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The abundance and distribution of heterotrophic and autotrophic nanoflagellates in the NE Subarctic Pacific Doherty, Sean Patrick 1995

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The Abundance and Distribution of Heterotrophic and Autotrophic Nanoflagellates in the NE Subarctic Pacific by SEAN PATRICK DOHERTY B.A., Skidmore College, 1991  A THESIS SUBMITTED IN PARTIAL F U L F I L M E N T OF T H E REQUIREMENTS FOR T H E D E G R E E OF MASTER OF SCffiNCE in T H E F A C U L T Y OF GRADUATE STUDIES (Department of Zoology)  We accept this thesis as conforming to the required standard  T H E UNIVERSITY OF BRITISH COLUMBIA February 1995 © Sean Patrick Doherty, 1995  In  presenting this  degree at the  thesis  in  University of  partial  fulfilment  of  this thesis for  department  or  by  his  or  scholarly purposes may be her  representatives.  permission.  of  J S L s^s> i  The University of British Columbia Vancouver, Canada  DE-6 (2/88)  for  an advanced  Library shall make  it  agree that permission for extensive  It  publication of this thesis for financial gain shall not  Department  requirements  British Columbia, I agree that the  freely available for reference and study. I further copying of  the  is  granted by the understood  that  head of copying  my or  be allowed without my written  Abstract  In the NE subarctic Pacific, the marine microbial food web, specifically the heterotrophic and autotrophic nanoflagellates (HNF and ANF), and cyanobacteria and heterotrophic bacteria, is not well understood. Further, studies of these populations have almost been exclusively done at Station P (50°N, 145°W) only in the spring and summer. The abundance and distribution of the above micro-organisms was investigated along Line P (between 48°N, 126°W, and 50°N, 145°W) in May, 1993, and February and May, 1994. This is the first study to examine their horizontal distribution, and obtain winter data on their abundance and distribution in this region. HNF, ANF, cyanobacteria and heterotrophic bacteria were identified, enumerated and biomass was estimated by epifluorescence microscopy. In May 1993, ANF and HNF biomass and abundance was an order of magnitude higher at most stations, compared to 1994 cruises, and May 1993 vertical profiles averaged 5.7* 10 cells L" at Station P. In February and May 1994, ANF and HNF 6  1  population abundance and biomass was separated into three size fractions; the 2 to 5 um size group dominated. During both May cruises, a mirdmum in abundance and biomass of HNF, ANF and cyanobacteria was observed at Stations P12 and P16, which is ascribed to water mass changes along Line P. Winter abundance and biomass estimates of ANF, HNF, cyanobacteria and heterotrophic bacteria populations were comparable to those in May 1994, indicating that predator prey relationships remain functional at this time of  year. Carbon budgets of winter and late spring HNF and their prey populations indicated that prey (cyanobacteria and heterotrophic bacteria) population biomass was sufficient to support the carbon requirement of the HNF in February and May 1994. In February 1994, at station P4 the combined biomass of cyanobacteria and heterotrophic bacteria was five times the requirement of the HNF, and 1.4 times this amount at Station P, further demonstrating the maintanence of predator/prey trophodynamics during the winter.  iv  Table of Contents ABSTRACT TABLE OF CONTENTS  ii iv  LIST OF TABLES  vii  LIST OF FIGURES  viii  ACKNOWLEDGEMENTS  x  DEDICATION  xi  QUOTATION  xii  1. INTRODUCTION  1  1.1 Pelagic Microbial Food Web  1  1.2 The NE Subarctic Pacific- An Unusual Environment  5  13 Plankton Dynamics at Station P  7  1.4 Microbial Ecology at Station P  9  1.5 Heterotrophic Nanoflagellates and Bacteria  11  1.6 Thesis Goals  14  2. METHODS  18  2.1 Sample Collection  18  2.2 Epifluorescence Microscopy (EFM)  19  23 Cell Enumeration  20  2.4 Biomass conversions  22  2.5 Physical Data  23  V  2.6 Statistical Analysis  23  2.7 Heterotrophic Bacteria and Nutrient Data  23  2.8 Graphing  24  2.9 Integration  24  3. RESULTS  24  3.1 Line P, May 1993 3.1.1 Cruise background information 3.1.2 Heterotrophic nanoflagellates 3.1.3 Autotrophic nanoflagellates 3.1.4 Cyanobacteria and heterotrophic bacteria  24 24 25 26 28  3.2 Line P, February 1994 3.2.1 Cruise background information 3.2.2 Heterotrophic nanoflagellates 3.2.3 Autotrophic nanoflagellates 3.2.4 Cyanobacteria and heterotrophic bacteria  29 29 29 31 33  3.3 Line P, May 1994 3.3.1 Cruise background information 3.3.2 Heterotrophic nanoflagellates 3.3.3 Autotrophic nanoflagellates 3.3.4 Cyanobacteria and heterotrophic bacteria  34 34 34 36 37  3.4 Statistical Analysis  38  4. DISCUSSION  84  4.1 Station P 4.1.1 HNF and ANF 4.1.2 Winter at Station P  84 84 86  4.2 Line P 4.2.1 HNF and ANF 4.2.2 Cyanobacteria and Heterotrophic Bacteria 4.2.3 Heterotrophic and Autotrophic Population Dynamics on Line P  89 89 90 91  43 Predator/Prey Relationships  93  4.4 Carbon Budgets  96  4.5 Conclusions  5. LITERATURE CITED APPENDIX  100  102 108  LIST OF APPENDED TABLES LIST OF APPENDED FIGURES  vu  List of Tables table 1. Station information for May 1993, 1994 and Feb. 1994 cruises..  40  Table 2. Integrated abundance and biomass (0-30 m) in May 1993, February 1994, and February 1994 of heterotrophic and autotrophic nanoflagellates, cyan6bacteria,and heterotrophic bacteria. 45 Table 3. Spearman correlation coefficients between heterotrophic and autotrophic nanoflagellates, heterotrophic bacteria, and cyanobacterial biomass (as carbon) for all cruises combined using data from all depths. • . ... . 83 :  Table 4. Heterotrophic nanoflagellate, and cyanobacteria, biomass (as carbon) mg C m" at Station P from Booth et al. (1993) and this study nd (May 1993,1994. , • 88 2  Table 5. Sampling times for HNF, ANF, cyanobacteria, and heterotrohic bacteria in May 1993. Taken from Table 1. _ _ .. _ •__ 95  Vlll  List of Figures Figure 1. The flow of carbon within the microbial food web. Figure 2. The 'Dilute Domain' in the N. E. subarctic Pacific, and subarctic Pacific surface layer current systems. • • • • • • • • , . . . • ___6 :  Figure 3. Gasol and Vaque's (1993) two explanations for the uncoupling of heterotrophic nanoflagellates, and heterotrophic bacterial abundance. •__ • 13 Figure 4. Map of the study area showing the latitude and longitude of stations P4, P12, P16, P20, P23a (Feb. 1994, only), and Station P. . . 17 Figure 5. Pattern for the enumeration of HNF and ANF. Figure 6. Salinity profiles on Line P in May 1993.  .  :  .  21  • •. .-  41  Figure 7. Mixed layer depth and the 1% light depth on Line P in May 1994, February 1994, and May 1994. . -. . • . . . . . . : • 42 Figure 8. Abundance in cells L" of total ANF and HNF in May 1993 at stations P12, P16, P20, and P26 , 1  43  Figure 9. Biomass in ug L" of total ANF and HNF in May 1993 at stations P12, P16, P20, and 1  Station P. Figure 10. Figure 11.  .•  •  •  _  rface plot of total HNF abundance on Line P in May 1993.  44  •  rface plot oftotalHNF biomass on Line P in May 1993.  .  rface plot of total ANF abundance oh Line P in May 1993. .  .  ,  46  -  47  Figure 12. •  48  Figure 13. rface plot of total ANF biomass on Line P in May 1993. Figure 14. Figure 15. Figure 16. Figure 17. Figure 18.  .  •  -••  49  anobacterial abundance in May 1993 at station P12, P16, P20, and Station P.  50  rface plot oftotalCyanobacterial abundance on Line P in May 1993.  51  rface plot of total Cyanobacterial biomass on Line P in May 1993. .  52  undance of heterotrophic bacteria and bacterial production at Station P in May 1 9 9 3 . _ 53 inity profiles for Line P in February 1994.  Figure 19. abundance).  - •  •. •  • •  -. •  ... , • - •  •• • • •  54 55  Figure 20. HNF and ANF biomass at station P4 in Feb. 1994 (three size fractions arid total biomass). _ 56 Figure 21. HNF and ANF biomass at station P23a in Feb. 1994 (three size fractions and total biomass).57 Figure 22. Total HNF and ANF abundance at stations P12, and P16 in Feb. 1994.  -  ,  58  Figure 23. HNF and ANF abundance at station P23a in Feb. 1994 (three size fractions and total abundance).  .  __.  :  :  • .• , •  :  Figure 24. Total HNF abundance on Line P in February 1994.  5  .  Figure 25. Total HNF biomass on Line P in Feb. 1994.  6 . . .  - 6  Figure 26. HNF and ANF biomass at station P16 in Feb. 1994 (three size fractions and total abundance): Figure 27. Total ANF abundance on Line P in February 1994.  6  Figure 28. Total ANF biomass on Line P in February 1994.  , . •. ,  Figure 29. Cyanobacterial abundance in Feb. 1994 at station P4, P12, P16, and P23a. Figure 30. Cyanobacterial abundance on Line P in Feb. 1994.  6  __  Figure 31. Cyanobacterial biomass on Line P in Feb. 1994.  •  . •  •  6  ,  6  Figure 32. Heterotrophic bacterial abundance at station a) P4 and b) Station P in Feb. 1994 Figure 33. Salinity profiles for Line P in May 1994.  6  .  6 d  :  Figure 34. ANF arid HNF abundance at P4 in May 1994 (three size fractions and total abundance).  1  Figure 35. ANF and HNF biomass at P20 in May 1994 (three size fractions and total biomass).  1  Figure 36. Total HNF arid ANF abundance in May 1994 at stations P4, P12, P16 and P20.  1  Figure 37. Total HNF and ANF abundance in May 1994 at Station P.  • •  1  Figure 38. Total HNF and ANF biomass in May 1994 at stations P4, P12, P16 and P20 _ _ Figure 39. Total HNF and ANF biomass in May 1994 at Station P. Figure 40. Total HNF abundance on Line P in May 1994. Figure 41. Total HNF biomass on Line P in May 1994.  . ..  1 .  .•  -  . ;  .  7  .__ 1  - •  1  Figure 42. Total ANF abundance on Line P in May 1994.  ,  7  Figure 43. Total ANF biomass on Line P in May 1994.  7  Figure 44. Cyanobacterial abundance at station P4 in May 1994.  8  Figure 45. Cyanobacterial abundance on Line P in May 1994.  _ _  Figure 46. Cyanobacterial abundance at Station P in May 1994.  :  ..  8 •. .  $  Figure 47. Late spring carbon budgets (mg C m ) for May 1993 and 1994 for stations P4, P12, P16, P20, and Station P(P26). 9 2  :  :  Figure 48. Winter carbon budget for stations P4, P12, P16, and Station P(26).  ______?  Acknowledgements Of the many people who have lended assistance over the course of this thesis I would first like to express my appreciation to Dr. Philip Boyd for his advice, encouragement, and critical review of the numerous rough drafts. I thank Dr. A. G. Lewis for giving me the opportunity to accomplish this thesis, and for providing financial support. I am grateful to the members of my committee for their comments. I also thank Dr. T. R. Parsons, Dr. P. J. Harrison and Dr. F. J. R. Taylor for their loaning of microscopical equipment. I thank Dr. Evelyn Lessard for her instruction in epifluorescence microscopy. Special thanks to Captain Anderson and the crew of the J. P. Tully for their assistance with work at sea. For their comradery and granting me numerous consultations I thank the following people: Marc Wen, Rob Goldblatt, James Powlik, Linda Greenway, Dr. David Montagnes, Rowan Haigh, and the graduate students of the Harrison lab. Thanks are not enough for the support and encouragement given to me by Christine. I am grateful to my parents for their support and for providing me with the tools to complete this study.  xi  To my parents  xii  •  That which gives light must endure burning. Victor FrankI  1  1. Introduction 1.1 Pelagic Microbial Food Web The traditional paradigm of a diatom-copepod-fish pelagic food web is now thought to be an incomplete view of the marine food web (Goldman et al, 1979; Azam et al, 1983; Pomeroy and Wiebe, 1988; Eldridge and Sieracki, 1993). Beginning in the early 1980's, researchers began to uncover and quantify a spectrum of marine micro-organisms (Pomeroy, 1992). This was largely due to the development of improved handling techniques to accommodate the fragility of the small cells, and to enumeration techniques such as epifluorescence microscopy and the introduction of selective fluorochromes (Porter and Feig, 1980; Davis and Sieburth, 1982; Haas, 1982; Cafon, 1983; Sherr and Sherr, 1983; Martinussen and Thingstad, 1991; Sherr et al, 1993). The fluorochromes generally bind to proteins in the cytoplasm or to DNA, such as, 4',6diamidinO-2-phenylindole (DAPI). Compared to light microscopy, epifluorescence microscopy is a more effective way for microscopists to enumerate cells as small as picoplankton, as well as, to differentiate between heterotrophs and autotrophs through the use of chlorophyll autofluorescence. The microbial food web is composed of a complex community of heterotrophic and autotrophic cells between 0.02 um to 200 um (viruses and bacteria to ciliates), encompassing three orders of magnitude (micro: 10", nano:10", pico:10~ ). Within these size groups there are 6  9  12  complex relationships between predator and prey. It was once thought that all heterotrophic nanoflagellates (HNF.e.g., Chrysophyceae, Choanoflagellida) fed on bacteria, regardless of HNF size. Sherr and Sherr (1991) have demonstrated that among the HNF, predator-prey relationships operate on a much finer size scale, with observations indicating that the prey of heterotrophic  2 nanoflagellates change depending upon predator size. It may now be more correctly stated that HNF <5 um preferentially feed on heterotrophic bacteria and cyanobacteria. Those >10 um feed on small diatoms and the smaller autotrophic and heterotrophic flagellates. Although the general rule is that predators feed on smaller prey it is not strictly so. Heterotrophic dinoflagellates in culture (30 um x 30 um) have been observed to feed on diatoms much larger than themselves (62 um x 1.9 um) (Jacobsen and Anderson, 1992), further demonstrating the complexity of predator prey relationships within the microbial food web. The modern view of the marine foodweb is that of a highly dynamic and balanced system (Pomeroy and Wiebe, 1988; Eldridge and Sieracki, 1993; Legendre and Rassoulzadegan, in press) (with the incorporation of the microbial component), which contains complex trophic pathways between autotrophs and heterotrophs (Fig. 1). In addition to its ecological importance, the recognition of the microbial food web has led to revisions of processes, such as, nutrient cycling (N) (Goldman et al, 1987) and carbon flux. For example, carbon flux models have been developed (Goldman, 1988; Legendre and LeFevre, 1989) that consider the transport of carbon out of the mixed layer by large senescent diatoms, faecal pellets, and marine snow, as well as, a substantial portion, which remains in the mixed layer, i.e., does not sink, through dissolution and heterotrophic bacterial remineralization into dissolved organic and inorganic carbon. That portion which is kept in the mixed layer is generally composed of senescent small cells which are autotrophic and heterotrophic components of the microbial food web, and are, therefore, not heavy enough to escape the mixed layer for deposition on the seafloor. Legendre and Rassoulzadegan (in press) hypothesize that there is a trophic continuum consisting of four possible trophic structures in pelagic marine environments, and that the view of  3 only two distinct food webs, the herbivorous (traditional) and microbial (loop), is an oversimplification. The four possible trophic structures in this continuum are the herbivorous food web, multivorous food web, microbial food web, and the microbial loop. The food webs are largely dependent on the amount of NO3" which is entering the system, where the herbivorous food web receives most and the microbial loop receives the least; consequently, since these two trophic arrangements are at extremes, Legendre and Rassoulzadegan (in press) state that they are ephemeral and likely to give way to the other, more stable food webs. For example, the herbivorous food web is likely to be seen at the time of a spring bloom, when there is a large amount of NCV, diatoms and zooplankton. In this scenario the flow of carbon in figure 1 would largely be between microphytoplankton and mesozooplankton. In time, the N0 " is depleted, due 3  to blooming phytoplankton, and the system changes to the more stable multivorous food web, where there is said to be an equal amount of grazing pressure on phytoplankton by the mesozooplankton and the microzooplankton (Fig.l). The shift from a herbivorous to a multivorous food web demonstrates that in any one region it is possible to see a progression of the food webs during the course of the year (Legendre and Rassoulzadegan, in press). However, in regions of the ocean where nutrients remain high year round and chlorophyll is low, the so called high nutrient low chlorophyll regions (HNLC), Legendre and Rassoulzadegan (in press) hypothesize that the multivorous food web is dominant The research for this thesis was conducted in the NE subarctic Pacific, a HNLC region, where the mesozooplankton exhibit little grazing pressure, 6-15% of daily primary production (Dagg, 1993), and is more likely to be dominated by the microbial food web rather than the multivorous food web.  4  Figure 1. The microbial food web. Heterotrophic nanoflagellates, HNF; heterotrophic bacteria, HB; Cyanobacteria, Cyano; autotrophic nanoplankton, ANP; dissolved organic carbon from exudation, grazing, and sloppy feeding by mesozooplankton, DOC. Arrow represent theflowof carbon.  