Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Factors controlling the winter dominance of nanoflagellates in Saanich Inlet, British Columbia Watanabe, Leslie N. 1978

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Notice for Google Chrome users:
If you are having trouble viewing or searching the PDF with Google Chrome, please download it here instead.

Item Metadata


831-UBC_1978_A6_7 W38.pdf [ 4.86MB ]
JSON: 831-1.0094493.json
JSON-LD: 831-1.0094493-ld.json
RDF/XML (Pretty): 831-1.0094493-rdf.xml
RDF/JSON: 831-1.0094493-rdf.json
Turtle: 831-1.0094493-turtle.txt
N-Triples: 831-1.0094493-rdf-ntriples.txt
Original Record: 831-1.0094493-source.json
Full Text

Full Text

FACTORS CONTROLLING THE WINTER DOMINANCE OF NANOFLAGELLATES IN SAANICH INLET, BRITISH COLUMBIA by LESLIE N. WATANABE B.Sc., University of British Columbia, 1974 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Zoology We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA March, 1978 © Leslie N. Watanabe, 19 78 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h C o lumbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s • u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f ZOOLOGY The U n i v e r s i t y o f B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 D a t e MARCH 8. 1978 i i ABSTRACT The alternation between a summer diatom population and a winter nanoflagellate population in Saanich Inlet is documented. Factors controlling the winter dominance by nanoflagellates, as well as the spring and f a l l transitions, are considered. Field monitoring of temperature, sali n i t y , light, nitrate and si l i c a t e concentrations, and zooplankton size and abundance was conducted for the year November, 1975 to October, 1976 and compared with the pattern of phytoplankton succession during that time. This was supplemented with laboratory experimentation on the effects of light, temperature and photoperiod, as well as metabolic excretions and hydrocarbon pollution, on the growth of diatoms and nanoflagellates in unialgal culture and natural populations. Factors which were considered to be non-contributory to the winter dominance by flagellates included nutrient concentrations, grazing, excretions, and hydrocarbon pollution. Factors of some importance included temperature, photoperiod and water st a b i l i t y . The single factor of major importance was light intensity. Diatoms were found to be incapable of growth at winter light levels while flagellates were able to do so, due to their ability to maintain themselves high in the water column, and possibly due to a capacity for heterotrophy. A qualitative model i s presented which relates the succession of phytoplankton in Saanich Inlet to temporal changes in various environmental parameters. i i i TABLE OF CONTENTS Page ABSTRACT i i LIST OF TABLES v LIST OF FIGURES ; v i ACKNOWLEDGEMENTS ix INTRODUCTION 1 DESCRIPTION OF THE STUDY AREA 4 MATERIALS AND METHODS 6 A. Field Measurements 6 B. Experimental ..-7 1. Metabolite experiment .8 2. Hydrocarbon experiment 11 3. Light and temperature experiments 12 a. Pure cultu-res 12 b. Natural populations 13 RESULTS 1 5 A. Field Observations. ; 15 1. Temperature and salinity 15 2. Light i 8 3. Nutrients 18 4. Phytoplankton 23 5. Zooplankton 26 B. Experimental 26 i v 1. Metabolite experiment 26 2. Hydrocarbon experiment 30 3. Light and temperature experiments 35 a. Pure cultures 35 b. Natural populations 45 DISCUSSION 57 A. Non-Contributing Factors 57 1. Nutrient concentrations 58 2. Grazing 59 3. Chemical interactions 60 4. Hydrocarbon pollution 64 B. Factors Contributing to Winter Flagellate Dominance 64 1. Light 64 2. Photoperiod....... ....74 3. Temperature 75 4. Water sta b i l i t y 76 C. Summary of Phy toplankton Dynamics 79 1. Winter 80 2. Spring 80 3. Summer 81 4. F a l l 85 D. Problems 86 E. Proposed Research 87 CONCLUSION. 88 BIBLIOGRAPHY. ... 89 APPENDIX 103 V LIST OF TABLES Table Page I Summary of light and temperature experiments using natural phytoplankton populations 14 II Copepod size classification (based on body lengths obtained from Fulton, 1972) ..27 III Species composition of a natural phytoplankton population before and after 8 days of incubation with varying concentrations of No. 2 Fuel. O i l 36 IV Summary of literature on light constants of various species of algae 66 V Light constants for 4 diatom species arrd co r re spo i - ' depths in Saanich Inlet during the summer and winL-v i LIST OF FIGURES Figure Page 1 Location of the study area..... 5 2 Set-up for the metabolite experiment 10 3 Temperatures at 0, 5, 10, and 20 m at station "A," November, 1975 - October, 1976 16 4 Salinity structure at station "A," November, 1975 -October, 1976 17 5 Total daily photosynthetically active radiation (PAR) , 400-700 nm, measured at.the land station, November, 1975 - October, 1976 19 6 Depth profiles of light intensity (yE m - 2 sec - 1) at station "A," November, 1975 - October, 1976 20 7 Depth profiles of nitrate concentration (yg-at N l - 1 ) at station "A," November, 1975 - October, 1976 21 8 Depth profiles of s i l i c a t e concentration (yg-at Si l " 1 ) at station "A," November, 1975 - October, 1976 22 9 Biomass of major phytoplankton groups at station "A," November, 1975 - October, 1976 24 10 Species succession in phytoplankton at station "A," March - December, 1976 25 11 Abundance of three size classes of copepods sampled from 25-0 m at station "A," December, 1975 -December, 1976 28 v i i Figure Page 12 Growth of Chrysochromulina kappa and Thalassiosiva novdenskioldii i n the metabolite-experiment 29 13 Two types of effects of hydrocarbons on the growth of phytoplankton. A. The response of Katodinivm rotundatum to No. 2 Fuel O i l : the length of the lag phase of growth increased with increasing hydrocarbon concentration. B. The response of Thalassiosiva sp. 1 to 1-methylnaphthalene: growth rate decreased with increasing hydrocarbon concentration 31 14 The effects of No. 2 Fuel O i l and 1-methylnaphthalene on the growth rate and growth lag in 7 species of phytoplankton and i n a natural population 33 15 Growth rate versus light intensity curves for phytoplankton i n culture. A. 12°C. B. 6°C 37 16 The effect of temperature on growth versus light intensity curves of algae in culture. A. Skeletonema oostatian. B. Chrysoohromulina kappa 39 17 Photosynthetic rate versus light intensity curves for phytoplankton in culture. A. Cells not adapted to light conditions, previously grown at 2.7-5.2 klux (39-74 pE m~2 sec" 1). B. Cells grown one week at individual light intensities •. 40 18 Effect of light intensity on c e l l volume.. 43 19 Effect of light intensity on chlorophyll content 44 20 Effect of light.intensity:on.the composition of a natural phytoplankton population: cells ml"-1 after 4*44-days' growth at 12°C and continuous illumination at various light intensities .47 Effect of light intensity on the ratio (by c e l l numbers) of flagellates to diatoms after 4-14 days' growth at 12°C and continuous.illumination at various intensities...48 Effect of varying the i n i t i a l composition of a natural phytoplankton population on i t s response to light intensity. Both populations were grown 5-8 days at 12°C with a 12-12 photoperiod. 50 Effect of photoperiod on the response of natural populations of phytoplankton to light intensity. A. Ratio of flagellates to diatoms after 4-14 days' growth at 12°C. B. Growth rates under continuous illumination or 12-12....... 51 Effect of temperature on the response of natural populations of phytoplankton to light intensity. A. Growth rates. B. Flagellate-to-diatom ratios 54 Schematic representation of the relative light tolerances of diatoms and flagellates. A. Growth rate versus light' intensity curves for a hypothetical phytoplankton community of 3 species of diatoms and 1 flagellate. B. Generalized curves which include a l l species of diatoms and flagellates..69 Nitrate concentration and the changes in biomass of centric diatoms and flagellates in the top 20 m during the summer of 1976 83 Vertical distributions.of centric diatoms and flagellates on days of maximum and minimum diatom numbers .84 i x ACKNOWLEDGEMENTS I would l i k e to thank Dr. T.R. Parsons, of the Univ e r s i t y of B r i t i s h Columbia, I n s t i t u t e of Oceanography, f o r introducing me to the f i e l d of oceanography, for his continued guidance and encouragement throughout my studies-, and, not l e a s t , f or providing the laboratory f a c i l i t i e s i n which to conduct my research. Thanks to Dr. "Mac" Takahashi, resident s c i e n t i s t at the CEPEX i n s t a l l a t i o n , P a t r i c i a Bay, for a s s i s t i n g me i n many of my endeavours, and for providing many stimulating ideas i n the early stages of my research. I greatly appreciate the work of the CEPEX s t a f f and s c i e n t i s t s who c o l l e c t e d most of the f i e l d data: Dr. W.H. Thomas and Mr. D.L. Seibert, of Scripps I n s t i t u t e , La J o l l a , who provided the phytoplankton f l o r i s t i c s data, Peter A. K o e l l e r , who provided the zooplankton counts, Janet Barwell-Clarke, Merelene Austin, and Peter Borgman, who ran the nu t r i e n t analyses, Robin Brown, Peter K o e l l e r , and Craig Wagstaff, who c o l l e c t e d the water samples and performed in situ measurements of l i g h t and temperature. I am g r a t e f u l to Ms. Rosemary Waters, of the University of B r i t i s h Columbia, I n s t i t u t e of Oceanography, for teaching me a l l about nanoflagellates, and f o r providing many of the cultures for my studies. Special thanks to Robin Brown for h i s advice, encouragement, and patience through a l l stages of my work. X I also thank the National Research Council of Canada for t h e i r f i n a n c i a l support. 1 INTRODUCTION It i s recognized that diatoms and nanoflagellates (flagellated phytoplankters less than 20 ym in their greatest diameter!) possess certain inherent physiological differences which allow one group or the other to predominate in a given area. Ryther (1969), for example, described three generalized plankton communities from three different zones of the ocean (oceanic, continental shelf and upwelled), each of which was characterized by a specific type of phytoplankton. The low-nutrient, stable conditions of the open ocean, he predicted, would favour nanoflagellate populations, while the nutrient-rich, turbulent environment of upwelled zones would support macrophytoplankton, including large, chain-forming diatoms and dinoflagellates. A continental shelf type of community would be inter-mediate. On the basis of experiments with diatoms and nanoflagellates Parsons and Takahashi (1973a) similarly predicted that, depending on three major factors—nutrient concentration, st a b i l i t y of the water column, and light intensity—either a diatom or a nanoflagellate community would develop. Other instances may be found in the literature which correlate the relative abundances of diatoms_and nanoflagellates , (sometimes a working definition which I have evolved from that given by Parsons and Takahashi (1973b), citing Dussart (1965). They define "nanoplankton" asas plankton within the size range 2-20 ym. Since phytoflagellates smaller than 2 ym were rarely encountered in my work, I have omitted the lower size limit from my definition. 2 approximated as the ratio of net- and nanoplankton) with specific environ-mental parameters (e.g., Yentsch and Ryther, 1959; Malone, 1971; Eppley, 1972; Durbin et al. , 1975). Any factor in the environment can potentially regulate the ratio of diatoms to nanoflagellates. However i f one were to consider the pro-perties of the two groups some factors would intuitively become more important than others. Clearly the st a b i l i t y of the water column must have some effect. If the water is stable, as is the case d.fc highly st r a t i f i e d environments, the nanoflagellates would benefit by their motility which would enable them to remain within the euphotic zone. In upwelled or otherwise mixed conditions i t is not intuitively obvious which group would be favoured, as cells of both diatoms and nanoflagellates could be main-tained in suspension. The importance of sinking, upwelling and other mixing phenomena has been discussed by Smayda (1970) and Schone (1970). A second factor of intuitive significance is the concentration of s i l i c a t e in the water. Relatively few nanoflagellates (with the obvious exception of the s i l i c o f l a g e l l a t e s , chrysophytess possessing an internal siliceous skeleton) require s i l i c a t e , while diatoms are clearly dependent on i t . Munk and Riley (1952) predicted that when any nutrient at a l l i s reduced to limiting concentrations, surface area-toirvoil!ume.1.relationships permit more efficient uptake by small cells. This prediction, as well as the significance of water s t a b i l i t y , is borne out by the observation that the oceanic environment, which is typically stable and oligotrophic, is dominated by nanoflagellates (Wood and Davis, 1956; Holmes et al. , 1958; Bernard and Lecal, 1960; Wood, 1963a). 3 Several other environmental factors have been considered. Yentsch and Ryther (1959) and Durbin et al. (1975) observed changes in net- to nanoplankton ratios corresponding to temperature variations off New England. Light intensity has been mentioned as one of three factors thought to be significant, by Parsons and Takahashi (1973a). Zooplankton are known to graze selectively with respect to food size (Mullin, 1963; Parsons et at. , 1967; Richman and Rogers, 1969; Hargrave and Geen, 1970) and therefore could conceivably regulate phytoplankton c e l l size. Smayda (1963) stressed the importance of c e l l metabolites as growth stimulators and inhibitors, and their role in succession. In pollution experiments, low levels of hydro-carbons (Lee and Takahashi, 1977; Lee et al. , in press) and copper (Thomas and Seibert, 1977) have been found to favour the growth of nanoflagellates. Some investigators have made the generalization that smaller cells tend to grow in t r i n s i c a l l y more quickly than larger cells (Odum, 1956; Williams, 1964; Saijo and Takesue, 1965), although this observation is subject to question (as w i l l be seen in this study). A complete evaluation of a l l of these factors has not been attempted for any one location. The purpose of the present investigation was to attempt to do this for Saanich Inlet, B.C. This north temperate fjord has an annual cycle of phytoplankton which is broadly characterized by the presence of nanoflagellates in the winter and diatoms throughout much of the remainder of the year, not an unusual pattern for these waters (e.g., Buchanan, 1966). To simplify the problem, the investigation was restricted primarily to the winter population of nanoflagellates. The question became, "Which factors are c r i t i c a l to the winter dominance of nanoflagellates over diatoms in Saanich Inlet?" and in particular, "What changes occur in the f a l l and spring which bring about the shift from diatoms 4 to nanoflagellates and vice versa?" A combination of empirical and experimental approaches was used. A l l pertinent parameters were measured for a one-year cycle and compared with phytoplankton composition. Those which were considered to show some correlation with the diatom-to-nano-flagellate ratio were further investigated by means of controlled experi-ments. Factors such as metabolites and pollution effects were studied in laboratory situations only. Qualitative observations such as these could provide the basis for quantitative modelling and ultimately the abil i t y to manipulate the composition of the phytoplankton in an area such as Saanich Inlet. DESCRIPTION OF THE STUDY AREA Saanich Inlet is a fjord located at the southeast end of Vancouver Island (Fig. 1). It is 24 km long and 7.2 km wide at i t s widest point. There i s a submerged s i l l at the mouth, approximately 75 m deep, behind which the basin deepens to 234 m. Above the s i l l depth the properties of the water are continuous with those in the approaches, but below the s i l l depth the water is isolated, oxygen-deficient, and usually contains hydrogen sulphide. Freshwater runoff into the inlet is negligible, and originates mainly from the approaches. It provides a weak, counterclockwise estuarine circulation above the s i l l depth. The water below the s i l l i s flushed rarely, only when dense water from the approaches is able to cascade over the s i l l into the deep basin. A positive salinity gradient, ranging from 14°/oo to 29°/oo at the surface to 31.2°/oo in the deep basin, exists year-round. The waters 6 of the inlet are thus s t r a t i f i e d at a l l times. A sharp surface pycnocline persists year-round, and is associated chiefly with the thermocline in summer and the halocline in winter. Winds are evidently not sufficient to produce a mixed layer in the inlet. Occasional storms do not result in turbulent mixing, but rather displacement of surface layers, followed by seiche-type oscillations. The hydrography of Saanich Inlet has been described more completely by Herlinveaux (1962, 1968, 1972). MATERIALS AND METHODS A. Field Measurements Observations of temperature, s a l i n i t y , light, s i l i c a t e , nitrate, phytoplankton and zooplankton were made continuously for the year November, 1975 - October, 1976 at station A (Fig. 1). Total photosynthetically active radiation (PAR) was measured continuously at the land station using a quantum scalar irradiance meter (Booth, 1976), totalled daily and expressed as an average for each 24-hour period. Light penetration into the water column was measured weekly at approximately noon using a 4TT quantum meter (Booth, 1976). By combining data on total PAR and penetration i t was possible to producellight profiles which approximated daily averages (probably overestimated due to the use of noon light penetration data). In situ temperature profiles were taken weekly using a thermistor which was incorporated into the quantum meter assembly. 