per square meter for five elevations (in relation to Chart Datum), April 1976 to January 1977 62,63 X LIST OF APPENDICES Appendix Page 1. Secchi depth and surface and subsurface (1.5 m) salinity and temperature measure ments. March 1976 to January 1977 92 2. Diurnal surface and subsurface (1.5 m) salinity (parts per thousand) measurements. May 2, July 2 8 and October 4, 19 76. January 18, 1977 93 3. Diurnal air, surface and subsurface (1.5 m) temperature (°C) measurements. May 2, July 28 and October 4, 1976. January 18, 1977 .... 94 4. Diurnal Secchi depth and photosynthetically active radiation (PAR) measurements. May 2, July 28 and October 4, 19 76. January 18, 1977 95 5. Net oscillations of sediment surface levels -measurements and statistics. June 19 76 to January 1977 96 6. Statistics of standing crop information (organic dry weight per quadrat) used for optimum quadrat size determination 9 7 7. Organic dry weight in grams per square meter for five elevations (Chart Datum). April 1976 to January 1977 98 8. Analysis of variance summary table for mean leaf standing crop (organic dry weight in grams per 0.25 square meter quadrat) 99 9. Density in turions per square meter for five elevations (Chart Datum). April 19 76 to January 1977 100 10. Analysis of variance summary table for mean turion density (turions per 0.25 square meter quadrat) 101 11. Reproductive turion density (per square meter) for five elevations. June to August, 1976 102 12. Analysis of variance summary for slopes of the regressions of turion numbers on organic dry weight for five elevations (Chart Datum) 103 xi Appendix Page 13. Mean biomass of intertidal (0.8 m) eelgrass in grams per square meter (organic dry weight) . April 1976 to January 1977 104 xii ACKNOWLEDGEMENTS Financial assistance for this study was provided by the British Columbia Hydro and Power Authority. I am especially indebted to Mr. R. Dundas and Dr. R. Ferguson of the Environmental Group of this agency. The assistance received from this agency and these individuals is gratefully acknowledged. My committee members, Dr. R. E. Foreman, Dr. P. G. Harrison and Dr. C. D. Levings, provided encouragement, advice and constructive criticism during the study. I am also indebted to my committee chairman, Dr. Runeckles. I am sincerely grateful to my fellow students, Herb Klassen, Ed Medley and Dave Swinbanks, for their valuable field assistance. Tidal information was provided by Mr. W. J. Rapatz, Regional Tide Superintendent. Mr. Bill Tupper of the British Columbia Institute of Technology gave valued informa tion on aerial photography. Dr. J. Luternauer of the Geological Survey of Canada was most helpful in providing information concerning the geological setting of the Fraser River foreshore. I appreciate the assistance of these individuals. I am particularly indebted to my supervisor, Professor V. C. Brink, for his help, patience and guidance throughout the course of this work. Finally, I am deeply moved by the support, assistance and extreme patience received from my wife, friend, confidante and colleague, Anne. 1. INTRODUCTION 1.1. Purpose of the Study Most of the British Columbia coastline is typically precipitous; the shallow protected areas necessary for the successful establishment of seagrass meadows are relatively rare along our coast. The extensive sand and mud flats of the Fraser River Delta support large meadows of the north temperate seagrass Zostera marina L. (eelgrass). Z. marina, a marine Angiosperm, is a member of the family Potamogetonaceae, subfamily Zosteroideae, genus Zostera, and subgenus Zostera (den Hartog 19 70). The importance of eelgrass to invert-ebrates, fish and waterfowl populations is well-documented in the North American and European literature (Phillips 1975, Thayer et al 1975). In recent years, proposals to develop the tidal flats for residential, industrial and recreational purposes have been increasing. In addition to direct losses of eelgrass habitat, these developments may also have detri mental effects on the remaining eelgrass habitat through alteration of current patterns and water quality, and increased industrial and recreational traffic along the fore shore. To minimize the deleterious effects of various developments on the eelgrass resource of the Fraser River Delta, information is required on the habitat requirements and growth characteristics of eelgrass in the area. The purpose of this study is to provide some of that information. 2 1.2. Previous Research In a comprehensive study of the seasonal growth of some seventy taxa of benthic marine plants in Great Pond estuary, Massachusetts, Conover (19 58) found that the relations of environmental factors to the growth and distri bution of Z. marina were not well-defined. High standing crop values of eelgrass were found in those sections of the estuary where salinities ranged from 12 to 32%o , lower values were obtained in areas where the salinity range was 1 to 30%o , and eelgrass was not present in areas having less than l%o salinity. Standing crop maxima and minima for eelgrass were associated with the annual maxima and minima of insolation and water temperature. Conover suggests that these two factors, temperature and light, play leading roles in the seasonal growth of eelgrass in Great Pond. Setchell's scheme (1929) describing various growth, developmental and phenological activities of eelgrass based on 5°C water temperature increments has not been borne out in the recent works of Burkholder and Doheny (196 8), McRoy (1969) and Phillips (1972). Based on information from transplant experiments, Phillips (1974) suggests that the lower depth limit of eel grass growth in Puget Sound, Washington is determined by light availability. Controlled field experiments in southern California by Backman and Barilotti (1976) confirmed that eelgrass turion density is a function of irradiance received by the plants. A turion is a leafy branch arising from the 3 horizontal rhizome. In Chesapeake Bay on the Atlantic Coast, Orth (19 73) found that the sediments associated with dense stands of eelgrass are more poorly sorted and contain higher fine fractions than the sediments from areas of less dense eel grass growth. Similarly, Stout (19 76) describes a relation ship between the occurrence of very fine-grained sands and silts and the presence of eelgrass beds. These sediment characteristics are attributed by both authors to a trapping action by eelgrass. Eelgrass has not been observed growing on sand in previous studies of eelgrass populations on the Pacific Coast. Phillips (1972) and Stout (1976) describe the habitat factors associated with eelgrass for Puget Sound, Washington and Netarts Bay, Oregon respectively. Taxonomic classification of the members of the genus Zostera has been, to a large extent, based on leaf measurement information and the vertical distribution of the plants. Two forms of Zostera marina are recognized on the Atlantic Coast of North America (Setchell 1920, Harrison and Mann 1975) and Alaska (McRoy 1972) . A short, narrow-leafed form inhabits the shallow intertidal and upper subtidal zones of these areas. The taller, broad-leafed form is found in the deeper subtidal waters. Along the Pacific Coast of North America, from British Columbia to California, the shallow-water and deeper-water forms are present but a size shift appears to have occurred. The narrow, short form of the intertidal and 4 shallow subtidal reaches of this area corresponds to the tall, broad-leafed form of the Atlantic Coast (Scagel 1961) and Alaska . (Phillips 1972). The tall, wide-leafed form of the central Pacific Coast, often referred to as Z. marina var. latifolia Morong, has much wider and longer leaves than the typical form (Setchell 1927). Considerable taxonomic con fusion exists within geographical areas; leaf length of the larger form Z. marina f. latifolia described by Outram (1957) for southern British Columbia is the same as that for the short, narrow-leafed form Z. marina var. typioa {marina) described by Scagel (1961) for British Columbia coastal waters. Setchell (1927) felt that the slow rise in water temperature observed for areas inhabited by Z. marina var. latifolia resulted,in a longer growing season which allowed for the full vegetative development of the plant. The typical form of the Atlantic Coast was thus merely an underdeveloped form of var. latifolia. Setchell (1927) did not attempt to account for the short, narrow growth form (var. angustifolia) of the Atlantic Coast described in an earlier work (Setchell 19 20) and makes no mention of the presence of the typical form of the Atlantic Coast along the Pacific Coast. Den Hartog (19 70) felt that there was considerable overlap of the upper size limit of the typical form and the lower size limit of var. latifolia and regarded the two forms as phenotypes of the taxon, Z. marina. In Humboldt Bay, northern California Keller (196 3) found an increase in mean turion length of intertidal Z. marina 5 with increased depth but failed to remark on the significance of this relationship in this and in a later paper (Keller and Harris 1966) . A similar relationship of increased leaf dimensions with depth was observed by Phillips (19 72) in Puget Sound, Washington. He used reciprocal turion transplants across two tidal zones (intertidal and subtidal) and leaf measurements of turions from three broad tidal zones (MLLW, MLLW to LLLW, and below LLLW) to investigate the influence of depth on leaf dimensions. In the United States, mean low water (MLW), the average of all low waters, is the plane which represents Chart Datum on the Atlantic Coast and mean lower low water (MLLW), the average of the lower of the two low waters each day, is the plane for the Pacific Coast (Chapman 1960). Phillips (1972) concluded that the variation in leaf dimensions across tidal zones was attri butable to phenotypic plasticity and discounted the validity of varietal distinctions based on leaf measurement information for Puget Sound eelgrass. An increase in leaf length with depth has been reported for other seagrasses (Strawn 1961). An inverse relationship of leaf length and depth for Z. marina is reported by Burkholder and Doheny (1968) for Long Island, New York but is not substantiated elsewhere in the literature. Tidal elevation exerts considerable influence on other characteristics of eelgrass populations. These include reproductive and vegetative turion density, leaf standing crop, biomass and phenology. Studies of eelgrass turion density on the Pacific Coast of North America report 6 conflicting results. Keller and Harris (1966) found that the highest elevation they considered (0.3 meters above MLLW) had the lowest turion density; more significantly, however, their data reveal that turion density decreased above and below mean lower low water (MLLW). This relation ship was also reported from Puget Sound, Washington (Phillips 19 72) where turion density decreased from MLLW with greater depth and Alaska (McRoy 19 72) where subtidal eelgrass density was less than intertidal turion density. Reproductive turion density was also greater in the inter tidal zone of Puget Sound (Phillips 1972). Conversely, Stout (1976), working in Netarts Bay, Oregon, found that deep water eelgrass had significantly higher total and reproductive turion densities than shallow water eelgrass. She considered shallow and deep water eelgrass as distinct groups but failed to provide any elevational or morphological information for the two types. In the same study Stout found that the deep water eelgrass had a much higher biomass per square meter than the shallow water eelgrass. These results do not agree with those of other Pacific Coast eelgrass studies. Phillips (1972) reported that intertidal biomass