5  1.2 The NE Subarctic Pacific- An Unusual Environment In the ocean region between the coast of Vancouver Island, B.C. and Ocean Weather Station P (50°N, 145°W) there are changes in both the physical and chemical environments, as well as in the biota. There are a number of water masses in this region: just off the coast is a region of upwelling in the spring and summer, to the west of which is a dilute water mass or 'Dilute Domain' which extends seaward to 160°W (Fig. 2a). Station P is situated in the Subarctic Current which forms off the coast of Japan and diverges east of Station P, branching north, into the Gulf of Alaska and the Alaskan Current System, and south into the California Current System (Fig. 2b). Chemical gradients have also been observed in this region (Wong, unpublished data), as well as biological gradients such as observations of high coastal salp abundances which decline around 135°W (Wen, pers. comm.). Investigators have sought an explanation for the continuous absence of phytoplankton blooms beyond 300 km offshore in the subarctic Pacific (Heinrich, 1962, Miller, 1993 and references therein). This is contrary to the classical understanding of pelagic production processes, where the continuous availability of nitrate, phosphate and silicic acid in the upper water column, coupled with strong seasonal stratification, should allow phytoplankton stocks to increase, resulting in a spring bloom (Miller, 1993). In this scenario, the phytoplankton bloom should deplete nutrients in the mixed layer resulting in a large decrease in phytoplankton abundance until autumn winds destratify the water column, a seasonal process common to the North Atlantic (Parsons and Lalli, 1988). Observations from Canadian Coast Guard weatherships patrolling at Station P (50°N,145°W) show that in this area there are no obvious phytoplankton blooms and that year round chlorophyll remains close to 0.3 mg m" (Miller, 1993). The low 3  Figure 2. A) The 'Dilute Domain' in the NE subarctic Pacific and B) subarctic Pacific surface layer current systems. Bothfigurestaken from Favorite et aL (1976).  7 levels of chlorophyll are characteristic of an oligotrophic region (Parsons et al, 1984), however, this region is not limited by macronutrients; the mixed layer nitrate concentration has a typical annual low of 6 uM (Miller, 1993). Hydrographic conditions at Station P are also conducive to a spring bloom, with an upper water column that is well stratified in the spring and early summer resulting in a shallow mixed layer (Favorite et al, 1976).  1.3 Plankton Dynamics at Station P The inital explanation for the absence of a spring bloom in the NE subarctic Pacific was proposed by Heinrich (1967) and is known as the major grazer hypothesis. The hypothesis states that large filter feeding copepods (Neocalanus, Eucalanus, and Metridia) are the principal grazers and are responsible for maintaining phytoplankton stocks at observed low, constant levels, consequently preventing a spring bloom. Heinrich (1967) proposed that the eggs of the numerically dominant Neocalanus species are spawned in the winter ensuring that the young will be present in the upper water column before phytoplankton stocks could escape grazing control .(Miller, 1993). This theory has recently been disproven through work done on the Subarctic Pacific Ecosystem Research (SUPER) cruises. Dagg (1993) observed that copepod grazing capacity in spring was insufficient (by about an order of magnitude) to control phytoplankton stocks. In addition, it was found that copepods were not feeding to a significant extent on phytoplankton (Dagg and Walser, 1987; Dagg, 1993). Frost's (1993) ecosystem model, also indicates that feeding activity of the mesozooplankton is too low to account for the consumption of phytoplankton, and the maintenance of low phytoplankton stocks. There are now two fundamental theories that have been presented to explain the absence of spring phytoplankton blooms at Station P (Fig. 3): first, high rates of daily primary production  8  are balanced by commensurate loss processes, dominated by intense grazing pressure by microzooplankton (Evans and Parslow, 1985; Frost 1987), and/or, second, that phytoplankton specific growth rates are limited by some essential trace element, such as Fe, resulting in phytoplankton production rates that are lower than expected for the prevailing algal standing crop, and thus, mOre easily balanced by natural in situ loss processes (Welschmeyer et al., 1993) The arguments are not mutually exclusive, in fact they complement each other (Frost, 1991; Miller et al, 1991; Welschmeyer et al, 1993). Of the loss processes outlined by the first argument for the absence of spring phytoplankton blooms, the primary loss process for phytoplankton standing stocks is grazing by the microzooplankton. When investigated further, measured microzooplankton grazing rates were, indeed, commensurate with the estimated specific growth rates of the dominant size classes (Strom and Welschmeyer, 1990). This is the basis of the SUPER group's work, a hypothesis called the 'mixing and micrograzer hypothesis'. This hypothesis states that the phytoplankton-microzooplankton linkage remains established and functional throughout the year because the permanent halocline, region of rapidly changing salinity, at a depth of about 110 m, acts as a barrier to mixing processes, preventing deep mixing in winter months of the upper water column, such that phytoplankton are able to actively photosynthesize and their production can support microzooplankton grazers. However in the past, no data on the abundance of components of the microbial food web have been obtained from Station P during the winter. Therefore, the winter data presented in this thesis will enable the mixing and micrograzer hypothesis to be tested, and permit the opportunity to assess the importance of the microbial food web in this region in the winter.  The second hypothesis (above) was introduced because the open subarctic Pacific is dominated in biomass by both autotrophic and heterotrophic cells between 2-5 um (Booth et al, 1993; Welschmeyer et al, 1993). Martin et al. (Martin and Fitzwater, 1988; Martin et al. 1989; Martin et al 1991b) hypothesized that the absence of some micronutrient, such as iron, is limiting the growth of larger cells. Although iron depletion may be playing a role in the NE subarctic Pacific by limiting the growth of larger cells while the smaller cells are not iron-limited, therefore, the low algal biomass and high productivity require an active role by loss processes, such as grazing, in contributing to the overall dynamic balance (Welschmeyer et al, 1993). This balance between top-down (grazing) and bottom-up controls (temperature, nutrients) is a component of the present study.  1.4 Microbial Ecology at Station P The Frost ecosystem model (1993) has incorporated much of what was discovered during the SUPER cruises, to make predictions about processes in the subarctic Pacific and provides a good framework for discussing the structure of the foodweb at Station P. Frost (1993), however, does not include a variable for iron limitation in his model because, the phytoplankton assemblage is composed of small cells which are, as he states, growing at their maximum growth rate (1 d~l), (Welschmeyer et al, 1993) and are limited solely by grazing from microzooplankton. The few large cells (1276 autotrophic cells L~l >24 um including flagellates, dinoflagellates, diatoms >20 pm, and cryptomonads (Booth et al, 1993)), which do grow are either grazed by the mesozooplankton or the larger protistan grazers, such as the dinoflagellates (Lessard, 1991). Model predictions by Frost (1993) also show that it is unlikely that control of the  10 microzooplankton is held by the mesozooplankton, although they may gain substantial nutrition from them. It is also probable that microzooplankton predation mortality is controlled within the microbial food web by the larger microzooplankton (Stoecker and Evans, 1985). The distribution of the larger microzooplankton (i.e., ciliates) is probably related to food supply and predator abundance (Strom, 1990). However, Wheeler et al (1989) found that bacterial production and the populations of autotrophic picoplankton and heterotrophic pico and nanoplankton experienced strong diel periodicity, indicating the need for sampling on shorter time scales for analysis of the relationships i  among the various componets of the microbial food web. Further, Wheeler et al. (1989) have shown through ship board experiments that there is a diel periodicity in NH4 uptake and +  regeneration at Station P. Nitrogen uptake by phytoplankton was maximal during the day, and regeneration took place exclusively at night Limitations of the Frost model (1993) include its inability to account for the variability of chlorophyll a and dissolved nitrogenous nutrients (N) as they were observed during the SUPER cruises (Frost, 1993). This could stem from the dynamic relationship between predator and prey within the microbial loop, where changes in species composition and associated physiological properties are poorly understood and may account for the variability (Frost, 1993). The Frost (1993) model also does not address the role of heterotrophic bacteria, primarily because their inclusion in the model would demand the addition of two additional compartments in the model, dissolved organic substrates (Kirchman et al, 1990) and predators of the bacteria, i.e., the HNF. Frost (1993) stated that the functional roles of these additonal compartments are poorly understood, however, Kirchman et al (1993) report that because heterotrophic bacteria  11  constitute a large reservoir of carbon and nitrogen in the subarctic Pacific, they need to be included in modelling ecosystem dynamics of the region. Cole et al. (1988) found that there is a high correlation between bacterial and phytoplankton production in both fresh and saltwater (coastal and open ocean) ecosystems. This is primarily because bacterial production is controlled by "bottom up" factors such as substrate supply and temperature (Kirchman et al., 1993). Substrate supply is mainly derived from phytoplankton exudates, such as dissolved organic matter (DOM), specifically dissolved free amino acids (DFAA) (Kirchman, 1990). In the subarctic Pacific, Kirchman et al. (1993) found that, although, bottom-up processes explained the average level of bacterial production for the ecosystem, they explain little of the daily and monthly variation in bacterial production. The variation in bacterial production over shorter time scales are probably due to "top-down" control, i.e., grazing from HNF. Top-down control is also likely to be responsible for the apparent lack of correlation between bacterial and primary production on both daily to monthly time scales (Kirchman, et al., 1993).  1.5 Heterotrophic Nanoflagellates and Bacteria Despite the contributions made by the SUPER group to our understanding of the open subarctic Pacific, there is still much to be learned about the region (Miller, 1993 and references within). For example, little is known about the HNF and their prey selection. In the past it was suggested that predation by protozoans might be the main process maintaining constant bacterial abundance (Sherr et al, 1986). However, there is evidence that heterotrophic nanoflagellate abundance (HNF) and HB abundance may not be coupled. Gasol and Vaque (1993) collected HNF and HB abundance data from a variety of aquatic systems and did not find a strong correlation between the two groups in freshwater, marine (coastal and open ocean) and benthic  12  environments. They have given three explanations for this: First, other organisms are important predators of bacteria and/or other loss processes could be more important than predation (Fig. 3). They found HNFs and HB to be less coupled in both fresh and marine eutrophic systems than oligotrophic systems. This may be the result of an increase in heterotrophic ciliate numbers, since ciliates are significant bacterial predators and are generally found at higher abundances in coastal regions compared to the open ocean (Sherr and Sherr, 1987), However, in the subarctic Pacific Strom et al. (1993) found ciliate abundance to be comparable to coastal regions (e.g., 10 -10 3  4  cells L" , Washington coast) at Station P (10 -10 cells L" ). Therefore, the gradual coupling 1  3  4  1  between HNFs and HB from the coast, seaward to Station P, as a function of a decrease in competition with ciliates may not be seen. Second, Gasol and Vaqu6 (1993) found that HNFs may also use other sources of carbon other than HB, such as dissolved organic carbon, autotrophic picoplankton (cyanobacteria) and other heterotrophic/autotrophic nanoplankton (Fig. 3). In addition, HNFs may be preferentially selecting large and actively growing HB (Gonzalez et al., 1990). Lastly, there may be significant top-down control on HNFs, meaning that they may not be allowed to reach abundances that resources (heterotrophic bacterial abundance) would potentially support (Gasol and Vaque', 1993). This grazing control of HNFs could come from grazing by ciliates or larger nano/microflagellates, such as in the North Atlantic (Weisse and Scheffel-MOser, 1991). However at Station P, Strom et al. (1993) has found, that estimated ingestion of phytoplankton by ciliates only averaged 14% of the daily primary production. Based on microscopical studies (Booth et al., 1993; Strom et ai, 1993) it was suggested that heterotrophic flagellates,  13  Figure 3. Gasol and Vaque's (1993) two explanations for the uncoupling between heterotrophic nanoflagellates, HNF, and heterotrophic bacterial abundance, HB. 1) Competition for HB between grazers (HNF and heterotrophic ciliates), and 2) the use of other sources of carbon, such as, dissolved organic carbon (DOC) by HNFand/or picophytoplankton (pico) and nanoplankton (heterotrophic and autotrophic) (NP).  14  specifically those <20 um (HNFs), may be substantial grazers of phytoplankton at Station P. The lack of correlation between HNFs and heterotrophic bacteria may also be a function of the complexity of the microbial food web, and, therefore, a function of the combined influence of topdown and bottom-up controls.  