7 Water samples for sal i n i t y , nutrient and phytoplankton analyses were collected using a diaphragm type pump (JABSCO Products ITT Model 34600), at a flow rate of 1-5 gal/min. Samples were either taken from discrete depths or integrated over desired intervals. Salinity was measured using an Autosal salinometer (Guildline Instruments Model 8400). Nitrate and si l i c a t e concentrations were analysed weekly following the methods given by Strickland and Parsons (1972). Water for both analyses was prefiltered through Gelman type A-E glass fibre f i l t e r s . Nitrate was always measured immediately following water sampling; water for s i l i c a t e analysis was frozen i f not measured immediately. Phytoplankton samples for f l o r i s t i c s analysis were preserved with Lugol's iodine, concentrated by settling (Lund et at. , 1958; Utermohl, 1958; Uehlinger, 1964), and counted using inverted, phase microscopy. Cell counts were converted to carbon according to Strathman (1967). Zooplankton were sampled from 25-0 m using 20 cm bongo nets fitt e d with 202 ym Nitex mesh, preserved with 10% buffered formalin, s p l i t ( i f required) using a Folsom plankton s p l i t t e r , and counted under a dissecting microscope. B. Experimental Natural phytoplankton populations and a l l seawater used were collected by diaphragm pump as described previously. Seawater used for culture media was filt e r e d through 0.45 ym Millipore f i l t e r s and autoclaved for 1 hour at low temperature and pressure to avoid precipitation of si l i c a t e . Unialgal cultures of the following species were maintained in E.S. Medium (Provasoli, 1968; Appendix 1) at 12°C -± 1C°, illuminated from the side by cool white fluorescent lamps (3-5 klux or 70-120 yE m"2 sec - 1) on a 16-8 (16 h light, i 8 h dark) light-dark cycle: Species Bacillariophyceae Skeletonema costatum (Grev.) Cleve Thalassiosira nordenskioldii Cleve Thalassiosira sp. 1 Thalassiosira sp. 2 Pjrymnesiophyceae (=Haptophyceae) Chrysoohromulina kappa Parke & Manton Cryptophyceae Chroomonas salina (Wisl.) Butcher Cryptomonas profunda Butcher Dinophyceae Katodinium rotundatum |Lohm.) Loeblich III Euglenophyceae Eutreptiella cf. gymnastiaa Throndsen Eutreptiella sp. Source of Culture (1) (1) (2) (2) (1) (2) (1) (1) (1) (2) Strain No. NEPCC 18 NEPCC 252 NEPCC 188 NEPCC 65 NEPCC 44 NEPCC A2 (1) Northeast Pacific Culture Collection (NEPCC), UBC (2) Saanich Inlet, isolated by author Bioassays were conducted to test the effects of metabolites and hydrocarbons, neither of which was monitored in the f i e l d , on diatoms and flagellates. In addition, experiments on the effects of light intensity, photoperiod and temperature were performed to assess their roles in deter-mining phytoplankton composition in the winter. 1. Metabolite experiment The purpose of this experiment was to determine whether or not the presence of a diatom population stimulated or inhibited the growth of 9 a flagellate population (and vice versa) in the presence of excess nutrients and otherwise favourable conditions for growth. The experimental set-up is shown in Fig. 2. Sections of Fisherbrand cellulose dialysis tubing (pore size 4.8 nm or approximately 12,000 daltons molecular weight) were cleaned 1 and sealed at one end. These were f i l l e d with 150 ml of cultures of either Thalassiosira nordenskioldii or Chrysoohromulina kappa. Another dialysis tubing "bag" was f i l l e d with equal amounts of Thalassio-sira and Chrysoohromulina. The total biomass (as measured by in vivo fluorescence) was approximately equal in a l l "bags." These were sealed with plastic clips and suspended in clean 5% E.S. medium (Appendix 1) in 4 1-1 beakers as follows: beaker 1: Thalassiosira alone beaker 2: Chrysoohromulina alone beaker 3: Thalassiosira and Chrysoohromulina in separate bags beaker 4: Thalassiosira and Chrysoohromulina mixed in the same bag Stirrers were added to the beakers to prevent the formation of gradients near the bag walls. A l l cultures were then allowed to grow under continu-ous illumination by fluorescent light at 3-5 klux (70-120 yE m - 2 sec - 1) at 12°C Dialysis tubing cleaning procedure, used to remove heavy metals and UV-absorbing impurities: 1. Boil tubing 3 h in 5% Na 2C0 3. 2. Rinse in running tap water. 3. Repeat. 4. Boil i n 50 mM EDTA, pH 8.0. 5. Store in 0.1 mM EDTA. 6. Before use, b o i l and rinse in d i s t i l l e d water. 7. Handle with gloves to prevent contamination. 11 ± 1C°. Bags containing T h a l a s s i o s i r a were mixed once daily by inverting gently several times, in order to prevent settling of the ce l l s . In vivo fluorescence was measured daily using a Turner Model 111 fluorometer and growth rates calculated from the equation (Parsons and Takahashi, 1973b): = \ l o g 2 N t N o (1) where N is the i n i t i a l biomass as estimated by in vivo fluorescence (or o c e l l counts), N i s the biomass at time t, and u is the specific growth rate in doublings per day. For the mixed culture c e l l counts were performed daily using inverted, phase microscopy, and growth rates calculated from equation (1). 2. Hydrocarbon experiment Bioassays tested the effects of No. 2 Fuel O i l (a crude oil) and 1-methylnaphthalene (a member of the toxic naphthalene fraction of oils) on the growth of diatoms and nanoflagellates in culture and in mixed natural populations. Species assayed in culture included the diatoms T h a l a s s i o s i r a sp. 1 and Skeletonema oostatum, and the flagellates Chroomonas salina, Cryptomonas profunda, E u t r e p t i e l l a clmgyrhn^siiica^rEutreptiella7sp. and Katodinium rotundatum. The natural population was obtained by Niskin bottle from 1 m at station "A" in Saanich Inlet, in November, 1976. A seawater extract of the No. 2 Fuel O i l was made by adding 4 ml of the fuel o i l to 200 ml of autoclaved, f i l t e r e d sea water in a 500 ml flask and sti r r i n g gently for 12 h. The mixture was transferred to a separatory funnel and allowed to separate for 2 h, after which time the water phase was drawn off, giving a f i n a l concentration of 9 mg volatile 12 hydrocarbon per l i t r e (Lee, personal communication). 1-methylnaphthalene (Eastman-Kodak, Rochester, New York) was diluted with ethanol to give a stock solution of 1 yg y l - 1 . In a separate assay ethanol was shown to have no measurable effect on the algae up to the maximum concentration used, 960 yl/200 ml. The 1-methylnaphthalene and fuel o i l extract were added to s t e r i l e glass bottles containing the cultures (or natural sea water) and immediately sealed. Final hydrocarbon concentrations ranged from 0 to 4800 yg 1~1 1-methylnaphth.alene and 0 to 500 yg l - 1 No. 2 Fuel O i l . A l l bottles were incubated at 12°C, under fluorescent light, 25-30 klux (350-425 yE m - 2 sec - 1),.with a 12-12 photoperiod. In vivo fluorescence was measured daily, and microscope counts were made on the natural seawater samples at the beginning and end of the experiment. Growth rates were calculated from equation (1) (see metabolite experiment). 3. Light and temperature experiments Bioassays tested the effects of varying light intensity, photo-period and temperature on the growth of diatoms and nanoflagellates in pure culture, and of natural summer and winter populations. a. Ture cultures. Species used included the diatoms Skeletonema costatum and Thalassiosira sp. 1 and 2 and the nanoflagellates Katodinium rotundatum, Eutreptiella sp., Cryptomonas profunda and Chrysoohromulina kappa. To avoid any possible effects of the unnaturally high nutrient concentrations present in culture medium (see, for example, Maddux and Jones, 1964; McAllister et al., 1964), the experiments were run using 5% E.S. medium (nitrate, approximately 27 yg-at N l - 1 ) , plus 10% s i l i c a t e mixture for diatoms (approximately 99 yg-at Si l - 1 ; see Appendix 1 for concentrations of other nutrients). Cells were grown to logarithmic phase (5 to 10 days) 13 in the dilute medium. Light intensities at this time ranged from 2.7 to 3.9 klux (39 to 55 yE m - 2 sec - 1) for Katodinium, Cryptomonas and Chryso-ohromulina, and 5.0 to 5.2 klux (72 to 74 yE m - 2 sec - 1) for Skeletonema, Thalassiosira and Eutreptiella. During the experimental period, various light levels were produced by f i t t i n g light screens consisting of one or more layers of black or white netting over the bottom of 125-ml BOD bottles and blackening the rest of the bottle. The resulting light intensities inside the bottles ranged from 100% to 0.50% of the incident light, or 27 to 0.14 klux (388 to 1.94 yE m - 2 sec - 1) in the incubator described below. One hundred and twenty ml aliquots of the cultures were dispensed into the bottles and incubated at 12°C or 6°C, illuminated from below by a bank of 6 cool white 40w fluorescent lamps with a 12-12 photoperiod. In vivo fluorescence was measured daily and growth rates calculated (equation 1). In the 12°C experiment, pigments (spectrophotometric method—Strickland and Earsons, 1972), 1 1 +C productivity, and c e l l size and appearance were analysed on day 0 and after the cells had reached logarithmic phase of their growth in their new light regimes. b. Natural populations. Water was collected from station "A" from 1 m on December 1, 1976, 15 m on May 5, 1977, and 5 m on August 19, August 25, and September 8, 1977. With the exception of the December 1, 1976 collection (in which nutrient concentrations were high—nitrate >20 yg-at N l - 1 , s i l i c a t e >50 yg-at Si l - 1 ) the water was enriched with 5% E.S. medium with s i l i c a t e (nitrate oa. 2(7 yg-at N l - 1 , s i l i c a t e ca. 49 yg-at Si l - 1 ) . One hundred and twenty ml aliquots were dispensed into the BOD bottles described above and incubated as summarized in Table I, illuminated as before from below by a bank of 6 cool white 40w fluorescent lamps. 14 Table I. Summary of light and temperature experiments using natural phytoplankton populations. r -, . Duration of Experiment Source of Water T C Photoperiod L U J - t u r e Experiment Medium ,, . (days) 1 Stn.A lm 1/12/76 12 12-12" none added 8 2 Stn.A 15m 12/5/77 12 24- "0 5% E.S.+Si 4-14 3 Stn. A 5m 19/8/77 12 12-12 5% E.S.+Si 5 4 Stn.A 5m 25/8/77 6 12-72 5% E.S.+Si 8 5 Stn.A 5m 8/9/77 6 12-12 5% E.S.+Si chemostat 25 15 In the f i f t h experiment (Table I) a crude chemostat system was used in order to maintain steady, non-nutrient-limited growth. A 4-ml aliquot from each sample was removed daily and replaced with an equal quantity of E.S. medium with s i l i c a t e (an addition of 18, 33 and 1 yM of nitrate, s i l i c a t e and phosphate respectively). At 1-week intervals, larger volumes were removed (10 ml on days 7 and 21, 28 ml on day 14) and replaced with 5% E.S. medium with s i l i c a t e . Growth was maintained in this way for 25 days. Measurements of in vivo fluorescence were taken daily and growth rates calculated (equation 1) for a l l 5 experiments. Floristics analyses were performed at the beginning and the end of a l l experiments, and additionally on days 7 and 14 for experiment no. 5. RESULTS A. Field Observations 1. Temperature and salinity Fig. 3 shows the temperatures in the top 20 m at station "A" for the year November, 1975 to October, 1976. There was a significant seasonal variation at a l l depths, ranging from a mean of 7°C for the top 20 m in the winter to about 12°C in the summer. Salinity profiles (Fig. 4) show that there was a year-round gradient in salinity in the top 20 m, which would tend to maintain the stability of this layer. In winter and early spring there was a layer of markedly lower salinity in the top 2 m which disappeared during the summer. Figure 3. Temperatures at 0, 5, 10, and 20" m at station "A," November, 1975 - October, 1976. NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT Figure 4. Salinity structure at station "A," November, 1975 - October, 1976. Salinities are shown in parts per thousand. 18 This layer was 1 to 2C° cooler than the underlying water and probably originated as river runoff (and direct precipitation). It was physically distinct from the subsurface water, as evidenced by the sharp temperature and salinity clines at the boundary. 2. Light PAR varied seasonally over an order of magnitude, from a winter minimum of 20 yE m - 2 s e c - 1 to a summer maximum of 200 yE m - 2 s e c - 1 (Fig. 5). Winter water was generally much clearer than summer, but because of the large difference in incident light, the quanta available at a given depth was much less (Fig. 6). The only exceptions to this were during intense summer blooms when the turbidity occasionally rose enough to reduce light at 20 m to winter levels. These were s t r i c t l y short-term reductions, however. 3. Nutrients Nitrate, s i l i c a t e and phosphate concentrations were high and uniform with depth a l l winter (greater than 20 yg-at 1 _ 1, 40 yg-at l - 1 and 1.5 yg-at l - 1 respectively in the top 20 m; see Fig. 7,8). Beginning in March surface levels showed a rapid decline and remained low unti l September when they gradually began to increase to winter levels. Occasional upwelling events following storms renewed surface nutrient supplies during the summer. 250 r 200 150 100 50 Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Figure 5. Total daily photosynthetically active radiation (PAR), 400 - 700 nm, measured at the land station, November, 1975 - October, 1976. 7 \ ^ f P t h p r o f i l e s o f nitrate concentration (yg-at N l " 1 ) at station "A," November, 1975 -October, 1976. DEPTH, m o- n w o m 01 ro o m oi ^ w o 23 4. Phytoplankton Diatoms and nanoflagellates alternately form the dominant Saanich Inlet phytoplankton in summer and winter respectively (Fig. 9). Larger flagellates, chiefly dinoflagellates, seldom dominate the phytoplankton, and although they formed, at times, as much as 40% of the total biomass during the summer of 1976, they were always outnumbered by diatoms. Fig. 9 shows the pattern of phytoplankton biomass.composition by group. The end of the 1975 cycle of diatom dominance is seen on November 4. This was followed by a rapid decline in the diatom population which did not recover again u n t i l mid-April, 1976. The winter (November to March) nanoflagellate population included a mixture of cryptomonad genera, including Cryptomonas, Chroomonas , Hemiselmis and Plagioselmis , haptophytes —Chrysochromulina and Dicrate riaj-the prasinophyte Pyramimonas , the chrysophyte ApedineVla, and a small dinof lagellate, Katodinium rotvcndatvm. The biomass a l l winter was very low (10 pg C l - 1 , 5 ug chl a l - 1 or less). The beginning of the spring bloom was marked by a sharp increase in the nanoflagellate biomass in early March, followed by a diatom (and, secondar-i l y , dinoflagellate) increase in early April which rapidly outgrew the flagellate bloom. This i n i t i a l diatom burst was dominated by Thalassiosira spp. (68.7%), Skeletonema costatum (11.2%), and Chaetoceros spp. (3.0%). By mid-May,CGhaetoceros spp. comprised more than 90% of the total biomass and remained dominant for most of the summer (Fig. 10). Following the diatom crash at the end of August the population was briefly dominated by flagellates, although the total phytoplankton biomass was very low. A fi n a l autumn diatom bloom, composed exclusively of Chaetoceros spp., occurred i n September, and by mid-October the winter phytoplankton community was re-established (Fig. 10). 