always exceeded subtidal biomass at his Bush Point, Washington study site and at Alki Point, Washington subtidal biomass only exceeded intertidal biomass from July to September when a large increase in sub tidal leaf standing crop occurred. Eelgrass biomass in creased from the upper limit of eelgrass growth (0.5 meters above MLLW) to -0.5 meters and decreased gradually thereafter 7 to its lower limit of -2.75 meters in southern California (Backman and Barilotti 1976). Similarly, Keller and Harris (1966) describe an increase in leaf standing crop of inter tidal eelgrass from its upper limit of 0.3 meters above MLLW to -0.3 meters and a slight decrease at the lowest ele vation (-0.5 meters) they studied. The influence of tidal elevation, across broad tidal zones, on such phenological events as seasonal changes in leaf and rhizome standing crops, total biomass and turion density is described for Puget Sound by Phillips (1972). This review of previous ecological studies of Z. marina indicates that certain morphological, biomass, and population characteristics of eelgrass are influenced by environmental factors which change with depth. The confusion which exists in the literature as to the true nature of the change in these characteristics with depth can be attributed to: 1. studies conducted over only a portion of the tidal range of eelgrass (Keller 1963, Keller and Harris 1966) 2. studies describing the influence of tidal elevation on only one or two parameters (Burkholder and Doheny 196 8, Phillips 1974) 3. studies comparing eelgrass characteristics across broad tidal zones, e.g. intertidal and subtidal (McRoy 1972), shallow and deep (Stout 1976). Liebig^s law of the minimum, that plant yield is dependent on the nutrient present in minimum quantity, has been generally expanded to the broader ecological concept of 8 limiting factors, i.e., that the condition which approaches or exceeds the limits of tolerance of an organism is said to be a limiting factor. The upper limit of Z. marina growth is determined by desiccation of the plant which, in turn, is a function of tidal exposure and substrate composition (den Hartog 19 70). The factor controlling the lower limit of eelgrass is light availability (Phillips 1972, Backman and Barilotti 1976). In turbid coastal and estuarine waters, water clarity in fluences the light environment of eelgrass (Burkholder and Doheny 196 8) and, consequently, the photosynthetic activity of the plant. It is reasonable to expect that these two very different limiting factors, light and desiccation, influence the previously described characteristics of eelgrass in different ways as its upper and lower distributional limits are approached. A study of seasonal changes in total and reproduc tive turion densities, leaf standing crop and leaf and rhizome dimensions, from the upper to the lower limits of eelgrass growth, provides a means of determining the influence of tidal elevation on eelgrass characteristics. Such a study would also provide insight into the ways in which limiting factors influence the vegetative characteristics of eelgrass near its tolerance limits. 1.3. Objectives of the Study-Considering the purpose of the study, and previous autecological research on eelgrass, the following objectives were established: 1. To assess the seasonal and diurnal changes in environ mental factors of eelgrass habitat on southern Roberts Bank. 2. To determine the influence of tidal elevation, from the upper to the lower limits of eelgrass distribution, on eelgrass standing crop, reproductive and total turion densities, and leaf and rhizome dimensions during the growing season. 3. To describe biomass changes of eelgrass during a growing season. 4. To collate the above information to better understand the habitat requirements and growth characteristics of eel grass on southern Roberts Bank. 10 2. THE STUDY AREA The study area, shown in Figure 1, is approximately 20 kilometers south of the City of Vancouver- The geograph ical location of the study site, adjacent to and south of the Tsawwassen Ferry Terminal Causeway, is 49° 00' N. latitude, 123° 07' W. longitude. Roberts Bank adjoins the southern Strait of Georgia between the main distributary channel of the Fraser River and the Canada-USA International Boundary. The study site is approximately 6 kilometers due south of the mouth of the south arm of the Fraser River. Field reconnaissance and information from aerial photographs and topographic maps were used in the selection of the study site, as shown in Figure 2. A uniform cover of eelgrass from the upper to the lower elevational limits of eelgrass growth, and accessibility, both on foot and by boat, were major con siderations in selecting the study site. The Fraser River Delta is composed of recent sedi ments several hundreds of feet thick over Pleistocene sediments (Mathews and Shepard 1962). An excellent summary of the geology of the Fraser River Delta is given by Luternauer (Hoos and Packman 19 74) . Kellerhals and Murray (1969) describe the sedimentary characteristics of the tidal flats covered by eelgrass in Boundary Bay. Previous vegetation studies of the Fraser River estuary have been largely descriptive and all but two have ignored the submerged vascular plants. General marsh des criptions are provided by Forbes (1972a,b), McLaren (1972) 11 Fig. 1. Aerial photo mosaic of the Fraser River Delta showing location of the study area. 13 Fig. 2. Diagram of the study site showing transect locations. 14 CANADA U.S.A.'' 15 and Hillaby and Barrett (1976). Forbes (1972c) provides rough maps and estimates of eelgrass coverage for the Fraser River foreshore and Boundary Bay. Historical changes in the Roberts Bank eelgrass bed and habitat and population char acteristics of Roberts Bank eelgrass are described in an environmental impact assessment of Roberts Bank port expansion prepared for the National Harbours Board, Port of Vancouver (1977) by Beak Consultants Ltd. Yield estimates of the major emergent marsh plants are given by Yamanaka (19 75) but information on the submergent vegetation is lacking. Similarly, Burgess (1970) describes the importance of various emergent species to several species of dabbling ducks on the Fraser foreshore marshes. Burgess reports that the physical environment of the tidal marshes exerts strong influences on the composition and distribution of the vegetation. The estuarine waters adjacent to the Fraser River foreshore are highly stratified (Hoos and Packman 19 74) , a factor which is strongly influenced by wind and tide-driven currents. Tides in the southern portion of the Strait of Georgia are of the mixed, mainly diurnal type. At the study site the mean tidal range is 3.05 meters; for large tides the range averages 4.69 meters. Mean water level, the average of all hourly observations, is 2.96 meters. During the summer, extreme lower low water associated with 'the spring tides occurs near midday; in the winter, near midnight. The times are reversed for extreme higher high water (Canadian Hydrographic Service 19 76). In Canada, Chart Datum (CD) is 16 the plane of lowest normal tides and is therefore below mean lower low water (MLLW). At the study site MLLW is 1 meter above CD. Development proposals for areas along the Fraser River foreshore have increased greatly in recent years. The proximity of the Fraser River Estuary to the large and rapidly growing metropolis of Vancouver, the increasing recreational demands of the populace, and the progressive industrialization of the area are all important factors in the encroachment on foreshore lands. Several of the proposed developments are discussed in Hoos and Packman (1974) and Harris and Taylor (1973). The influence of the adjacent urban and industrial areas on the water quality of the lower reaches of the Fraser River is discussed at length by Dorcey (1976). On southern Roberts Bank recent developments have taken the form of port and causeway construction. The Tsawwassen Ferry Terminal and Causeway were constructed in 1960. In 1970 the Westshore Terminal port facility and cause way were built across southern Roberts Bank. In addition, several power and telecommunication cables have been laid across the intertidal sand flats of Roberts Bank. Current proposals to further develop southern Roberts Bank include a multi-fold expansion of the Westshore Terminal port facility. Depending on the ultimate form of the port expansion, the effects on the eelgrass resource of southern Roberts Bank will vary from slight to considerable. 17 3. ENVIRONMENTAL FACTORS IN RELATION TO EELGRASS HABITAT 3.1. Materials and Methods Seasonal changes in salinity, temperature and water clarity were determined from measurements made every 2 weeks from April to August 19 76 and monthly thereafter to January 1977. Diurnal changes in salinity, temperature, water clarity and light were monitored on four occasions during the study period, corresponding to the spring, summer, fall and winter conditions in the study area. Figure 3 is a schematic profile of the study site. All measurements were taken just seaward of the lower boundary of the eelgrass bed and, with the exception of the diurnal monitoring program, were made between 10.0 0 and 14.0 0 hours. Salinity and temper ature were measured in situ, at the surface and 1.5 meters below surface, with a YSI Model 14 86 portable Salinity-Conductivity-Temperature meter. This instrument measures electrical conductivity and temperature and computes salinity from these measurements. The manufacturer lists its accuracy at +0.1°C at -2°C for temperature and +0.7%o at 20%o for sali nity . A 30 cm (diameter) Secchi disc was used to measure the transmission of visible light through the water column. The disc was lowered into the water until it disappeared and slowly raised until it reappeared. Secchi depth, a measure of water clarity, was recorded as the average of these two readings. Diurnal changes in photosynthetically active 18 Fig. 3. Schematic profile of the study site showing transect elevations in relation to Chart Datum. 20 radiation (PAR) were measured with a LI-COR Model LI-185 Quantum/Radiometer/Photometer equipped with an underwater quantum sensor. The upper limit of eelgrass growth was determined using predicted tidal information for the Secondary Port of Tsawwassen contained in the 19 76 Tide and Current Tables of the Canadian Hydrographic Service. Transect A was estab lished just within the upper boundary of the eelgrass bed and the other four transects were located at 0.5^ meter depth intervals with a survey stadia rod. The lower limit of eelgrass growth was determined at the same time. The eleva tion of transect A was later confirmed using hourly tidal readings from the Tsawwassen Tidal Station for 19 76 obtained from the Institute of Ocean Sciences, Fisheries and Marine Service, Environment Canada, Victoria. This information was also used to determine tidal exposure of transects A and B for 1976. As there was a need for very accurate information concerning tidal elevations, transects A and B were surveyed from Bench Mark "Geod. No. 66-C-045" located in the wall of the Hull Maintenance Building, Tsawwassen Ferry Terminal, on March 12, 1977. A Keuffel and Esser alidade and plane table were used for the survey. There was good agreement (+3 cm) between the surveyed elevations and those determined from inter polation of hourly tide heights. A technique similar to that described by Ranwell et al (1974) was used to monitor sediment surface level oscillations within the eelgrass bed. Twenty 2.5 cm diameter and 30 cm long wooden stakes were pushed into the substrate until 10 cm protruded at 10 meter intervals across the eelgrass bed from the upper to the lower limits of eel grass growth. The length of stake protruding was measured at intervals from July 1976 to January 1977. -Plexiglas tubes 10 cm long (inside diameter 4 cm) were used to remove sediment cores from areas adjacent to the stakes in October 19 76, and the upper 5 cm of each core was subjected to various physical and chemical determinations. Carbonate carbon was determined following the gravimetric method for loss of carbon dioxide described by Black (1965). Organic matter content was found by loss in weight on ignition at 550°C (Wood 1975) and was converted to organic carbon content by division with a factor of 1.8 as recom mended by Trask (19 39). Dry sieving with a set of nested US Standard Sieves (4.0 to 0.1 cm openings) was used to perform the particle size analysis. Approximately 40 g of dry sediment were placed in the top sieve and the set of sieves was shaken on a ROTAP machine for 2 minutes. 