1.6 Thesis Goals This thesis research has investigated the population dynamics of autotrophic (e.g., Prymnesiophyceae, Chrysophyceae, Prasinophyceae, Booth et al, 1993) and heterotrophic nanoflagellates (e.g., Choanoflagellida.Chrysophyceae, Dinophyceae, Booth et al, 1993) as well as, cyanobacteria and heterotrophic bacteria. The first goal of this thesis research was to estimate the abundance and distribution of these groups along Line P at Stations P4, P12, P16, P20, and P26 (Station Papa or Station P) in the open subarctic Pacific (Fig. 4). This is thefirststudy in this region to look at the distribution of these groups from coastal (P4) to oceanic waters in the NE subarctic Pacific. The nanoflagellate data collected at Station P will build upon a much smaller data set (Booth et al, 1993 and references within) on these organisms. Prior to the SUPER group the only other study of this region looking at microzooplankton (Lebrasseur and Kennedy 1972) was limited in collection (i.e., used plankton nets) and preservation methodology, consequently, they reported low concentrations (<35 L" ) of animals < 225 um in size. The 1  SUPER program is the most comprehensive study at Station P, and the most complete study of the autotrophic and heterotrophic components of the food web. Only with the introduction of sampling techniques which accommodate the fragility of the small cells, and epifluorescence microscopy, have considerably more accurate estimates of microzooplankton and phytoplankton been attainable. Further, the ability of epifluorescence to distinguish autotrophs from  15 heterotrophs has allowed ecologists to "rediscover these organisms" (Lessard 1991), greatly improving our understanding of their role in the marine food web. The second goal of the thesis was to obtain winter data concerning the above groups. Little research has been done during the winter because it was thought that the weather would hinder sampling efforts. Winter data are important to assess whether or not the producer-grazer linkage remains intact through the winter months at Station P, as predicted (Evans and Parslow, 1985). Frost's model (1993) indicates that there should be significant phytoplankton production levels and a substantial stock of microzooplankton grazers at this time of year (approx. 10 mg C m~3). The maintenance of the producer-grazer linkage is thought to be the key tenet in suppressing a spring phytoplankton bloom at Station P (Fig. 4) (Miller, 1991). Therefore, winter standing stock data will better our understanding of the heterotrophic arid autotrophic community in the spring and summer, because the degree of coupling between grazers and phytoplankton in the winter determines what proportion of the above communities will enter into early spring. Since, the heterotrophic and autotrophic nanoflagellates are dominate in the subarctic Pacific, an understanding of their standing stocks during this time of year is crucial to our understanding of both the heterotrophic and autotrophic communities in this region. The third goal of this thesis was to explore the trophic relationships between the HNFs and possible prey items (i.e., top-down control by HNF), including: cyanobacteria, heterotrophic bacteria, autotrophic nanoflagellates (ANFs), and any of the measured, bottom-up, environmental parameters (i.e., temperature, mixed layer depth, 1% light depth of irradiance, N0 \ and NH/). 3  This study is limited by its inablity to look at fluxes of carbon between predator and prey. Therefore, comparisons will be made between abundance and biomass (as carbon) through the use  16  of carbon budgets of the above groups. In this way the relationship between HNF and their prey will be examined to see if there is a HNF prey preference, and if the preference changes on Line P, both temporally and spatially.  17  o  §  o  S  o  8  18  2. Methods 2.1 Sample Collection Samples were collected during 3 cruises (May 1993, February 1994, and May 1994) at 5 stations along Line P: P4, PI2, PI6, P20, P23a (February 1994 only) and P26 (Station Papa or Station P) (Fig.4). The sampling program for this study, followed that of the CTD (conductivity, temperature and depth) profiling program of the Institute of Ocean Sciences, Sydney, BC, and therefore, prevented sampling of any stations other than those listed above. One vertical profile was taken at each station and six depths were sampled using either 30 L (all cruises) or 10 L (February and May 1994) GO-FLO bottles attached to a kevlar hydrographic wire. Sampling depths were selected based on photosynthetically active radiation (PAR) light profiles. Three pseudo replicate samples were gently siphoned (Gifford and Dagg, 1992) from each GO-FLO using either silicone (May 1993) or polyethylene tubing (February and May 1993), directly into (i.e., not letting the water run down the sides of the bottle) either an acid washed 1 L glass jar (May 1993) or a pre-cleaned 500 ml Nalgene polycarbonate bottle (February and May 1993). Pseudo replication was used because there was insufficient time available to obtain three discrete profiles at each station. Samples were analyzed using epifluorescence microscopy to estimate the population abundances of heterotrophic and autotrophic nanoplankton, as well as cyanobacteria.  19  2.2 Epifluorescence Microscopy (EFM) Samples werefixed,filteredand stained at sea, to ensure that chlorophyll autofluorescence would be preserved for later microscopical enumeration of the cells. Prior to fixation glutaraldehyde was diluted to 10% (v/v) and filtered through a 45 mm diameter 0.22 um porosity Millipore GSfilterto remove particulates (Lessard, pers. comm). All samples werefixedto a final concentration of 1% (v/v) glutaraldehyde. Samples were filtered and stained within 48 h of sampling. Prior tofiltrationand staining, samples were gently agitated within the jar or bottle by rotating them end over end to resuspend the cells. Ten mL subsamples were taken from each jar or bottle, measured out into a small graduated cylinder, and then poured into a filter funnel over a 25 mm diameter 0.8 um porosity Poretics polycarbonate, Irgalan Black-stainedfilter,with a 0.45 um porosity Millipore HA backing filter. The sample was then drawn down to 5 mL, under low vacuum (<100 mm Hg), for staining. The first fluorochrome used to stain the cells for microscopical enumeration was 4',6diamidino-2-phenylindole dihydrochloride hydrate (DAPI) (Sigma Chem. Co., Saint Louis, MO) (Porter and Feig, 1980). DAPI was allowed to stain at a concentration of 6-10 ug mL" for at 1  least 7 min after which time proflavine hemisulfate (Haas, 1982) was added at a final concentration of 1 ng ml" and was allowed to stain for 2 min. DAPI is a molecular stain specific 1  to the adenine and thymine pairs in DNA; prOflavin hemisulfate is a protein stain and can overstain a sample if left to stain at too high a concentration or for too long. Proflavine was used because it aided the viewing of heterotrophic flagellates under blue light excitation; filter sets were then switched to UV excitation to see DAPI fluorescence and to check that those cells seen under blue  20 light excitation contain a nucleus (i.e., that they were actually cells to be counted and not particulate matter). After the addition of both DAPI and proflavine to the sample, a microsope slide was prepared by placing a drop of Cargille type FF non-fluorescing immersion oil in the center of the slide and laying a coverslip on top to spread out the oil. After staining was completed, the coverslip was removed and the 0.8 um porosity filter was placed on top using flat-bladed forceps, with the sample side up. Another small drop of oil was added to the previously oiled side of the coverslip and then placed oiled side down onto the top of the filter. The cover slip was then secured to the microscope slide with clear nail polish. The slide was then stored in a -20° C freezer until enumeration.  2.3 Cell Enumeration Cells were sized using a calibrated ocular grid. Only total HNF, total ANF (2-20 um), and cyanobacteria populations were enumerated for the May 1993 cruise. For the winter and late spring 1994 cruises three size fractions were enumerated for HNF and ANF populations, including: HNF and ANF (2-5 um), HNF and ANF (5-10 um), and HNF and ANF (10-20 um). The sample wasfirstviewed at lOOx magnification to observe the distribution of cells on the filter. A Zeiss standard microscope with a HBO 50 watt light source, blue light (BP450-490, FT510, LP520), and UV filter sets (BP365, FT393, LP397) was used for enumeration of nanoflagellates at lOOOx magnification using a neofluar lOOx objective. At least 100 cells of the most abundant nanoflagellate size group and 80 fields were counted. Between 200 and 300 cells were counted for cyanobacteria at 10 separate locations on thefilter.Because cells canfitthrough a hole smaller than their diameter an unknown proportion of cyanobacterial cells was likely lost during  21  Figure 5. Pattern for enumeration of cells. Filter, Poretics black stained filter. Figure not to scale.  22 filtration with the 0.8 um Pdretics filter. The pattern used for counting flagellates follows figure 5, where at least 20 fields were enumerated in each direction while being careful to stay at least 15 fields away from the edge of thefilteredarea and the irregularities in cell distribution which occur there. Because small autotrophic nanophytoplankton can be confused for ANF which have lost their tails it is likely that a portion of ANF abuncances were, in fact, autotrophic nanoplankton other than ANF.  2.4 Biomass conversions An average cell size was estimated separately,for all HNF and ANF, in May 1994, based on cell measurements of 20 cells for each group. In February and May 1994, an average cell size was taken for each size class of nanoflagellate, each based on length and width measurements of 20 cells . Cell volume equations, used to compute biomass.were those of Wetzel and Likens (1991). Cells 2-5 um were generally spherical, equations for those cells >5 um were chosen based on their shape, e.g., elipsoid, elipsoid cone. Carbon conversions were conducted in various ways and depended primarily on size. A value of 210 fg of carbon per cell was used for cyanobacteria spp. (Waterbury et al, 1986, Booth et al, 1993). For cells <4 um in diameter a value of 0.22 pg C um" was used (Mullin et al, 1966, Booth et al, 1993), and for cells >4 um, the following 3  equation from Strathman (1967) was used:  log C = -0.460 + 0.866(log V)  where C is cell carbon and V is cell volume.  23 2.5 Physical Data Physical data was provided by the Institute of Ocean Sciences, Sydney B.C. for all three cruises. Temperature and salinity vertical profiles were obtained using a Guildline CTD (Smith Falls, Ontario), conductivity, temperature and depth profiling instrument, in February and May 1994. In May 1993 a Sea Bird temperature pressure transmissometer was used to obtain temperature and salinity profiles. In situ vertical profiles of photosynthetically active radiation (PAR) were made using a LICOR 1000 sensor. The mixed layer depth was estimated by determining the median depth of the region in the upper water column where a 0.5°C decrease in temperature was first observed (after Levitus, 1982). 2.6 Statistical Analysis A Spearman nonparametric correlation was used on abundance biological data (HNF, ANF, cyanobacteria, heterotrophic bacteria) for correlation analysis using the computer programs SigmaStat (landel Scientific) and SAS. Multiple linear regressions were done between total ANF biomass and abundance (dependent variable) vs. environmental parameters (independent variables), such as, surface temperature, salinity, mixed layer depth, N0 \ and NIL/. 3  2.7 Heterotrophic Bacteria and Nutrient Data Heterotrophic bacterial data was provided by Philip Boyd. Bacterial sampling was as for HNFs, and preparation and enumeration follow that of Turley and Hughes (1992), where a 25 mm, 0.2 um porosity, black stained Poretics filter was used for filtration. NH/ and N0 " data 3  used for statistical analysis (multiple linear regressions) was provided by Diana Varela. N i l / and N0 " were measured shipboard using a Technicon Auto Analyzer after Slawyk and Maclsaac 3  (1972) and Wood et al (1967), respectively.  24 2.8 Graphing All scatter/line plots were produced using the computer program SigmaPlot (Jandel Scientific). The surface plots of abundance and biomass were constructed with the computer program Axum (Trimetrix). All surface plots have a smaller inset plot which is another view of the larger plot on the same page. 2.9 Integration HNF, ANF, cyanobacteria, and heterotrophic bacteria were integrated by the following method: cell abundance and/or biomass was averaged between the first two depths and multiplied by the change in depth and then repeated down the profile until all depths have been included in the integration. For example, abundances at 0 m and 10 m were 1.0*10 cells L" , and 1.5*10 6  1  6  cells L" , respectively. The average abundance (1.3*10 cells L" ) is then multiplied by 10 m. This 1  6  1  is then repeated for abundances at 10 m and the next depth, and so on for the entire profile. The resulting numbers are then summed.  3. Results Tables and figures referred to in the following sections have all been placed at the end of the results section, beginning on page 40. Error bars for all line plots are of pseudo replicates (i.e., because only one vertical profile was obtained at each station the error is that found within each GO-FLO bottle). 3.1 Line P, May 1993  3.1.1 Cruise background information The May 1993 cruise was thefirstof three cruises, and one of two late spring cruises. Sampling commenced on May 12th at Station P4 andfinishedat Station P26 on May 23rd (Fig.  25  4). The maximum surface temperature on Line P of 10.5°C was found at Stations P4 and P12, and decreased to a minimum of 7°C at P20. Surface temperature then increased to 8°C at Station P26 (Table 1). Mixed layer salinity ranged between 32. 4 to 32.5 along Line P with the higher salinities being found at Station P, except at 150 m where there was an unexplained decrease in salinity which may be the result of a technical problem with the CTD (Fig. 6). The depth where 1% of incident radiation was recorded, ranged from 40 m at P4 to around 50 m at stations P20 and P (Fig. 7a), however, at P12 and P16 the 1% light depth could not be measured because sampling was done before dawn (the values presented in figure 7a for PI2 and PI6 are in consideration of the light profile at station P4, and are not actual measurements). The mixed layer depth was estimated to be 35 m at P4, increased to 48 m at stations P12 and P16, then decreasing again to 30 rh at stations P20 and P26 (Fig. 7a). Abundance and biomass data for HNF, ANF, cyanobacteria, and heterotrophic bacteria are provided in Appendix.  3.1.2 Heterotrophic nanoflagellates HNF and ANF were not placed into smaller size groups while counting (e.g., 2-5 urn), as was done for both cruises in 1994, and there were no data obtained from Station P4. Both abundance and biomass vertical profiles at P12 were homogeneous to 30 m (avg. 7.9* 10 cells L" 6  \ 42 ug C L" ; Figs. 8a, 9a), while at P16, abundance and biomass were relatively low at the 1  surface, then increased to a maximum at 50 m of 1*10 cells L" and 55 ug C L" (Figs. 8b, 9b ). 7  1  1  Abundance and biomass levels in May 1993 were observed between 0 to 5 m of 1.3*10 cells L" , 7  1  58 ug C L" at Station P20 and then began decreasing to abundances around 1*10 cells L" down 1  5  1  to 50 m, which was below the mixed layer (Figs. 8c, 9c). The two vertical profiles of abundance and biomass at Station P were quite different, in vertical distribution, and relative to the other  26 stations on Line P; the first profile had the lowest surface abundance and biomass for Line P between 0 to 7 m (avg. 5.2* 10 cells L"\ 27 ug C L" ), after which abundance increased to 30 m 6  1  and then decreased again once below the mixed layer depth at 30 m (Figs. 8d, 9d). Two days later, the second profile at Station P fluctuated with depth, but would have been homogeneous between 2 to 30 m if it were not for a decrease at 16 m of 4.3* 10 cells L" (Fig. 8e). The second 6  1  profile at Station P also decreased below the mixed layer to 1.5*10 cells L" and 7.7 ug C L" . 6  1  1  The HNF population integrated (0-30 m) abundance varied little between P12 and the first profile of abundance at Station P and averaged 2.3* 10 cells m". However, the second profile of 8  2  abundance at Station P was much lower than the other profiles at 1.5* 10 cells m" (Table 2). s  2  FigureslO and 11 show how the HNF abundance and biomass, respectively, are generally higher throughout the water column at P12; abundance then remains relatively high at the surface, relative to the rest of Line P, but decreases at depth.  