0 - 1 0 m 0 - 1 2 m 0 - 2 0 m 1,000 - 1 0 0 h o 3 01 to < o CD lOh-N A N O F L A G E L L A T E S DIN 0 FJ_ AG E L L ATES' j\ CENTRIC DIATOMS /PENNATE DIATOMS-Figure 9. Biomass of major phy t oplankt on groups at station "A," November, 1975 - October, 1976. Bars indicate depths over which sam-ples were taken at various times of the year. nanoflagel-lates centric diatoms pennate diatoms dinoflagel-lates NOV DEC JAN FEB MAR APR MAY JUN J U L AUG S E P NJ Figure 10. Species succession in phytoplankton at station "A," March - December, 1976. Bars indicate depths over which samples were integrated at different times of the year. nanoflagellates, Chaetoceros, Thalassiosira, Skeletonema. 26 5. Zooplankton Fig. 11 shows abundances over the year December, 1975 - December, 1976 f o r three s i z e classes of copepods (defined i n Table I I ) . Copepods smaller than 2.0 mm i n length were present year-round but were most abundant during the period A p r i l - November. Copepods l a r g e r than 2.0 mm were present only from March to November; abundances greater than 100 m occurred only from A p r i l through August and again i n l a t e October and early November. The periods of greatest abundance for small copepods and of presence f o r large copepods correlate with and lag s l i g h t l y behind the summer and f a l l blooms of phytoplankton. B. Experimental 1. Metabolite experiment F i g . 12 shows the growth of Thalassiosira nordenskioldii and Chrysoohromulina kappa when grown separately ( p h y s i c a l l y and chemically), together (physically and chemically), and together chemically but separated p h y s i c a l l y . When the two species were separated p h y s i c a l l y the growth rates i n both cases were unchanged whether or not they were allowed to i n t e r a c t chemically. Thalassiosira grew s l i g h t l y f a s t e r than Chrysoohro-mulina (doubling rates were 1.82-1.87 and 1.38-1.44 doublings d a y - 1 r e s p e c t i v e l y ) . When the two species were mixed together (in the same d i a l y s i s bag), Thalassiosira grew more quickly than i t had alone, while Chrysoohromulina grew more slowly (growth rates were 2.56 and 1.13 doublings day - 1 r e s p e c t i v e l y ) . However, Thalassiosira senesced i n the mixed culture three days a f t e r the i n i t i a t i o n of the experiment, while Chrysoohromulina maintained logarithmic growth u n t i l the conclusion of the experiment. o Thus i t appears that intimate contact of c e l l s of the two species may a f f e c t t h e i r growth rates while simply sharing the same medium does not. 27 Table II. Copepod size classification (based on body lengths obtained from Fulton, 1972). Body.yLength Species and Stages <1.0 mm Pseudocdtanus minutus I-III Paracalanus parvus I-V Metridia padfioa I-II Coryaaeus cf. anglicus 1.0-2.0 mm Calanus spp. I-III Metridia pacifica III-V Pseudbaalanus minutus IV-adult Paracalanus parvus adult Microoalanus sp. Scolecithricella Aaartia Tortanus Oithona Onoea Centropages Metridia pacifica adult Epilabidocera >2.0 mm Calanus spp. IV-adult 28 >2 mm Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Figure 11. Abundance of three size classes of copepods sampled from 25-0 m at station"A," December, 1975 - December, 1976. <1.0 mm, 1.0-2.0 mm, >2.0 mm total body length. 29 Figure 12. Growth of Chrysoahromulina skioldii in the metabolite experiment, measured for cells grown in individual measured for cells in mixed culture. kappa and Thalassiosira norden-in vivo fluorescence, dialysis bags, c e l l count, 30 2. Hydrocarbon experiment Hydrocarbons affected two aspects of growth in phytoplankton: they inhibited (or occasionally stimulated) the doubling rate of the cells during logarithmic growth, or they influenced the length of the lag phase of growth prior to the onset of logarithmic growth (see Fig. 13). In a l l but one instance (experiments involving the dinoflagellate Katodinium rotundatum) , 1-methylnaphthalene had the former effect only, while No. 2 Fuel O i l affected both aspects of growth. It is likely that inhibition of the logarithmic doubling rate of the cells represents a true toxic effect of the hydrocarbon resulting in an inability to reproduce at a normal rate, while the delay of growth represents a waiting period during which the cells manage to resist the toxic effects of the hydrocarbon until volatilization, removal by bacterial activity, or adsorption has reduced the eoncentrationstboancaeceptableel'evel. The latter situation would be expected to arise more often with a hydrocarbon mixture (as in the case of a fuel o i l ) than with a pure compound: one can envision the volatile toxic aromatic fractions being•removed after a few days (depending on i n i t i a l concentration), followed by phytoplankton growth limited by the presence of less toxic, less volatile naphthalenes. In Fig. 14 doubling rate has been plotted against hydrocarbon concentration for individual species and the natural population. The duration of the lag phase is plotted for No. 2 Fuel O i l only. From the monospecific experiments i t can be seen that despite the small number of species used there was not general enhancement of flagellate species with respect to diatom species, either in terms of logarithmic doubling rate or duration of the lag phase, involving 1-methylnaphthalene or No. 2 Fuel Oil. No flagellates were ever stimulated by either hydrocarbon relative 31 Figure 13. Two types of e f f e c t s of hydrocarbons on the growth of phyto-plankton. A. The response of Katodinium votundatum to No. 2 Fuel O i l : the length of the lag phase of growth increased with increasing hydro-carbon concentration. B. The response of Thalassiosira sp. 1 to 1-methylnaphthalene: growth rate decreased with increasing hydrocarbon concentration. 32 33 Figure 14. The effects of No. 2 Fuel O i l and 1-methylnaphthalene on the growth rate and growth lag in 7 species of phytoplankton and in a natural population. Dashed lines represent growth in the controls. GROWTH LAG, days GROWTH RATE, doublings day-' o •9: is -— . I s I §• I p ro c CP O O S 01 T O o c D_ T3 O •O C o 3 CO 4^ 35 to the controls, while Skeletonema eostatum grew s l i g h t l y f a s t e r at No. 2 Fuel O i l concentrations less than or equal to 300 Pg l - 1 than with no hydrocarbon added. The fac t that there was no s i m i l a r i t y i n the responses of two species of the same genus of euglenoflagellate (see F i g . 14: EutveptieUa sp. and E. cf. gymnastioa) suggests that there are no broad generalizations that can be made about the responses to hydrocarbons by d i f f e r e n t taxonomic groups, and that resistance to or enhancement by hydrocarbons varies at the species l e v e l at l e a s t . Incubation of a natural winter population with varying concen-tratio n s of No. 2 Fuel O i l did not produce any s i g n i f i c a n t change i n the 8-day species composition with increasing hydrocarbon concentration (Table I I I ) . The population did s h i f t from a flagellate-dominated s i t u a t i o n to a diatom-dominated one, but t h i s occurred i n the controls as w e l l as the treated samples, i n d i c a t i n g that factors other than hydrocarbons were func t i o n a l i n bringing about the change. 3. Light and temperature experiments a. Pure cultures. Growth rate versus l i g h t i n t e n s i t y curves are given i n - - -Fi g . 15. At 12°C (Fig. 15A), approximately a mean summer temperature for the upper 20 m of Saanich I n l e t (see F i g . 3), Skeletonema costatum grew more quickly than any f l a g e l l a t e or diatom tested at a l l l i g h t i n t e n s i t i e s except 0.14 klux (1.94 pE m - 2 s e c - 1 ) . At th i s i n t e n s i t y , Eutreptiella sp. was the only species demonstrating a p o s i t i v e growth rate, possibly due to heterotrophic c a p a b i l i t i e s which are known to be common among euglenophytes (Droop, 1974). An i n t e n s i t y of 0.14 klux (1.94 pE m - 2 s e c - 1 ) i s very low, even for winter conditions (see F i g . 6). According to these data, at 12°C, Skeletonema should outgrow any of the 36 Table III. Species composition of a natural phytoplankton population before and after 8 days' incubation with varying concentrations of No. 2 Fuel O i l . Cells ml - 1 Day 0 Day 8 Species 0 5 50 500 yg l " 1 Flagellates Pyramimonas sp. 9 Chrysoohromulina kappa 63 Chrysoohromulina ericina 5 Chrysoohromulina sp. 5 Apedinella sp. 8^  Eutreptiella sp. + Cryptomonads 137 Katodinium sp. 25 Unidentified dinoflagellates 4 Total flagellates 256 0 0 0 0 Diatoms Skeletonema oostatum + 220,000 85,000 130,000 77, ,000 Chaetoceros spp. + - - 1,400 — Chaetoceros spores - 4,600 1,200 4,900 2, ,900 Thalassiosira sp. 5 4,200 4,400 9,900 21, ,000 Coscinodiscus sp. + - 350 940 _ Nitzschia delicatissima + 2,100 2,600 8,900 2, 600 Cylindrotheca sp. + - - 240 — Thalassionema sp. + 1,400 180 1,200 — Unidentified pennates 5,700 5,100 2,100 6, 200 Total diatoms 12 238,000 98,830 159,580 109, 700 (+) present (-) absent 24 A. 12 °C B. 6 ° C Figure 15. Growth rate versus light intensity curves for phytoplankton in culture. A. 12°C. B. 6°C. 38 other five species tested, in the absence of other limiting factors. At 6°C (Fig. 15B) , a.typical winter temperature (see Fig. 3), Skeletonema costatum again outgrew the flagellate Chrysoohromulina kappa at a l l intensities greater than 0.14 klux (1.94 yE m-2 s e c - 1 ) , although the growth rates of both species were reduced at the lower temperature (Fig. 16). Thalassiosira sp. 2 grew faster than Skeletonema at intensities greater than about 6 klux (86 yE m-2 s e c - 1 ) . The prediction one would make on the basis of these data resembles that at 12°C: in the absence of other limiting factors, diatoms should be able to outgrow flagellates at light intensities much above 0.14 klux (1.94 yE m-2 sec - 1 ) (with a 12-12 photoperiod). In other words diatoms should outgrow flagellates at a l l times of the year, i f light intensity alone is the c r i t i c a l factor. The curves for photosynthetic rate versus light intensity i n non-adapted cells (adapted to the temperature and nutrient regimes, but not adapted to the various light levels 1) closely resemble the curves obtained for growth rate versus light intensity (Fig. 17A). The only exceptions are Eutreptiella which seemed to be able to grow relatively quickly on a low photosynthetic rate compared to the other species (due to alternate modes of nutrition?), and Katodinium which grew more slowly thank would be expected from the relative photosynthetic rates of the six species. In adapted cultures (cultures which were allowed to attain logarithmic growth at each of the various light levels, usually 5-10 days), Pre-experimental light.intensities were low compared to the test intensities, and ranged from 2.7 to 5.2 klux (39-74 yE m - 2 s e c - 1 ) , depending upon the species. Refer to methods, section B3a. A. Skeletonema costatum B. Chrysochromu/ina kappa g U ^ t J l ' ^ J h e e f f ! ° ! ° f t e m P e r f t u r e o n growth versus l i g h t i n t e n s i t y curves of algae i n culture Skeletonema costatum. B. ChrysochvomuUna kappa. culture. A. INITIAL WEEK ...x _ .••'X Chrysoohromulina •/" Thalassiosira sp. I y Cryptomonas I / TJlalassiosira S P - 1 •  / / ,4 Chrysoohromulina + U\ -o Eutreptiella ^ J ^ f - ° ~ -..<^ + Katodinium ~* Skeletonema -* Cryptomonas o~" o Eutreptiella 19_ 0 ••' 1 0 I 2 0 1 '30 klux o;0 , io ~ 100 200 300 400 uE m-2soc-l 0 100 200 20 30 klux L I G H T I N T E N S I T Y L I G H T I N T E N " Figure 17. Photosynthetic rate versus light intensity curves for phytoplankton in culture. A. Cells not adapted to light conditions, previously grown at 2.7-5.2 klux (39-74 yE m - 2 s e c - 1 ) . B. Cells grown one week at individual light intensities. o 41 some of the curves changed drastically (Fig. 17B). The light-saturated AP photosynthetic rate of Chrysoohromulina increased greatly, as did Additionally there i s evidence in the adapted cells of photoinhibition at the highest intensity, although this may be artifactual, since i t is represented by a single data point. A similar development of photoinhibi-tion was observed in Katodinium. There was l i t t l e change in the curves for either Eutreptiella or Cryptomonas , although in C^ptomonasphotoinhibi-tion was lost at high intensities. The 1^ values (Tailing, 1957) of the two diatoms species increased AP as they adapted to the various light intensities. The TT (and presumably AP P ) value for Thalassiosira sp. 1 increased, but for Skeletonema TT max A l decreased. This was rather unexpected, and may represent senescence in the Skeletonema cultures. This i s rather unfortunate, as there i s a strong possibility that, had the culture not senesced, the overall picture of flagellate and diatom growth rates in adapted cultures would have been very different. From Fig. 17B i t appears that, once cells have adapted to the various light intensities, some flagellates—Chrysoohromulina in particular — c a n photosynthesize more effici e n t l y than diatoms at light intensities much below about 27 klux (388 yE m - 2 s e c - 1 ) . At intensities less than about 10 klux (143 yE m-2 sec - 1) only Eutreptiellawss Hess ee'fficient. than Thalassiosira. If the curves are extrapolated one can see that above 27 klux (388 yE m 2 sec -1) Thalassiosira would overtake Chrysoohromulina which was saturated and perhaps inhibited at that intensity. However due to the unconvincing nature of the Skeletonema data this line of reasoning may or may not be warranted. 42 Comparing the P vs. I curves with the p vs. I curves (Fig. 17 and 15A respectively) i t appears that the growth rates represented in Fig. 15A are more closely linked to the photosynthetic rates in unadapted cells than in adapted cel l s . Since growth rates were determined for the days between measurements of photosynthetic rates on unadapted and adapted cell s , and not following adaptation, this is entirely possible. Determination of u vs. I curves would probably have been better conducted on light-adapted cel l s . Several biochemical and morphological changes were associated with growth at varying light intensities. Volumes of the light-adapted cells (i.e., grown to the onset of stationary phase at the experimental intensities, or about 5-10 days, depending on the intensity and the species) were calculated for samples of 20 cells per light intensity per species, by approximating the shape of the cells of each species to a geometrical figure and microscopically measuring the appropriate dimensions: Skeletonema and T h a l a s s i o s i r a cells were likened to cylinders, Chrysoohromulina to spheres, and Cryptomonas, E u t r e p t i e l l a and Katodinium to ellipsoids. In a l l species except Thalassiosira, c e l l volume decreased with decreasing light intensity, although in Chrysoohromulina this tendency was very slight and cells of E u t r e p t i e l l a were extremely variable in size (Fig. 18). With the exception of T h a l a s s i o s i r a sp. 1 a l l species tested showed a predictable increase in surface area-to-volume ratio at low light intensities. This could be an adaptation to maximize the illumination of the chloroplasts within the c e l l s . Alternately, smaller cells with reduced energy demands could mean increased efficiency at low light levels. I am unable to suggest a reason for the reversal of this trend in Thalassiosira. (Note that the volume of Skeletonema cells was considerably greater at 0.14 klux—1.94 43 Figure 18. Effect of light intensity on c e l l volume. 44 Figure 19. Effect of light intensity on chlorophyll content. 