3.2. Habitat Factors 3.2.1. Salinity 3.2.1.1. Seasonal Changes The 1.5 m salinity (Figure 4) was consistently greater than surface salinity except for one anomalous set 22 Fig. 4. Surface and 1.5 m salinities and temperatures at the study site and mean monthly air temperature at Vancouver International Airport (Monthly Record, Meteorological Observations in Canada, Atmospheric Environment, Fisheries and Environment Canada, April 1976 to January 1977). Mean monthly air temperature plotted at the midpoint of each month. 23 A 1 M I j I j I A I S I 6 I N I fj I J I MONTH \ \ \ A I M I J I J I A I S I 0 I ti I fj I J I MONTH 24 of measurements in mid-winter. Surface and 1.5 m salinity differences are on the order of 1 to 2%o in the spring and early summer, and increase two- to threefold by late summer. The pronounced salinity stratification is maintained until winter. 3.2.1.2. Diurnal Changes The diurnal salinity measurements of Figure 5 reflect, to a great extent, the pertinent features of the seasonal salinity changes. Observations of May 2, 19 76 and January 18, 1977 show that the water column was well mixed in the winter and spring. On.July 28, 19 76 the higher sali nity at 1.5 meters was maintained across two complete tidal cycles. By October the salinity difference of surface and subsurface waters was greater than that observed during the summer. 3.2.2. Temperature 3.2.2.1. Seasonal Changes Seasonal trends in water temperature resemble salinity in that the thermal stratification apparent in the summer disappears during the rest of the year (Figure 4). The seasonal increase and decrease in water temperature fol lows the mean monthly air temperature curve for Vancouver International Airport, 20 kilometers north, closely until fall when the curves diverge and the mean monthly air temperature becomes increasingly lower than the sea temperature. 25 Fig. 5. Diurnal surface and 1.5 m salinities. May 2, July 2 8 and October 4, 19 76. January 18, 19 77. 26 3.2.2.2. Diurnal Changes Figure 6 indicates that winter and spring surface and subsurface water temperatures were very constant over the 24-hour sampling period. The water column is well mixed during these seasons. In the summer the temperature of the air is warmer than that of the surface water which is, in turn, warmer than the deeper water. The diurnal temperature information for October 4, 1976 illustrates how the warming effect of the sun can influence the temperature relationships of the air and surface and subsurface waters. As the sun rose above the horizon, air temperature increased and surpassed first subsurface, then surface water temperature; a concomitant rise in surface water temperature above subsurface water temperature also occurred. 3.2.3. Light 3.2.3.1. Seasonal Changes There is an obvious inverse relationship between the seasonal discharge cycle of the Fraser River and the Secchi depth of waters at the study site (Figure 7). 3.2.3.2. Diurnal Changes Secchi depth measurements and light data collected during the diurnal monitoring sessions show more variability within than between sampling sessions. No trends could be discerned from the information as gathered (Appendix 4). Diurnal air temperatures and surface and 1.5 m water temperatures. May 2, July 2 8 and October 4, 1976. January 18, 1977. PACIFIC DAYLIGHT SAVING TIME 30 Fig. 7. Secchi depth (meters) at the study site and maximum daily discharge (thousands of cubic meters per second) of the Fraser River at Hope, B.C. for each month from March 19 76 to January 19 77. 32 Atmospheric conditions on the four days selected for diurnal monitoring were highly variable. May 2, 1976 was overcast with periods of rain showers. Morning fog which cleared away before noon, bright sunshine during midday and high clouds by late afternoon occurred on July 28, 19 76. October 4, 1976 was sunny with cloudy periods and January 18, 19 7 7 was cloudy with a few sunny periods. 3.2.4. Tidal Range and Percentage Exposure At the study site the upper limit of eelgrass growth was 0.85 meters Chart Datum (-0.15 m MLLW) (Figure 2) and the lower limit was -1.25 m CD (-2.25 m MLLW); thus the depth range for eelgrass in this area is approximately 2 meters. Percentage exposures were calculated for the' two intertidal transects (A and B) from hourly tidal readings at the Tsawwassen Tidal Station, located 1 kilometer west of the study site, for 19 76. Two methods were used. The first method totalled the number of hours during which the study elevations were exposed in 1976 and this total was expressed as a percentage of the total number of hours in 19 76. This method indicated that transect A was exposed 1.00% of the year and transect B, 0.034% of 1976. The second, more detailed method entailed direct interpolation of tidal heights between all hourly observations which included but did not encompass the two elevations. This method revealed that transect A had a percentage exposure of 0.9 36 and transect B was exposed 0.006% of the year. The first method over-33 estimated the percentage exposure of the lower elevation (transect B) by more than fivefold. 3.2.5. Substrate 3.2.5.1. Surface Level Changes Figure 8 depicts net substrate surface level oscillations observed at the study site within the boundaries of the eelgrass bed. There was an accumulation of sediments until late summer when sediments were transported out of the eelgrass bed. The overall erosion observed during the study period was approximately 2 cm. 3.2.5.2. Physical and Chemical Characteristics Results of a mechanical analysis of sediment samples collected at 10 meter intervals across the eelgrass bed at the study site are shown in Table 1. The sample taken at the upper edge of the eelgrass bed is better sorted than samples taken at 10, 20 and 30 meters inside the upper edge , which are the most poorly sorted of all. Sorting of samples more than 30 meters from the upper edge increases with depth until just before the lower edge of eelgrass is reached. A moderate decrease in degree of sorting occurs near the lower distributional limit of eelgrass. Fines content (Figure 9) exhibits a similar decline with depth at distances greater than 30 meters from the upper edge and a slight increase near the lower limit. 34 \ Fig. 8. Net oscillations of sediment surface levels, July 19 76 to January 19 77. Mean + Standard Error. 35 -3.0 J 1 A 1 S 1 6 1 N 1 D 1 J MONTH 36 Table 1. Particle size composition of sediments Particle Size (%) Distance (m) 0.10 mm 0.25 mm 0.50 mm from Upper Edge to to to of Eelgrass Growth <0.10 mm .0.25 mm 0.50 mm 1.0 mm > 1.0 mm 0 33.86 57.70 5.11 1.44 1.89 10 32.21 44.03 21.22 1.23 1.31 20 21.06 47.67 27.66 1.78 1.83 30 22.29 43.47 29.55 2.42 2.26 40 33.87 54.22 6.96 1.72 3.23 50 26.78 62.26 5.47 1.08 4.40 60 23.87 66.48 4.58 .88 4.19 70 21.75 69.22 4.85 .66 3.51 80 18.82 71.96 5.30 .64 3.28 90 18.68 69.77 4.75 3.35 3.45 100 14.74 74.25 6.94 .86 3.06 110 11.57 77.61 7.66 6.26 2.53 120 11.89 76.68 8.02 .80 2.61 130 10.31 76.98 8.29 1.36 3.06 140 9.61 80.47 6.88 .65 2.38 150 8.05 79.95 8.61 1.27 2.12 160 8.47 78.80 9.12 1.06 2.56 170 14.17 73.26 7.73 1.34 3.51 175 15.34 70.52 8.90 1.70 3.55 180 12.23 72.36 12.17 1.54 1.69 Fig. 9. Sediment samples taken at 10-meter intervals from the upper to the lower limits of eelgrass growth: a. Percentage of fines b. Percentages of organic and carbonate carbon. i 38 39 The apparent anomaly that the stations located 10, 20 and 30 meters inside the upper edge have lower percentages of fines than adjacent stations and yet are more poorly sorted is explained by the high larger sand fractions (greater than 0.5 mm diameter) of these stations. Percentage contents of carbonate carbon and organic carbon (Figure 9, Table 2) decline with distance from the upper limit of eelgrass growth. A moderate increase is noted for both near the lower edge of eelgrass. 3.2.6. Waves and Currents Although current velocities were not measured at the study site, general observations made during the study period indicate only gentle currents occur across the eel grass bed. Excessive wave action did not appear to be an important factor at the study site as it is protected by the adjacent Tsawwassen Ferry Terminal Causeway and, to a lesser extent, by nearby Point Roberts peninsula. 3.3. Discussion Zostera marina L. is a euryhaline, eurythermal seagrass which inhabits the shallow, protected coastal waters where suitable substrate is available (Table 3). The salinity, temperature and water motion conditions of southern Roberts Bank are close to the world-wide optima for these habitat factors as indicated by Table 3. The other habitat factors studied, light, substrate and exposure, appear to account Table 2. Organic and carbonate carbon contents of sediments Content (%) Distance (m) from Upper Edge of Eelgrass Growth Organic Carbon Carbonate Carbon 0 .96 2.45 10 1.12 3.03 20 .89 2.14 30 .83 1.90 40 1.19 2.68 50 1.03 2.42 60 .86 1.96 70 .97 1.86 80 .88 2.02 90 .84 2.09 100 .96 1.81 110 .64 1.54 120 .69 1.93 130 .62 1.90 140 .71 1.53 150 .62 1.26 160 .62 1.48 170 .79 1.98 175 .70 2.17 180 .59 1.81 41 Table 3. Comparisons of habitat factors affecting eelgrass growth (modified from Stout 1976, and Phillips 1972) TEMPERATURE Range World-wide Optimum World-wide Southern Roberts Bank 0 - 40.5°C 10 - 20°C Range 7.8 - 17.5°C SALINITY Range World-wide Optimum World-wide Southern Roberts Bank Range SUBSTRATE Range World-wide Optimum World-wide Southern Roberts Bank Range Freshwater - 42%o 10 - 30%o 13.8 - 30.0%o pure firm sand to pure soft mud mixed sand and mud sand to mixed sand and mud WAVE MOTION Range World-wide Optimum World-wide Southern Roberts Bank waves to.stagnant water little wave action, gentle currents gentle currents, low wave shock DEPTH Range World-wide Optimum Puget Sound Southern Roberts Bank Range MLLW to -30 meters -1 to -4 meters MLLW to -2 meters 42 for the narrow depth distribution of eelgrass on southern Roberts Bank. Den Hartog (19 70) states that the depth attained by eelgrass depends greatly on light intensity and hence water clarity, suspended materials in the water column, etc. The ability of eelgrass to extend to greater depths in other areas of the Pacific Coast having clearer waters (Phillips 1972, Backman and Barilotti 1976) suggests that the turbid water of the Fraser River discharge is responsible for the elevated lower limit of eelgrass on the Fraser River foreshore. In Florida, Strawn (1961) found that tidal exposure was the major factor influencing the zonation of tropical seagrasses. Based on a sample of six 1-week periods over the year, percentage exposures were calculated for six elevations in Humboldt Bay, northern California (Keller and Harris 1966). These determinations indicated that the upper limit of eel grass growth (0.3 m above MLLW) was exposed to the air.about 15 percent of the time. In my study area, transect A (0.8m above CD, 0.2 m below MLLW), located just