3.1.3  Autotrophic nanoflagellates The ANF population in May 1993 was usually lower in abundance than the HNF  population, at stations along Line P, and attimesHNF abundance could be 7timesthat of ANF (e.g., Fig. 8c). However, ANF biomass was usually higher than HNF biomass; for example at P12 ANF biomass was 7timesthat of the HNF population (Fig. 9a). The vertical distribution of ANF population abundance also varied between stations. At P12, surface abundance was around 3*10 cells L" , increased to around 4*10 cells L" at 20 m 6  1  6  1  and decreased again at 40 m to the previous abundance (Fig. 8a). ANF biomass at P12 varied with depth similarly to abundance, and ranged between 47 ug C L" to 68 ug C L" (Fig. 9a). 1  1  ANF abundance at Stations P16 and P20 was homogeneous from 0-30 m, and averaged 2.3*10  6  27  cells L" and 2.5*IO cells L" , respectively (Fig. 8b,c). Biomass generally decreased with depth at 1  6  1  PI6 and ranged between 39 ug C L" to 26 ug C L" (Fig. 9b), while at P20 biomass was variable 1  1  near the surface and was homogeneous from 5-30 m (avg. 29 ug C L" ) and increased to 75 ug C 1  L" at 55 ni, which was below the mixed layer (Fig. 9c); this biomass was the highest recorded 1  along Line P in May 1993. At Station P, there were differences on the distribution of ANFs with depth. In the first profile, abundance increased with depth and the second was nearly homogeneous with depth; ANF abundances were the lowest recorded in May 1993 in the upper 10 m at P (avg. 0-7 m, 1.1*10 cells L" ) and the abundance averaged 2.4*10 cells L" for the entire second profile (Fig. 6  1  6  1  8d, e). Biomass generally increased with depth in both profiles ranging from 18 ug C L" to a 1  maximum of 59 ug C L" below the mixed layer in the first profile, and 33 ug C L" to 48 ug C L" 1  1  1  at the mixed layer in the second (Fig. 9d, e). Integrated abundance and biomass (0-30 m) fluctuated along Line P with a maximum at P12 of 1.2 *10 cells m" and 1875 pg C m ; this biomass was also higher than HNF integrated 8  2  2  biomasses along Line P. The integrated ANF population was found to have a higher abundance and biomass at the second profile of Station P which was opposite to the HNF population (Table 2). The surface plots show that both abundance and biomass are relatively homogeneous at P12 in comparison to the rest of the line (Figs. 12,13). At stations west of P12, abundance and biomass are generally low at the surface and increase with depth below the mixed layer at Stations P20 and P.  28  3.1.4 Cyanobacteria and heterotrophic bacteria The vertical profiles for cyanobacterial abundance were homogeneous from P12-P20 between 5 to 40 m, and averaged around 2.8* 10 cells L" at P12 and P16 (Fig. 14a, b). At P20, 7  1  abundance increased to an average of 3.2* 10 cells L" (Fig. 14c), and then decreased by as much 7  1  as an order of magnitude near the surface at Station P (e.g. profile 1, Fig. 14c). Profile two, at Station P, was generally homogeneous between 0 to 10 m (avg. 2.3* 10 cells L" ), but increased 6  1  between 20-50 m and averaged 4.5* 10 cells L" , both profiles at Station P had approximately the 6  1  same abundance from 20 m to 50 m. Integrated abundance and biomass show a large decrease in abundance between P20 to P26 with a maximum at P20 of 9.5* 10 cells m 8  decreasing to 1*10 cells m 8  2  2  (193 ug C m") 2  (22 ug C m") at the first profile at Station P (Table 2); however 2  abundance generally decreases below the mixed layer. The surface plots (Figs. 15,16) also clearly illustrate that there was a decrease in abundance at P16, similar to that found for the ANF, but that abundance and biomass were relatively high at stations P12-P20, except at 55 m at P20 (Fig. 14c), and then decreased dramatically, at all depths at Station P (Fig. 15, 16). Heterotrophic bacterial abundance generally decreased with depth at most stations on Line P, but fluctuated in the upper 5 m at stations P4, PI2, P20, and to a lesser extent at P26 (See appendix). At Station P, abundance also generally decreased with depth below 7 m and ranged between 1.2*10 cells L" to 0.4*10 cells L" (Fig. 17). Integrated abundance and biomass were 9  1  8  1  highest at P4 and P12 (avg. 3.1*10 cells m", 60 ug C m") and decreased at P16 to a minimum 10  2  2  of 1.9*10 cells m" (281 ug C m") and increased towards Station P (Table 2). Heterotrophic 10  2  2  bacterial production, as measured by thymidine incorporation, was highest near the surface at P4 and 12 (2.1 pmol TdR incorporated h" and 3.3 pmol TdR incorporated h", respectively), but at 1  1  29 all other stations surface values ranged between 0.7 to 1.1 pM TdR incorporated h") (e.g., Fig. 1  17). 3.2 Line P, February 1994 3.2.1 Cruise background information Sampling during this winter cruise began at P4 on February 8th, and due to poor weather conditions, station P23a was the most westward station reached on Line P. The weather also prohibited veritical profile sampling at stations P12 and P16 on the westward leg of the cruise, but profiles were obtained at both stations on the return leg with sampling ending at PI2 on February 16th. Surface temperature ranged from 9.5°C (P4) to 7.3°C at (P23a), and mixed layer salinity for Line P ranged beween 32.3 to 32.5, the latter being found at Station P23a (Fig. 18). The halocline was found between ca. 60 m at P4 to ca. 80 m at Station P23a (Fig. 18), and determined the depth of the mixed layer. The 1% light depth was only obtained at stations P4 and P16R*; consequently, sampling depths at station P23a were chosen considering the light profile at P4. Sampling depths at P12 were similarly chosen using the light profile obtained at P16. As for all cruises, abundance and biomass data for HNF, ANF, cyanobacteria, and heterotrophic bacteria are provided in Appendix.  3.2.2 Heterotrophic nanoflagellates In both February and May 1994, HNF and ANF were visually separated during enumeration into different size classes. The 2-5 um size group dominated the HNF population abundance at all stations on Line P (e.g., P4, Fig. 19) and ranged between 50% to 98% of the  The 'R' indicates that the station was sampled on the return leg of the cruise.  30  total HNF abundance at discrete depths, while the 5-10 um and 10-20 um size groups usually composed less than 25% and 13% of total abundance, respectively. The total HNF biomass on Line P was mainly composed of 2-5 um and 5-10 um flagellates (e.g., P4, Fig. 20), although, the 10-20 um size group which generally made up less than 20% of the total HNF biomass, at times made up to 43%. The main reason why the 10-20 um size group may at times constitute a significant proportion of the biomass is because the larger cells contain more carbon per cell when compared to the 2-5 um and 5-10 um groups. For example, at a depth where both groups are contributing relatively the same amount of carbon to total HNF, such as at Station P23a at 15 m (Fig. 21), we can compare cell densities and the amount of carbon contributed by one cell from each group. The abundance of the 2-5 um and 10-20 um size groups was 3.24* 10 cells L" and 5  1  3.79* 10 cells L" , respectively, but the amount of carbon contributed by one cell from each group 4  1  was 7.5*10"* ug C cell" and 3.6*10" ug C cell" by the 2-5um and 10-20 um size groups, 1  5  1  respectively. Five times as much carbon is in a typical cell in the 10-20 um size group compared to the 2-5 um size group. The vertical profiles of total HNF abundance for P4 (Fig.l9d) and P12 and P16 (Fig. 22) were all homogeneous with depth; average abundances were between 1*10 L" and 3*10 L" , 5  1  5  1  with a maximum profile average of 3.1*10 cells L" at P16. The loop* samples obtained at P20 5  1  were within the range of the previous stations, averaging 1.9*10 cells L" . Average abundance 5  1  was at a maximum at Station P which was partially due to a surface peak of 1.5*10 cells L" (Fig. 6  1  23). The remainder of the Station P profile was homogeneous and higher than abundances found at previous stations, with an average of 4.2*10 cells L" . Biomass profiles at P4-P16 were also 5  1  * The "loop" is the non-toxic shipboard seawater pumped supply system, which pumps water from 3-4 m below the ship. The loop is relatively gentle, however, some cells may be damaged by it.  31  generally homogeneous with depth, and between Stations P4-P20 biomass was rarely greater than 2.5 ug C L" . At Station P23a, biomass decreased with depth and ranged between 7 ug C L" to 1  1  O^ugCL- (Fig. 21). 1  Integrated* abundance was low at P4 (0-30 m, 9.3* 10 cells m~; 0-75 m, 1.9*10 cells m") 6  2  7  2  and P12 (0-30 m, 5.8*10 cells m"; 0-75 m, 1.3*10 cells m") and increased at stations along 6  2  7  2  Line P to a maximum at Station P of 3.4* 10 cells m" (3.4* 10 cells m") cells m". The 3-D plot 7  2  7  2  2  f  of total HNF abundance (Fig. 24) shows that there is a minimum at all depths at P12, although, in the plot for biomass this minimum is not as apparent (Fig. 25).  3.2.3 Autotrophic nanoflagellates The 2-5 um size group dominated the abundance of the ANF population at all stations (e.g., Fig. 19) and was rarely found to comprise <90% of the total ANF abundance. The 5-10 um and 10-20 um groups comprised roughly 10% and 2% of the total ANF abundance, respectively. Total ANF biomass was also dominated by the 2-5 um size group at stations on Line P, where they seldom comprised between 70% to 80% of the total ANF biomass. The 5-10 um size group and the 10-20 um size group made up approx. 30% and <10%, respectively. The ANF population was greater than the HNF population sometimes by as much as 7 times the abundance ofHNF(e.g.,P4,Fig. 19). At P4, the ANF total abundance was homogeneous to 50 m and decreased to a minimum of 2.6* 10 cells L" at 75 m, below the mixed layer (Fig. 19). This was the lowest abundance 5  1  recorded in May 1994. P12 abundance was generally higher than that of P4 and, beyond surface  * Unless otherwise indicated integrations with parentheses are from 0-75 m; and those without parentheses are from 0-30 m. There is a great deal of interpolation between points in the 3-D surface plots, and they are used here only to observe general trends; consequently, specific values at discrete depths should not be extrapolated from them. T  32  fluctuations, was homogenous from 10 to 75 m averaging 5.3* 10 cells L" (Fig. 22a). The 5  1  biomass profiles for P4 and P12 both varied with depth (e.g., Fig. 22a) and ranged between 2.312.5 ug C L" and 1.2-9.1 ug C L" , respectively. Abundances were generally higher at stations 1  1  west of P12, reaching a maximum average of 1.7*10 cells L" at P16. ANF abundance (3 m) 6  1  from P20 loop samples were comparable to those noted at P16 and averaged 1.3* 10 cells L" . 6  1  The vertical profile at Station P for total ANF abundance was similar in shape to that of the HNF (i.e., a maximum at the surface which decreased to 15 m and remains homogenous below that depth to 75 m) although, ANF abundances were much higher at Station P (avg. 1.4* 10 cells L" ) 6  1  (Fig. 23). The biomass at P16 peaked at the surface and was homogeneous between 2 to 60 m (avg. 12 ug C L" ) (Fig. 26). However, at Station P23a, total biomass fluctuated with depth and 1  ranged between 7 to 25 ug C L" (Fig. 21). Relative to other stations on Line P, integrated* ANF 1  abundance was low, at stations P4 and PI2. For HNF abundance, a minimum of 2.1*10 cells m" 7  (4.1* 10 cells m") was found at P12 (Table 2). At station PI6, integrated abundance was at a 7  2  maximum of 6.7*10 cells m" (1.4* 10 cells hi" ) and then decreased slightly at Station P (Table 7  2  8  2  2). Integrated biomass was variable along Line P, high at P4, (0-30 m, 274 mg C m'; 0-75 m, 2  654 mg C m"), low at station P12 (0-30 m, 205 mg C m"; 0-75 m, 279 mg C m") then increasing 2  2  2  to the maximum values, at P16 (0-30 m, 435 ug C L" , 896 mg C m") and then decreasing by 2  2  about 100 ug C m" at Station P (Table 2). The minimum integrated values at PI2 are visible in 2  both the abundance (Fig. 27) and biomass (Fig. 28) surface plots of Line P, February 1994. The minima seen in the surface plots of HNF (Figs. 24,26) abundance, at P12, is much more distinct in both ANF abundance and biomass plots, although note that there is only a sample at 3 m  * Unless otherwise indicated integrations with parentheses are from 0-75 m; those without parentheses are from 030 m.  2  33  representing station P20 and that points above and below are interpolated by the graphing program (i.e., not representative of actual data).  3.2.4 Cyanobacteria and heterotrophic bacteria Cyanobacterial abundance was highest, at P4, relative to other stations, and was homogeneous 0-55 m (avg. 1.4*10 cells L" ) (Fig. 29a). At station P12, abundance was at a 7  1  minimum and averaged 6.2* 10 cells L" for the profile, which was homogenous with respect to 6  1  the standard error of the mean (Fig. 29b). Although abundance was much lower (avg. 0-60, 7.5*10 cells L" ), the profile at P16 (Fig. 29c) was similar to P4 in its vertical distribution. At 6  1  Station P23a, cyanobacterial abundance was homogeneous throughout the profile and averaged 8.3*10 cells L" (Fig. 29d), which was similar to the average of the samples taken from the loop 6  1  at P20 (8.5* 10 cells L" ). Biomass averages ranged between 1.3 ug C L" to 5 ug C L" on Line 6  1  1  1  P. Integrated abundance was at a minimum at PI 2, a similar trend to that found for the HNF and ANF integrated abundance of 2*10 cells m" (0-75 m, 4.7*10 cells m"; 0-30 m, 41 ug C m , 08  2  8  2  2  75 m, 97 ug C m ); and the integrated maximum of 4.7* 10 cells m" (0-75 m, 9.1*10 cells m";02  8  2  8  2  30 m, 102 ug C m"; 0-75 m,192 pg C m") was found at P4 (Table 2). The minima in abundance, 2  2  at PI2, and biomass that was seen for the HNF and ANF were also found when surface plots were constructed for cyanobacterial abundance and biomass along Line P (Figs. 30,31). The surface plots clearly show the high abundance, over 0-60 m, at Station P4 followed by a sharp decrease in abundance and biomass at all depths at P12, after which there is a gradual increase at all depths towards Station P. Vertical profiles for heterotrophic bacteria were only obtained from Stations P4 and P23a; loop samples were obtained from all other stations. At P4, abundance generally decreased with  34  depth and ranged between 8.7*10 cells L" to 3.1*10 cells L" (Fig. 32a). Loop samples for P128  1  8  1  P20 were lowest at P12 with 5.9*10 cells L" and continued to increase past P16 to a value of 8  1  7.4* 10 cells L" at P20. At station P23a, abundance fluctuated with depth and ranged between 8  1  5.8*10 cells L" and 8.4 *10 cells L" (Fig. 32b). Heterotrophic bacterial production at the 8  1  8  1  surface was generally around 1 pM TdR incorporated h" on the outward leg of the cruise. 1  3.3  Line P , May 1994  3.3.1 Cruise background information The May 1994 cruise commenced a few days later than the May cruise of the previous year, with sampling starting at P4 on May 15th andfinishingat Station P on May 23rd. Surface temperature* at P4 was 11.9°C and decreased seawards to a minimum of 7.8°C at Station P (Table 1). Mixed layer salinity ranged from 32.3 at P4 to 32.5 at Station P (Fig. 31). The depth of the 1% light level was at its shallowest at P4 (45 m), increased to its maximum depth at P16 (85 m) and then decreased through P20 to Station P (60-65 m) (Fig. 7c); this was dissimilar to the pattern found for Line P in May 1993 (Fig. 7a). Mixed layer depths could not be determined because of the unavailability of temperature and salinity profiles for all stations on Line P. A repository of HNF, ANF, cyanobacteria, and heterotrophic bacteria abundance and biomass data is provided in Appendix. 3.3.2  Heterotrophic nanoflagellates The HNF population abundance was dominated by the 2-5 um size group at all  stations, ranging between 74 to 99% of the total HNF at discrete depths (e.g. Fig. 34). However,  * Surface temperatures were not available for May 1994, so a temperature from <15 m has been reported; it is assumed that it is representative of the mixed layer (Table 1).  