45 yE m~z s e c - 1 — t h a n at any of the i n t e n s i t i e s immediately higher. This i s doubtlessly due to the fact that no growth occurred at t h i s l i g h t i n t e n s i t y ; i n f a c t c e l l s died very early i n the experiment. Therefore the c e l l s measured i n t h i s case would represent the o r i g i n a l inoculum of r e l a t i v e l y large c e l l s . ) In Eutreptiella and Thalassiosira c e l l s there was a marked increase i n the ch l o r o p h y l l content per c e l l as l i g h t i n t e n s i t y decreased (Fig. 19). This i s consistent with the theory that c e l l s tend to increase the concen-t r a t i o n of t h e i r photosynthetic pigments i n an e f f o r t to use more e f f i c i e n t l y the decreased a v a i l a b l e l i g h t . The ch l o r o p h y l l content of Skeletonema, Katodinium and Cryptomonas showed no change over the b r i g h t e r range of i n t e n s i t i e s but quickly increased as l i g h t decreased to below a threshold value which was d i f f e r e n t for each species. This probabihy.brepresents the same e f f e c t as was observed with Eutreptiella and Thalassiosira, except that these three species can withstand much lower i n t e n s i t i e s before c h l o r o p h y l l concentration i s increased. The c h l o r o p h y l l content of Chrysoohromulina c e l l s was v a r i a b l e and showed no dependence on l i g h t i n t e n s i t y over the range tested. b. Natural populations. Results obtained using pure cultures were somewhat confusing due to the apparent importance of adaptation, and the i n t r i n s i c problems i n dealing with cultures. A rather t e n t a t i v e conclusion could be drawn to the e f f e c t that l i g h t i s not important i n regulating diatom-f l a g e l l a t e abundances, as diatoms seem to be able to grow f a s t e r than f l a g e l l a t e s at any normally encountered i n t e n s i t y . However, the p o s s i b i l i t y that these r e l a t i v e growth rates can change as the c e l l s adapt to t h e i r new environments places the whole hypothesis i n doubt. 46 Experiments with natural populations produced more consistent results. When a natural summer population of phytoplankton, comprised chiefly of the diatoms Skeletonema aostatum, Nitzsehia delicatissima, Chaetooeros spp., Thalassiosira spp. and the nanoflagellate Chrysoohromulina spp., was incubated at 12°C and varying light levels (experiment 2, Table I) there was a clear tendency for the diatom species to outnumber the flagellates at high intensities and for the flagellates to dominate at low intensities (Fig. 20). Note that each'species had i t s own light optimum: Skeletonema at about 2.9 klux (41.5 yE m - 2 s e c - 1 ) , Nitzsehia at about 6.9 klux (99.3 yE m - 2 s e c - 1 ) , Chaetooeros at 27 klux (388 yE m - 2 sec - 1) or higher. It is interesting that the optimum for Chrysoohromulina was at about 17 klux (244 yE m - 2 sec - 1) although i t was not dominant at this intensity. Instead i t was outnumbered by the diatoms Nitzsehia and Chaetooeros. In the region where i t dominated i t seemed to do so only "by default:" i t dominated only because of i t s tolerance to low light levels where the diatoms could not grow. A plot of flagellate-to-diatom ratios (by c e l l numbers) is shown in Fig. 21. The downward peak at 2.9 klux (41.5 yE m~2 sec - 1) represents a peak in diatom abundance, specifically Skeletonema eostatum, as can be seen by comparing the curve with Fig. 20. The beginnings of another diatom peak, partly due to Chaetooeros and partly due to the decrease in flagellate abundance, can be seen above 20 klux (300 yE m - 2 s e c - 1 ) . Below 1.2 klux (17.3 yE m - 2 sec _ 1 2 the flagellate-to-diatom ratio increases rapidly, not due to any increase in flagellate number, but rather to a dropoff in diatom abundance. This basic relationship seems to be independent of a number of other factors, including the i n i t i a l population, photoperiod, and temperature. IO5 O-I I Mtzsch/a chaetoperos TOTAL FLA6ELL,^IES-^y j / Chrysochromulina t i i I I I 10 10 100 LIGHT INTENSITY 100 klux 1,000 uEin mrzsec-' Figure 20. Effect of light intensity on the composition of a natural phyto-plankton popula-tion: cells ml - 1 after 4-14 days' growth at 12°C and continuous illumination at various light intensities. 48 Figure 21. Effect of light intensity on the ratio (by c e l l numbers) of flagellates to diatoms after 4-14 days' growth at 12°C and continuous illumination at various light intensities. 49 Fig. 22 illustrates two experiments run under identical conditions (12°C, 12-12) , using natural populations collected in December and August (experiments 1 and 3, Table I). Although the absolute value of the ratios varies between the two populations, the shapes of the two curves are almost identical, indicating that light had the same effect on two very different phytoplankton populations. Fig. 23A shows the influence of photoperiod on the basic flagellate-diatom light effect. The two curves illustrate the same general principle: decreased light intensity results in an increase in the flagellate-to-diatom ratio, while higher light intensities allow diatoms to increase in abundance. Longer photoperiods also allow single diatom species to grow at lower light intensities than possible with shorter photoperiods. For example, the Skeletonema "peak" at 12-Hf i s at 17 klux (244 yE m - 2 sec - 1) while at 24-0 the peak is at 2.9 klux (41.5 yE m - 2 s e c - 1 ) . Apparently dim light can (to a point) be integrated over time to produce an effect similar to brighter light of shorter duration. This effect can be seen in growth rate versus intensity curves as well (Fig. 23B). Here the growth rates for populations grown (to stationary phase) with a 24-0 photoperiod are generally higher than those grown (to stationary phase) with a 12-12 photoperiod. However, i t also seems from Fig. 23B that i f the intensity is insufficient to support a positive growth rate longer photoperiods make l i t t l e difference. The fact that there were more flagellates overall in the popula-tions which wase illuminated continuously is likely a function of the original compositions of the two populations rather than an effect of photoperiod. The fact that the flagellate-to-diatom ratio was much higher at low intensities in the continuously illuminated cultures than in the 12-12 cultures may indicate that the total light energy available with a 12-12 50 10 10 lOOklux J 1 1 10 100 1,000 uE m-2sec-' LIGHT INTENSITY Figure 22. Effect of varying the i n i t i a l composition of a natural phyto-plankton population on i t s response to light intensity. Both populations were grown 5-8 days at 12°C with a 12-12 photoperiod. Points show ratios of flagellates to diatoms (by ce l l numbers) in the i n i t i a l populations. 51 LIGHT INTENSITY Figure 23. Effect of photoperiod on the response of natural populations of phytoplankton to light intensity. A.. Ratio of flagellates to diatoms after 4-14 days' growth at 12 C. Points show ratios in the i n i t i a l popu-lations. B. Growth rates under continuous illumination or 12-12. 53 photoperiod i s insufficient to support basal metabolism in a l l c e l l s , so that cells die and the flagellate-to-diatom ratio becomes variable. On the other hand continuous low level light may support basal c e l l maintenance in flagellates but not diatoms, thereby increasing the flagellate-to-diatom ratio. The effect of temperature on the growth rates of natural popula-tions i s shown in Fig. 24A. The population grown at 12°C achieved a higher light-saturated growth rate than did the 6°C population. Under favourable conditions growth rate is a function of photosynthetic rate, and since the light-saturated photosynthetic rate of a population is a function of temperature* i t i s not surprising that the light-saturated growth rate should also be temperature-dependent. The rate of increase in growth rate with an increase in light intensity ( ^ ) J o n the other hand, does not AP appear to be temperature-dependent. This again is not unexpected, s i n c e — does not vary with temperature, aoes not J r One consideration which is not shown in Fig. 24A is the duration of the lag period between the beginning of the experiment and the i n i t i a t i o n of growth. At 12°C there was no lag—growth commenced immediately—while • at 6°C there was a 4-day lag period. Since the i n i t i a l populations were collected during the summer (mean ambient temperature, 12°C) the lag period which occurred when the temperature was reduced to 6°C doubtlessly represents an adaptation phase. The ratios of flagellates to diatoms after one week's growth at 12°C and 6°C are shown in Fig. 24B. The two curves are very similar in shape, with diatom peaks at 17.1 klux (244 yE m - 2 sec - 1) and flagellate numbers increasing above and below this point. However, the 6°C curve is more pronounced—that i s , the diatom peak is better defined and there are 54 LIGHT INTENSITY Figure 24. Effect of temperature on the response of natural populations of phytoplankton to light intensity. A. Growth rates. B. Flagellate-to-diatom ratios. Points show ratios in the i n i t i a l populations. 1-week curves, 2 weeks, 3 weeks. 55 001 1 014 i.a A <f -J i i i i • I 10 10 -J 1 — \ — 1-94 ' 10 100 UGHT INTENSITY fe uE r r f W 56 no anomalous values at the lowest light intensity. Secondly, at 6 C the whole curve is shifted toward flagellate dominance. The latter observation may be due to the fact that diatoms were i n i t i a l l y far more abundant in the 12°C experiment than in the 6°C experiment—and this is probably a major consideration—however both observations may also be accounted for by the possibility that diatoms grow better at 12°C than at 6°C. Perhaps at 12°C they are less sensitive to light intensity changes because they are at a favourable temperature. At 6°C they may be temperature stressed and so are more sensitive to sub-optimal light intensities. It may be argued that, while this may be true, i t is also true that the original populations were growing at 12°C and that therefore they would of course by stressed at 6°C. However after two and even three weeks the sharpness of the diatom peak and the overall increase in flagellates had increased and not decreased. Were this the case one would expect that after two or three weeks the populations would have adapted to the new temperature and the curve would have begun to look more like the 12°C curve instead of less like i t . Therefore i t seems reasonable to conclude that Saanich diatoms i n t r i n s i c a l l y prefer 12°C to 6°C, and that at 6°C they are stressed and restricted to narrower light intensity ranges than they would be at 12°C. In Fig. 24B i t is possible to see the progress of light adaptation in diatoms. The peak in a l l curves is due to the diatom Skeletonema eostatvm. One can see how, with time, the peak shifted to the l e f t — t h a t i s , Skeletonema gradually adapted to dimmer and dimmer light intensities. However this adaptation had a lower limit, as is evidenced by the fact that the relative abundance of flagellates below 2.9 klux (41.5 yE m-2 sec - 1) increased with time. Therefore i t seems reasonable to conclude that at 6°C Skeletonema w i l l never grow at intensities less than 2.9 klux (41.5 yE m - 2 57 s e c - 1 ) . Secondly, i t is important to note that the Skeletonema peak did not widen to include the lower light intensities but in the f i r s t two weeks the upper tolerance limit decreased as well as the lower limit. This seems to indicate some synergistic effect of temperature and light intensity such that at low temperatures the light intensity optimum is also lower. This may relate to a general slowing down of the whole physiology of the c e l l with decreased temperature. DISCUSSION The winter dominance in Saanich Inlet by flagellates has been documented for the period 1975-1976. This is known to occur on a regular basis (Takahashi, personal communication). Buchanan (1966) has documented a similar pattern for Indian Arm, another British Columbia fjord. On the basis of experimental findings some conclusions may now be drawn as to the relative importance of various physical, chemical and biological factors involved in mediating this phenomenon, as well as the crash of diatoms in the f a l l and their return in the spring. Factors under consideration include temperature, light intensity, photoperiod, water s t a b i l i t y , nutrient concentrations, pollution by hydrocarbons, grazing, chemical interactions among species, and what I have called " i n t r i n s i c growth rates," which refers to the success of species under optimal growth conditions. A. Non-Contributing Factors Certain factors may be eliminated at the outset as unimportant to the control of the flagellate-diatom cycle. These include nutrient concen-trations, grazing, chemical interactions among species, and hydrocarbon 58 pollution. 1. Nutrient concentrations i Despite the fact that competition for nutrients has classically been considered an important determinant of phytoplankton succession (e.g., Dugdale, 1967; Eppley et at., 1969; Semina, 1972; Parsons and Takahashi, 1973a; Titman and Kilham, 1976), i t i s unlikely that i t plays such a role in the spring and f a l l diatom-flagellate changeovers in Saanich Inlet. Nitrate, s i l i c a t e and phosphate levels were high and consistent before, during and after the period of flagellate dominance. Decreases in nutrient concentrations occurred only after the spring diatom bloom was initiated, indicating that the decreases were caused by diatom uptake, rather than the diatom bloom being brought about by decreases in nutrient levels. Similarly, nutrient levels were high well before the f a l l diatom crash and the shift to a flagellate population. Moreover, the models of- both Semina (1972) and Parsons and Takahashi (1973a) predict that increased nutrient concentrations favour the growth of large cells.RyRy.ther's (1969) model predicted that nutrient-rich upwelled waters would favour large, chain-forming diatoms while oligotrophic oceanic waters would favour nanoflagellates. On the other hand, summer in Saanich Inlet is a period of highly changeable nutrient concentrations. Nitrate in particular frequently reaches limiting concentrations in the surface layers. It i s possible that at this time nutrients could play an important role in regulating succession among diatom species or allowing occasional flagellate blooms to occur. However, this role of nutrients is beyond the scope of the present discussion which is limited to the major changes which occur in the spring and f a l l , from a flagellate-dominated winter population to a diatom-dominated summer population and vice versa. 59 2. Grazing The purpose of monitoring zooplankton abundance was to determine whether or not herbivores have a regulating effect on the relative abundances of diatoms and nanoflagellates in the inlet. Since copepods are by far the most important grazers in Saanich Inlet, only these were considered. In order to evaluate their potential effects on phytoplankton they were grouped into three size classes: less than 1.0 mm total body length, 1.0 to 2.0 mm, and greater than 2.0 mm. Copepods of different sizes are known to prefer different sizes of food, even within a single species (Mullin, 1963; Nival and Nival, 1973, 1976; Lamport, 1974). The smallest category of copepods (less than 1.0 mm), including copepodite stages of Paracalanus parvus, Pseudocalanus minutus and Metridia pacifica, were assumed to be incapable of subsisting on a diet of large diatoms, the chain lengths of which may exceed 1.0 mm. These animals would be largely restricted to a nanoflagellate diet. The largest category (greater than 2.0 mm), including adult Metridia pacifica and Calanus spp., was considered to be capable of f i l t e r i n g the larger diatoms as well as the nanoflagellates, but unable to live on nano-flagellates alone unless present in great numbers. For example, Raymont and Gross (1942) showed that adult Calanus finmarchicus could subsist on a diet of small phytoplankton (1-3 ym) but that their survival was greatly improved by the presence of larger diatoms. The intermediate category (1.0-2.0 mm), including juvenile stages of the larger copepods and adult stages of small copepods, was considered to be capable of using phytoplankton of a l l sizes. Adult Pseudocalanus minutus, for example, were found by Poulet (1974) to be opportunistic, feeding on anything between 3.57 and 57 ym depending on abundance. However there is evidence that larger phytoplankton are selected when available (Mullin, 1963; Hargrave and Geen, 1970). 60 Fig. 11 shows that copepods in the two smaller size categories were present year-round while the larger copepods "disappeared" from December to March, almost exactly when the diatoms "disappeared" (Fig. 9.). Were grazers responsible for the changes in diatom-to-nanoflagellate ratios the expected pattern would be reversed: that i s , diatoms would be grazed down to low numbers when large grazers appeared and bloom following the disappearance of large grazers. It is therefore apparent that copepod l i f e cycles are timed to phytoplankton cycles and not vice versa. 