inside the upper boundary of eelgrass, was exposed approximately 1 percent of the time during 1976. If desiccation, and hence tidal expos ure, does indeed control the upper limit of eelgrass as postulated by den Hartog (1970) and Keller and Harris (1966), how then can this great disparity in percentage exposure for the upper limit of two Pacific Coast eelgrass populations be accounted for? The answer lies in the fact that desiccation is determined, to a great extent, by substrate characteristics as well as exposure periods. The only sediment information provided for Humboldt Bay (Keller and Harris 1966) are references to patches of bare mud within the eelgrass bed; the sediment in my study area was sand. The greater water-holding capacity of mud may account for the presence of eel grass higher in the intertidal zone of areas having muddy substrates. On southern Roberts Bank the sandy substrate limits the exposure tolerance of eelgrass and thereby in fluences the upper distributional limit of the plant. Net changes in substrate surface levels observed at the study site are the result of changes in prevailing seasonal winds and wave action. The study site is in the lee of the Tsawwassen Ferry Terminal Causeway and protected from the prevailing northwest summer winds; a depositional environ ment is thus maintained within the boundaries of the eelgrass bed. During the fall and winter the prevailing winds are from the southeast and the study site receives more wave action. There is a resultant net decrease in sediment surface levels at this time of year. The high percentage of fines (less than 0.1 mm diameter) and organic carbon and the poorly sorted sediments observed near the edges of eelgrass growth provide strong support for the baffling action of the vertical edge of an eelgrass bed proposed by Orth (19 7 3). Organic carbon content and the percentage of fines was positively correlated (r = 0.89) for the samples. Carbonate carbon (largely shell fragments) also had high values near the upper and lower limits of eelgrass growth. Field observations indicated that benthic infauna populations of bivalves were highest near the edges of eelgrass growth. My interpretation of the strong correlation of organic and carbonate carbon (r = 0.79) across the eelgrass bed is that the infaunal distribution reflects food abundance (organic carbon) which is concentrated near the upper and lower edges of the eel grass bed as the nutrient-laden currents are slowed by eelgrass. Various aspects of the data require further con sideration and elaboration to assess the validity of the data as gathered. The salinity, temperature and Secchi depth measurements have the limitation of being "point in time" observations. This limitation becomes even more apparent when the highly variable conditions of the estuarine environment are considered. The diurnal monitoring program was undertaken to, among other things, place the seasonal changes in a better perspective. As noted earlier, weather conditions for three of the four diurnal monitoring sessions were unsettled; the extent to which the variable conditions are reflected in the measurements taken is uncertain and for this reason only general trends were extrapolated from the data. Sediment samples were collected in October 1976. Figure 8 indicates that the surface levels of the substrate fluctuated during the study period and for this reason it is reasonable to assume that the results of the sediment analyses may have been quite different had the samples been collected at some other time. Future studies on the inter actions of sediments and marine angiosperms should include the dynamic nature of the sediments in experimental design considerations. 4. STANDING CROP, TURION DENSITY, BIOMASS AND LEAF , MEASUREMENT STUDIES 4.1. Materials and Methods A stratified random sampling technique was used to determine seasonal changes in eelgrass standing crop, turion density and leaf dimensions at five tidal elevations. Anchor blocks were placed at the upper and lower edges of eelgrass growth and joined by a rope which thus bisected the eelgrass bed (Figure 2). Transect A was established just within the upper edge of eelgrass growth and the remaining four tran sects were located at 0.5 meter depth intervals across the eelgrass bed. The lowest transect, transect E, was just inside the lower limit of eelgrass and was 2.0 meters below the highest transect. Fifty-meter long nylon lines, marked at 1 meter intervals, were anchored parallel to the depth contours at 0.5 meter depth intervals. The transect lines were placed in such a way that they were bisected by the rope joining the anchor blocks at the upper and lower eelgrass limits. A ran dom number generator was used to select two numbers between 1 and 50 for each elevation and sampling sites were located along the study transects at these numbers. A 0.25 square meter (0.5 m x 0.5 m) steel quadrat was placed on either side of the transect at each of the two locations and all of the turions rooted within the quadrat were clipped at sediment level and placed in cotton sacks. To avoid the possible effects of increased insolation experienced by areas immediately adjacent to sampled quadrats, only alter nate possible sample locations were included, that is to say, sample sites were located at whole meter intervals. SCUBA was used for underwater sampling of the vegetation. Samples were transported to the laboratory and total and reproductive turion counts were made. Individual samples were then washed for 2 minutes in a portable Hoover washing machine to remove epiphytes and spun for 1 minute in the machine to remove adherent water. The machine proved to be very effective in removing epiphytes from the eelgrass leaves. The weight of the sample after spinning is referred to as wet weight. Dry weight and organic (ash-free) dry weight deter minations were made following the techniques and terminology of Westlake (1963). Transect E was not established in time for the first sampling session (April 5 and 6, 1976) but an analysis of standing crop (organic dry weight) data from the four 0.25 square meter quadrats collected from each of the other four elevations indicated that transect A had a higher relative variability than the others. The following data illustrate this: Transect Coefficient of Variation A 0.46 B 0.17 C 0.18 D 0.29 The number of samples for transect A was increased to six for the remainder of the study period to reduce sample variability for this elevation. On April 15, 1976 a program using five different quadrat sizes was conducted to determine the optimum quadrat size for sampling eelgrass. The following figures indicate the effect of quadrat size on relative variability (sample variability relative to the mean of the sample): Quadrat Coefficient of Percentage Area (m2) Variation Standard Error f 1.0 0.27 13.33 0.5 „ 0.33 11.82 0.25 0.22 6.50.04 0.56 11.22 0.01 1.90 26.98 Percentage standard errors were calculated by the method of Bordeau (1953). Appendix 6 contains additional information. The 0.25 square meter quadrat had the lowest relative variability and its use was continued for the remain der of the study. Several attempts were made to sample the root and rhizome components of the vegetation to complement the leaf standing crop studies. The use of a coring device and a post hole auger met with very limited success due to the sandy 48 nature of the sediments, and underwater digging reduced visibility to nil in a matter of seconds. Consequently the underwater biomass sampling program was dropped; however, intertidal biomass sampling in areas adjacent to transect A was conducted from April 1976 to January 1977 during suitably low tides. Four random samples (0.25 square meter quadrat) were gathered on each collection date. Turions were clipped at sediment level and later enumerated. , The sediment was excavated to the lowest root level, generally 20 cm to 30 cm, and sieved through a 0.4 cm metal screen. The root and rhizome material retained by the screen was later hand cleaned and sorted in the laboratory. Dimensions of the longest in tact leaf of each turion and random rhizome diameters were recorded for four sampling sessions from August 19 76 to January 19 77. Two samples were selected at random from the four collected at each elevation during the six standing crop and density sampling sessions of August 19 76 to January 19 77. Leaf length and width were measured from the longest intact leaf of each turion. Intact leaves were identified by their rounded tips. 4.2. Standing Crop Eelgrass samples were collected from each of five elevations on 16 occasions during the period of April 19 76 to January 19 77 (Appendix 7). A total of 36 4 quadrats were sampled during the study period for leaf standing crop 49 determinations. All of the statistical analyses follow Zar (1974). Percentage dry weight (of wet weight) and percentage ash content (of dry weight) statistics are illustrated: Percent Dry Weight Percent Ash Content Determinations 323 343 Mean 12.45 13.98 SD 1.68 4.79 SE 0.09 0.26 Range 9.71 to 18.95 5.58 to 25.72 A three-factor analysis of variance (Zar 19 74) with factors A (elevation) and B (time) fixed and factor C (sample location) random was performed on the quadrat leaf standing crop data. The first sampling session was not included in the analysis of variance due to missing informa tion. In addition, one location, representing two samples, was randomly deleted from the transect A data for each sampling session. This was done so that the number of samples for each elevation and sampling time were identical. The analysis of variance calculations were performed on a hand calculator. The following null hypotheses were formulated and tested: 1. Ho: Organic dry weight per quadrat the same for all five elevations 2. Ho: Organic dry weight per quadrat the same for all 15 sampling times 3. Ho: Organic dry weights per quadrat between loca tions within elevations and times are the same 50 4. HQ: Organic dry weight per quadrat differences among elevations are independent of differences among times (i.e., absence of A x B interaction) Table 4 summarizes the analysis of variance for leaf standing crop; an expanded version is presented in Appendix 8. 4.2.1. Temporal Changes The analysis of variance for leaf standing crop showed that organic dry weight per quadrat was not the same for all 15 sampling sessions. A Newman-Keuls Multiple Range Test was employed to determine between which sampling dates differences existed. Unfortunately, the significance level for this type of test is the probability of encountering at least one Type I error while comparing all the pairs of means. The test was not powerful enough to discern where, among the 15 sampling session means, true differences in organic dry weights occurred. A simpler, although much less sensitive, approach was tried. The means of the 15 sampling sessions were divided into three groups of five and a grand mean, in grams organic dry weight per quadrat, was calculated for each group. The results were: Sessions 2-6 7-11 12-16 Period April 18-June 13 June 28-Aug. 25 Sept. 28-Jan. 18 Mean (g) 8.73 8.40 3.42 This information suggests that eelgrass standing crop persists at a fairly high and constant level from late 51 Table 4. Analysis of variance summary table for mean leaf standing crop (organic dry weight in grams per 0.25 square meter quadrat) Hypothesis Calculated F Critical F Conclusion Elevation (factor A) Time (factor B) Location (factor C) 4. A x B 16.55** FO.01(1),4,70 = 3-60 Reject HQ 8.36** F0.01(1),14,70 = 2.35 Reject HQ 3.21** Fo.Ol(l),70,140 = 1-60 Reject HQ 1.14ns F0.01(l),50,70 = 1-83 Accept HQ spring until late summer. There appears to be a drastic decline in the late summer and early fall period during which more than 50 percent of the standing stock is lost. A low and constant standing stock is maintained during much of the winter. Appendix 7 reveals the same general trends. Figure 10 graphically portrays this seasonal cycle of mid summer abundance, late summer decline, and reduced standing crop throughout the winter. 