35  they did not always dominate biomass at these depths because, as was previously mentioned in section 3.2.2, the larger cells (5-20 um) contribute more carbon per cell; therefore, the larger cells may at times contribute the same amount of carbon as the 2-5 um group even though the larger cells are less abundant. This was demonstrated at most stations on Line P, where both the 2-5 um (max. 90%) and 5-10 um (max. 70%) size groups made large contributions to the biomass at certain depths, except for P20 where all three size groups made substantial contributions (Fig. 35). In general, there was a decrease in the HNF abundance with depth at stations P4-P20 (Fig. 36). However at Station P, both profiles of HNF were homogeneous with depth (e.g. Fig. 37), averaging 4.6* 10 cells L" . Between stations P4 and P20, total abundance was around 10 cells 5  1  s  L"\ except at the deeper depths of P16 where cells decreased to 10 L" . Biomass distribution 4  1  was more variable with depth than abundance, especially at P4, (e.g. Fig. 38a) but also it generally decreased with depth from P4 to P20. At P4 and P20 total biomass was <10 ug C L"  1  throughout the profile, and at P12 and P16 it was <2 ug C L" . In contrast to the abundance 1  profiles at Station P, biomass increased with depth in both profiles (Fig. 39). The first profile was found to have a higher average biomass (2.7 ug C L" ) than the second profile (1.7 ug C L" ). 1  1  The integrated abundance and biomass of the HNF population was high at P4 (2.27*10  7  cells L" , 264 ug C L" ), low at P16 (7.27* 10 cells L" , 32 ug C L" ), and then increased again at 1  1  6  1  1  P20 (1.22* 10 cells L" , 94 ug C L" ). Abundance continued to increase at Station P, both vertical 7  1  1  profiles being similar with averages of 1.7*10 cells L" . There was, however, a large difference 7  1  between the two vertical profiles of biomass (Table 2, Figure 39) which was largely attributed to a change in mean cell size. It was interesting to note that the general pattern of abundance and  36  biomass, including only thefirstprofile of Station P, was similar in shape to that of the 1% light depth (Fig. 7). this pattern was also seen in the surface plot* of total HNF abundance (Fig. 40) and, to a lesser extent, in the plot of biomass (Fig. 41).  3.3.3 Autotrophic nanoflagellates The ANF population was also dominated in abundance by the 2-5 um group on Line P, and ranged between 47 to 87% of the total ANF abundance. Total ANF biomass was largely dominated by this group as well, (10-90%) although the 5-10 um group did make some substantial contributions at certain depths (4-70%). With the exception of P4, the ANF were always higher in both abundance and biomass than the HNF, although the vertical distribution was often much more variable in comparison to the HNF on Line P. Total abundance was around 10  5  cells L" at stations P4-P16 and 10 cells L" at P20 and P26. Only at P4 do the HNF and ANF 1  6  1  populations have similar abundance and biomass from 0 to 15 m with the ANFs averaging 7.6* 10  5  cells L" ; however below this depth to 45 m, and throughout all other station profiles, ANF total 1  abundance and biomass was higher than that of the HNF. P12 total abundance was homogenous throughout the profile with the exception of a near surface minimum of 3.5* 10 cells L* (Fig. 5  1  36b); biomassfluctuatedwith depth, ranging from 2.4 to a maximum of 7.3 ug C L" at 60 m 1  (Fig. 38b). At P16 ANF total abundance was homogeneous throughout the profile averaging 5.2* 10 cells L" , while at P20 abundance was higher and only homogeneous from 0 to 35 m 5  1  (1.3* 10 cells L") and decreased below this depth. Biomass was variable at both P16 and P20, 6  1  but it also tended to decrease with depth (Fig. 38c, d). At Station P, abundance was constant and consistently high with depth in thefirstprofile, with an average abundance of 1.6*10 cells L" ; 6  f  The values for Station P are averages of the two profiles.  1  37  the second profile fluctuated moderately with depth, and had a higher average abundance of 2*10 cells L" which was much higher than any of the previous profiles (Fig. 37). Although there 6  1  was some fluctuation, an increase with depth was seen in both profiles of total biomass at Station P, each with a deep maximum of at least 10 ug C L" (Fig. 39). 1  A N F abundance and biomass integrated 0 to 30 m, shows a similar distribution in comparison to the HNF, with only a few differences. As with the HNF, peaks in abundance and biomass do not necessarily correspond because of changes in cell size. Integrated abundance was found to be high at P4 (3.7* 10 cells m" ); it then decreased to a minimum at P12 7  2  (1.9*10 cells m" ), instead of at the HNF minimum of P16 (7.3*10 cells m" ), and then increased 7  2  6  2  through to Station P with a maximum for the entire line coming from the second profile (8.5* 10  7  cells m") (Table 2). Biomass exhibited a similar pattern, but west of the maximum at P4 (465 pg 2  C m") another peak was found at P20 (346 mg C m ) instead of at Station P with its higher 2  2  abundance. Although abundance was higher in the second profile (two days later) at Station P, biomass was 1.5 times lower than the first profile (Table 2), again due to a change in average cell size. These patterns are also seen in the surface plots of abundance and, as with the HNF, to a lesser extent in those of biomass (Fig. 43). In both plots it is easy to see the higher abundance and biomass at opposing ends of Line P with a minimum at all depths around P12 and PI6, which is similar to the pattern seen in both HNF and A N F abundance and biomass of the previous cruise in February 1994.  3.3.4 Cyanobacteria and heterotrophic bacteria Between 0 to 10 m, cyanobacteria were homogeneous in most profiles of Line P. However, below this there was some fluctuation and a general decrease with depth at stations P4  38 to P20 (e.g. Figs. 44,45). At Station P the population was high and homogeneous with depth, as was observed with the ANF (Fig. 46). Biomass distribution was similar to that of abundance and will be addressed below through integrated values. Cyanobacteria integrated abundance 0 to 40 m at Station P was found to have a similar distribution to the HNF population although it was more subtle because abundance was relatively high everywhere except P12, and (Table 2) in contrast to the pattern found for the HNF, a higher cyanobacterial abundance was found in the second profile taken at Station P (Table 2, Fig. 46). The high integrated abundance was more clearly seen when converted to biomass, with all stations except for P16 (72 ug C L" ) above 110 1  ug C L"\ the minimum for the line being equal to the value found at Station P in February 1994. With the exception of a peak at P16 (Table 2), heterotrophic bacteria were generally uniform along line P, averaging 2.6* 10 cells m". However, they also had a minimum at P12 as 10  2  did the ANF. Surface bacterial production was high at P4 (1.7 pmol TdR incorporated h") and 1  remained around 0.3 pmol TdR incorporated h" at stations P12-P20. An increase in production 1  was then seen at Station P although it was still lower than that seen at P4 (0.7 pmol TdR incorporated h").. 1  3.4 Statistical Analysis  The Spearman non-parametric correlations were chosen to look at relationships between HNFs and ANFs, cyanobacteria, and hetertotrophic bacteria. Data from all three cruises were grouped together, and correlations were run with different groups of stations (i.e., P4-P12, P4P16, P16-P26, and P20-P26 (Table 3); to determine if there were any changes in the relationship between predator and prey, as stations nearer the coast, P4 and PI2, were removed from the correlation). The Spearman correlations yielded a number of significant relationships (i.e., Table  39  3, numbers in bold). The highest coefficients were found between autotrophs and heterotrophs of the same size. The correlation coefficients between heterotrophs and autotrophs of the same size generally (r ) increased with the addition of westward stations. This was especially true for the 2s  5 um and 5-10 um HNF and ANF (Table 3). For example, the correlation coefficients between 25 um HNF and ANF were not significant for P4-P12,however, the coefficient for stations P4-P16 was 0.41, and increased to 0.81 for P16-P26, and reached a maximum of 0.88 for stations P20 and P26. The relationship found between the 2-5 um HNF and cyanobacteria, seemed to be higher at stations nearer to and including P4, where correlation coefficents were found at a maximum of 0.8 (P4-P12) and gradually decreased as stations P4-P16 were removed from the correlation, to a minimum correlation coefficient of 0.45 (P20-P26). To test the relationship between integrated ANF abundance, biomass (0-30), and environmental parameters (i.e., mixed layer depth, temperature, and nitrate, and ammonium) multiple linear regressions were performed on combined data from all three cruises, where ANF abundance and biomass were dependent variables and the environmental parameters were the independent variables. Regression results indicated that both integrated (0-30) autotrophic abundance and biomass vs. mixed layer depth, temperature, NCV, and NH/ reduced stepwise to the mixed layer depth were not significant.  40  Table 1. Station information for May 1993,1994 and February 1994 cruises. Temp denotes surface temperature °C; MLD denotes mixed layer depth (m). N/A denotes data that was not available. Loop refers to the shipboard seawater pumped supply system, which pumps water from a depth of 3-4 m.  Date  Time  Temp  MLD  11:45-12:45 5:10-5:40 3:43-5:00 12:50-13:00 19:00-20:30 21:00-22:00  10.5 10.5 9.5 7.0 8.0  35 48 48 30 30  5/23/93  P4 P12 P16 P20 P26 P26  8.0  30  2/8/94 2/16/94 2/15/94 2/11/94 2/13/94  P4 P12R P16R P20 P23a  14:00-15:00 10:30-11:30 11:00-12:00 21:00 Loop 15:00-16:00  9.5 9.3 9.1 8.0 7.3  60 80 80 80 80  5/12/94 5/14/94  P4 P12  21:00-22:00 9:00-10:00  11.9 10.5  5/15/94 5/16/94 5/18/94 5/21/94  P16 P20 P26 P26  11:00-1200 18:00-19:00 20:30-21:30 11:00-12:00  9.9 8.5 7.8  N/A N/A N/A N/A N/A N/A  5/12/93 5/17/93 5/18/93 5/19/93 5/21/93  Station  N/A  May 1993 Salinity 31  32  33  34  Figure 6. Salinity profiles (%c) on Line P in May 1993.  35  36  42  May 1993  i 0  5  1  1  February 1994  r  l 5  0  10 15 20 25 30  Station  Station • O  1 1 1 r 10 15 20 25 30  Mixed Layer Depth 1% light deph  May 1994  20 H  §• 60 H Q 80 H 100  i 5  r 10 15 20 25 30 1  1  1  Station  Figure 7. Mixed layer depth and the 1% light depth at sampled stations on Line P. a) May 1994, there are two points at Station P (P26) because two profiles were taken there (See Table 1); b) February 1994, and c) May 1994, mixed layer depth is not presented because temperature data (°C) was not available for this cruise.  May 1993 Cells*"! 0 L6  Cells*10 L-  1  0 1 2 3 4 5 6 7 8 9  6  0  2  4  6  1  8 10 12  Figure 8. Abundance in cells L" of total ANF (•) and HNF (O) in May 1993 at stations a) P12, b) P16, c) P20, d) Station P, profile 1, and e) Station P, 2 days later. Error bars are standard error of the mean (n=: 1  Figure 9. Biomass in ng L" of total ANF (•) and HNF (O) in May 1993 at stations a) P12, b) P16, c) P20, d) Station P, profile 1, and e) Station P, profile 2,2 days later. Symbols and error bars as in Figure 8. 1  45  «1 .s w  s  X N \C 0 0 rt o\ m <N Tt- m  H  tfl  «5  5 If  <^ s Z  s o o o ©© ^ * rt * O; * t-; * ©* A IS CS l—<  1-4  8  ^  ^ ^  £i  8 ^ V) O  ^  ^  $  ,S-  (-J  rtSSlrtxSS-H * * es ON  rt rt <* t-- m s T t v-> Z  ©  ©  ©  ©  rt  rt  i—I  ©  V©  V} rt Tf OO cs cn cs' cs'  rt  rt  ^  * * * * * >^  co cn rt cs cn  S3  in N \o  cs  S  n  O z rt a s S £ g r t O O C S S ^ S ^ s  N  OO  rt  ©  ©  N  t cn fs ^- cs  © >o  IP  oo  ^ © 4$Z 25 * Z rt 00  S  03  O  *  M  22  Z  s 5 ^  I IP  4*  oo  ©  oo  ©  oo  ©  oo  ©  i—l  r-4  i-4  i—i  *  *  *  *  T t  IO 0\'  rt  VO  rt  rt  a  2 rt  \p  n  0^0  oo M  0^ 0  )0  OO  00  00  0Q_  OO  OO  0Q  © © © © <b C> <b <ti i — I i — l l — l r t ~ ^ ~ ^ i « « | » « t  *  *  *  *  *  *  *  *  cs' cs' cs' ON >t >/S  vo  S  r- oo Tt cs ©  T t cs C~ © © cs  ©  ©  ©  ©  ©  i—I  i—I  rt  i—I  rt  oo  \0 rt  ^  s 1:3  , e  ©  ©  ©  ©  s  |3  ©'©'©'©'b'b'fe'k  PM ON PN cs  »  O  fl o\  n 6-  f) 0fj\ ON f) f) 9\ i i i i . H  •  os i  0\  {{  R  A  R  !(  R  S 2 2 S§S  *  *  *  *"!  * "1  ri c  *  *  ^  <j  * ^  >t  V~l  ON  rt  * ££2 * ^ Tf > Os ON ON os Os • i • • i -fi ^ -D -D 0) 4) ^ tV ^> ta ta ta ta fc<  ^  ~ i ~ i  ©  ©  © © * * r- o\ cn rt  rt  oo cs  \d  <o  NO  CS H cn  *  ro  CS Tt cn ON  Tt o\ i-i  Tt  © © © * * * cn i-i © c s >o vo  ©  * ©  oo  © •b "© b rt rt rt rt cs * * cn * c*s t-; * * Tt "-s <N <vi cs' ON rt rt rt  * * * * * * * * cn oo t-; oo o\ «-> T t  * in ON ^  wQ  N  M  &  ll  ©  rtrtrtrtrt  -  ON  n rt  NO  * * * * * * f S T t CS T t rt rt IT) VO IO t~ m  <1 5s * * * * Z T t rt en cn cs cs cs' cs'  cn  cn  IOrt rt rt rt  IS Z  ©  * * * * * * Cn Tf © \ ON rt  VI  C S C S T t l O ^ O r N O O t N .  ©  *  ©  ©  rrt  ^ g h  H  Tt ON •  R  « o C- 5 b  PN M  r<  Tt Tt Tf Tt Tt ON  ON  ON  ON  R  R  R  R  I  I  I  •  ON •  R  48  May 1993 Cells*10 L 7  0.0 0.7 1.4 2.1 2.8 3.5 4.2 4.9  Cells *10 L" 7  Cells*10 L  1  7  1  0.0 0.7 1.4 2.1 2.8 3.5 4.2 4.9  Cells*10 L"  1  6  0.0 0.7 1.4 2.1 2.8 3.5 4.2 4.9  A A  Profile 1 Profile 2  Figure 14. Cyanobacterial abundance in May 1993 at stations: a) P12, b) P16, c) P20, d) Station P, profile 2 is 2 days after profile 1. Error bar is standard error of the mean (n=3).  51  53  P26 May 1993 Cells*"! 0 L" 9  0.2  i  0.4  r  0.6  i  i  0.8  i  1  1.0  i  1.2  i  ~~r  1.4  I  0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 pmol Tdr incorporated h  1  Figure 17. Abundance of heterotrophic bacteria (#) and bacterial production (D) at Station P (P26) in May 1993. Error bars are standard error of the mean, for bacterial production only, (n=3), where bars are not visible error is small.  February 1994 Salinity  31  32  33  34  Figure 18. Salinity profiles (%c) for Line P in February 1994.  35  55  P4: February 1994 Cells*10 L6  0.0  Cells*10 L  1  6  0.3 0.6 0.9 1.2 1.5  1  0.00 0.03 0.06 0.09 0.12  o -  10 20 30 40 Q .  <D  50 -  Q 60 70 80 90 Cells*10 L" 4  0.0  0.7 J  1.4 UW-LI  Cells*10 L  1  6  2.1 2.8 I  0.0 0.3  1  0.6 0.9  L  Figure 19. HNF (O) and ANF (•) abundance at station P4 in Feb. 1994. a) cells 2-5 um, b) cells 5-10 urn, c) cells 10-20 um, d) total HNF and ANF. Error bars as in Figure 8. Note different scales.  56  P4: February 1994 u.g C L-  pig C L"  1  0  2  4  6  8  1  10 12  0.0 0.5 1.0 1.5 2.0 2.5 3.0  Figure 20. HNF (O) and ANF (•) biomass at station P4 in Feb. 1994. a) cells 2-5 urn, b) cells 5-10 um, c) cells 10-20 um, d) total HNF and ANF. Error bars as in Figure 8. Note different scales.  57  P23a: February 1994 pig C Lr  0  5  10  1  15 20 .25  ixg  0  2  4  C L"  1  6  8  10 12  Figure 21. HNF (O) and ANF (•) biomass at station P23a in Feb. 1994. a) cells 2-5 um, b) cells 5-10 um, c) cells 10-20 um, d) total HNF and ANF. Symbols and error bars as in Figure 8.  58  February 1994 Cells*10 L" 5  1  Cells*10 L"  1  2 3 4 5 6 7 8 9  6  1  0.0 0.5 1.0 1.5 2.0 2.5 3.0  90 -  Figure 22. Total HNF (O) and ANF (#) abundance at stations a) P12, and b) P16 in Feb. 1994. Error bars as in Figure 8.  59  P23a: February 1994 Cells*10 L5  0.0 0 -  Cells* 10 L-  1  5  1  0.8 1.6 2.4 3.2 4.0  0.0 0.5 1.0 1.5 2.0 2.5 3.0  J  1  i  l  1  1  1  10 20 30 sz Q . CD  40 50 -  Q 60 70 80 90 Cells*10i L1-1 4  4  Cells* 10 l_6  1  0.0 0.5 1.0 1.5 2.0 2.5 3.0  Figure 23. HNF (O) and ANF (•) abundance at station P23a in Feb. 1994. a) cells 2-5 um, b) cells 5-10 um, c) ceUs 10-20 um, d) total HNF and ANF. Error bars as in Figure 8.  61  62  P16: February 1994 ng C L-  1  tig C L'  1  Figure 26. HNF (O) and ANF (•) biomass at station P16 in Feb. 1994. a) cells 2-5 um, b) cells 5-10 um, c) cells 10-20 um, d) total HNF and ANF. Error bars as in Figure 8.  63  65  February 1993 Cells*10 L6  0  2  4  6  8  1  10 12 14 16  Cells*10 l_6  1  0 1 2 3 4 5 6 7 8 9  10  Figure 29. Cyanobacterial abundance in Feb. 1994 at stations a) P4, b) P12, c) P16, and d) P23a. Error bars are standard error of the mean (n=3).  66  67  68  February 1994 Cells*10 L 9  Cells*10 L  1  9  0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0  0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 pmol Tdr incorporated h  1  0.56  0.63  0.78  0.70  0.84  0.77  0.90  1  0.84  0.96  pmol Tdr incorporated hr  1  Figure 32. Heterotrophic bacterial abundance (©) and bacterial production (Ll) at station a) P4 and b) Station P23a in Feb. 1994. Eerror bars are standard error of the mean (n=3).  