3. Chemical interactions Several authors have suggested that excretions of algal and bacterial cells may stimulate or inhibit the growth of other algal species and thereby influence succession patterns (Johnston, 1963; Provasoli, 1971; Provasoli and Carlucci, 1974). This has fostered the concept of water "preconditioning" which implies that one species of algae (or bacteria) must release some organic compound, such as a vitamin, into the water before the succeeding species can grow. Alternatively one algal species may ex-crete compounds which inhibit the growth of competitors. The possibility that such a mechanism is operational in the diatom-flagellate succession pattern in Saanich was tested i n the metabolite experiment, in which the most common winter nanoflagellate, Chrysoohromulina kappa, and the f i r s t spring diatom, Thalassiosira, were grown together and separately. When the two species were placed in separate dialysis bags but in the same culture medium, free exchange of substances such as vitamins, amino acids, simple proteins, sugars and so on (any substance with a molecular weight of 12,000 daltons, the pore size of the dialysis membrane, or less) could occur between the two species, although they were kept apart physically. The fact that there was no difference in growth rate whether or not the two species 61 were allowed to exchange metabolites i n t h i s manner indicates there was probably no biochemical i n t e r a c t i o n between them which involved molecules smaller than 12,000 daltons. This s i z e range includes most of the growth regulators known to be present i n plants: vitamins, auxins, g i b b e r e l l i n s , k i n e t i n s , and cytokinins. When Thalassiosira andzChrysochromulina were grown i n mixed culture the growth rate of Thalassiosira was enhanced and that of Chryso-ohromulina was reduced. This could be due to a marked difference i n nutrient uptake rates at the concentration of nutrients used. If Thalassiosira c e l l s were taking up nutrients more quickly than the Chrysoohromulina c e l l s , t h i s could have created a microenvironment i n which nutrient l e v e l s were reduced ( r e l a t i v e to the s i t u a t i o n where Chrysoohromulina was growing alone), and hence caused a reduction i n i t s growth rate. The Thalassiosira c e l l s , on the other hand, were, i n e f f e c t , i n more d i l u t e culture than they were when grown alone (since the t o t a l biomass i n each d i a l y s i s bag was held constant). If Chrysoohromulina were indeed a poorer competitor f o r nutrients than other Thalassiosira c e l l s , the growth rate of the Thalassiosira c e l l s would be enhanced i n mixed culture. The f a c t that the c e l l s i n the d i a l y s i s bags were very concentrated(e.g., 50,000 c e l l s Chrysoohromulina and 6,000 c e l l s Thalassiosira per ml on day 3; see F i g . 12) increases the p o s s i b i l i t y that such a mechanism was involved. This concept of micro-scale nutrient l i m i t a -t i o n has been discussed by Gavis (1976) and Pasciak and Gavis (1974). It was also observed i n mixed cul t u r e that Thalassiosira senesced before Chrysoohromulina, suggesting that i t had a greater uptake threshold (higher K g) f o r the l i m i t i n g n u t r i e n t than Chrysoohromulina. Chrysoohromu-lina, with i t s apparently lower threshold for uptake, was able to continue to grow. A l t e r n a t e l y , perhaps Chrysoohromulina was able to u t i l i z e alternate nitrogen sources, such as organic nitrogen, when inorganic sources were depleted, whereas Thalassiosira was not. 62 If chemical interactions were involved in either of these two instances, for example a release by Chrysoohromulina of some inhibitor which affected Thalassiosira after 3 days, one would expect that these same observations would have been made in the situation where Chrysoohromulina and Thalassiosira were grown in separate dialysis bags but sharing the same medium, that i s , interacting chemically but not physically. The'fact that the growth of the two species in this situation resembled much more closely the patterns observed when they were completely separated, suggests that either metabolic interactions were not occurring, or that the substance in question was too large to pass through the dialysis bag walls. However i t has already been shown that most growth regulators known to be present in plants w i l l readily pass through the dialysis bag walls. My conjectures as to the nutrient kinetics of diatoms and flagel-lates are consistent with reports in the literature. Caperon and Meyer (1972) measured nitrate uptake rates in steady-state cultures of Dunaliella, Monoohrysis and Cyolotella. Maximum uptake rates per unit carbon (V x) were 0.0182, 0.0158 and 0.0858 g-at N (g-at.C) - 1 h" 1 respectively: the diatom took up nitrate at a rate five times faster than the green or the chrysophyte. Eppley et all. (1969) measured maximum nitrate uptake rates in four diatoms which ranged from 0.285-227 x 10 - 7 mole c e l l - 1 h - 1 and in the flagellate Emiliana huxleyi 0.046 x 10" 7 mole c e l l - 1 h - 1 : again the diatoms could take up nitrate 6-5,000 times more quickly than the flagellate. These findings agree with the hypothesis that, under crowded conditions, Thalassiosira might have been able to outcompete Chrysoohromulina for nutrients and therefore grew faster. At low nutrient concentrations, on the other hand, there is evidence that small flagellates have an advantage. Half-saturation constants for 63 n i t r a t e determined by Eppley et al. (1969) ranged from 0.4-9.3 yM for four species of diatoms but the K g value f o r the f l a g e l l a t e Emiliana huxleyi was equal to 0.10 yM. Thus at low n i t r a t e concentrations the f l a g e l l a t e was more e f f i c i e n t . The_ a b i l i t y , of f l a g e l l a t e s to outcompete diatoms £ oiriorgani 'C;, nitrogen-sources has_beeni.observed by Ry ther (1954). was due to the 6 ^ i u t e r . e n o -jf _ e j . l s " . " . •.. . T-hesesobs.erv.ationsis support . the hypothesis that Chrysoohromulina was able to o u t l a s t Thalassiosira i n mixed culture due to i t s a b i l i t y t o function at the reduced nitrafeet l e v e l s which would have been present a f t e r several days' growth. Admittedly t h i s discussion i s based on the r e s u l t s of a s i n g l e experiment under a sin g l e set of favourable conditions. Therefore i t would be presumptuous to generalize and to state that metabolites are d e f i n i t e l y not involved i n f l a g e l l a t e - d i a t o m i n t e r a c t i o n s . However, the purpose of the experiment was to determine whether or not metabolites play a f u n c t i o n a l r o l e i n the spring and f a l l changeovers from f l a g e l l a t e to diatom and back to f l a g e l l a t e populations i n Saanich I n l e t . Conditions at both of these times are comparable to those' used i n t h i s experiment: nutrients are abundant, l i g h t l e v e l s are somewhat low but able to support growth i n both species (see l i g h t experiments), temperatures are moderate, and so on. As w e l l , the species used were i s o l a t e d from Saanich I n l e t , and represent the most common winter f l a g e l l a t e and the f i r s t spring diatom. On t h i s basis i t seems reasonable to conclude that the conditions chosen f o r the experiment bear enough resemblance to the natural s i t u a t i o n that we can state that metabolites are probably not important to the spring and f a l l population changes which occur i n Saanich I n l e t . Moreover, the fa c t that the same s h i f t s occur yearly, regardless of the species composition of the phytoplankton, i s 64 further reason to suppose that metabolites do not play a major role in the observed seasonal shifts in Saanich Inlet phytoplankton. 4. Hydrocarbon pollution In experiments with large plastic containers in Saanich Inlet, Lee (Lee and Takahashi, 1977; Lee et al. , in press) found that low level hydrocarbon pollution favoured the growth of nanoflagellates. Experiments conducted in the present investigation revealed no such enhancement of nanoflagellates by hydrocarbons, either in pure culture or mixed natural populations. It is possible that in the case reported by Lee, the flagellates observed were colourless heterotrophs liv i n g off the organics released by dying phytoplankters, as no distinction was made between colourless and photosynthetic flagellates. Colourless flagellates are abundant i«n Saanich Inlet and commonly outnumber the phytoflagellates by as much as an order of magnitude. In the present study the only species found to be enhanced by the presence of hydrocarbons was in fact a diatom, Skeletonema costatum, whose growth was enhanced by the presence of No. 2 Fuel O i l in concentra-tions less than or equal to 300 ug l - 1 . No algae (with the possible excep-tion of one species of green s o i l algae-see Kruglov and Paromenskaya, 1970) have been found to metabolize hydrocarbons, and the probable mechanism for stimulation appears to be the improvement of membrane permeability which would affect equally phytoplankters o f f a l l taxonomic groups (Dunstan et al.3 1975). B. Factors Contributing to Winter Flagellate Dominance .1. Light Of a l l the factors which combine to produce flagellate dominance in the winter, light appears to be the single most important factor. 65 Parsons and Takahashi in their 1973(a) model of factors controlling c e l l size concluded that light was one of three important factors, along with nutrient concentration and sinking rate. Takahashi et al. (in press) showed that light was the sole factor responsible for depressed primary productivity in the winter in Saanich Inlet. Steemann-Nielsen (1955) observed that " i n highly productive regions having a rich supply of nutrient salt, light intensity is the most important limiting factor. It is also limiting in high latitudes during winter in regions that lack stability of the water column...." Growth versus intensity and photosynthesis versus intensity relationships derived for various Saanich phytoplankters in pure culture did not show this. Results were inconsistent, probably as a result of adaptation problems. There are numerous reports of values for I, , I , rC c I ^ and so on, in the literature; however results here are just as incon-sat ' ' J sistent, due to the wide variety of units used for measuring light intensity and the d i f f i c u l t y in interconversion, as well as preconditioning and adapt-ation problems with the cells themselves. For example, in three separate reports, values for I for Skeletonema eostatwn at 20°C varied from 64 sat to 400 yE m~2 s e c - 1 (Curl and McLeod, 1961; McAllister et al., 1964; Jorgensen, 1970). From the cumulated results of many studies there are no apparent trends in responses to light intensity among species of diatoms, dinoflagellates or nanoflagellates (Table IV). Despite the scatter of values for various growth constants, certain consistencies do exist in the literature with respect to morphologi-cal and chemical responses of algae to light intensity. Results from the present study and others have shown that within a single species, i t is common for small cells to be favoured (e.g., Winokur, 1948; Brown and Table IV. Summary of literature on light constants for various species of algae, to yE m~2 s e c - 1 using the following conversion factors: A l l values were converted 1 klux =92.9 ft-c = 5 x IO - 3 ly min - 1 (Westlake, 1965) 1 ly min 1 = 1 g cal cm 2 mm - 1 = 6.97 x 104 yW cm - 2 = 6.97 x 102 kerg cm - 2 s e c - 1 = 3200 yE m"2 s e c - 1 (Hollaender, 1956) Species Preconditioning I T°C Exptal T°C X c h I sat ''"opt I. , Basis Reference inn lb Avg. of 7 greens 160 20 20 80 y Ryther, 1956 Euglena 51 517 y Cook, 1963 Chlorella 18 y Myers, 1946; Stepanova, 1963 Nannochloris sp. 582 86 21 27-29 hetero. 138 y Thomas, 1966 Dunaliella tevtiolecta 320-480 25 25 42 400 ps McAllister et al. , 1964 960-1280 25 25 42 960 ps McAllister et al. , 1964 Monochrysis lutheri 20 32 320 ps McAllister et al., 1964 Isochrysis galbana 32 ? Kain and Fogg, 1958 Amphidinium carteri 32 400 ps McAllister et al. , 1964 Gyrnnodinium splendens G.. simp lex Gyrnnodinium sp. 581 Gyrnnodinium sp. 582 Gonyaulax polyedra Provocentvum graaile P. mi cans Peridinium Avg. of 4 dinos  86 86 21 21 23-26 23-26 6.1 6.1 130 130 320-1280 32-128 96-320 80-160 >74 >96 >74 >74 160 20 20 160 19-21 5-18 16 160 19-21 >18 16 48 20 20 20 19 400 y Thomas et al. , 1973 y Thomas, 1966 y Thomas, 1966 y Thomas, 1966 y Hastings & Sweeney, 1964 y Barker, 1935 y Kain and Fogg, 1960 y Barker, 1935 y Barker, 1935 y Ryther, 1956  Skeletonema costatum n 112-208 192-256 64-96 40.0 ps Curl and McLeod, 1961 ps Curl and McLeod, 1961 ps Jorgensen, 1970 ps McAllister et al., 1964 Table IV (continued) Preconditioning Exptal Species I T C T C I I. I „ I „ L u-u Basis Reference F c k sat opt mhib Chaetooeros affinis 86 14-16 14-16.5 74-123 448-928 ps Tailing, 1960 Chaetooeros sp. 581 86 21 23-26 1.8 104 y Thomas, 1966 Cosoinodisous exoentrious 192 512 1 Jenkins, 1937 Biddulphia regia 192 512 1 Jenkins, 1937 Asterionella japonica 112 ? Kain and Fogg, 1958 8 64 320 PS Steemann-Nielsen, 1949 Asterionella sp. 16 288 640 ? Tailing, 1957 Nitzsehia dissipata 256 ? Wassink and Kersten, N. olosterium f. 1945 minutissima 4.5 9.3 ps Mann and Myers, 1968 Avg. of 3 diatoms 160 20 20 400 y Ryther, 1956 Natural, northern, October 96 Steemann-Nielsen, 1937 Natural, Berggn, May 192 Berge, 1957 W. P a c i f i c 448 Steemann-Nielsen and A l ' - ; ' ' ' Kholy, 1956  68 Richardson, 1968; Jorgehsen, 1970) and for pigment content to increase at low intensities (Sargent, 1940; Myers, 1946; Kratz and Myers, 1955; Brody, 1958; Steemann-Nielsen et al., 1962; Jorgensen, 1964; Waaland et al. , 1974). Such observations are consistent with a strategy to maximize ut i l i z a t i o n of available light by increasing the amount of sensitive material and increas-ing the area illuminated-to-volume ratio. According to such a strategy, low light levels should favour the growth of nanoplankton. Unlike studies with pure cultures, incubations of natural populations consistently showed that diatoms have narrow tolerance ranges to light relative to flagellates, and that the lower thresholds of diatoms are higher than those of flagellates. A schematic representation of this is given in Fig. 25A. If for a simple, hypothetical phytoplankton community of three diatoms and one flagellate, D^, D 2 and D 3 represent the growth versus light intensity curves for the three diatom species, and Fj the curve for the flagellate species, then between points A and C, and above D, diatoms w i l l dominate, and below A, and between C and D, flagellates w i l l dominate. Note that although diatom D 2 and the flagellate have similar light optima, the diatom w i l l always dominate at those intensities due to a higher in t r i n s i c growth rate. In those regions where i t is dominant the flagellate appears to do so only "by default:" that i s , there is no particu-lar reason why i t should dominate except that there is no diatom which w i l l grow properly at those intensities. According to findings in the present study this simplified scheme is not unrealistic. Although the shapes of the individual curves may vary with other environmental conditions such as temperature, photoperiod and nutrient concentration, the basic relationships represented i n Fig. 25A seem to hold. A B C D LIGHT INTENSITY Figure 25. Schematic representation of the r e l a t i v e l i g h t tolerances of diatoms and f l a g e l l a t e s . A. Growth rate versus l i g h t i n t e n s i t y curves f o r a hypothetical phytoplankton community of 3 species of diatoms and 1 f l a g e l l a t e . B. Generalized curves which include a l l species of diatoms and f l a g e l l a t e s . Diatoms L I G H T I N T E N S I T Y 71 If we were to extrapolate to include a l l diatoms and flagellates, the relationship would probably resemble that shown in Fig. 25B. As a group, flagellates can grow over a much wider range of light intensities than diatoms, but within their narrow "corridor" of suitable light intensi-ties, diatoms have higher growth rates than flagellates and therefore would be expected to dominate a phytoplankton community living within the "corridor 1. 