4.2.2. Influence of Depth The analysis of variance conducted for leaf standing crop revealed that organic dry weight per quadrat is not the same for all five elevations (F = 16.55**). Results of a Newman-Keuls Multiple Range Test show that the mean standing crops of the highest and lowest transects (0.8 and -1.2 m respectively) are not significantly different (q = 2.10) from one another. Similarly the standing stocks of the three middle elevations are not significantly different (q = 2.16) from each other; however, they are significantly different (q = 5.11*) from those of the highest and lowest elevations (Table 5). The differences in leaf standing crops for the five study elevations are shown in Figure 10. The later summer and early fall decline in standing stocks mentioned in section 4.2.1. is. very pronounced for the three middle elevations (0.3, -0.2 and -0.7 m). Both the magnitude and rate of decline in leaf standing stock are noticeably less for 53 Fig. 10. Mean leaf standing crop (grams per square meter) for five elevations (in relation to Chart Datum), April 19 76 to January 19 77. 90 0.8 A r M I 1 I J I "A I S 1 6 I N I D I 7 I MONTH Table 5. Newman-Keuls Multiple Range Test for the mean leaf standing stocks (organic dry weight in grams per 0.25 square meter quadrat) at five elevations Elevation (m) 0.8 -1.2 0.3 -0.2 -0.7 Ranks of Sample Means 1 2 3 4 5 Ranked Sample Means 3.60 4.88 7.98 8.51 9.29 tomparison Difference SE q P ^0.05,120,p Conclusion 5 us 1 5.69 .61 9.37 5 3.917 Reject HQ* Reject Ho* 5 us 2 4.42 .61 7.27 4 3.685 5 us 3 1.31 .61 2.16 3 3.356 Accept HQ 5 us 4 0.79 .61 1.30 2 Do not test 4 us 1 4.90 .61 8.07 4 3.685 Reject HQ* 4 us 2 3.63 .61 5.97 3 3.356 Reject HQ* 4 us 3 0.53 .61 0.87 2 Do not test 3 us 1 4.38 .61 7.21 3 3.356 Reject HQ* 3 us 2 3.10 .61 5.11 2 2.800 Reject Ho* 2 us 1 1.27 .61 2.10 2 2.800 Accept HQ Overall Conclusion 0.8 = -1.2 * 0.3 = -0.2 = -0.7 transects A and E (0.8 and -1.2 m, respectively) which are nearest the upper and lower edges of the eelgrass bed. 4.3. Turion Density The vegetative axes of eelgrass consist of both horizontal, indeterminate rhizomes and erect annual axes with determinate growth. Clusters of foliage leaves, called turions, arise from both vegetative axes. Reproductive turions are terminal in Z. marina (den Hartog 1970) and during the study were differentiated from vegetative turions on the basis of their light yellow-green colour and sympodial branching habit. Total and reproductive turion counts from a total of 338 quadrats (0.25 square meter) were collected from April 1976 to January 1977. A three-factor analysis of variance (Zar 1974) with factors A (elevation) and B (time) fixed and factor C (sample locations) random was conducted on the total and reproductive turion density data. 4.3.1. Influence of Time and Elevation on Total Turion Density Turion counts were not made on all of the samples from the first and second sampling sessions (April 1976). To facilitate the turion density analysis of variance partial information from the first two sampling sessions were ex cluded from the calculations. Thus, only the last 14 sampling sessions were included in the analysis of variance. To further facilitate the analysis of variance 57 calculations data for two of the six quadrats from transect A were deleted at random from each sampling session. Thus, turion counts of four quadrats from each of five elevations sampled on 14 occasions were used in the analysis of vari ance calculations to test the following null hypotheses: 1. Ho: Turion density per quadrat is the same for all five elevations (Factor A) 2. Ho: Turion density per quadrat is the same for all 15 sampling sessions (Factor B) 3. Ho: Turion density per quadrat between locations within elevations and times is. the same (Factor C) 4. Ho: Turion density per quadrat differences among elevations are independent of differences among times (Absence of A x B interaction) Appendix 9 contains turion density information collected during the study. Table 6 summarizes the analysis of variance for turion density and Appendix 10 presents more analysis of variance information for mean turion density. Highly significant differences in total turion density existed between elevations and times, and between locations within elevations and times (Table 6). There was no significant interaction of elevation and time on total turion density. Newman-Keuls Multiple Range Tests were used to determine which treatment means (of five elevations and 15 sessions) were different. Table 7 shows the results for the mean turion densities of the five elevations. Turion densities of the highest and lowest transects (0.8 and -1.2 m respectively) were significantly different from one another 58 Table 6. Analysis of variance summary table for mean total turion density (turions per 0.25 square meter quadrat) Hypothesis Calculated F Critical F Conclusion 1. Elevation (factor A) 2. Time (factor B) 3. Location (factor C) 4. A x B 13.52** 8.59** 2.345** 1.393ns F0.01(l),4,70 = 3-60 Reject HQ FO.Ol(l),13,70 = 2.40 Reject HQ F0.01(l),70,140 = 1-60 Reject HQ FQ.OKI) ,50,70 = 1-83 Accept HQ 59 Table 7. Newman-Keuls Multiple Range Test for total turion density (turions per 0.25 square meter quadrat) means at five elevations Elevation (m) -1.2 0.8 -0.2 0.3 -0.7 Ranks of Sample Means 1 2 3 4 5 Ranked Sample Means 9.93 13.23 16.89 17.20 19.38 Comparison Difference SE q p 30.05,120,p Conclusion 5 vs 1 9.45 1.02 5 vs 2 6.14 1.02 5 vs 3 2.48 1.02 5 vs 4 2.18 1.02 4 vs 1 7.27 1.02 4 vs 2 3.96 1.02 4 vs 3 0.30 1.02 3 vs 1 6.97 1.02 3 vs 2 3.66 1.02 2 vs 1 3.30 1.02 9.29 5 3.917 Reject Ho* 6.04 4 3.685 Reject HQ-2.44 3 3.356 Accept HQ 2.14 2 Do not test 7.15 4 3.685 Reject HQ* 3.90 3 3.356 Reject HQ* 0.30 2 Do not test 6.85 -3 3.356 Reject HQ* 3.60 2 2.800 Reject HQ* 3.25 2 2.800 Reject HQ* Overall Conclusion -1.2 * 0.8 * -0.2 = 0.3 = 0.7 60 and from the three middle elevations, between which no significant differences existed. The lowest elevations (-1.2 m) had the lowest turion density (40 turions per square meter). Densities for the middle elevations ranged from 67 to 77 turions per square meter. The highest eleva tion had an intermediate density (53 turions per square meter). The Newman-Keuls Multiple Range Test gave incon clusive results for comparisons of mean turion densities between sampling sessions. This test often produces ambiguous results for comparisons with large numbers of treatment means (Zar 19 74). However, an overall seasonal trend showing a decline in total turion density from summer to winter is seen in Table 8. Summer turion density is halved by mid-winter. Figure 11 depicts the seasonal decline in total turion density for the five transect elevations. The general timing of turion losses seems constant for all elevations; there do, however, appear to be great differences in the rate and magnitude of the decline in density between elevations. Similar winter turion density (approximately 40 turions per square meter) appears to be reached at the same time (October) for all elevations. During the summer the three middle elevations had turion densities twice as great as those of the upper and lower elevations and, consequently, both the rate (turion loss per unit time) and extent (turion loss per square meter) of the observed decline must have been much greater for these middle elevations. Table 8. Total turion densities (turions per 0.25 square meter quadrat) for fourteen sampling sessions, May to December 1976 Ranks of Sample Means Ranked Sample Means Month Sampled 1 22.95 May 2 21.90 May 3 21.05 July 4 20.05 June 5 18.95 August 6 16.55 May 7 15.30 June 8 14.65 August 9 13.00 July 10 11.60 September 11 10.70 January 12 10.15 November 13 9.20 October 14 8.50 December 62 Fig. 11. Mean total turion numbers per square meter for five elevations (in relation to Chart Datum), April 1976 to January 1977. 63 A f M I ~J I 3 n A I S I 0 I N I fj I J I MONTH 4.3.2. Influence of Time and Elevation on Reproductive Turion Density A two-factor analysis of variance without repli cation was performed on the reproductive turion density information (Appendix 11) collected during the study. During the period in which reproductive turions were present (May to August) no significant differences in reproductive turion densities were found between elevations or sampling times (Table 9), but may occur. However, certain general trends are apparent in the reproductive turion density data of Appendix 11. Peak flowering occurred during June and July. The three middle elevations had a longer period during which reproductive turions were present than had the highest and lowest eleva tions. Flowering was essentially completed at the highest elevation before it began at the lowest elevations. 4.4. The Influence of Depth on Organic Weight per Turion To investigate the relationship of organic dry weight per turion and tidal elevation, a simple linear re gression equation was calculated for each of the five elevations using the turion density (per quadrat) and standing crop (grams per quadrat) data. The linear regres sion of organic dry weight (dependent variable) on turion number (independent variable) for the five elevations is presented in Table 10. The equations indicate that the 65 Table 9. Analysis of variance summary table for mean reproductive turion density (turions per square meter) Source of Variation SS DF MS Total 46.97 27 Elevation 11.13 4 2.78 Time 4.57 5 0.91 Remainder 31.27 18 1.74 To test HQ: No difference among elevations. Calculated F = 1.60 Fo.05(1),4,18 = 2.93ns To test HQ: NO difference among times. Calculated F = 0.53 FQ.05(1),5,18 = 2.77ns , Table 10. Linear regression equations of organic dry weight (g) on turion numbers per quadrat for five elevations Elevation Number of Coefficient of (CD) Observations Equation Determination 0.8 m 88 Y = 0.21 x +0.79 0.57 0.3 m 64 Y = 0.51 x -0.71 0.64 -0.2 m 62 Y = 0.56 x -1.34 0.80 -0.7 m 64 Y = 0.45 x -0.06 0.68 -1.2 m 60 Y = 0.53 x -0.57 0.78 * 67 regression coefficient (slope) of the best fit regression line for the highest elevation (0.8 m) differs from those of the other elevations. An analysis of variance procedure was used to test the significance of each of the regressions. The null hypothesis HQ: P = 0 was rejected for all five elevations as highly significant differences existed for each (Appendix 12). The next statistical procedure employed was an analysis of covariance testing for significant differences between the regressions of the five elevations. The null hypothesis that the slopes of all five regressions (for five elevations) were equal was rejected due to the highly signi ficant calculated F value (Table 11). A Newman-Keuls Multiple Range Test was used to determine which slopes were different from which others. Table 12 reveals that the slope of.the best fit regression line for the highest elevation (0.8 m) exhibits a highly significant difference from the slopes of the regressions for the other elevations. My inter pretation is that the turions of the highest elevation have a much lower foliage (per turion) than is found at the lower elevations. Using, the same .data the following calcu lation taken from the leaf standing crop and turion density analyses of variance is recorded. Elevation (m)  0.8 0.3 -0.2 -0.7 -1.2 .Organic Dry Weight (g) 3.60 7.98 8.51 9.29 4.87 Turion Density 13.23 17.19 16.89 19.37 9.93 Organic Dry Weight (g) 0.27 0.46 0.50 0.48 0.49 