May 1994 Salinity  31  32  33  Figure 33. Salinity profiles (%c) for Line P in May 1994.  34  35  70  P4: May 1994 Cells*10 L 6  0.0  1  0.3 0.6 0.9 1.2 1.5  Gells*10 L 6  1  0.00 0.07 0.14 0.21 0.28  Figure 34. HNF (O) and ANF (•) abundance at P4 in May 1994. a) cells 2-5 urn, b) cells 5-10 um, c) 10-20 um, and d) total ANF and HNF. Error bars are standard error of the mean (n=3).  71  P20: May 1994 Jig C Lr  1  \LQ  0 2 4 6 8 10121416  0.0  0.7  1.4  2.1  2.8  CL  1  0.0 0.5 1.0 1.5 2.0 2.5 3.0  0 2 4 6 8 10 12 14 16  Figure 35. HNF and (O) arid ANF (•) biomass at P20 in May 1994. a) cells 2-5 um, b) cells 5-10 um, c) 1020 (im, and d) total ANF arid HNF. Error bars as in Figure 34.  72  Figure 36. Total HNF (O) and ANF (•) abundance in May 1994 at stations a) P4, b) P12, c) P16 and d) P20. Error bars as in Figure 34.  P26: May 1994  Figure 37. Total HNF (O) and ANF (#) abundance in May 1994 at Station P. a) profile 1, b) profile Error bars as in Figure 34.  74  May 1994 pig C Lr 0  0  5  2  1  [19  10 15 20 25 30 i i I I i  6  8  10  C L'  1  0 1 2 3 4 5 6 7 8  0  2 4 6 8 10 12 14 16  Figure 38. Total HNF (O) and ANF (•) biomass in May 1994 at stations a) P4, b) P12, c) P16 and d) P20. Error bars as in Figure 34.  75  Figure 39. Total HNF (O) and ANF (#) biomass in May 1994 at Station P. a) profile 1, b) profile 2. Error bars as in Figure 34.  76  77  78  79  80  P4: May 1994  Figure 44. Cyanobacterial abundance at station P4 in May 1994. Error bars are standard error of the mean (ri=3).  81  \/S\\SO  P26: May 1994 Cells*10 L" 7  1  .3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 J  1  1  .  I |  Figure 46. Cyanobacterial abundance at Station P in May 1994. Solid line, profile 1, dotted line, profile days later. Error bars are standard error of the mean (n=3).  H 2  i 2  P20-P26  P16-P26  ;  -0.08  0.81  0.02  0.54  -0.15  0.12  0 26  0.33 0.23 0.10  ills -0.22  0.88 -0.3 -0.3 0 72 V. / id  -0.19  0.47 -U.JO  -0.2 0.22 0.25 ft 71  -0 64  -0 26  0.68 0.44  -0.05 0.26 0.24  0.65 0.35  0 06  0.16 0.25 0.33  0.01 -0.14 0.37  0.20  0.41  0.45  0 OS  0.44 0.43 0.33  -0.10  0.40 0.52  0.41  -0.02  0.31 0.28  -0.25 0.25  0.46  1  0.29  % 0.06 0.39 0.32 0.14  fa  P4-16  | P4-12  ft  XSI  -0.12 0.16 0.18  0.21 0.17 0.07 0.24  -0.25 -0.07 0.001 -0.32  -0.40 -0.27 0.11 -0.24  HB  -0.03 -0.26  0.45  0.21 0.01  0.60  -0.06  0.62 0.33  0.26 -0.23  CY 0.80  -0.3 -0.3  0.88  0.01 -0.14  0.81  0.25  0.43 0.35  0.35  0.41  0.12  TA  |  ©  —S  84  4. Discussion The absence of an obvious spring bloom in the NE subarctic Pacific has stimulated research in the region for several decades (Heinrich, 1967; Miller and SUPER Group, 1988; Booth, 1993). This thesis has furthered past research by studying a broader region in the NE subarctic Pacific (from coastal to open ocean at Station P, obtaining much needed winter data (Miller, 1993; Frost, 1993), and by further exploring the relationships between HNF and their prey, through analysis of abundances and by the use of carbon budgets. Through the sampling of stations on Line P, an east/west transect of the region from P4 to Station P permitted the study of variability in abundance and biomass data for ANF, HNF, cyanobacteria and heterotrophic bacteria, as well as, the potential relationship between each of these groups and environmental factors, such as, chemical and physical data from the region. Further, the winter biological data is the first data set concerning the microbial food web from the NE subarctic Pacific. In addition to the general increase in our understanding of winter ecology of the ecosystem at Station P, this thesis provides a test of the predictions put forth by modelers (Frost, 1993), that winter autotrophic and heterotrophic standing stocks are relatively high in comparison to late spring values in this region. 4.1 Station P 4.1.1 HNF and ANF In contrast to this study, where both abundance and biomass (as carbon) profiles were presented for ANF, HNF, cyanobacteria and heterotrophic bacteria, the research (Booth et al, 1993) conducted as part of the SUPER program, presented biomass, but only presented average abundance, of all six cruises (their Table 9) of each group studied (total heterotrophs and  85  autotrophs; excluding mesozooplankton, heterotrophic bacteria). The majority of their data were presented in terms of biomass (as carbon) for the autotrophic and heterotrophic populations. The 2-5 um ANF and HNF dominated both the abundance and biomass at Station P in February and May 1994, as they have in other studies in this region (Booth et al, 1993), as well as in other open ocean regions, such as, the equatorial Pacific (Chavez et al, 1990) and coastal regions in the North Sea (Geider, 1988). The taxa of the nanoflagellate populations were not identified during this study, however, heterotrophic nanoflagellate populations (2-5 um) at Station P (May 1993, 1994) were likely composed of similar taxonomic groups as were found by Booth et al (1993) in May. However, nothing is known of winter taxa in this region. Booth et al. (1993) identified heterotrophic nanoflagellates from the following groups: Choanoflagellida (2-5 um), Chrysophyceae (2-10 um), Dinophyceae (5-24 um), Cryptophyceae (5-10 um), and Bodonidae (2-10 um). Autotrophic nanoflagellates found by Booth et al. (1993) were from the following groups: Prymnesiophyceae (2-24 um), Prasinophyceae (2->24 um), Dinophyceae (5->24 um), Chrysophyceae (2-10 um), and Cryptophyceae (5-24 um). In both the HNF and ANF populations at Station P during this study, the 5-10 um groups were often found to make contributions to biomass comparable to those of the 2-5 pm groups, again similar tofindingsby Booth et al (1993), but the 5-10 pm groups contributions were generally less than 20% of the total HNF and ANF biomass at any one depth. The average abundances of total HNF found at Station P by Booth et al. (1993) are well within the ranges obtained from this study during the 1994 cruises; however, in May 1993, total HNF abundance was an order of magnitude higher, around 10 cells L" (Fig. 8d, e). HNF 6  1  biomass was also much higher during the May 1993 cruise in comparison to the other cruises.  86  The total HNF biomass averaged 993 mg m" (0-30 m, Table 2) in May 1993 at Station P; the 2  highest value found by Booth et al (1993) was 651 mg m" (5-25 m) in September 1987, and then2  May observations were only around 400 mg m". The high biomass found by this study may be an 2  artifact of calculated carbon conversion. In May 1993, an average cell size was chosen during all counts of HNF and ANF, whereas Booth et al. (1993) measured the dimensions of every cell they counted. In general, biomass estimates are very sensitive to changes in cell size. For example, the HNF integrated biomass for the first profile at Station P in May 1993 was 1247 mg m", but if the 2  average cell diameter is changed from 3 um to 2.5 um, a 17% difference, the biomass decreases to 773 mg m , a 37% decrease in cell volume and biomass, respectively. Although, this 2  demonstrates that it is possible for the biomass in May 1993 of the present study to have been reduced, it is still between 16-86% higher than all observations made by Booth et al. (1993) in the spring and summer.  4.1.2 Winter at Station P Although Station P was not sampled in February 1994, it is likely that P23a is representative of the region because of the high degree of both horizontal and vertical mixing associated with a prolonged period of stormy weather at that time. Integrated HNF abundances (0-30 m) were the same in February and May 1994 and about an order of magnitude lower than May 1993 (Table 2). The ANF integrated abundance was lower in February, compared to the two late spring cruises, but the biomass was considerably higher than in May 1994. This was due to an increase in size and abundance of the cells in the 5-10 um and 10-20 um size groups. It is, however, important to note that the mixed layer depth was around 75 m in February and, if cells were integrated to that depth, the abundance is doubled for both the ANF and HNF populations,  87  and biomass is 1.5 times larger. If integrated to 75 m, winter values of HNF and ANF are higher than all other cruises, which means that there is a larger standing stock of HNF and ANFs in the winter compared to summer, a function of a deep mixed layer. Therefore, the carrying capacity of of the upper water column is higher in the winter. The HNF and ANF winter abundance data supports the hypthesis of Miller (1993) and Evans and Parslow (1985) that there is a relatively high standing stock of autotrophic and heterotrophic cells at Station P, which is primarily due to the presence of a permanent halocline at around 100 m (Dodimead et al, 1963), permitting net growth of the phytoplankton, which in turn, supports the heterotrophic population. The relatively high winter standing stocks of HNF and ANF, cyanobacteria, and heterotrophic bacteria indicate that the relationships between predator and prey remain functional throughout the winter season (see Section 4.3). Statistical analysis of the autotrophic and heterotrophic populations revealed few correlations between the above groups; therefore, possible explanations to changes in abundance and biomass may be due to variables not measured by this study, such as, changes in species composition and/or species shifts in predator and/or prey. However, it should be noted that past studies at Station P did not observe changes of this nature. Although, standing stocks of the above groups are comparable to those of the following summer, the species composition is not necessarily the same during both seasons. It is possible that there may be shifts in species composition of the HNF and/or in prey preference from winter into spring/summer. For example, integrated cyanobacterial abundance (0-30 m) in February (62 mg C m") was similar to May 1993 (35 mg C m"), the cyanobacterial 2  2  population was, however, low in May 1993 relative to the rest of Line P, see below), but both of the previous cruises were much lower compared to the following May (1994) (150 mg C m"). 2  The high cyanobacterial abundance in May 1994 goes against general trends found during this cruise, where all other heterotrophic and autrophic populations were low relative to May 1993. The decrease in cyanobacterial abundance in Feb. 1994 and May 1993, relative to May 1994, may indicate that there was a shift in the HNF population to a species which prefers to feed on cyanobacteria, or a shift in the prey preference of one species of HNF. Fluctuations in the cyanobacterial population were also observed by Booth et al. (1993); they found that cyanobacterial biomass in May 1988 was low, compared to this study, and that there was a concomitant increase in HNF biomass. When compared to the previous May cruise of that study, the opposite was found; cyanobacteria were relatively high in biomass and HNF had a low biomass, relative to the other SUPER cruises (Table 4). Table 4. Heterotrophic nanoflagellate, HNF, and cyanobacteria, cyano, biomass (as carbon) mg C m' at Station P. Booth etal. (1993) May data from their Table 9. May 1993 and 1994 data are from this study. 2  Booth et al. Booth et al. May-93 May-94 May-94  . HNF 198 484 784 122 ,47  Cyano 142 62 35 123 150  The heterotrophic bacterial abundance was also lower during the winter, relative to May 1993 and 1994, but the ANF biomass in the winter was 1.7-2.7 times higher than the following May (1994). Assuming that there was an adequate supply of substrate for the heterotrophic bacteria, control of their abundance is not bottom-up, but is more likely to be top-down. This is to be expected since Kirchman et al. (1993) attributed changes in heterotrophic bacterial biomass on daily to monthly time scales to grazing, i.e. top-down control. They were also unable to correlate heterotrophic bacterial production and primary production on these short time scales,. Bacterial production in winter was similar to that found in May 1993 (Fig. 15). Therefore, in the  absence of statistical confirmation, the control of heterotrophic bacteria probably comes from a combination of top-down and bottom-up processes, i.e. temperature and nutrients, where topdown control may not only come from the HNF but also from the heterotrophic ciliates whose numbers were found to be higher in February when heterotrophic bacteria were lowest, compared to late spring/early summer, (Boyd et al, submitted). Ciliates are capable of ingesting cells <1 um at high rates (Sherr and Sherr, 1987). However, more data is needed to aid in the discrimination between top-down and bottom-up controls of heterotrophic bacterial populations.  4.2 LineP 4.2.1 HNF and ANF The ANF dominated both abundance and biomass of the total nanoflagellate population on Line P in February and May 1994, but not in May 1993. During the latter cruise the integrated abundances (0-30 m) of HNF were between 2 to 4 times that of the ANF. The integrated HNF abundance in May 1993 was also generally much higher at all stations on Line P compared to the 1994 cruises. For example, at P12 in May 1993, integrated abundance was 2.4* 10 Cells m" and 8  2  in May 1994 it was 9.7* 10 cells m" (Table 2); this is a 24-fold difference between years. 6  2  However, if biomass is compared there is a 34-fold difference, where May 1993 was the higher of the two years. In contrast to the HNF, the ANF integrated abundance in May 1993 was similar to both 1994 cruises; biomass, however, was 13 times that of May 1994 and 9 times that of February 1994, further illustrating how much more abundant the HNF were in May 1993 and that cell volumes were larger for both HNF and ANF.  90  The HNF and ANF integrated (0-30) population abundances and biomasses were generally high at P4 and then decreased to a minimum at either P12 or PI6, depending upon the year and type of flagellate. The HNF and ANF were both at a minimum at P16 in May 1993, at P12 in February 1994 and, in May 1994. HNFs were at a minimum at P16, but ANFs were at a minimum at PI2. West of PI6, abundance and biomass generally increased again towards Station P, sometimes reaching levels higher than what was seen at P4. This was seen in all cruises on Line P, and possible reasons are discussed in Section 4.2.3. HNF and ANF cell densities in May 1993 were 10 cells L" , and both abundance and biomass increased below the mixed layer at 6  1  Stations P12, P16, and P (Figs. 8b, c, d; 9b, c, d). In 1994 HNF and ANF were 10 cells L" from 5  1  P4 to P16 and then increased to 10 cells L". Cell densities and biomass of HNF and ANF in May 6  1  1993 on Line P were similar to those found in the open North Atlantic in May 1989 (Sieracki et al, 1993). In comparison, densities of HNF found in the Chesapeake Bay estuarine outflow plume ranged from 10 -10 L" (McManus and Fuhrman, 1990), and in the oligotrophic waters of 5  7  1  the northwest Mediterranean Sea, densities ranged between 10 -10 cells L" (Ferrier-Pages and 4  5  1  Rassoulzadegan, 1994). ANF populations ranged between 10 -10 cells L" in the Atlantic, on a 5  6  1  transect between the Canary Islands and South Florida (Davis et al, 1984, Estep et al, 1986), and 10 cells L" in the North Sea (Geider, 1988). These studies indicate that in general, coastal 6  1  regions yield higher ANF abundances than the open ocean.  4.2.2 Cyanobacteria and Heterotrophic Bacteria Cyanobacteria integrated abundance was never <10 cells m" during all cruises, although 8  2  integrated abundance was higher during both May cruises compared to the winter cruise. An exception to this was that the lowest abundance that was found during all cruises occurred at  91  Station P in May 1993, which may have resulted from the cooler temperature,(i.e.bottom-up control), and to increased grazing pressure (i.e., top-down control). The increase being a result of a possible shift in prey specificity by the HNF, as discussed in Section 4.1.2, however as was previously mentioned species composition was not studied, and results from statistical analysis have not indicated that there is a strong relationship between predator and prey at Station P. The minimum observed around stations PI2 and PI6 in HNF and ANF abundance and biomass was also observed for cyanobacteria abundance and biomass during both 1994 cruises but not in May 1993 where the minimum may be the result of sampling in a different water mass, as discussed in Section 4.2.3. Cyanobacterial densities during the May cruises were comparable to those found by Booth et al. (1993) at Station P and, as they pointed out, to those found in the equatorial Pacific (Chavez et al, 1990), although subarctic temperatures were much lower (see Discussion; Boothia/., 1993).  