1" Parsons refers to this corridor in a recent model of diatom-flagellate interactions (Parsons ;eifcaa^lf;oinap.ferss) _. x'«. y „. Why should such-a situation exist? What allows flagellates to be so much more independent of light intensity? Why should diatoms have in t r i n s i c a l l y higher growth rates? Flagellates are of course motile and in many cases phototactic, so that i t is possible that they are able to seek out depths in the water column where optimum conditions of light intensity exist. Diurnal vertical migration is known to exist among dinoflagellates (Holmes et al., 1967; Eppley et al., 1968) and has been reported for natural phytoplankton populations (Wood, 1963b). The fact that many flagellates w i l l actively seek out their own preferred light conditions (i.e., avoid both dim and overly bright light intensities) is commonly used to separate them from diatoms and other non-motile forms, as well as from each other, in culture studies (e.g., Halldal, 1958; Tsuji, 1973). Clearly this is not the sole mechanism for flagellate tolerance of wide ranges of light intensity, since i n determinations of photosynthesis versus intensity and growth versus intensity curves they are held in bottles at fixed light intensities. Brown and Richardson (1968), working with 18 species of algae, concluded that "the degree to which light intensity is an influence can be directly related to the degree to which an alga is a photo-autotroph. We can simulate a series with increasing dependence upon light 72 among the algae tested as follows: Astasia, Ochromonas, Euglena, Chlorooocaum,..." Among centric diatoms the capability for facultative heterotrophy i s rare (Lewin, 1963; Lylis and Trainor, 1973; Droop, 1974). The only species which have been reported to have this a b i l i t y are Cyelotella evyptica and Coscinodiscus sp. on glucose (Kuenzler, 1965; Hellebust, 1971; White, 1972). Among pennates the a b i l i t y to use organic substrates i s common (Lewin and Lewin, 1960; Lewin, 1963; Chansang, 1975). The majority of euglenoids are obligate heterotrophs (Droop, 1974), and facultative heterotrophy has been demonstrated among pigmented haptophytes (Rahat and Jahn, 1965; Rahat and Spira, 1967; Provasoli and Pintner, 1968), cryptophytes (Antia et al., 1969), chrysophytes (Pringsheim, 1952; Aaronson and Baker, 1959), chlorophytes (Chodat* and Schopfer, 1960; Shihara and Krauss, 1965), prasinophytes (Turner, 1970) and blue-greens (Kenyon et al., 1972). It i s entirely possible that at limiting light intensities many flagellates can supplement their photoautotrophic nutrition with hetero-trophic nutrition and thus are able to maintain growth during the winter where diatoms cannot. On a broader scale i t i s intuitively reasonable that flagellates as a group should have wider tolerances to light intensity, as they represent a taxonomically much more diverse assemblage than do diatoms. Diatoms a l l belong to the class Bacillariophyceae i n the phylum Chrysophyta, while flagellates include members of many algal phyla, including not only the Chrysophyta but the Chlorophyta, Euglenophyta, Haptophyta (sometimes considered a class of Chrysophyta), Cryptophyta, Pyrrophyta and Rhaphidophyta. Thus the diversity of pigment spectrum and internal structure is considerably greater among the flagellates than the diatoms, and therefore i t might be expected that as a group they would be suited for a wider range of conditions 73 than would diatoms. Brown and Richardson (1968) showed that i n general chlorophyll c , fucoxanthin and per i d i n i n - c o n t a i n i n g algae grow best at i n t e n s i t i e s of 780 f t - c (8.4 klux or approximately 130 yE m-2 sec 1 ) , while phycobilin-containing algae grow best at 400 f t - c (4.3 klux or approximately 70 y E m-2 s e c - 1 ) , and chlorophyll &-containing algae at 1000 f t^c (10..:8,-klux. or approximately 170.yE m-2 s e c - 1 ) . F l a g e l l a t e s are represented i n a l l three of these categories while no diatoms contain phycobilins or chlorophyll b . This corresponds w e l l with the "diatom co r r i d o r " concept, mentioned e a r l i e r , which refers to the narrow, moderate-level range of l i g h t i n t e n s i t y where diatoms w i l l grow, as compared to the much broader range over which f l a g e l l a t e s w i l l grow. Given that f l a g e l l a t e s are adapted to much broader ranges of l i g h t conditions than are diatoms, how then do diatoms compete at a l l ? I t was observed that within t h e i r optima diatoms grow much more quickly thankdo f l a g e l l a t e s . The same observation has beert' made by Eppley (personal communication), although i t c o n f l i c t s with reports made by others (Odum, 1956; Williams, 1964; Saijo and Takesue, 1965). I t i s possible that the metabolic costs of locomotion are such that the amount of energy devoted to growth and reproduction i s reduced i n f l a g e l l a t e s , whereas i n non-motile diatoms r e l a t i v e l y more energy can be devoted to growth. Knoechel (personal communication) has suggested that f l a g e l l a t e s s u f f e r greater losses on the basis of c e l l numbers, due to t h e i r f r a g i l i t y : apparently following c e l l d i v i s i o n l y s i s of 1 of the daughter c e l l s i s not uncommon. Diatoms, with t h e i r s t u r d i e r construction, would be less subject to such losses. A l t e r n a t i v e l y , perhaps when c e l l s are l i g h t saturated some other c e l l process such as nutri e n t uptake becomes l i m i t i n g . Perhaps f a s t e r uptake and as s i m i l a t i o n of nutrients i s what 74 enable diatoms to grow more quickly than flagellates. There was some indication of this in the metabolite experiment. 2. Photoperiod Many researchers have reported increased growth rates at a given light intensity as photoperiod is increased (e.g., Tailing, 1955; Castenholz, 1964; Eppley and Sloan, 1966; Paasche, 1967). In some cases an increase in photoperiod reduced the compensation light intensity (e.g., Paasche, 1968), and often the threshold for photoinhibition (e.g., Castenholz, 1964; Paasche, 1968). Typically however the saturating light intensity does not change (e.g., Castenholz, 1964; Paasche, 1967), although i n Ditylwn brightwellii apparently i t does (Paasche, 1968). The growth rate of Biddulph-ia auvita is independent of day length within the range 9 to 15 hours light per 24 hours (Castenholz, 1964). In most cases reported in the literature, then, as well as in the present study, increasing the photoperiod increases growth rate, lowers I and I ^ ^  but has l i t t l e or no effect on I . Decreasing the photoperiod of course S cL u would have the opposite effect. In the natural population incubation studies, increasing the photoperiod had the effect of shifting the species dominance relations such that individual species peaks occurred at lower intensities. Presumably shortening the day would again have the opposite effect. A typical winter photoperiod in Saanich Inlet might be 8-16, a typical summer photoperiod about 16-8. The change in photoperiod probably has the effect of exaggerating the seasonal variations in available light. Therefore an intensity of 100 yE m sec which in the summer may be able to support the growth of species A, may be insufficient to do so in the winter. In experiments conducted in the laboratory the 75 photoperiod used was 12-12, so that light optima determined for individual species may be underestimated for winter conditions and overestimated for summer. Photoperiod has been reported to have regulatory effects on cellular functions such as pigment synthesis (e.g., Sorokin, 1957; Lorenzen, 1959; Cook, 1961; Castenholz, 1964; Jorgensen, 1966) and c e l l division (e.g., Tamiya et al., 1953; Sweeney and Hastings, 1962; Jorgensen, 1966; Pirson and Lorenzen, 1966; Paasche, 1967; Eppley et a l . , 1967; Tanoue and Aruga, 1975), but there is no evidence that diatoms and flagellates differ in this respect. 3. Temperature Winter temperatures reduced the growth rates of both diatoms and flagellates in pure culture (Fig. 16), but diatoms were judged to be more sensitive to the lower temperatures than were the flagellates. This conclusion was made on the basis of experiments with natural populations, in which gradual increases in the flagellate-to-diatom ratio were seen in a summer population placed at 6°C. These changes were slow, however, on the order of weeks. By comparison, light-induced population shifts occurred in days, much more quickly than temperature-induced shifts, so that temperature must be considered a secondary factor in the diatom-to-flagellate shift which occurs in the f a l l . Unfavourably low temperatures caused the light tolerance ranges of diatoms to narrow. The combined effects of decreasing light intensity, narrowed light tolerances ranges and decreasing temperature would serve to hasten the f a l l crash of diatoms, while the more tolerant flagellates would persist, though suffering somewhat from the poorer growth conditions. 76 Curiously, although present experiments showed consistently that flagellates are able to survive at lower temperatures than diatoms, several reports i n the literature show the opposite to be true (Yentsch and Ryther, 1959; Durbin et al. , 1975; see review by Eppley, 1972). It seems the "diatom corridor" concept applies not only to light but to temperature and other factors as well. 4. Water s t a b i l i t y Salinity data showed that a positive salinity gradient is main-tained year-round in Saanich Inlet. This gradient i s sufficient to main-tain the stability of the water column. Two properties of the inlet show how unusually stable the water of Saanich Inlet i s . Below the s i l l depth (about 75 m) the inlet is anoxic, the oxygen supply being replenished only occasionally when dense outside water s p i l l s over the s i l l into Saanich. Secondly, winds, which normally cause turbulent mixing in the surface layers of the water column, in Saanich do so only to a minimal extent. Instead the effect of winds i s to push the surface "skin" of low salinity water toward one end or out of the inlet (depending on wind direction) , .' resulting in the upwelling of subsurface water, and followed by seiche-type oscillations upon cessation of the winds (Herlinveaux, 1962). Such events could only occur in an unusually stable body of water. Vertical water motion in Saanich is minimal. Two possible mechanisms exist for upward transport, both weak. The f i r s t is the upwelling mentioned above which follows stO'ims. The sedond i s entrainment by the surface freshwater layer. This however is sporadic and restricted primarily to winter and spring due to the weak nature of the estuarine circulation in the inlet (Herlinveaux, 1962). 77 Sinking is therefore a major consideration for phytoplankton cells in Saanich Inlet. Flagellates have a tremendous advantage in this respect. Diatoms could be severely restricted by vertical mixing events. It i s easy to see how in a stable environment such as Saanich Inlet diatoms with good flotation mechanisms would have an, advantage over more rapidly sinking species. If experimentally determined values for saturating light intensity and compensation light intensity of various diatom species are compared with light profiles in Saanich, some indication can be obtained of favourable and compensation depths for each species. The compensation light intensity for Skeletonema oostatum (calculated as the mean value of I measured in the experiments conducted in this study) was 17.3 yE m - 2 s e c - 1 . Since this species had the lowest measured value for I of a l l r c diatoms encountered, i t s compensation intensity must represent the compensation intensity for Saanich Inlet diatoms as a whole. Comparing the value of 17.3 yE m - 2 s e c - 1 with the light profiles in Fig. 6, we obtain compensation depths of 2.5 m on December 16, and 7.5 m on June 21. Saturating light intensities for Nitzsehia delioatis.sima, Thalassiosira spp., Skeletonema oostatum, and Chaetooeros spp. ranged from 183 to 263 yE m - 2 s e c - 1 . These intensities exist in Saanich Inlet only during the summer in a surface "skin" less than 1 m deep.1 Under these circumstances a diatom in Saanich Inlet is rarely light saturated but may easily become light limited. In order to survive, i t must remain above i t s compensation depth of 2.5 m during the winter or 7,5 m r.n i ' • 1 This calculation i s based on data from Fig. 6. Since light values in this figure represent 24-hour averages, i t is entirely possible that saturating light intensities could exist below this surface layer for several hours around mid-day. 78 compensation depth of 2.5 m during the winter or 7.5 m in the summer. (Note that the concept of c r i t i c a l depth does not apply here as there i s no mixed layer.) If a moderate sinking rate of 1 m day 1 is assumed, survival can only be maintained i f upwelling events occur every 2.5 days in the winter and 7.5 days in the summer. If sinking rates are greater than'.c 1 m day - 1 or i f cells are not brought to the surface then of course upwelling must occur more often. Values calculated for survival do not account for processes such as encystment. Actual values for survival in total darkness may be as g great as 9 weeks at 10 C for Skeletonema costatum and more than 30 weeks at 10 C for Chaetoceros gracilis (Antia, 1976). 79 If cells have been surviving at sub-compensation intensities, growth does not begin immediately upon reillumination. Smayda and Mitchell-Innes (1974) observed a lag period of 5 days for Ditylum brightwelliiat 15°C after 46 days in the dark, and longer tor Skeletonema costatum. Due to slower metabolic rates one would expect this lag to be even longer at lower temperatures. Thus in winter i f a cell is brought to the surface following a storm i t must be able to remain afloat long enough to go through the growth-initiating processes which occur during lag phase before increases in numbers can occur. Clearly, neither is there sufficient upwelling nor are diatoms able to remain afloat long enough for this to occur in the winter. The fact that water maintained at surface light intensities produced healthy diatom cultures following incubations of 1 week supports this hypothesis. The absence of'large dinoflagellates during the winter months may be a function of temperature. The small Katodinium votundatum appears to be an exception, since i t is a common winter flagellate. However, larger dinoflagellates, despite their capability for phototaxis, may be limited by the cold temperatures of the winter euphotic zone. C. Summary of Phytoplankton Dynamics It is now possible to construct a qualitative model of the seasonal events in Saanich Inlet. Light appears to be the single most important consideration. The unusually stable nature of the water column and the seasonal change in photoperiod and temperature contribute to reinforce the light effect. Nutrient concentrations may be important during the summer only. Grazing, pollution and chemical interactions among species are of minimal significance. 80 1. Winter In winter reduced solar radiation i s the overall limiting factor to primary productivity in Saanich Inlet. Additionally, shortened days effectively reduce the available light even further, and low temperatures decrease the tolerance of diatoms to sub-optimal light intensities. The range of favourable intensities exists in a shallow layer of water, perhaps 5 m deep, in the surface of the in l e t . t The upper 2 m of this is most frequently occupied by water up to 10°/oo less saline than that immediately below. For flagellates i t is f a i r l y simple to remain within that narrow subsurface band of water where favourable conditions exist. Foe diatoms i t is virtually impossible. While storms may occasionally re-seed the surface with dormant diatom cells or spores, they s t i l l require a period of up to 5 days or more before active growth can be initiated. Well before that time they have usually sunk to below their compensation depths. The low biomass of diatoms which does exist in the winter must consist of these dormant ce l l s , along with perhaps some very small cells with exceedingly slow sinking rates, such as small, single-celled Chaetooeros danicus or Thalassiosira, as well as pennates which are able to rely in part on heterotrophy. Flagellates, less affected by low light intensities, and some with the a b i l i t y to live heterotrophically, can grow in the winter even i f they are not phototactic. Chrysoohromulina kappa, for example, a common winter flagellate, is not phototactic but is known to assimilate several organic substances in dim light (Pintner and Provasoli, 1968). 