per Turion 68 Table 11. Analysis of covariance summary testing for significant differences between slopes of linear regression lines of organic dry weight on turion numbers for five elevations Regression Number of Regression Residual Residual Observations Coefficient SS DF Elevation (m) 0.8 88 0.21 96.98 86 0.3 64 0.51 586.75 62 -0.2 62 0.57 489.28 60 -0.7 64 0.45 524.51 62 -1.2 ' 60 0.53 182.83 58 Pooled 1880.35 Common 0.45 4669.32 Calculated F = 12.62** Fo.Ol(l),4,300 = 3.38 Conclusion: Reject %:£().8 =£0.3 =£-0.2 =£-0.7 =£-1.2 69 Table 12. Newman-Keuls Multiple Range Test for differences between slopes of linear regressions of organic dry weight on turion numbers for five elevations Elevation (m) 0.8 0.3 -0.2 -0.7 -1.2 Ranks of Regression Coefficients 13 5 2 4 Ranked Regression Coefficients 0.21 0.51 0.57 0.45 0.53 Comparison Difference SE q p 30.01,300,p Conclusion 5 vs 1 .36 .032 11.42 5 4.603 Reject HQ 5 vs 2 .12 .038 3.11 4 4.403 Accept Ho 5 vs 3 .07 .042 1.55 3 Do not test 5 vs 4 .05 .041 1.15 2 Do not test 4 vs 1 .32 .027 11.66 4 4.403 Reject HQ 4 vs 2 .07 .042 1.70 3 Do not test 4 vs 3 .02 .046 0.41 2 Do not test 3 vs 1 .30 .037 8.12 3 4.120 Reject HQ 3 vs 2 .05 .044 1.21 2 Do not test 2 vs 1 .25 .033 3.38 2 3.643 Reject HQ Overall Conclusion of Slopes 0.8 ^ 0.3 = -0.2 = -0.7 = -1.2 70 4.5. Biomass Intertidal eelgrass biomass was sampled during low tides from April 1976 to January 19 77. Sampling sessions were undertaken at approximately 1-month intervals and were conducted during very low tides when the intertidal eelgrass was exposed. The results of the biomass sampling program are contained in Appendix 13. Percentages of above and below substrate parts were constant from April to July 1976 (Table 13). A drastic decline in intertidal leaf standing crop in August 19 76 greatly altered the ratio in subsequent samplings. Rhizome standing crop did not appear to change during the sampling period. During the spring and early summer the leaf standing crop was about two-thirds and the root and rhizome standing crops about one-third of the total biomass. By late summer and fall the above and below substrate portions each constituted about 50 percent of the biomass. 4.6. Leaf Measurements Leaf length and width were measured on the longest intact leaf of each turion collected during the regular standing crop and turion density sampling sessions from August 1976 to January 1977. The information is summarized in Table 14. There is a general decline in leaf width from August to January for all five elevations. A similar decline in leaf length is apparent for the same period but there is Table 13. Percentages of above substrate (leaf) and below substrate (roots and rhizomes) standing crops, April 1976 to January 1977 Date Percentage Percentage Above Substrate Below Substrate 16.4.76 61.9 38.1 15.5.76 72.7 27.3 12.6.76 67.2. 32.8 10.7.76 64.4 35.6 7.8.76 42.1 57.9 24.8.76 49.8 50.2 25.10.76 56.1 43.9 23.11.76 47.3 52.7 17.1.77 53.0 47.0 Mean 59.3 40.7 72 Table 14. Leaf measurements for five elevations, August 1976 to January 1977 Elevation (m) 0.8 0.3 -0,2 -0.7 -1.2 Leaf Length (cm) August . Mean 54. .9 104. ,3 102, .8 99, .9 94, .5 SE 5. ,53 20. ,0 9, .37 8, .03 8, .25 September Mean 56. ,0 71. ,4 80, .7 87 .9 69, .8 SE 4. ,09 8. ,51 9 .65 7 .90 9, .56 October Mean 55. ,0 59. ,3 49 .7 69 .3 70, .3 SE 5. ,67 8. .11 11 .23 9 .40 8, .30 November Mean 39. ,3 42. .6 54 .7 40 .5 60, .7 SE 3. .45 6. .79 5, .71 4 .63 7, .85 December Mean 39. .6 45. .6 42 .7 55 .0 54, .0 SE 3. ;43 4. .30 5 .72 6 .90 11, .37 January Mean 31. ,6 29. .6 41 .4 41 .0 42 .6 SE '3. .89 2. .61 3 .91 2 .23 2 .96 Leaf Width (cm) August Mean 0. .61 0. .69 0 .60 0 .66 0 .66 SE 0. .022 0, .058 0 .029 0 .031 0 .036 September Mean 0. .58 0. .62 0 .65 0 .60 0 .56 SE 0. .027 0, .029 0 .027 0 .026 0 .041 October Mean 0. .51 0, .57 0 .61 0 .56 0 .55 SE 0, .028 0, .028 0 .040 0 .039 0 .031 November Mean 0, .53 0, .56 0 .49 0 .46 0 .56 SE 0, .021 0, .043 . 0 .020 0 .019 0 .029 December Mean 0, .52 0, .54 0 .54 0 .57 0 .52 SE 0, .025 0 .022 0 .033 0 .025 0 .037 January Mean 0, .50 0 .40 0 .52 0 .58 0 .58 SE 0, .025 0 .017 0 .020 0 .016 0 .023 a striking dissimilarity between the highest elevation (0.8 m) and the others. In August, mean leaf length for the highest elevation is approximately one-half that of the other elevations. By January, mean leaf length for the upper elevation has been reduced by 40 percent; however, mean leaf length for the other elevations has declined by about 60 percent. Mean winter leaf length (of the longest intact leaf on each turion) appears to be the same for all five elevations and thus the lower elevations experience a greater and more rapid change in mean leaf length during the fall. There appears to be a time lag associated with increasing depth for the observed changes in mean leaf length. In August the 0.3 and -0.2 m elevations had the greatest mean leaf length, in September the -0.2 and -0.7 m elevations, October the lowest two elevations, and by November the greatest mean leaf length was observed at the lowest elevation. Table 15 shows the same seasonal decline in leaf length and width of samples collected adjacent to the 0.8 m elevation for the biomass determinations (August 19 76 to (Vide Table 14) January 1977). Disregarding the anomalous readingsvfor August, which may be largely attributed to sampling error, the other values are similar to those obtained during the regular sampling sessions (Table 14). The changes in mean rhizome diameter are difficult to interpret because of the relatively short period in which measurements were taken. During excavation the rhizomes were often cut with the shovel 74 Table 15. Leaf and rhizome measurements for samples collected at 0.8 meters (in relation to Chart Datum), August 1976 to January 1977. Number of observations in brackets Aug. 76 Oct. 76 Nov. 76 Jan. 77 Leaf Length (cm) Mean 30 .80 (87)- 55 .48 (27) 48 .74 (22) 26. 89 (43) SE 1 .08 4 .76 4 .39 1. 43 Leaf Width (cm) Mean 0 .45 (87) 0 .54 (27) 0 .56 (22) 0. 47 (43) SE 0 .01 0 .02 0 .03 0. 01 Rhizome Mean 0 .37 (87) . 0 .41 (92) 0 .47 (61) 0. 40 (96) Diameter (cm) SE 0 .02 0 .01 0 .01 0. 01 blade. As diameters were measured on individual rhizome segments, each rhizome may have been represented several times in each sample. 4.7. Discussion The influence of factors associated with tidal elevation on eelgrass leaf dimensions, vegetative and repro ductive turion densities and standing stocks have been investigated in several other Pacific Coast eelgrass studies (see section 1.2.). Leaf measurements taken during this study indicate that the eelgrass of southern Roberts Bank corresponds to the short, narrow-leafed form (Z. marina var. typiea) of Scagel (1961). The larger form Z. marina var. latifolia was not encountered during the study. Leaf dimen sions of Roberts Bank eelgrass are similar to those of Puget Sound eelgrass (Phillips 19 72). The relationships of increased leaf length with greater depth described for other Pacific Coast eelgrass populations (Phillips 1972, Keller and Harris 1966) and other seagrasses (Strawn 1961) is further supported by this study. On Roberts Bank, turion densities were highest at the three middle elevations studied, intermediate near the upper limit of eelgrass growth and the lowest near the lower limit of eelgrass distribution. Keller and Harris (1966) found the same relationship of depth and turion density in northern California. In Puget Sound, Washington Phillips (19 72) found that intertidal turion density was five times as great as subtidal turion density in the clear waters i surrounding Bush Point and only twice as great in the turbid waters off Alki Point. Both Puget Sound study sites also exhibited a decrease in turion density with increasing depth. Eelgrass density on Roberts Bank is low compared to other Pacific Coast eelgrass populations (Phillips 1972, Keller 1963, Stout 1976) and a lack of comparable habitat information (e.g. water clarity) from these other areas limits speculation as to the reasons for these regional differences in population characteristics. , The findings of this study reveal that the mean leaf standing crops of the highest and lowest elevations were significantly lower than the mean leaf standing crops of the three middle elevations, which, in turn, were not significantly different from each other. This relationship of reduced i standing crop near the upper and lower limits of growth is similar to that reported by Keller and Harris (1966) in California. The standing crop values of eelgrass on Roberts Bank closely resemble the values obtained by Phillips (1972) at his Alki Point, Washington study site. The standing crops of eelgrass at Alki Point, where the water was turbid, were much lower than at his Bush Point study site, where the water was clearer. Similarly, total biomass at Alki Point was much lower than at Bush Point. Both standing crop and biomass appear to be strongly influenced by water clarity. Sampling difficulties did not allow me to collect information on subtidal biomass. Intertidal biomass of eelgrass on southern Roberts Bank is comparable to the biomass of one of the intertidal stations at Alki Point, Washington (Phillips 1972). Seasonal changes in vegetative and reproductive turion densities, leaf standing crop, biomass and, to a limited extent, leaf measurements have been studied in Puget Sound, Washington by Phillips (1972). The information collected during this study indicates that southern Roberts Bank eelgrass undergoes seasonal cycles similar to Puget Sound eelgrass. For both locations, leaf standing crop and turion density reach minimum values in January and maximum values from May to July. However, Phillips did not record the great losses in leaf standing crop and turion densities in the late summer which were observed in this study. Previous studies on eelgrass productivity and leaf dynamics have not considered the loss of whole turions as being a significant factor in the determination of net production.and for this reason may have grossly underestimated actual net production. Phillips did not report seasonal changes in mean leaf dimensions but did find that reproductive turions first appeared in April in Puget Sound. On southern Roberts Bank, reproductive eelgrass turions were first observed in mid-May and had disappeared by mid-August. The reasons for the shortened reproductive season observed during this study were not investigated; however, Backman and Barilotti (1976) found that flowering is affected by reduced irradiance. The turbid estuarine waters of Roberts Bank reduce the amount of light available to eelgrass and a similar inhibition 78 in flowering may be the result of reduced irradiance in this area. During the study, two problem areas arose which warrant further comment in regard to future investigations of seagrasses. One of the criteria used in the selection of the study site was the apparent homogeneity of the eel grass bed. No areas of bare substrate or sparse eelgrass growth were observed at the study site; however, the data collected indicate that considerable patchiness existed within the eelgrass meadow. Highly significant differences between locations within study elevations and sampling sessions were found for both turion density (Table 6) and leaf standing crop (Table 5). The patchy distribution of eelgrass plants within an eelgrass meadow should be incorpor ated into sampling schemes of future investigations. The problems encountered in trying to assess total plant biomass originate in the difficulties of sampling the root and rhizome components of eelgrass. Consistent results were not obtained for root to rhizome to shoot ratios or for the organic dry weight determinations of these components during the study, even after laborious hand sorting and cleaning of the roots and rhizomes. A much greater degree of sophistication in approach and technique will be required to obtain consistent and useful results. 