4.2.3 Heterotrophic and Autotrophic Population Dynamics on Line P In May 1993 and 1994 there was a minimum in abundance and biomass of HNF, ANF and cyanobacteria around P12 and P16. Since this minimum was found for all of these groups, it seems likely that there is bottom-up control of their abundance and biomass in this region. Further, strong top-down control of cyanobacteria and HNF populations is not shown statistically, contrary to what was expected. However, multiple linear regressions betweeen ANF biomass and bottom-up controls (i.e., temperature, nutrients, mixed layer depth) did not indicate that there was a significant relationship with these environmental parameters either. In addition to changes in the above populations, high salp densities near the coast have been observed to  92 decrease (e.g., May 1993, Wen, pers. comm.), as well as, indications of chemical gradients in this region (Wong, unpublished data). A possible explanation may come from Favorite et a/.'s (1976) characterization of a "Dilute Domain", a less saline water mass, in the NE subarctic Pacific which is formed by the westward extrusions of dilute plumes from the Columbia River, Strait of Juan de Fuca, Queen Charlotte Sound and Dixon Entrance (Fig. 2). The domain is isolated from the coast by surrounding domains, e.g., Transition, Upwelling, and Ridge Domains, and is bordeied by a region with a salinity around 33. The Dilute Domain may provide an explanation for the presence of a minimum in abundance, and sometimes in biomass, of HNF, ANF, and cyanobacteria during both 1994 cruises. This minimum may indicate that there is a transition zone in the abundance and biomass of the HNF, ANF and cyanobacteria starting somewhere beyond Station P4 (48 39°W, 126 40°N) and before P20 (49 34°W, 138 40°N) a distance of approximately 955 km. The shift from the surrounding higher salinity domains to the Dilute Domain was stated to have been particularly evident at 100 m (Favorite et al, 1976); this is concordant with salinity data at 100 m from all three cruises of the present study (e.g., Fig. 18). It is unclear whether or not this decrease in abundance and biomass of HNF, ANF, cyanobacteria, and heterotrophic bacteria is due to changes in salinity occurring across the Dilute Domain, however, Taylor and Waters (1982) also observed low abundances in this region, relative to the coast, around iO  5  flagellates L" . The dilute domain appears to have been present in May 1993 at 100 m (Fig. 6), 1  however, abundance and biomass were much higher during this cruise at all stations on Line P, indicating a change which is to date unexplained. In addition to their salinities, these domains may be characterized by other variables, e.g., trace metal availability or other water properties.  4.3 Predator/Prey Relationships Although statistically significant correlation coefficients between HNF and their prey were generally low, e.g., <50%, the 2-5 um HNF abundance were found to be more highly correlated with cyanobacterial abundance at stations closer to the coast. However, competition for cyanobacteria with ciliates may explain the low correlations; Strom (1993) found ciliate populations at Station P comparable to coastal numbers. Therefore, it may not be appropriate to imply that oceanic stations should exhibit a stronger correlation between the HNF and cyanobacteria, due to the removal of larger microzooplankton, (e.g., ciliates, which would compete with the HNF for cyanobacteria, as was hypothesized by Gasol and Vaque (1993) between HNF and heterotrophic bacteria). There are a number of possible explanations for the inability to see this trend: There may be a gradual shift in the species of cyanobacteria, possibly to one which is non-nutritious to the HNF as was found in laboratory experiments for the ciliate Fabrea salina (Repak, 1986). The HNF may shift from feeding on heterotrophic bacteria to feeding on cyanobacteria (or vice versa), although there were no high correlations between HNF and heterotrophic bacteria. Between station P20 and Station P, the large decrease in cyanobacterial abundance, may have been a result of HNF shifting to feed more heavily on cyanobacteria, since temperature, mixed layer depth, and the depth of the 1% light level did not change. Murphy and Haugen (1985) also found gradients in cyanobacterial numbers in the Atlantic (open ocean) unattributable to changes in temperature, which they hypothesized may be the result of a gradient in some unmeasured nutrient HNF may be exhibiting a type of size selective grazing as was observed in experiments (Gonzalez et al, 1990) with heterotrophic bacteria.  94  At all stations on Line P it was observed, as it was at Station P (Booth et al, 1993), that cyanobacterial cells were smaller at the surface when compared to larger brightly fluorescing cells at depth, which may be the result of size selective grazing by the HNF (Gonzalez et al, 1990). Observations of cells that fluoresce more brightly at depth have also been observed in the Atlantic, which was attributed to a within-species increase in phycoerythrin content or fluorescence yield (Murphy and Haugen, 1985). It also seems that the HNF would not be able to feed solely on heterotrophic bacteria, especially at Station P where the bacterial assemblage has a slow turnover of once every 10 days (Kirchman et al, 1993), compared to every 2 days in a Georgian estuary in the summer (Sherr et al, 1989), the difference being attributed to differences in bottom-up controls, i.e., temperature and nutrients. Since only 'snapshots', i.e., single vertical profiles at most stations, were obtained of the populations at each station, the failure to see a stronger relationship on Line P may be a function of some sort of time lag between predator and prey. The sampling program for this thesis was however dictated by the concurrent CTD sampling program. The inability to correlate heterotrophic and autotrophic populations, from the three cruises of this study, is not uncommon, and was also observed at Station P (Booth et al, 1993), in the North Sea (Geider, 1988), and the northern Baltic Sea (estuarine) (Schiewer and Jost, 1991; as seen in Booth et al., 1993). However, variation in the composition of algal communities is the rule not the exception, meaning that the inability to correlate the heterotrophic and autotrophic populations is not surprising (Booth et al, 1993; Scheffer, 1991; Tobiesen, 1991). Diel oscillations in autotrophic flagellates <2 pm, and heterotrohic flagellates <2 um and 1-10 um observed by Wheeler (1989), where the heterotrophs were found at a maximum  abundance at the beginning of the day and autotrophs at the end of the day, may be extrapolated to the population variation in this data set and explain some of the variation in the data of this thesis since sampling was done at different times of the day at each station (e g, May 1993, Table 5 ). The further inability to correlate HNF and heterotrophic bacteria is also not surprising,  Table 5. Sampling times for HNF, ANF, cyanobacteria, and heterotrohic bacteria in May 1993. Taken from Table 1. Station P4 P12 P16 P20 P26 P26  Sampling Time Noon Pre-dawn Late afternoon Night Night Night  since field studies have not been able to support the existence of strong top-down control on their populations (Ducklow and Carlson, 1992). In estuarine waters (Sherr etal., 1989), out-of-phase oscillations (i.e., low heterotrophic bacterial abundance do not correspond with expected peaks in HNF abundance, of bacterioplankton and heterotrophic protozoan standing stocks over periods of days to weeks) have been demonstrated, similar to findings in coastal areas (Fenchel, 1982; Andersen and S0rensen, 1986; Rassoulzadegan and Sheldon, 1986). The inability to correlate HNF with heterotrophic bacteria may also be the result of top-down control obscuring the influence Of bottom-up control on bacteria oh daily and monthly time scales, as was demonstrated by Kirchman et al. at Station P (1993). Integrated heterotrophic bacterial abundance (0-30 m) was lower in Feb. 1994 in comparison to both May cruises, but the HNF population in February was similar to that found in May of that year (Table 2). Heterotrophic bacterial standing stocks  96 may be controlled by grazing from nano- to microzooplankton in the late spring and limited by bottom-up control and, to a lesser extent, grazing by flagellates and ciliates in the winter. However, it is not possible to separate the influences of top-down and bottom-up controls with this data set. At Station P the consequent increase of mesozooplankton from winter to summer may also be indicative of a shift in the trophic structure of the food web, from a microbial food web (MFW) in the winter, with a relatively high standing stock of HNF, ANF, cyanobacteria, and heterotrophic bacteria, to a multivorous food web (MuFW) in the summer with the increase in mesozooplankton biomass and predation; although, this is unlikely since during the summer the mesozoopankton only account for 15% of grazing. This is contrary to Legendre and Rassoulzadegan (in press) who state that the MuFW should dominate in the winter. However, they do not state exactly how much grazing pressure needs to be exerted by the mesozooplankton to enable a MuFW to exist. Their food web continuum hypothesis does not state what quantitative changes in heterotrohic and autotrophic populations need to occur in order for there to be a shift from the microbial food web to the MuFW.  4.4 Carbon Budgets To better study the trophodymanics of the microbial food web as outlined by the third goal of this thesis, carbon budgets for each station were constructed for (Fig. 47) late spring (Fig. 48) and winter cruises. More specifically, they aided in exploring the nature of the relationship between prey populations, primarily cyanobacteria and heterotrophic bacteria, and the HNF. ANF were also added to the budgets because it is possible that the HNF, especially those larger than 10 um, were grazing a portion of ANF population. The data from Station P presented in the winter budget is part of a budget already presented by Boyd et ai (submitted), the only difference  97  being that in their budget the data was represented in terms of mg C m~, measured over the water 3  column, instead of mg C m . The integrated values are the same as those presented in Table 2. 2  In winter, the biomass of the cyanobacteria and heterotrophic bacteria, where measured, seem to be more than sufficient to support the carbon requirements of the HNF. At station P4, the combined biomass of cyanobacteria and heterotrophic bacteria was 5 times the requirement* of the HNF, and at Station P it was 1.4 times. This is due both to a decrease in heterotrophic bacteria and cyanobacteria, and because the HNF population at Station P was 3 times that found at P4; which may indicate that the predators of the HNF, e.g. the ciliates and dinoflagellates, at station P4 are more abundant and actively grazing the HNF population. In contrast to the winter, the May 1993 carbon budget indicates that there is not enough carbon from prey populations at any station on Line P to support the HNF carbon requirement. As was previously discussed (section 4.1.1,4.2.1), the HNF abundance and biomass was much higher in May 1993, largely due to unexplained reasons. Consequently the HNF biomass requirement was much higher (e.g. 6.5 times at P12, than what was found in May 1994 and higher than what was found by Booth et al, (1993) at Station P). It is doubtful that the insufficient prey abundance was simply a result of sampling at a high point in a HNF population oscillation because it was observed at all stations on Line P. Heterotrophic bacteria and cyanobacteria in May 1994 ranged between 1-8.8 times HNF requirements on Line P, with the highest value being found at PI6 where both HNF and cyanobacterial biomasses were at a minimum, but heterotrophic bacteria were at their maximum biomass (integrated 0-30 m). This further illustrates that as predicted, winter populations are  * The carbon requirement of the HNF was calculated after Fenchel (1982). The HNF biomass was multiplied by 1/gross growth efficiency. The gross growth efficiency is 40%.  98  P4Mayl993  P12Mayl993  P4 May1994 P16 May1993  P16 May1994  P 12 May 1994 P20 M a y 1993  P20 May1994  P26 M a y 1993  P26 M a y 1994  Figure 47. Late spring carbon budgets (mg C m") for May 1993 and 1994 for stations P4, P12, P16, P20, and Station P(P26), data was not obtained at P4 in May 1993. Labels for all stations follow that of P4. Cyanobacteria, Cy; heterotrophic nanoflagellates, HNF; autotrophic nanoflagellates; heterotrophic bacteria, HB. Numbers in parentheses are HNF carbon requirements, Biomass*l/gross growth efficiency (40%) from Fenchel (1982). 2  99  Figure 48. Winter carbon budget for stations P4, P12, P16, and Station P(26). Labels for all stations follow that of P4. Cyanobacteria, Cy; heterotrophic nanoflagellates, HNF; autotrophic nanoflagellates; heterotrophic bacteria, HB. Numbers in parentheses are HNF carbon requirements, calculated from data as in Fig. 46.  100  comparable to those found in early spring and early summer (section 4.1.1,4.1.2). However, in contrast to the winter, HNF biomass at Station P in May 1994 was almost twice that of P4 although prey populations were similar, possibly indicating an increase in the grazing activity of the predators of the HNF at that time.  4.5 Conclusions This study has provided the first information about the distribution of nanoflagellate populations, as well as cyanobacteria and heterotrophic bacteria, in the NE subarctic Pacific by being the first to sample at several stations on Line P and not just at Station P. This allowed comparisons between stations which are influenced by the coast and those that are truly oceanic, like Station P, and those stations which are nearer to the coast. Findings show that both the heterotrophic and autotrophic nanoflagellates were dominated by the 2-5 um size class, 50-99% of HNF and 47-90% of ANF, at most stations on Line P during February and May 1994. This study has also indicated that the microbial food web likely dominates the subarctic Pacific and not the multivorous food web, contrary to the hypothesis of Legendre and Rassoulzadegan (in press), primarily because the mesozooplankton generate little grazing pressure in this region. Further results show that stations P12 and P16 may have lower standing stocks relative to the rest of Line P which is apparently not due to top-down control, but may be indicative of a transition zone between water masses, based on physical data; however, more data are required from this region. This study has also been the first to produce a winter data set of the above groups from the region, which showed that winter nanoflagellates, cyanobacteria, and heterotrophic bacteria can be found at levels comparable to late spring/early summer, concurring with the hypothesis of Miller (1993). Consequently, carbon budgets have shown that the biomass of the heterotrophic  101  bacteria and cyanobacteria was sufficient during Feb. and May 1994 to meet the carbon requirement of the H N F population, indicating that their turnover times were similar during these months.  The high biomass of the nanoflagellate population in May 1993 is left unexplained by this study, but points to the need for longer time series observations of this group and their prey, similar to the time series by Booth et al, (1993) and to more frequent (diel) sampling, such as that done by Wheeler et al, (1989), both at Station P. Due to the complex nature of the microbial food web, i.e., diel oscillations and difficulty in separating influences of top-down and bottom-up controls, there are few firm conclusions regarding the populations studied. However, statistics have indicated little bottom-up influence, but there was some evidence of top-down control on cyanobacterial abundance.  