2. Spring A number of changes occur in the spring. Solar radiation increases, deepening the euphotic zone. Calmer seas increase penetration 81 of s u n l i g h t at the sea s u r f a c e , and daylength i n c r e a s e s ; both of these events e f f e c t i v e l y deepen i t f u r t h e r . As temperatures r i s e diatoms become b e t t e r able to s u r v i v e at p r e v i o u s l y l i m i t i n g l i g h t i n t e n s i t i e s . The f i r s t i n d i c a t i o n of the s p r i n g bloom, however, comes before the diatoms begin to grow. As was seen e a r l i e r , although f l a g e l l a t e s grow i n the w i n t e r t h e i r growth i s improved i n warmer, b r i g h t e r c o n d i t i o n s . As s p r i n g approaches then, the f i r s t event i s an increase i n f l a g e l l a t e numbers. Gradually l i g h t i ncreases to a p o i n t where the euphotic zone i s deep enough to com-pensate f o r t h e s s i n k i n g rates of the diatoms. Note that i n the case of a very windy s p r i n g , or a s p r i n g w i t h large volumes of snow melt (and hence increased entrainment i n the estuary) upwelling may cause the bloom to a r r i v e e a r l i e r than i n a calm s p r i n g . An uncommonly c l o u d l e s s s p r i n g may have the same e f f e c t . The f i r s t diatoms to bloom should be those w i t h lowest l i g h t requirements. Among those, f a s t e r growth r a t e s and simply presence i n the water w i l l determine e x a c t l y which species w i l l bloom. From experiments i n t h i s study, Thalassiosira spp. , Skeletonema oostatum and Nitzsehia delioatissima were a l l found to have s i m i l a r , low r e q u i r e - r ments f o r l i g h t . Looking at the data f o r 1975-1976 phytoplankton ( F i g . 10), Nitzsehia was never present, and Thalassiosira and Skeletonema bloomed co n c u r r e n t l y . Chaetooeros, w i t h higher l i g h t requirements, bloomed much l a t e r . 3. Summer Summer co n d i t i o n s were neveo-rexamined i n the present study, except as a b a s i s f o r comparison w i t h the w i n t e r . However, on the b a s i s of some experimental f i n d i n g s and by l o o k i n g at the trends i n the f i e l d monitoring program, some i n d i c a t i o n can be gained of the dynamics of summer phytoplankton succession i n Saanich I n l e t . 82 In summer growth, conditions were favourable for both diatoms and flagellates. However due to their apparent abi l i t y to grow faster than flagellates under favourable conditions (whatever the mechanism), diatoms dominated the phytoplankton almost without exception. Diatoms appeared to be regulated by the availability of nitrate. When light conditions became favourable in the spring the diatoms bloomed, but soon the nitrate supply was depleted, and they and the flagellates crashed. Wind then became instrumental in upwelling new nutrient supplies (as well as seed diatom stock) which enabled production to be renewed (see Fig. 26). Flagellates were no less abundant in the summer the winter. Although i t i s likely that they were outcompeted by diatoms for nitrate, they may have been able to u t i l i z e alternate, less abundant sources of nitrogen, such as organic nitrogen. There is some evidence that flagellates can outcompete diatoms for this source (Ryther, 1954). Alternately there exists the possibility that flagellates and diatoms were separated vertically in the water column, although there was no indication of this in Saanich Inlet profiles (Fig. 27). In many instances during the summer a diatom bloom was preceded by a small flagellate increase which decreased again as the diatoms began to grow (Fig. 26). It may be that flagellates are quicker to respond to a boost in the nutrient supply but are eventually overtaken by diatoms. There was no evidence during the summer studied, to support the idea that flagellates proliferate between diatom blooms during periods of nitrogen depletion. It is interesting to note that, approaching the summer solstice (June 21), the overall nitrate level in the top 20 m gradually decreased, 83 — •- E a £ o 90 1800 80 I600H 70 I400h MAY JUN SEP OCT Figure 26. Nitrate concentration and the changes in biomass of centric diatoms and flagellates in the top 20 m during the summer of 1976. nitrate, centric diatoms, flagellates, f average wind speed >10 km h - 1 . At (J) , a bloom (of diatoms?) may have occurred but may have not been observed: chlorophyll a which was sampled during this period rose from 2.70 ug l - 1 on June 21 to 10.9 and 8.04 yg l - 1 on June 24 and 28 respectively, then f e l l back to 1.54 yg l - 1 on July 1. B I O M A S S , u g C I " 1 O 20 40 CF) o 10 20 (F) n 0 . 10.00 . 20P0 (D) Q 500 10.00(D) MAY 17 . MAY 31 0 10 20 oO 40 C,F) 0 10 20 30 ( F ) J U N 7 J U N 14 Figure 27. V e r t i c a l d i s t r i b u t i o n s of c e n t r i c diatoms and f l a g e l l a t e s on days of maximum and minimum diatom numbers. 85 and following the solstice i t gradually increased again (Fig. 26). In Fig. 7 i t can be seen that this was due to changes in the depth of the nitrate depleted layer. This undoubtedly relates to the deepening of the euphotic zone to i t s maximum around the solstice and i t s shallowing after that date. As the euphotic zone deepened, .diatom productivity could occur deeper, and hence nitrate was depleted down to greater depths; as the euphotic zone became shallower so did the nitrate depleted layer. The effect of light can be seen even in the summer. 4. F a l l The sequence of events in the f a l l is essentially the reverse of spring. The euphotic zone gradually shallows; temperature and daylength become more restrictive. Perhaps diatoms survive longer than might be expected from thresholds demonstrated in the spring or in laboratory experiments, as has been shown to be possible. Eventually they must crash however, and then the flagellates take over "by default." Although i t was not observed in 1976 i t is conceivable that a period of sunny and/or windy weather could produce an isolated f a l l bloom, probably of a low-light tolerante species such as Skeletonema, Thalassiosira or Nitzsehia, after the main diatom crash; however i t would likely be short-lived. An indication of the c r i t i c a l light intensities in the spring and f a l l can be obtained by comparing Fig. 5 and 9. A line drawn through the graph of total daily solar radiation (Fig. 5) at about 2100 yE m-2 sec' intersects the curve at almost precisely the onset of the spring diatom 1 The decline in diatom numbers is truly a "crash," occurring within a week or less. See for example the rapid decrease in diatom biomass at the beginning of November, 1975, in Figure 9. 86 bloom and the f a l l crash. Therefore, in Saanich Inlet, depending upon conditions of cloud cover, wind mixing and seed species, the spring diatom bloom and f a l l crash should occur when the daily solar radiation levels reach 100 pE m - 2 s e c - 1 . D. Problems Several approximations and sacrifices in methodology acted as sources of error in the present study. 1. Light profiles were calculated from available data on total daily solar radiation and percent transmission of light through the water column at noon. Since the amount of light reaching any depth is a function of sun angle, sea conditions and cloud cover, a profile calculated from data taken at noon may not be representative of the day: in fact i t undoubtedly overestimated the average light penetration for the day due to variations in sun angle. Diurnal variationsiin intensity are not considered: a l l data were given as averages over a 24-hour period. Actual intensities varied from perhaps three times higher than those given in Fig. 6 at noon to zero at night. Since light varied seasonally over an order of magni-tude, the problem is likely not serious. 2. Different quantum meters were used to measure light in the laboratory and the f i e l d , although their sensitivity ranges were comparable. The light sources were also different. For these reasons and that presented above, data from the laboratory and f i e l d are only roughly comparable. 3. Samples for phytoplankton counting were integrated over varying depths, making i t d i f f i c u l t to make comparisons from day to day. 4. Under ideal circumstances a l l light experiments should have been conducted concurrently, especially those involving natural populations. However since only a single incubator capable of maintaining a single temp-erature and photoperiod was available this was impossible. Fortunately the composition of the population did not affect the outcome of the experiments. 87 5. Experiments involving phytoplankters in pure culture produced inconsis t-tent results. From reports in the literature as well as the present study i t appears that depending upon the clone and i t s physiological state the behaviour within a single species may vary widely (see Table IV). For this reason i t appears wise to regard the interpretation and ecological significance of culture studies with some caution. 6. Adaptation seems to be a problem with any physiological study. This was encountered with the pure culture experiments, and there is no reason to expect that i t should not also arise with natural populations. However the fact that results proved to be f a i r l y consistent whether the actual population was obtained during the summer or winter suggests that the observations made were applicable year-round. The process of adaptation was observed in the long-term experiment, and although changes did occur, the basic light-growth relationships persisted. 7. Many of the conclusions were based on a single year's f i e l d study. Data obtained over several years would have provided a superior basis for s tudy. E. Proposed Research Further research is indicated on the role of nutrients and upwelling in regulating summer succession. Davis and Harrison (unpublished) have shown in preliminary work with continuous culture of natural populations that reduced nitrogen turnover rates favour the growth of flagellates. Work of this type with natural populations may be of greater ecological value than pure culture determinations of nutrient kinetics. Further experimentation with light thresholds as described in this study may provide the basis for a mathematical model which compares those thresholds with measured sinking rates, c e l l survival and light levels 88 to p r e d i c t the timing and sequence of the spring diatom bloom and f a l l crash. I f t h i s i s combined with knowledge obtained on n u t r i e n t e f f e c t s i t should become possible to manipulate phytoplankton populations. CONCLUSION The competition between diatoms and f l a g e l l a t e s i n Saanich I n l e t seems totbeenot so much a competition but rather a matter of s u r v i v a l f or diatoms. F l a g e l l a t e s have wide tolerance ranges f o r a number of environ-mental factors and can grow year-round. However t h e i r growth rates are slow. Diatoms on the other hand can grow quickly but only under l i m i t e d circumstances. Therefore when we consider factors regulating the r a t i o of diatoms to f l a g e l l a t e s i n Saanich I n l e t , we are i n r e a l i t y looking at factors which regulate diatoms. When they are favourable, diatoms grow and outnumber the f l a g e l l a t e s ; when they are unfavourable the diatoms die and only the f l a g e l l a t e s remain. 89 BIBLIOGRAPHY Aaronson, S. and H. Baker. 1959. A comparative biochemical study of two species of Ochromonas.• J. Protozool. 6: 282-284. Antia, N.J. 1976. Effects of temperature on the darkness survival of marine microplanktonic algae. Microbial Ecology 3: 41-54. • , J.Y. Cheng and F.J.R. Taylor. 1969. The heterotrophic growth of a marine photosynthetic cryptomonad (Chvoomonas salina). Proc. int. Seaweed Symp. 6: 17-29. Barker, H.A. 1935. The culture and physiology of the marine dinoflagel-lates. Arch. Mikrobiol. 6: 157-181. Berge, G. 1957. The primary production in the Norwegian Sea, June 1954, as measured by an adapted 1 4C-technique. Symposium of the Intern. Council for the Explor. of the Sea, Bergen, 1957. Preprint C/22. Bernard, F. and J. Lecal. 1960. Plancton unicellulaire recolte dans l*oc£an Indien par le Charrot (1950) et le Norsel (1955-56). Bull. int. Oceanogr., Monaco 1166: 1-59. Booth, CR. 1976. The design and evaluation of a measurement system for photosynthetically active quantum scalar irradiance. Limnol. Oceanogr. 21(2): 326-336. Brody, M. 1958. The participation of chlorophyll and phycobilins in the photosynthesis of red algae. II. Observations on cellular structure of Porphyridium omentum. Ph.D. dissertation, Univ. I l l i n o i s . Microfilms L.C. Card No. Mic 58-1686 I. Brown, T.E. and F.L. Richardson. 1968. The effect of growth environment on the physiology of algae: light intensity. J. Phycol. 4: 38-54. 90 Buchanan, R.J. 1966. A study of the species composition and ecology of the protoplankton of a British Columbia inlet. Ph.D. disserta-tion, University of British Columbia. 268 pp. Caperon, J. and J. Meyer. 1972. Nutrient-limited growth of marine phyto-plankton — I I . Uptake kinetics and their role in nutrient-limited growth of phytoplankton. Deep-Sea Res. 19: 619-632. Castenholz, R.W. 1964. The effect of daylength and light intensity on the growth of l i t t o r a l marine diatoms in culture. Physiologia PI. 17: 951-963. Chansang, H. 1975. Growth physiology and the glucose transport system of the pennate diatom, Amphora coffeaeformis var. perpusilla. Ph.D. dissertation, University of Miami. Chodat, F. and J.F. Schopfer. 1960. Effets de synergie des conditions simultanees de carboautotrophie et deecarboheterotrophie observees dans la croissance de quelques algues. Schweiz. Z.. Hydrol. 22: 103-110. Cook, J.R. 1961. Euglena gracilis in synchronous division. II. Biosyn-thetic rates over the l i f e cycle. Biol. Bull. 121: 277-289. . 1963. Adaptations in growth and division in Euglena effected by energy supply. J. Protozool. 10: 436-444. Curl, H., Jr. and G.C. McLeod. 1961. The physiological ecology of a marine diatom, Skeletonema costatum (Grev.) Cleve. J. mar. Res. 19: 70-88. Droop, M.R. . 1974. Heterotrophy of carbon. Pages 530-559 in W.D.P. Stewart, ed. Algal physiology and biochemistry. University of California Press, Berkeley and Los Angeles. Dugdale, R.C. 1967. Nutrient limitation in the sea: dynamics, 91 identification and significance. Limnol. Oceanogr. 12: 685-695. Dunstan, W.M. , L.P. Atkinson and J. Natoli. 1975. Stimulation and inhibition of phytoplankton growth by low molecular weight hydrocarbons. Mar. Bi o l . 31: 305-310. Durbin, E.G., R.W. Krawiec and T.J. Smayda. 1975. Seasonal studies on the relative importance of different size fractions of phytoplankton in Narragansett Bay (USA). Mar. Biol.32: 271-287. Dussart, B.H. 1965. Les differences categories de plancton. Hydrobiologia 26 : 72-74 (with erratum). Eppley, R.W. 1972. Temperature and phytoplankton growth in the sea. Fish. Bull. 70: 1063-1085. ! , R.W. Holmes and E. Paasche. 1967. Periodicity in c e l l division and physiological behaviour of Ditytum brightwell'ti3 a marine planktonic diatom, during growth in light-dark cycles. Arch. Mikrobiol. 56: 305-323. , 0. Holm-Hansen and J.D.H. Strickland. 1968. Some observations on the vertical migration of dinoflagellates. J. Phycol. 4: 333-340. , J.N. Rogers and J.J. McCarthy. 1969. Half-saturation constants for uptake of nitrate and ammonium by marine phyto-plankton. Limnol. Oceanogr. 14: 912-920. and P.R. Sloan. 1966. Growth rates of marine phyto-plankton: correlation with light absorption by c e l l chlorophyll a. Physiologia PI. 19: 47-59. Fulton, J. 1972. Keys and references to the marine Copepoda of British Columbia. Fish. Res. Bd. Canada Tech. Rept. No. 313. 63 pp. 92 Gavis, J. 1976. Munk and Riley revisited: nutrient diffusion transport and rates of phytoplankton growth. J. mar. Res. 34: 161-179. Halldal, P. 1958. Action spectra of phototaxis and related problems in Volvocales, Utva-gametes and Dinophyceae. Physiologia PI. 11: 118-153. Hargrave, B.T. and G.H. Geen. 1970. Effects of copepod grazing on two natural phytoplankton populations 0 4 . tons a) • J. Fish. Res. Bd. Canada 27: 1395-1403. Hastings, J.W. and B.M. Sweeney. 1964. Phased c e l l division in the marine dinoflagellates. Pages 307-321 in E. Zeuthen, ed. Synchrony in c e l l division and growth. Interscience, New York. Hellebust, J.A. 1971. Kinetics of glucose transport and growth of CyeloteUa cryptica Reimann, Lewin and Guillard. J. Phycol. 7: 1-4. Herlinveaux, R.H. 1962. Oceanography of Saanich Inlet in Vancouver Island, British Columbia. J. Fish. Res. Bd. Canada 19: 1-37. . 