79 5. SUMMARY AND CONCLUSIONS The results of the study have been discussed in each section. The purpose of this portion of the study is to synthesize the previous discussions and findings in view of the stated objectives of the study. The discussion of eelgrass habitat factors on southern Roberts Bank showed that the restricted depth range encountered there was the result of desiccation and reduced light. In addition, the discussion of turion densities, leaf standing crops and leaf dimensions showed that signifi cant differences existed for some of these parameters at the different study elevations. How do the environmental factors of the study site relate to the differences in morphological, biomass and population^characteristics of eelgrass at the study site? What are the adaptive strategies which eelgrass has evolved to deal with the depth dependent factors controlling its upper and lower distribu tional limits? The information presented in this study indicates that the eelgrass of southern Roberts Bank can be grouped, on the basis of leaf standing crop, turion density and leaf measurements, into three distinct categories which correspond to three tidal zones. Near the upper limit of eelgrass growth, comparatively low standing crops and intermediate turion densities are observed. Mean leaf length is less than at lower elevations, as is organic dry weight per turion. In other areas, the upward extension of eelgrass depends greatly 80 on the degree of'desiccation" (den Hartog 1970); reduced blade length appears to be the adaptive mechanism employed by eelgrass in response to increase desiccation on Roberts .Bank. The three middle elevations studied exhibited high turion densities and large leaf standing crops. Mean leaf length and mean organic dry weight per turion were greater than at the highest elevation. It appears that optimal conditions for eelgrass growth and development are found at the intermediate portions of the depth range of eelgrass. The lowest elevation (-1.2 m) had the lowest mean turion density of all and yet maintained an intermediate leaf standing crop. Leaf length and organic dry weight per turion were the same as those of the middle elevations. Near the lower distributional limit, eelgrass responds to decreased light intensity by reducing turion density. Where light is limiting self-shading may become an important consideration and a mechanism which will reduce turion density, and thus shading will be advantageous to the plant. The major conclusions of the study are: 1. The salinity, temperature and water motion conditions of southern Roberts Bank are close to the world-wide optima for eelgrass growth. 2. The restricted depth distribution of eelgrass on southern Roberts Bank is due to the light environment and substrate characteristics of the area., 3. Reduced light availability in the turbid estuarine waters of southern Roberts Bank is responsible for the elevated 81 lower distributional limit of eelgrass found there. 4. The sandy nature of the sediments of the study area controls the upper distributional limit of eelgrass on southern Roberts Bank. 5. Sediments within an eelgrass bed experience pronounced seasonal changes in surface levels. 6. Fine sediment fractions and particulate organic matter are concentrated near the edges of eelgrass meadows. 7. Eelgrass undergoes pronounced seasonal changes in leaf 1 standing crop and turion density; a large decline in both takes place in late summer. 8. Flowering of eelgrass on southern Roberts Bank occurs from mid-May to mid-August; this relatively short reproductive season observed may be the result of reduced light availability. 9. Leaf standing crops are lower near the upper and lower limits of eelgrass beds. Leaf standing crop is greatest at intermediate elevations. 10. Turion density is highest at intermediate elevations, lower near the upper edge of the eelgrass bed and lowest near the subtidal distributional limit of eelgrass growth. 11. Organic dry weight per turion near the upper edge of . eelgrass growth is approximately one-half of the value of lower elevation turions. 12. During the summer the mean leaf length near the upper edge of the eelgrass bed is approximately one-half of the mean length of leaves from lower elevations; in winter mean leaf length is the same for all elevations. 13. The ratio of above substrate to below substrate standing crops is 2:1; during winter the ratio is 1:1. 14. Reduced leaf length appears to be a response to desiccation in eelgrass. 15. Reduced turion density appears to be a response to reduced light availability in eelgrass. 83 GLOSSARY 5 84 Biomass. The weight of all parts of all the plants on a unit area at a given time. Carbonate carbon. Carbonate carbon was used as an indirect measure of benthic bivalve populations in this study. The source of carbonate in marine sediments is generally shell fragments. Chart Datum (CD). In Canada, Chart Datum represents the plane of lowest normal tides. In the text positive and negative elevations refer to eleva tions above and below the specified reference plane (MLLW or CD). Dry weight. The weight of plant material after heating in z an oven at 105OC to constant weight. Fines. For the purpose of this study the sediments which passed through the finest (0.1 mm) sieve available constituted the fine fraction. Fresh weight. The true weight of the living plant. Organic carbon. The organic content of a sediment reflects the amount of particulate plant and animal residues present and thus provides a rough estimate of the food available for filter feeding infauna for the purposes of this study. Organic dry weight. The loss in weight of plant matter after ignition at 550°C. Also known as ash-free dry weight. Prostrate. Horizontal, trailing along the ground. Quadrat. A square or rectangular area used to quantitatively sample vegetation. A 0.25 m2 (0.5 x 0.5 m) quadrat was used in this study. Reproductive turion. An erect stem bearing inflorescences. Rhizome. Horizontal, elongated, subterranean stem. Secchi disc. A round white disc which is lowered into the water column to provide an estimate of the trans mission of visible light in water and hence, water clarity. Standing crop. The weight of plant material that can be sampled or harvested by normal methods, at any one time, from a given area. Does not necessarily include all parts of plants or all plants. 85 Sympodial Branching. Occurs when the terminal bud loses its capacity for active growth and all subsequent growth occurs at the auxiliary shoots. Total turion density. Total number of turions (vegetative and reproductive) per unit area. Turion. A cluster of foliage leaves arising from a vegetative axis. Common usage does not adhere to the correct botanical definition which describes a turion as a winter bud on some water plants that becomes detached, overwinters, and under favorable conditions develops a new plant. Vegetative turion. A non-reproductive turion (i.e., not bearing inflorescences). Wet weight. Experimental value obtained after removing adherent water from plant material. BIBLIOGRAPHY 87 Backman, T. W. and D. C. Barilotti. 19 76. Irradiance reduction: effects on standing crops of the eel grass Zostera marina in a coastal lagoon. Mar. Biol. 34: 33-40. Black, C. A. et al.' (eds.). 1965. Methods of soil analysis. Am. Soc. Agron., Monogr. No. 9. 1,572 pp. Bordeau, P. F. 1953. A test of random versus systematic ecological sampling. Ecology 34(3): 499-512. Burgess, T. E. 19 70. Foods and habitat of four Anatinids wintering on the Fraser Delta tidal marshes. M.Sc. Thesis, Dept. of Zoology, Univ. of British Columbia. 124 pp. Burkholder, P. R. and T. E. Doheny. 1968. The biology of eelgrass, with special reference to Hempstead and South Oyster bays, Nassau County, Long Island, New York. Contr. No. 1227, Lamont Geol. Observatory, Palisades, N. Y. 120 pp. Canadian Hydrological Service, Fisheries and Marine Service, Environment Canada, Ottawa. 19 76 tide and current tables, Vol. 5, Juan de Fuca and Georgia Straits, British Columbia. Canadian Hydrological Service, Fisheries and Marine Service, Environment Canada, Victoria, British Columbia. 19 76 tidal elevations for the Tsawwassen Tidal Station. Unpublished data. Chapman, C. F. (ed.). 1960. Piloting, seamanship and small boat handling. Motor Boating, 572 Madison Ave., New York. 504 pp. Conover, J. T. 1958. Seasonal growth of benthic marine plants as related to environmental factors in an estuary. Publ. Inst. Mar. Sci. Texas 5: 97-147. Dorcey, A. H. J. (ed.). 1976. The uncertain future of the lower Fraser. Univ. of British Columbia Press, Vancouver, B.C. 202 pp. Forbes, R. D. 1972a. A floral description of the Fraser River estuary and Boundary and Mud bays. British Columbia Fish and Wildlife Br., Dept. of Recreation and Conservation. 9 4 pp. Forbes, R. D. 1972b. Additional catalogue to "A floral description of the Fraser River estuary, and Boundary and Mud bays, B.C." British Columbia Fish and Wildlife Br. Report. 20 pp. 88 Forbes, R. C. 1972c. A note on eelgrass (Zostera spp.), an addendum to "A floral description of the Fraser River estuary and Boundary and Mud bays, B.C." British Columbia Fish and Wildlife Br. Report. 2 pp. Harris, R. D. and E. W. Taylor. 1973. Human impact on estuarine habitat. Can. Wildl. Serv. Mimeo. Revision. 16 pp. Harrison, P. G. and K. H. Mann. 19 75. Chemical changes dur ing the seasonal cycle of growth and decay in eelgrass (Zostera marina) on the Atlantic coast of Canada. J. Fish. Res. Board Can. 32: 615-621. den Hartog, C. 19 70. The seagrasses of the world. North-Holland Publishing Co., Amsterdam. 275 pp. Hillaby, F. B. and D. T. Barrett. 1976. Vegetation communities of a Fraser River salt marsh. Tech. Report Series No. PAC/T-76-14. Habitat Protection Directorate, Fisheries and Marine Service, Environment Canada. 19 pp. Hoos, L. M. and G. A Packman. 1974. The Fraser River estuary. Status of environmental knowledge to 19 74. Report of the Estuary Working Group, Dept. of Environment, Regional Board, Pacific Region. Special Estuary Series No. 1. 518 pp. Keller, M. 1963. Growth and distribution of eelgrass (Zostera marina) in Humboldt Bay, California. M. Sc. Thesis, Humboldt State College. 53 pp. Keller, M. and S. W. Harris. 19 66. The growth of eelgrass in relation to tidal depth. J. Wildl. Mgmt. 30(2): 280-285. Kellerhals, D. and J. W. Murray. 1969. Tidal flats at Boundary Bay, Fraser River Delta, British Columbia. Bull. Can. Petrol. Geol. 17(1): 67-91. McLaren, K. A. 19 72. A vegetation study of the islands and associated marshes in the South Arm of the Fraser River, B.C., from the Deas Island Tunnel to Westham Island foreshore. Fish and Wildlife Br., British Columbia Dept. of Recreation and Conserva tion. 54 pp. McRoy, C. P. 1969. Eelgrass under Arctic winter ice. Nature 224: 818-819. McRoy, C. P. 1972. On the biology of eelgrass in Alaska. Ph.D. Thesis, Univ. of Alaska. 156 pp. 89 Mathews, W. H. and F. P. Shepard. 1962. Sedimentation of the Fraser River Delta, British Columbia. Bull. Amer. Assoc. Petrol. Geol. 46(3): 1416-1438. National Harbours Board, Port of Vancouver. 19 77. Environmental impact assessment of Roberts Bank port expansion. Vol. 4, App. B. The existing biological environment. Prepared by Beak Consultants Ltd., Vancouver, British Columbia. Orth, R. J. 1973. Benthic infauna of eelgrass, Zostera marina, beds. Chesa. Sci. 14(4): 258-269. Outram, D. N. 1957. Guide to marine vegetation encountered during herring spawn surveys in southern B.C. Fisheries Research Board of Canada, Pacific Biol. Station, Nanaimo, British Columbia. Circular No. 44 (Dec. 1957). Phillips, R. C. 1972. Ecological life history of Zostera marina L. (eelgrass) in Puget Sound, Washington. Ph.D. Thesis, Univ. of Washington. 154 pp. Phillips, R. C. 19 74. Transplantation of seagrasses, with special emphasis on eelgrass, Zostera marina L. Aquaculture 4(2): 161-176. Phillips, R. C. 1975. Seagrass: food in the inshore coast. Pacific Search, July/Aug. 1975. pp. 3-4. Ranwell, D. S.; D. W. Wyer; L. A. Boorman; J. M. Pizzey; and R. J. Walters. 1974. Zostera transplants in Norfolk and Suffolk, Great Britian. Aquaculture -4(2): 185-198. Scagel, R. F. 1961. Marine plant resources of British Columbia. Fish. Res. Board. Can. Bull. No. 127, Ottawa, 1961. 39 pp. Setchell, W. A. 1920. Geographical distribution of the marine spermatophytes. Bull. Torrey Bot. Club 47 (12) : 563-579 . Setchell, W. A. 1927. Zostera marina latifolia: ecad or ecotype? Bull. Torrey Bot. Club 54(1): 1-6. Setchell, W. A. 1929. Morphological and phenological notes on Zostera marina L. Univ. Calif. Publ. Bot. 14: 389-452. 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Prentice-Hall, Inc., New Jersey. 620 pp. 91 APPENDICES 92 APPENDIX 1: SECCHI DEPTH AND SURFACE AND SUBSURFACE (1.5 m) SALINITY AND TEMPERATURE MEASUREMENTS MARCH 1976 TO JANUARY 1977 Date Secchi Depth (meters) Salinity (parts per Tenperature (°C) thousand) Surface 1.5 m Surface 1.5 m 31.3.76 5.25 2.4.76 6.75 3.4.76 5.40 5.4.76 5.25 26.0 10.5 28.5 8.0 6.4.76 3.25 19.4.76 3.30 27.2 9.0 27.6 9.0 3.5.76 1.80 14.5.76 1.60 28.0 11.0 28.0 10.5 31.5.76 2.30 26.3 11.6 27.0 10.8 13.6.76 2.00 24.0 11.8 24.3 11.9 28.6.76 2.30 22.7 15.5 23.7 14.3 10.7.76 2.30 22.5 15.0 23.5 14.0 28.7.76 2.90 22.8 17.5 24.0 16.0 10.8.76 2.60 19.9 17.0 21.2 15.0 24.8.76 1.80 13.8 16.0 18.2 14.8 4.10.76 1.60 20.1 11.2 26.2 10.8 20.10.76 2.90 22.9 10.3 23.8 10.4 23.11.76 4.10 21.4 8.0 30.0 7.8 22.12.76 4.10 22.5 8.2 27.6 8.6 18.1.77 5.40 26.5 8.0 26.0 8.0 APPENDIX 2: DIURNAL SURFACE AND SUBSURFACE (1.5 m) SALINITY (PARTS PER THOUSAND) MEASUREMENTS. MAY 2, JULY 28 AND OCTOBER 4, 1976. JANUARY 18, 1977. Time (PDST) May 2 July 28 October 4 January 18 Surface 1.5 m Surface 1.5 m Surface 1.5 m . Surface 1.5 r 0000 26.3 26.3 21.8 23.2 15.7 19.3 01.00 02.00 26.3 26.3 15.5 22.0 03.00 04.00 18.0 19.2 05.00 24.2 24.3 06.00 24.2 24.2 23.8 25.1 19.5 22.5 07.00 08.00 24.0 25.0 22.9 26.0 24.0 25.8 09.00 10.00 23.7 24.2 20.8 25.2 20.1 26.2 11.00 27.2 27.2 12.00 24.0 24.7 24.0 24.7 20.4 22.5 13.00 26.5 26.0 14.00 24.7 25.0 22.8 24.0 21.2 22.3 15.00 27.2 27.2 16.00 23.6 23.5 20.8 22.2 21.8 24.7 17.00 27.0 27.3 18.00 23.5 24.6 22.2 23.8 21.75 23.8 19.00 27.2 27.5 20.00 24.0 26.0 24.2 27.2 20.5 21.9 21.00 27.2 27.3 22.00 24.0 21.5 23.0 21.3 20.4 23.00 26.8 26.8 24.00 24.0 23.8 26.5 21.0 20.2 APPENDIX 3: DIURNAL AIR, SURFACE AND SUBSURFACE -(1.5 m) TEMPERATURE (°C) MEASUREMENTS MAY 2, JULY 28 AND OCTOBER 4, 1976. JANUARY 18, 1977. Time May 2 July 28 October 4 January 18 Surface 1.5 m Surface 1.5 m Air Surface 1.5 m Air Surface • 1.5 m Air oooo 12.5 12.5 14.5 13.8 16.3 10.4 10.8 9.5 01.00 7.5 7.5 14.0 02.00 12.5 12.5 10.0 11.5 10.4 03.00 04.00 10.0 10.8 9.0 05.00 8.0 8.0 12.0 06.00 11.0 11.0 13.4 12.8 14.2 10.1 11.0 9.2 07.00 08.00 11.0 11.5 14.75 12.25 20.5 10.8 11.0 9.8 09.00 10.00 11.33 11.5 17.0 14.0 26.25 11.2 10.8 10.8 11.00 7.6 7.6 7.5 12.00 11.5 11.75 16.0 14.0 23.0 11.8 .10.3 14.1 13.00 8.0 8.0 9.6 14.00 11.6 12.0 17.5 16.0 20.0 12.6 11.8 14.5 15.00 8.2 8.1 12.9 16.00 11.75 12.0 15.3 14.8 18.2 12.5 11.2 14.8 17.00 8.2 8.0 10.6 18.00 11.5 11.25 14.8 13.8 17.2 12.1 11.5 12.5 19.00 8.0 7.9 8.2 20.00 11.0 10.5 14.8 12.6 15.8 12.5 12.1 11.8 21.00 7.8 7.8 8.2 22.00 11.5 15.0 14.8 16.0 11.8 12.2 12.9 23.00 7.8 7.8 8.0 24.00 12.0 15.0 12.5 15.9 11.5 11.8 12.9 95 APPENDIX 4: DIURNAL SECCHI DEPTH AND PHOTOSYNTHETICALLY ACTIVE RADIATION (PAR) MEASUREMENTS MAY 2, JULY 23 AND OCTOBER 4, 1976. JANUARY 18, 1977. Time (PDST) Secchi Depth (meters) PAR Quanta (microeinsteins per square meter per second) 10 cm Above Surface 1.5 m Surface May 2 06.00 2.1 30 7 08.00 2.1 49 12 10.00 2.2 180 42 12.00 2.2 150 23.5 14.00 2.2 195 52.5 16.00 1.0 350 78 18.00 1.8 100 35 20.00 2.2 12 3 July 28 06.00 3.1 170 45 19 08.00 3.9 1200 500 200 10.00 3.5 1900 1100 550 12.00 2.8 2200 1450 650 14.00 2.9 2500 1600 800 16.00 1.5 310 170 53 18.00 2.1 250 150 80 20.00 2.75 150 33 17 October 4 08.00 2.2 114 64 27 10.00 1.6 500 220 44 12.00 1.8 2150 975 325 14.00 2.4 2100 1050 450 16.00 2.4 2000 850 275 18.00 2.5 500 90 29 January 18 11.00 5.7 13.00 5.4 15.00 5.2 17.00 5.2 APPENDIX 5: NET OSCILLATIONS OF SEDIMENT SURFACE LEVELS -MEASUREMENTS AND STATISTICS. JUNE 1976 TO JANUARY 1977 Date 30.6.76 29.7.76 11.8.76 26.8.76 4.10.76 20.10.76 23.11.76 22.12.76 19.1.77 Number of 20 12 14 9 15 19 17 12 12 Observations sMean height (cm) 10.00 9.64 9.36 9.29 9.83 10.10 10.90 11.74 -11.87 of pegs above sediment surface Net change +0.36 +0.64 +0.71 +0.17 -0.10 -0.90 -1.74 -1.87 Standard Deviation 2.04 1.21 0.65 1.38 1.41 1.71 1.76 1.92 Standard Error 0.59 0.32 0.22 0.36 0.32 0.42 0.51 0.55 vo APPENDIX 6: STATISTICS OF STANDING CROP INFORMATION (ORGANIC DRY WEIGHT PER QUADRAT) USED FOR OPTIMUM QUADRAT SIZE DETERMINATION Quadrat Area Number of Quadrats Quadrat Dimensions Mean (g) SD (g) SE (g) Percentage SE CV. 1.0 m2 4 1 m x 1 m 16.69 4.45 2.22 13.33 0.27 0.5 8 0.71 m x 0.71 m 12.21 4.08 1.44 11.82 0.33 0.25 12 0.5 m x 0.5 m 5.53 1.25 0.36 6.52 0.22 0.04 25 0.2 m x 0.2 m 0.81 0.46 0.09 11.22 0.56 0.01 50 0.1 m x 0.1 m 0.20 0.37 0.05 26.98 1.90 APPENDIX 7: ORGANIC DRY WEIGHTS IN GRAMS PER SQUARE METER FOR FIVE ELEVATIONS (CHART DATUM) APRIL 1976 to JANUARY 1977 . 0.8 m 0.3 m -0.2 m -0.7 m -1.2 m Date Mean Date Mean Date Mean Date Mean Date Mean SE SE SE SE SE Apr. 6 9.91 Apr. 6 43.25 Apr. 6 43.37 Apr. 6 34.67 2.27 3.77 3.82 5.08 Apr. 17 18.61 33.0 , Apr. 19 36.78 Apr. 19 33.33 Apr. 19 30.30 3.31 4.41 8.82 4.37 6.80 May 2 16.32 May 3 42.43 May 3 33.60 May 3 37.31 May 3 17.93 2.63 5.43 3.84 1.77 9.82 May 14 22.02 May 14 49.98 May 14 50.29 May 15 53.41 May 15 12.43 4.17 9.13 11.86 8.60 5.19 May 30 13.68 May 31 32.01 May 31. 49.47 May 31 61.81 May 31 38.45 1.90 4.83 9.32 11.44 7.38 June 12 18.67 June 12 57.26 > June 12 38.61 June 13 55.67 June 13 22.35 2.14 10.91 9.14 9.35 6.85 June 27 16.05 July 2 47.97 July 2 46.91 July 2 37.07 July 3 . 12.69 3.05 15.16 5.63 2.17 4.43 July 10 16.30 July 10 47.44 July 10 88.40 July 10 59.38 July 10 38.42 2.43 17.93 23.74 17.05 11.22 July 28 17.72 July 29 41.12 July 29 15.02 July 28 26.12 July 28 8.82 3.58 4.22 7.43 11.15 2.90 Aug. 7 16.16 Aug. 10 41.22 Aug. 10 49.52 Aug. 10 53.23 Aug. 10 31.68 1.40 4.36 4.01 8.09 4.79 Aug. 25 13.03 Aug. 25 20.22 Aug. 26 35.69 Aug. 25 43.44 Aug. 25 18.81 2.14 3.66 6.88 8.77 9.51 Sept. 28 14.19 Oct. 4 11.35 Oct. 4 20.48 Oct. 4 32.23 Oct. 4 17.10 2.07 3.31 3.23 2.90 1.64 Oct. 25 14.21 Oct. 20 16.84 Oct. 20 10.62 Oct. 20 17.46 Oct. 20 12.04 1.74 3.88 5.26 .' 3.41 5.12 Nov. 23 9.57 Nov. 23 11.23 Nov. 23 17.59 Nov. 23 14.97 Nov. 23 16.10 1.80 0.87 3.38 2.99 3.32 Dec. 20 11.93 Dec. 20 14.14 DGC • 22 10.46 DGC • 22 11.65 Dec. 22 3.68 2.46 2.12 1.90 2.29 1.25 Jan. 18 10.46 Jan. 18 12.23 Jan. 19 7.00 Jan. 19 20.52 Jan. 19 11.90 1.51 1.54 1.72 3.24 3.73 APPENDIX 8: ANALYSIS OF VARIANCE SUMMARY TABLE FOR MEAN LEAF STANDING CROP (ORGANIC DRY WEIGHT IN GRAMS PER 0.25 SQUARE METER QUADRAT) Source of Variation SS DF MS Calculated F Critical F Conclusion Total 8,170.13 299 Elevation (A) 1,465.82 4 366.45 16.55** FO.Ol(l),4,70 =' 3.60 Reject HQ Time (B) 2,592.68 14 185.19 8.36** FO.Ol(l),14,70 = 2.34 Reject HQ Location (C) . 1,415.65 56 22.14 3.21** FO.Ol(l),70,140 = 1-60 Reject HQ A x B 1,660.57 75 25.28 l-14ns FO.Ol(l),50,70 = 1-83 Accept HQ Error 1,035.41 150 6.90 VD VD APPENDIX 9: DENSITY IN TURIONS PER SQUARE METER FOR FIVE ELEVATIONS (CHART DATUM) APRIL 1976 TO JANUARY 1977 0.8 m 0.3 m -0. 2 m -0. 7 m -1.2 m Date Mean Date Mean Date Mean Date Mean Date Mean SE SE SE SE SE Apr. 6 43 Apr. 6 89 Apr. 6 86 Apr. 6 119 9.84 3.77 0.86 4.07 Apr. 9 66 Apr. 19 106 Apr. 19 64 1.56 2.47 2.80 May 2 36 May 3 95 May 3 83 May 3 81 May 3 43 .2.05 3.30 2.56 3.09 5.72 May 14 63 May 14 106 May 14 123 May 15 123 May 15 36 3.74 ' 5.39 5.35 2.87 3.49 May 30 53 May 31 71 May 31 105 May 31 134 May 31 77 1.54 3.35 5.94 4.52 3.38 June 12 61 June 12 107 June 13 86 June 13 110 June 13 44 1.85 3.64 2.10 2.26 2.35 June 27 67 July 2 82 July 2 66 July 2 67 July 3 35 2.51 0.96 1.04 1.38 3.40 July 10 66 July 10 70 July 10 133 July 10 93 July 10 55 2.80 4.74 6.05 7.19 3.64 July 28 79 July 29 86 July 29 29 July 28 49 July 28 27 2.06 3.57 1.44 1.44 2.25 Aug. 7 79 Aug. 10 87 Aug. 10 72 Aug. 10 94 Aug. 10 47 1.30 2.28 0.42 3.28 1.11 Aug. 25 51 Aug. 25 44 Aug. 26 73 Aug. 25 81 Aug. 25 33 2.14 1.78 3.28 3.09 3.68 Sept. 28 53 Oct. 4 39 Oct. 4 44 Oct. 4 62 Oct. 4 40 2.07 2.56 2.49 1.19 2.28 Oct. 25 51 Oct. 20 38 Oct. 26 27 Oct. 20 43 Oct. 20 33 1.71 1.85 3.30 2.14 2.75 Nov. 23 43 Nov. 23 37 Nov. 23 46 Nov. 23 48 Nov. 23 35 1.68 1.03 1.66 1.36 0.86 Dec. 20 42 Dec. 20 43 Dec. 22 34 Doc• 22 _ 42 Dec. 22 14 1.58 1.75 0.65 1.85 1.19 Jan. 18 42 Jan. 18 58 Jan. 19 25 Jan. 19 58 Jan. 19 37 1.48 3.86 1.11 1.76 0.86 APPENDIX 10: ANALYSIS OF VARIANCE SUMMARY TABLE FOR MEAN TURION DENSITY (TURIONS PER 0.25 SQUARE METER QUADRAT) Source of Variation SS DF MS Calculated F Critical F Conclusion Total 21,287.43 279 Elevation (A) 3,128.41 4 782.10 13.52** F0.01(l),4,70 = 3-60 Reject HQ Time (B) 6,462.38 13 497.11 8.59** F0.01(l),13,70 = 2.40 Reject HQ Location (C) 4,050.25 70 57.86 2.345** F0.01(l),70,140 =1-60 Reject HQ A x B 4,191.89 52 80.61 1.393ns F0.01(l) ,50,70 = L83 Accept HQ Error 3,454.50 140 24.67 102 APPENDIX 11 : REPrClDUCITVE TURION DENSITY (PER SQUARE METER) FOR FIVE ELEVATIONS. JUNE TO AUGUST, 1976. Elevation (m) Date 0.8 0.3 -0.2 -0.7 -1.2 May 14, 15 Reproductive 0 3 0 0 0 Total 71 106 123 123 36 - % Reproductive 0 2.83 0 0 0 May 30,31 Reproductive 1 0 2 1 0 Total 51 71 105 134 77 % Reproductive 1.96 0 1.90 0.75 0 June 12, 13 Reproductive 5 3 0 1 0 Total 91 107 86 110 44 % Reproductive 5.49 2.80 0 0.91 0 July 2, 3 Reproductive 0 2 4 0 3 Total 100 82 66 67 35 % Reproductive 0 2.44 6.06 0 8.57 July 10 Reproductive 0 2 3 0 0 Total 70 70 133 93 55 % Reproductive 0 2.86 2.26 0 0 July ,28, 29 Reproductive 0 2 0 2 0 Total 69 86 29 49 27 % Reproductive 0 2.33 0 4.08 0 August 7 Reproductive 0 0 N 0 0 0 Total 79 87 72 94 47 % Reproductive 0 0 0 0 0 APPENDIX 12: ANALYSIS OF VARIANCE SUMMARY FOR SLOPES OF THE REGRESSIONS OF TURION NUMBERS ON ORGANIC DRY WEIGHT FOR FIVE ELEVATIONS (CHART DATUM) Elevation Number of Source of (meters) Observations Variation SS DF MS Calculated F F0.01(l),l,n-2 Conclusion 0.8 88 Total 224.74 87 Linear Regression Residual 127.76 96.98 1 86 127.76 1.13 113.30 6.96 Reject BQ-.B = 0 0.3 64 Total 1643.43 63 Linear Regression Residual 1056.68 586.75 1 62 1056.68 9.46 111.66 7.08 Reject HQ:P = 0 -0.2 62 Total 2481.98 61 Linear Regression Residual 1992.71 489.28 1 60 1992.71 8.15 244.36 7.08 Reject HQ: P = 0 -0.7 ~ 64 Total 1636.33 63 Linear Regression Residual 1111.82 524.51 1 62 1111.82 8.46 131.42 7.08 Reject HQ:£ = 0 -1.2 60 Total 841.38 59 Linear Regression Residual . 658.55 182.83 1 58 658.55 3.15 208.92 7.08 Reject EQ-.P = 0 I—1 o co 104 APPENDIX 13.: MEAN BIOMASS OF INTERTIDAL (0.8 m) EELGRASS IN GRAMS PER SQUARE METER (ORGANIC DRY WEIGHT) . APRIL 1976 TO JANUARY 1977. Leaves Roots Rhizomes Date Mean SE Mean SE Mean SE 16.4.76 28.80 0.25 4.36 0.20 13.37 0.26 15.5.76 16.98 1.18 1.80 0.15 4.58 0.34 12.6.76 27.45 1.64 3.70 1.18 9.69 1.88 10.7.76 25.33 2.62 3.09 0.24 10.91 1.84 7.8.76 7.90 1.84 1.00 0.24 9.85 1.85 24.8.76 10.68 0.68 1.76 0.29 9.01 2.29 25.10.76 10.64 3.77 1.05 0.47 7.27 2.93 23.11.76 10.10 1.82 0.97 0.21 10.29 1.76 17.1.77 9.29 1.58 1.30 0.23 6.95 1.21 

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