1968. Features of water movement over the " s i l l " of Saanich Inlet, June-July, 1966. Fish. Res. Bd. Canada Tech. Rept. No. 99. 34 pp. 19 72. Oceanographic features of Saanich Inlet, 9 May - 2 July, 1968. Fish. Res. Bd. Canada Tech. Rept. 300. 53 pp. Hollaender, A., ed. 1956. Radiation biology. III. Visible and near visible light. McGraw-Hill, New York. Holmes, R.W. 1958. Physical, chemical and biological observations obtained on expedition SCOPE in the eastern tropical Pacific, November - December, 1956. S.S.R., Fish. No. 279, U.S.F.W.S.: 1-117. 93 Holmes, R.W., P.M. Williams and R.W. Eppley. 1967. Red water in La Joll a Bay, 1964-1966. Limnol. Oceanogr. 12(3): 503-512. Jenkins, P.G. 1937. Oxygen production by the diatom Coscinodiseus excentrieus in relation to submarine illumination in the English Channel. J. mar. b i o l . Ass. U.K. 22: 301-343. J i t t s , H.R. , CD. McAllister, K. Stephens and J.D.H. Strickland. 1964. The c e l l division rates of some marine phytoplankters as a function of light and temperature. J. Fish. Res. Bd. Canada 21(1): 139-157. Hohnston, R. 1963. Sea water, the natural medium of phytoplankton. I. General features. J. mar. b i o l . Ass. U.K. 43: 427-456. Horgensen, E.G. 1964. Chlorophyll content and rate of photosynthesis in relation to c e l l size of the diatom Cyelotelta meneghiniana. Physiologia PI. 17: 407-413. . 1966. Photosynthetic activity during the l i f e cycle of synchronous Skeletonema c e l l s . Physiologia PI. 19: 789-799. 1970. The adaptation of plankton algae. V. Variation in the photosynthetic characteristics of Skeletonema costatum cells grown at low light intensity. Physiologia PI. 23: 11-17, Kain, J.M. and G.E. Fogg. 1958. Studies on the growth of marine phyto-plankton. I. Asterionella japonica Gran. J. mar. b i o l . Ass. U.K. 37: 397-413. and . 1960. Studies on the growth of marine phytoplankton. III. Troroeentrum mieans Ehrenberg. J. mar. b i o l . Ass. U.K. 39: 33-50. Kenyon, C.N., R. Rippka and R.Y. Stanier. 1972. Fatty acid composition and physiological properties of some filamentous blue—green algae. 94 Arch. Mikrobiol. 83: 216-236. Kratz, W.A. and J. Myers. 1955. Photosynthesis and respiration of three blue-green algae. PI. Physiol. 30: 275-280. Kruglov, Yu.V. and L.N. Paromenskaya. 1970. Detoxification of simazine by microscopic algae. Mikrobiologiya 39(1): 157-160. Kuenzler, E.J. 1965. Glucose-6-phosphate uti l i z a t i o n by marine algae. J. Phycol. 1: 156-164. Lamport, W. 1974. A method for determining food selection by zooplankton. Limnol. Oceanogr. 19: 995-997. Lee, R.F. and M. Takahashi. 1977. The fate and effect of petroleum in controlled ecosystem enclosures. Rapp. P.-v. R6un. Cons. perm, int. Explor. Mer 171: 150-156. , , J.R. Beers, W.H. Thomas, D.L.R. Seibert, P. Koeller, and D.R. Green. In press. Controlled ecosystems: their use in the study of the effects of petroleum hydrocarbons on plankton. In: Pollution and physiology of marine organisms. Lewin, J.C. 1963. Heterotrophy in marine diatoms. Pages 229-235 in CH. Oppenheimer, ed. Symposium on marine microbiology. Thomas, Springfield, 111. and R.A. Lewin. 1960. Auxotrophy and heterotrophy in marine l i t t o r a l diatoms. Can. J. Mic-robiol. 6: 127. Lorenzen, H. 1959. Die photosynthetische Sauerstoffproduktion wachsender ChXoveUa bei langfristig intermittierender Belichtung. Flora 147: 382-404. Lund, J.W.G., C. Kipling and E.D. LeCren. 1958. The inverted microscope 95 method of estimating algal numbers and the s t a t i s t i c a l basis of estimations by counting. Hydrobiologia 11: 143-170. Ly l i s , J.C. and F.R. Trainor. 1973. The heterotrophic capabilities of Cyalotella meneghiniana . J. Phycol. 9: 365-369. McAllister, CD., N. Shah and J.D.H. Strickland. 1964. Marine phyto-plankton photosynthesis as a function of light intensity: a comparison of methods. J. Fish. Res. Bd. Canada 21(1): 159-181. Maddux, W.S. and R.F. Jones. 1964. Some interactions of temperature, light intensity, and nutrient concentration during the contin-uous culture of N-itzschia clostevium and Tetraselmts sp. Limnol. Oceanogr. 9: 79-86. Malone, T.C 1971. Relative importance of nanno and net plankton as primary producers in the California current system. Fish. Bull. 69(4): 799-820. Mann, J.E. and J. Myers. 1968. On pigments, growth, and photosynthesis of Phaeodactyturn trioornutum. J. Phycol. 4: 349-355. Mullin, M.M. 1963. Some factors affecting the feeding of marine copepods of the genus Calanus. Limnol. Oceanogr. 8: 239-250. Munk, W.H. and G.A. Riley. 1952. Absorption of nutrients by aquatic plants. J. mar. Res. 11: 215-240. Myers, J. 1946. Culture conditions and the development of the photosyn-thetic mechanism. III. Influence of light intensity on photo-synthetic characteristics of Chlorella. J. gen. Physiol. 29: 429-440. Nival, P. and S. Nival. 1973. Efficacite" de f i l t r a t i o n des cop£podes planctoniques. Annls. Inst, oceanogr. 49: 135-144. 96 N i v a l , P. and S. N i v a l . 1976. P a r t i c l e retention e f f i c i e n c i e s of an herbivorous copepod, Aeartia clausi (adult and copepodite stages); e f f e c t s on grazing. Limnol. Oceanogr. 21: 24-38. Odum, H.T. 1956. E f f i c i e n c i e s , s i z e of organisms and community structure. Ecology 37: 592-597. Paasche, E. 1967. Marine plankton algae grown with light-dark cycles. 1. Coccolithus huxleyi. Physiologia PI. 20: 946-956, . 1968. Marine plankton algae grown with light-dark cycles. 2. Ditylum brightwellii and Nitzsehia turgidula. Physiologia PI. 21: 66-77. Parsons, T.R., P.J. Harrison and R. Waters. In6press. An experimental simulation of changes i n diatom and f l a g e l l a t e blooms. J. exp. mar. b i o l . e c o l . and M. Takahashi. 1973a. Environmental control of phytoplankton c e l l s i z e . Limnol. Oceanogr. 18(4): 511-515. and . 1973b. B i o l o g i c a l oceanographic processes. Pergamon Press, Oxford, New York, Toronto, Sydney and Braunschweig. 186 pp. Pasciak, W.J. and J. Gavis. 19 74. Transport l i m i t a t i o n of nutrient uptake i n phytoplankton. Limnol. Oceanogr. 19: 881-888. Pintner, I . J . and L. Prova s o l i . 1968. Heterotrophy i n subdued l i g h t of three Chrysoohromulina species. B u l l . Misaki Mar. B i o l . Inst., Kyoto Univ. 12: 25-31. Pirson, A. and H. Lorenzen. 1966. Synchronized d i v i d i n g algae. A. Rev. PI. P h y s i o l . 17: 439-458. Poulet, S.A. 1974. Seasonal grazing of Pseudocalanus minutus on p a r t i c l e s . 97 Mar. B i o l . 25: 109-123. Pringsheim, E.G. 1952. On the n u t r i t i o n of Ochvomonas . Q. J l . microsc. S c i . 93: 71-96. Pro v a s o l i , L. 1968. Media and prospects f o r the c u l t i v a t i o n of marine algae. Pages 63-75 in A. Watanabe and A. H a t t o r i , eds. Cultures and c o l l e c t i o n s of algae. Proc. U.S.-Japan Conf., Hakone, Sept., 1966. Japan. Soc. Plant P h y s i o l . . 1971. N u t r i t i o n a l r e l a t i o n s h i p s of marine organisms. Pages 369-382 in J.D. Costlow, ed. F e r t i l i t y of the sea. Gordon and Breach, New York. and A.F. C a r l u c c i . 1974. Vitamins and growth regulators. Pages 530-559 in W.D.P. Stewart, ed. A l g a l physiology and biochemistry. University of C a l i f o r n i a Press, Berkeley and Los Angeles. Rahat, M. and T.L. Jahn. 1965. Growth of Pvymnesium parvum i n the dark: a note i n i c h t i o t o x i n formation. J. Protozool. 12: 266-280. and Z. Spira. 1967. Specificity of glycerol for dark growth of Pvymnesium pavvum. J. Protozool. 14: 45-48.• Raymont, J.E.G. and F. Gross. 1942. On the feeding and breeding of Calanus finmavchicus under laboratory conditions. Proc. R. Soc. Edinb. 6IB: 267-287. Richman, S. and J.N. Rogers. 1969. The feeding of Calanus helgolandieus on synchronously growing cultures of the marine diatom Ditylum bvightmellii. Limnol. Oceanogr. 14: 701-709. Ryther, J.H. 1954. The ecology of phytoplankton blooms in Moriches Bay and Great South Bay, Long Island, New York. Biol. Bull. 106: 198-209. 98 Ryther, J.H. 1956. Photosynthesis in the ocean as a function of light intensity. Limnol. Oceanogr. 1: 61. . 1969. Photosynthesis and fish production in the sea. Science 166: 72-76. Saijo, Y. and K. Takesue. 1965. Further studies on the size distribution of photosynthesizing phytoplankton in the Indian Ocean. J. oceanogr. Soc. Japan 20: 264-271. Sargent, M.C. 1940. Effect of light intensity on the development of the photosynthetic mechanism. Plant Physiol. 15: 275-290. Schbne, H. 1970. Studies on the motion of the sea as an ecological factor for plankton organisms with special regard to marine diatoms. Int. rev. ges. Hydrobiol. 5,4: 595-677. Semina, H.J. 1972. The size of phytoplankton cells in the Pacific Ocean. Int. rev. ges. Hydrobiol. 57: 177-205. Shihara, I. and R.W. Krauss. 1965. Chlorella: physiology and taxonomy of 41 isolates. University of Maryland Press, College Park, U.S.A. Smayda, T.J. 1963. Succession of phytoplankton, and the ocean as a holocoenotic environment. Pages 260-274 in CH. Oppenheimer, ed. Marine microbiology. Thomas, Springfield, 111. . 1970. The suspension and sinking of phytoplankton in the sea. Oceanogr. Mar. Biol. Ann. Rev. 8: 353-414. » and B. Mitchell-Innes. 1974. Dark survival of auto-trophic, planktonic marine diatoms. Mar. Bio. 25: 195-202. Sorokin, C. 1957. Changes in photosynthetic activity in the course of c e l l development in Chlorella. Physiologia PI. 10: 659-666. 99 Steemann-Nielsen, E. 1937. The annual amount of organic matter produced by the phytoplankton in the sound off Helsingor. Meddr. Koimnn. Danm. Fisk.-og Havunders., Ser. Plankton 3(3). - 1949. A reversible inactivation of chlorophyll in vivo. Physiologia PI. 2: 247. . 1955. Production of organic matter in the oceans. J. mar. Res. 14(4): 364-386. and A.A.A1 Kohly. 1956. Use of 1 1 + C-technique in measur-ing photosynthesis of phosphorus or nitrogen deficient algae. Physiologia PI. 9: 144-153. , V.K. Hansen and E.G. Jorgensen. 1962. The adaptation to different light intensities in Chlorella vulgaris and the time dependence on transfer to a new light intensity. Physiologia PI. 15: 505-517. Stepanova, A.M. 1963. The effect of light on growth and photosynthesis of Chlorella. Vestnik Leningradskogo Univ. 21: 72-85. Strathmann, R.R. 1967. Estimating the organic carbon content of phyto-plankton from c e l l volume or plasma volume. Limnol. Oceanogr. 12: 411-418. Strickland, J.D.H. and T.R. Parsons. 1972. A practical handbook of seawater analysis. Fish. Res. Bd. Canada, Bull. 167 (2nd ed.). 310 pp. Sweeney, B.M. and J.W. Hastings. 1962. Rhythms. Pages 172-183 in R.A. Lewin, ed. Physiology and biochemistry of algae. Academic Press, New York. Takahashi, M., J. Barwell-Clarke, F. Whitney and P. Koeller. In press. Winter condition of marine plankton populations in Saanich Inlet, 100 B r i t i s h Columbia. I. Phytoplankton and t h e i r surrounding environment. J. exp. mar. B i o l . Ecol. T a i l i n g , J.F. 1955. The r e l a t i v e growth rates of three planktonic diatoms i n r e l a t i o n to underwater radiation and temperature. Ann. Bot. N.S. 19: 330-341. . 1957. Photosynthetic characteristics of some fresh-water plankton diatoms i n r e l a t i o n to underwater radiation. New Phytol. 56: 29-50. . 1960. Comparative laboratory and f i e l d studies of photosynthesis by a marine planktonic diatom. Limnol. Oceanogr. 5: 62-77. Tamiya, H., K. Shibata, T. Sasa, T. Iwamura and Y. Morimura. 1953. Effect of diurnally intermittent illumination on the growth and some c e l l u l a r characteristics of Chlovella. Pages 76-84 in J.S. Burlew, ed. Algal culture from laboratory to p i l o t plant. Carnegie Inst. Wash. Publ. 600. Tanoue, E. and Y. Aruga. 19 75. Studies on the l i f e cycle and growth of Platymonas sp. i n culture. Japan. J. Bot. 20(8): 439-460. Thomas, W.H. 1966. Effects of temperature and illuminance on c e l l d i v i s i o n rates of three species of t r o p i c a l oceanic phytoplankton. J. Phycol. 2(1): 17-22. , A.N. Dodson and C.A. Linden. 1973. Optimum l i g h t and temperature requirements for Gyrnnodinium splendens , a l a r v a l f i s h food organism. Fish. B u l l . 71: 599-601. and D.L.R. Seibert. 1977. Effects of copper on the dominance and the divers i t y of algae: controlled ecosystem p o l l u t i o n experiment. B u l l . mar. S c i . 27(1): 23-33. 101 Titman, D. and S.S. Kilham. 1976. Phosphate and s i l i c a t e growth and uptake kinetics of the diatoms Asterionella formosa and Cyclotella meneghiniana in batch and semicontinuous culture. J. Phycol. 12: 375-383. Tsuji, T. 1973. Distribution and function of flagellates in marine ecosystem with special reference to nitrogen metabolism by the red tide flagellates in coastal waters. Ph.D. dissertation, University of Tokyo, Tokyo, Japan. Turner, M.F. 1970. Page 13 in Scottish Marine Biological Association,' Report of the Council for 1969/70. Uehlinger, V. 1964. Etude statistique des methodes de denombrement planctonique. Archs. Sci. phys. nat. 17: 121-233. Utermohl, H. 1958. Zur Vervollkommnung der quantitativen Phytoplankton-Methodik. Mitt. int. Verein. theor, angew. Limnol. 9: 38 pp. Waaland, J.R., S.D. Waaland and G. Bates. 1974. Chloroplast structure and pigment composition in the red alga G r i f f i t h s i a pacifioa: regulation by light intensity. J. Phycol. 10: 193-199. Wassink, E.C. and J.A.H. Kersten. 1944. Observations on the photosynthesis and the chlorophyll fluorescence of diatoms. Enzymologia 11: 282-312. Westlake, D.F. 1965. Some problems in the measurement of radiation under water: a review. Photochemistry and Photobiology 4: 849-868. White, A.W. 1972. Facultative heterotrophy in marine diatoms. Ph.D. dissertation, Harvard University, Massachusetts. 179 pp. Williams, R.B. 196,4. Division rates of salt marsh diatoms in relation to salini t y and c e l l size. Ecology 45: 877-880. 102 Winokur, M. 1948. Growth relationships of Chlorella species. Am. J. Bot. 35: 118-129. Wood, E.J.P. 1963a. The relative importance of groups of protozoa and algae in marine environments of the southwest Pacific and east Indian Oceans. Pages 236-240 in CH. Oppenheimer, ed. Symposia on marine microbiology. Thomas, Springfield, 111. . 1963b. Some relationships of phytoplankton to envir-onmental Pages 275-285 in CH. Oppenheimer, ed. Symposia on marine microbiology. Thomas, Springfield, 111. and P.S. Davis. 1956. Importance of smaller phyto-plankton elements. Nature, Lond. 177: 438. Yentsch, CS. and J.H. Ryther. 1959. Relative significance of the net-p'hytoplankton and nanoplankton in the waters of Vineyard Sound. J. Cons. perm. int. Explor. Mer 24: 231-238. 103 APPENDIX I Composition of enriched sea water (E.S.) culture medium f o r algae (Provasoli, 1968). s. Enrichment 1. D i s t i l l e d water 100 ml 2. NaN0§ 3 350 mg 3. Na 2 glycerophosphate 50 mg 4. T r i s buffer 500 mg 5. Adjust pH to 7.6 6. Autoclave 7. Ee (as EDTA, 1:1 molar) 1 2.5 mg 8. P II metals 2 25 ml 9. Vitamin B l 2 (autoclave) 10 yg Thiamine (autoclave) 0.5 mg B i o t i n (prepare a s e p t i c a l l y ) 5 yg (These may be prepared as a si n g l e s o l u t i o n . Keep frozen.) 1 Dissolve 351 mg Fe(NH4) 2(SO^) 2.6H 20 and 330 mg Na2EDTA i n 500 ml d i s t i l l e d water; 1 ml of t h i s s o l u t i o n = 0.1 mg Fe. Autoclave. 2 P II Metal Mix (directions f o r making 100 ml of metal mix) 1 ml contains quantity f o r c o e f f i c i e n t quantity of s a l t s to 100 ml for s a l t add to 100 ml 1. Na 2 EDTA 1 mg 100 mg 100 mg Na2EDTA 2. Ee OCOli mg 1 mg X 4.9 4.9 mg FeCl 3.6H 20 3. Mn 0.04 mg 4 mg X 4.1 16.4 mg MnSO^.4H20 4. Zn 0.005 mg 0.5 mg X 4.4 2.2 mg ZnSO^HgO 5. Co 0.001 mg 0.1 mg X 4.77 0.48 mg CoSO^B^O 6. B 0.2 mg 20 mg X 5.7 114 mg H3BO3 AuAutoelave. To obtain E.S. medium add 2 ml E.S. enrichment to 100 ml f i l t e r e d sea water. For bacteria-free cultures s t e r i l i z e enrichment i n tubes, add a s e p t i c a l l y to f i l t e r - s t e r i l i z e d or autoclaved sea water. S i l i c a t e enrichment f o r diatoms: Add 1 ml Na 2Si0 3.9H 20 (2.8 g/100 ml) sol u t i o n and 0.2 ml 1 N HC1, admixed, per 100 ml of medium. 104 Approximate enrichment of nutrients obtained by using E.S. culture medium (concentrations in unless otherwise specified) Nutrient 100% E.S. - 5% E.S. Nitrate 538 27 Silicate 985 49 Phosphate 30 1. 5 Tris buffer 415 21 EDTA 15 0. .73 Iron 6. 4 0. ,32 Manganese 24 1. ,2 Zinc 0. 25 0. ,013 Cobalt 0. 055 0. ,0028 Boron 661 3. .0 Vitamin B12 0. 97 nM 0, .048 nM Thiamine 0. 19 0, .0097 Biotin 2. 6 nM 0, .13 nM 


Citation Scheme:


Citations by CSL (citeproc-js)

Usage Statistics



Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            async >
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:


Related Items