Improvements on this study would include making changes in the sampling program so that replicate profiles can be obtained at each station sampled, as well as allowing for sampling to be done at several times during the day and night More frequent sampling is important because, as both this study and Booth et al (1993) showed at Station P, these populations can change rapidly, on the order of days. 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Ammonium recycling limits nitrate use in the oceanic subarctic Pacific. Limnol. Oceanogr. 36: 729-750. Wood, E. D. and F. A. J. Armstrong and F. A. Richards (1967) Determination of nitrate in seawater by cadmium-copper reduction to nitrite. J. Mar. Biol. Ass. U.K., 47, 23-31.  108  Appendix The following tables contain all the raw abundance and biomass data collected in May 1993, February 1994 and May 1994 for the following groups: heterotrophic nanoflagellates, autotrophic nanoflagellates, cyanobacteria, heterotrophic bacteria, as well as heterotrophic bacterial production. Graphs of this data not presented in the thesis body are also provided in this appendix, including both scatter/line and 3-D surface plots. Surface plots are of the vertical profiles of abundance and biomass obtained at each station during the three cruises of this study. Inset graphs presented with the surface plots provide an alternative view.  109  List of Tables in Appendix Table A l . Total abundance (cells L *') of heterotrophic nanoflagellates, autotrophic nanoflagellates, and cyanobacteria. 109 Table A2. February 1994 abundance (cells L" ) of heterotrophic nanoflagellates (three size fractions and total abundance). 114 1  Table A3. February 1994 abundance (cells L" ) of autotrophic nanoflagellates (three size fractions and total abundance). 115 1  Table A4. May 1994 abundance (cells L' ) of heterotrophic nanoflagellates (three size fractions and total abundance). 116 1  Table A5. May 1994 abundance (cells L" ) of autotrophic nanoflagellates (three size fractions and total abundance). 117 1  Table A6. May 1993 biomass (as carbon) (ug C L" ) of heterotrophic nanoflagellates(three size fractions and total abundance). 118 1  Table A7. February 1994 biomass (as carbon) (ug C L" ) of heterotrophic nanoflagellates (three size fractions and total abundance. 119 1  Table A8. February 1994 biomass (as carbon) (ug C L" ) of autotrophic nanoflagellates (three size fractions and total abundance). 120 1  Table A9. May 1994 biomass (as carbon) (ug C L" ) of heterotrophic nanoflagellates (three size fractions and total abundance). 121 1  Table A10. May 1994 biomass (as carbon) (ug C L" ) of autotrophic nanoflagellates (three size fractions and total abundance). 122 1  Table A l l . February and May 1994 abundance (cells L' ) biomass (as carbon) 0*g C L" ) of cyanobacteria. 123 1  1  Table A12. Heterotrophic bacterial abundance and production (pM TdR incorporated h" ), in May 1993 and February 1994. 124 1  Table A13. Heterotrophic bacterial abundance and production (pM TdR incorporated h" ), in May 1993 and February 1994. 125 1  110  List of Figures Figure A l . Heterotrophic bacterial abundance and production at stations P4, PI2, PI6, and P20 in May 1993. 126 Figure A2. HNF and ANF abundance (three size fractions and total abundance) at Station P12 in Febrary 1994. 127 Figure A3. HNF and A N F abundance (three size fractions and total abundance) at Station P16 in Febrary 1994. 128 Figure A4. HNF and ANF biomass (as carbon, three size fractions and total abundance) at Station P12 in February 1994 129 Figure A5. HNF and ANF biomass (as carbon, three size fractions and total abundance) at Station P16 in Febrary 1994 130 Figure A6. Cyanobacterial abundance (cells L' ) in February 1994 at P16. 1  131  Figure A7. HNF and ANF abundance (cells L"\ three size fractions and total abundance) at Station P12 in May 1994. 132 Figure A8. HNF and A N F abundance (cells L ' , three size fractions and total abundance) at Station P16 in May 1994. 133 1  Figure A9. HNF and ANF abundance (cells L"\ three size fractions and total abundance) at Station P20 in May 1994. ; 134 Figure A10. Thefirstvertical profile of HNF and ANF abundance (cells L"\ three size fractions and total abundance) at Station P26 in May 1994. [ 135 Figure A l l . The second vertical profile of HNF and ANF abundance (cells L"\ three size fractions and total abundance) at Station P26 in May 1994. 136 Figure A12. HNF and ANF biomass (ug C L" , three size fractions and total abundance) at Station P4 in May 1994. 137 1  Figure A13. HNF and ANF biomass (ug C L , three size fractions and total abundance) at Station P12 in May 1994. 138 1  Figure A14. HNF and ANF biomass (jig C L"\ three size fractions and total abundance) at Station P16 in May 1994. 139 Figure A15. First vertical profile of HNF and ANF biomass (ug C L' , three size fractions and total abundance) at Station P26 in May 1994. : 140 1  Figure A16. Second vertical profile of HNF and ANF biomass (ug C L " \ three size fractions and total abundance) at Station P26 in May 1994. 141 Figure A17. Heterotrophic bacterial production, cyanobacterial and heterotrophic bacterial abundance in May 1994 at Staions P4 and P12. ' 142  Ill  Figure A18. Heterotrophic bacterial production, cyanobacterial and heterotrophic bacterial abundance in May 1994 at Staions P16 and P20. 143 Figure A19. Heterotrophic bacterial abundance and production in May 1994 at Station P26.  144  Figure A20. Surface plot of 2-5 um heterotrophic nanoflagellates on Line P (P12, P16, P20, P26) in May 1993. 145 Figure A21. Surface plot of 5-10 urn heterotrophic nanoflagellates on Line P (P12, P16, P20, P26) in May 1993. 146 Figure A22. Surface plot of 10-20 um heterotrophic nanoflagellates on Line P (P12, P16, P20, P26) in May 1993. . 147 Figure A23. Surface plot of 2-5 um autotrophic nanoflagellates on Line P (P12, P16, P20, P26) in May 1993. 148 Figure A24. Surface plot of 5-10 um autotrophic nanoflagellates on Line P (P12, P16, P20, P26) in May 1993. 149 Figure A25. Surface plot of 10-20 um autotrophic nanoflagellates on Line P (P12, P16, P20, P26) in May 1993. 150 Figure A26. Surface plot of 2-5 um heterotrophic nanoflagellates on Line P (P4, P12, P16, P23a) in February 1994. 151 Figure A27. Surface plot of 5-10 um heterotrophic nanoflagellates on Line P ( P4, P12, P16, P23a) in February 1994. 152 Figure A28. Surface plot of 10-20 um heterotrophic nanoflagellates on Line P (P4, P12, P16, P23a) in February 1994. 153 Figure A29. Surface plot of 2-5 um autotrophic nanoflagellates on Line P (P4, P12, P16, P23a) in February 1994. 154 Figure A30. Surface plot of 5-10 um autotrophic nanoflagellates on Line P ( P4, P12, P16, P23a) in February 1994. 155 Figure A31. Surface plot of 10-20 um autotrophic nanoflagellates on Line P (P4, PI2, PI6, P23a) in February 1994. ; 156 Figure A 32. Surface plot of 2-5 um heterotrophic nanoflagellates on Line P (P4, P12, P16, P20, P26) in May 1994. 157 Figure A33. Surface plot of 5-10 urn heterotrophic nanoflagellates on Line P (P4, P12, P16, P20, P26) in May 1994.\ 158 Figure A34. Surface plot of 10-20 um heterotrophic nanoflagellates on Line P (P4, P12, P16, P20, P26) in May 1994. 159 Figure A35. Surface plot of 2-5 nm autotrophic nanoflagellates on Line P (P4, P12, P16, P20, P26) in May 1994. 160  112  Figure A36. Surface plot of 5-10 um autotrophic nanoflagellates on Line P (P4, P12, P16, P20, P26) in May 1994. 161 Figure A37. Surface plot of 10-20 um autotrophic nanoflagellates on Line P (P4, P12, P16, P20, P26) in May 1994. :  1  6  1  113  Table A l . Total abundance (cells L of heterotrophic nanoflagellates, H F ; autotrophic nanoflagellates, A F , and cyanobacteria, Cyano. SE is standard error of the mean (n=3).  Abundance: cells /L  Abundance (cells L') 1  P12 Depth  0 2 5 20 30 40 P16 5 10 20 40 50 P20 0 2 5 17 40 55 P26-1 0 3 7 20 30 50 P26-2 0 2 7 16 30 45  HF 8.2E+06 8.1E+06 8.4E+06 7.8E+06 7.2E+06 4.6E+06 HF 8.2E+06 6.5E+06 9.3E+06 8.9E+06 1.1E+07 HF 1.1E+07 1.8E+07 1.0E+07 4.9E+06 4.4E+06 2.1E+06 HF 4.3E+06 5.6E+06 5.7E+06 9.1E+06 1.0E+07 4.3E+06 HF 7.4E+06 5.3E+06 5.4E+06 4.3E+06 5.4E+06 1.5E+06  SE 5.3E+05 8.3E+05 1.1E+06 7.6E+05 3.3E+06 1.8E+05 SE 3.6E+05 1.5E+06 2.9E+05 8.9E+05 6.0E+05 SE 3.7E+04 7.8E+06 1.3E+06 1.8E+06 1.6E+06 9.2E+04 SE 1.4E+06 7.6E+05 4.1E+05 8.0E+05 9.9E+05 5.3E+05 SE 1.9E+05 6.4E+05 6.1E+05 1.5E+05 5.6E+05 4.5E+04  AU 2.9E+06 3.2E+06 4.0E+06 4.2E+06 3.3E+06 3.0E+06 AU 2.4E+06 2.1E+06 2.3E+06 1.7E+06 1.6E+06 AU 1.6E+06 5.2E+06 1.8E+06 1.7E+06 1.9E+06 4.6E+06 AU 1.2E+06 1.1E+06 1.1E+06 2.4E+06 2.3E+06 3.6E+06 AU 2.2E+06 2.3E+06 2.1E+06 2.2E+06 3.0E+06 2.7E+06  SE 7.8E+05 3.0E+05 4.6E+05 1.1E+06 4.1E+05 1.3E+05 SE 2.1E+05 5.2E+05 4.4E+05 2.3E+05 2.0E+05 SE 1.6E+04 2.4E+06 1.3E+05 0.0E+00 1.6E+05 3.8E+05 SE 3.7E+04 1.6E+05 l;2E+05 7.4E+04 3.0E+05 3.4E+05 SE 2.1E+05 3.1E+05 8.4E+04 8.0E+04 4.6E+04 3.3E+05  Cyano SE 2.3E+07 3.5E+05 1.7E+07 1.9E+05 3.2E+07 1.2E+07 2.6E+07 4.1E+06 2.7E+07 4.7E+06 2.5E+07 2.8E+05 Cyano SE 3.2E+07 1.1E+06 1.9E+07 1.4E+07 2.3E+07 5.2E+06 3.8E+07 6.7E+06 3.3E+07 6.1E+06 Cyano SE 3.3E+07 8.5E+06 3.2E+07 5.8E+06 3.4E+07 1.8E+05 3.0E+07 2.4E+06 3.3E+07 1.6E+06 9.7E+06 6.2E+05 Cyano SE 2.4E+06 4.3E+05 2.8E+06 1.7E+05 1.9E+06 4.7E+05 5.0E+06 6.7E+05 4.2E+06 1.2E+06 4.3E+06 3.9E+05 Cyano SE 6.3E+06 3.5E+05 5.7E+06 T.2E+06 5.6E+06 7.7E+05 5.0E+06 4.5E+05 5.8E+06 3.0E+05 4.3E+06 5.7E+05  114  Table A2. February 1994 size group abundance (cells L' ) of heterotrohic nanoflagellates, HF. Total heterotrophic nanoflagellates, THNF. SE is standard error of the mean (n=3). 1  Abundance (cells L' ) 1  P4 Depth 0 3 12 35 55 75 P12 0 2 10 35 60 75 P16 0 2 10 35 60 75 P20 3 3 P23a 0 7 15 35 55 75  HF 2-5 Urn  SE  HF 5-10 u m  HF 10-20 u m  1.0E+05 2.3E+05 2.2E+05 2.4E+05 2.0E+05 1.3E+05  3.3E+04 9.5E+04 4.8E+04 1.8E+04 2.3E+04 1.5E+04  SE  3.2E+04 2.8E+04 2.0E+04 5.5E+04 3.3E+04 2.2E+04  1.8E+03 2.5E+03 8.8E+03 4.6E+03 1.1E+04 7.1E+03  1.7E+04 2.0E+04 5.0E+03 1.4E+04 7.6E+03 1.9E+04  2.1E+03 5.1E+03 2.5E+03 1.1E+04 0.0E+00 1.2E+04  1.5E+05 2.7E+05 2.4E+05 3.1E+05 2.4E+05 1.7E+05  1.7E+04 4.3E+04 3.7E+04 3.5E+04 3.1E+04 1.9E+04  1.4E+05 1.4E+05 9.7E+04 8.8E+04 1.1E+05 1.3E+05  1.3E+04 1.9E+04 2.1E+04 3.2E+04 4.7E+04 1.4E+04  3.7E+04 2.9E+04 3.1E+04 7.6E+04 3.4E+04 3.6E+04  1.2E+04 4.9E+03 1.2E+04 4.5E+04 9.7E+03 8.5E+03  1.4E+04 2.7E+04 2.0E+04 1.2E+04 1.7E+04 9.8E+03  6.8E+03 1.6E+04 3.2E+03 2.3E+03 2.8E+03 6.5E+03  1.9E+05 2.0E+05 3.2E+05 6.2E+05 5.9E+05 6.3E+05  1.9E+04 2.1E+04 5.4E+04 9.8E+04 7.0E+04 7.3E+04  2.8E+05 2.2E+05 2.7E+05 2.2E+05 4.0E+05 2.6E+05  2.2E+04 5.0E+04 3.0E+04 2.2E+04 1.5E+05 1.6E+04  1.2E+04 1.5E+04 2.5E+04 3.5E+04 4.3E+04 2.7E+04  6.5E+03 7.5E+03 6.1E+03 6.7E+03 1.6E+04 1.1E+04  7.5E+03 5.0E+03 0.0E+00 1.6E+04 7.5E+03 1.2E+04  6.5E+01 5.0E+03 0.0E+00 7.3E+03 4.4E+03 2.8E+03  3.0E+05 2.4E+05 2.9E+05 2.7E+05 4.5E+05 3.0E+05  4.5E+04| 3.8E+04 4.3E+04 3.4E+04 7.6E+04 4.1E+04  1.4E+05 1.2E+05  1.1E+04 1.6E+04  6.2E+04 3.8E+04  64E+03 1.1E+04  1.0E+04 7.6E+03  5.0E+03 4.4E+03  2.1E+05 1.7E+05  2.0E+04 1.8E+04  1.5E+06 4.5E+05 3.2E+05 2.9E+05 3.9E+05 44E+05  8.1E+04 7.4E+04 1.6E+04 3.6E+04 2.2E+04 5.1E+04  1.9E+04 2.4E+04 3.1E+04 1.6E+04 24E+04 7.5E+03  9.7E+03 5.0E+03 9.0E+03 2.5E+03 9.9E+03 4.3E+03  3.7E+04 3.6E+04 3.8E+04 1.2E+04 1.2E+04 2.1E+03  1.7E+04 1.1E+04 1.5E+04 4.8E+03 8.7E+03 2.1E+03  1.5E+06 5.1E+05 3.9E+05 3.1E+05 4.3E+05 4.5E+05  2.4E+05  SE  THNF  SE  7.3E+04I 4.9E+04 4.6E+04 6.3E+04 7.3E+04  115  Table A3. February 1994 size group abundance (cells L' ) of autotrophic nanoflagellates, HF. Total autotrophic nanoflagellates, TANF. SE is standard error of the mean (n=3). 1  Abundance (cells L' ) 1  P4 Depth 0 3 12 35 55 75 P12 0 2 10 35 60 75 P16 0 2 10 35 60 75 P20 3 3 P23a 0 7 15 35 55 75  AF  SE  AF 5-10 Hit  9.6E+05 7.2E+05 9.6E+05 9.2E+05 8.6E+05 2.5E+05  6.0E+04 3.8E+04 1.0E+05 8.9E+04 1.3E+05 6.4E+04  SE  9.7E+04 7.1E+04 8.6E+04 5.7E+04 8.4E+04 1.2E+04  4.3E+03 2.2E+04 4.2E+04 7.7E+03 1.9E+04 6.2E+03  2.4E+03 1.5E+04 2.5E+03 9.0E+03 0.0E+00 2.3E+03  2.4E+03 7.6E+03 2.5E+03 4.6E+03 0.0E+00 2.3E+03  1.1E+06 8.0E+05 1.0E+06 9.8E+05 9.5E+05 2.6E+05  1.5E+05 1.1E+05 1.6E+05 1.5E+05 1.4E+05 4.4E+04  6.1E+05 7.1E+05 5.5E+05 5.2E+05 4.6E+05 4.9E+05  4.4E+04 6.4E+04 1.4E+04 4.4E+04 4.5E+04 2.2E+04  6.6E+04 1.0E+05 4.0E+04 9.9E+03 7.4E+03 7.3E+03  9.3E+03 1.8E+04 2.0E+04 6.5E+03 4.4E+03 9.2E+01  2.5E+03 1.3E+04 2.2E+03 9.9E+03 7.4E+03 7.3E+03  2.5E+03 3.5E+03 2.2E+03 6.5E+03 4.4E+03 9.2E+01  6.8E+05 8.3E+05 4.6E+05 1.3E+05 9.7E+04 6.6E+04  9.8E+04 1.1E+05 7.9E+04 1.7E+04 1.3E+04 8.6E+03  2.0E+06 1.8E+06 1.9E+06 1.7E+06 1.9E+06 1.0E+06  7.0E+03 5.3E+04 9.6E+04 1.9E+05 2.8E+05 1.7E+04  6.9E+04 4.4E+04 7.8E+04 9.1E+04 7.2E+04 1.6E+04  2.5E+04 5.4E+03 1.5E+04 2.0E+04 1.9E+04 6.3E+03  8.5E+03 1.5E+04 1.1E+04 1.2E+04 3.3E+04 1.6E+04  5.3E+03 5.7E+03 1.1E+04 6.1E+03 2.3E+03 8.3E+03  2.1E+06 1.9E+06 2.0E+06 1.8E+06 2.0E+06 1.0E+06  3.3E+05 3.0E+05 3.1E+05 2.8E+05 3.1E+05 1.7E+05  1.1E+06 1.2E+06  6.1E+04 1.4E+05  9.5E+04 8.5E+04  1.7E+04 1.7E+04  2.2E+04 3.0E+04  8.5E+03 1.2E+04  1.2E+06 1.3E+06  1.7E+05 2.0E+05  2.2E+06 1.9E+06 1.2E+06 1.3E+06 1.3E+06 1.4E+06  1.5E+05 2.1E+05 1.4E+05 1.6E+04 2.8E+05 2.3E+04  6.2E+04 1.0E+05 5.3E+04 3.5E+04 2.8E+05 1.8E+04  3.6E+04 2.8E+04 9.8E+03 2.7E+03 2.5E+05 9.2E+03  4.4E+04 1.8E+04 6.8E+03 1.6E+04 3.6E+04 1.2E+04  1.3E+04 3.3E+03 3.4E+03 1.1E+04 7.3E+03 6.6E+03  2.3E+06 2.0E+06 1.3E+06 1.4E+06 1.6E+06 1.4E+06  3.6E+05 3.0E+05 2.1E+05 2.1E+05 2.2E+05 2.3E+05  2  -  5  AF 10-20 U.U,  SE  TANF  SE  116  Table A4. May 1994 size group abundance (cells L" ) of heterotrophic nanoflagellates, HF. Total heterotrophic nanoflagellates, THNF. SE is standard error of the mean (n=3). 1  Abundance (cells L' ) HF SE 5-10 nm SE 1  P4 Depth 0 2 6 15 25 45 P12 0 3 10 30 50 60 P16 0 5 12 35 70 85 P20 0 3 10 35 50 70 P26-1 0 2 6 25 45 60 P26-2 0 3 9 30 45 65  HF 2-5 nm  HF 10-20 mn  SE  THNF  SE  4.2E+05 4.0E+05 5.9E+05 4.9E+05 5.2E+05 1.4E+05  9.6E+04 7.3E+04 1.4E+05 6.6E+04 5.1E+04 3.8E+04  7.7E+04 UE+05 1.5E+05 9.4E+04 1.3E+05 2.2E+04  1.3E+04 2.9E+04 3.2E+04 2.2E+04 2.1E+04 7.4E+03  4.4E+03 6.5E+03 1.8E+04 3.6E+04 9.9E+03 1.2E+04  4.4E+03 3.9E+03 i.lE+04 9.9E+03 6.5E+03 2.3E+03  2.2E+05 2.3E+05 2.2E+05 2.2E+05 1.7E+05 1.4E+05  3.8E+04 4.3E+04 5.0E+04 4.8E+04 2.9E+04 1.2E+04  14E+04 1.2E+04 9.7E+03 2.2E+04 2.5E+04 2.3E+04  8.5E+03 8.2E+03 4.9E+03 74E+03 9.3E+03 7.7E+03  6.9E+03 2.4E+03 8.9E+03 2.5E+03 7.0E+03 1.5E+04  4.2E+03 2.4E+03 5.6E+03 2.5E+03 4.1E+03 1.0E+04  2.4E+05 2.5E+05 2.4E+05 2.5E+05 2.0E+05 1.7E+05  3.7E+04 3.9E+04 3.8E+04 3.8E+04 2.7E+04 2.0E+04  2.6E+05 2.2E+04 1.1E+05 7.3E+03 1.5E+05 2.7E+04 1.8E+05 4.3E+04 6.1E+04 1.2E+04 4.3E+04 14E+04  3.3E+04 1.1E+04 14E+04 1.8E+04 7.1E+03 6.8E+03  64E+03 5.8E+03 4.3E+02 9.9E+03 1.2E+02 7.4E+02  8.6E+03 4.3E+03 9.1E+03 2.5E+03 7.1E+03 4.2E+03  4.3E+03 2.2E+03 2.1E+03 2.5E+03 1.1E+02 2.2E+03  3.0E+05 1.2E+05 1.7E+05 2.0E+05 7.5E+04 5.4E+04  4.1E+04 1.7E+04 2.5E+04 3.1E+04 9.7E+03 7.4E+03  3.2E+05 2.6E+05 1.9E+05 3.0E+05 1.4E+05 7.5E+04  6.7E+04 7.0E+04 5.1E+04 4.0E+04 5.3E+03 1.4E+04  7.3E+04 5.3E+04 4.2E+04 3.9E+04 1.5E+04 8.3E+03  9.8E+03 1.2E+04 1.5E+04 1.5E+04 4.7E+03 5.5E+03  3.7E+04 2.8E+04 9.7E+03 2.0E+04 1.1E+04 8.5E+03  1.0E+04 1.3E+04 6.4E+03 1.1E+04 6.5E+03 3.1E+03  4.3E+05 3.4E+05 2.4E+05 3.6E+05 1.7E+05 9.2E+04  4.8E+04 4.3E+04 3.2E+04 4.7E+04 2.1E+04 1.2E+04  2.7E+05 3.1E+05 3.1E+05 4.1E+05 4.9E+05 6.5E+05  3.1E+04 7.4E+03 7.3E+04 3.7E+04 2.0E+05 8.2E+04  1.5E+04 2.0E+04 3.3E+04 4.9E+04 5.8E+04 5.6E+04  4.5E+03 9.2E+03 5.8E+03 44E+03 3.6E+03 1.9E+04  2.4E+03 7.6E+03 1.9E+04 1.5E+04 7.0E+03 44E+03  2.4E+03 4.3E+03 3.4E+03 1.5E+04 3.7E+03 4.4E+03  2.9E+05 3.4E+05 3.7E+05 4.7E+05 5.6E+05 7.1E+05  4.5E+04 5.0E+04 5.2E+04 6.3E+04 9.5E+04 1.1E+05  4.7E+05 3.7E+05 3.8E+05 4.1E+05 4.8E+05 54E+05  4.4E+04 7.4E+04 1.2E+05 1.3E+05 1.1E+05 7.0E+04  1.7E+04 7.4E+03 4.9E+03 4.9E+03 1.0E+04 2.0E+04  9.2E+03 2.5E+03 6.8E+03 9.3E+03 1.5E+04 3.3E+03  7.4E+03 2.5E+03 2.5E+03 0.0E+00 0.0E+00 9.3E+03  4.4E+03 2.5E+03 2.5E+03 O.OE+00 0.0E+00 3.0E+03  4.9E+05 4.1E+05 4.8E+05 3.7E+05 5.7E+05 2.9E+05  7.7E+04 7.0E+04 8.1E+04 8.5E+04 8.7E+04 4.8E+04  5.0E+05 5.1E+05 7.5E+05 6.2E+05 6.5E+05 1.8E+05  7.0E+04 6.3E+04 9.5E+04 7.4E+04 7.8E+04 2.4E+04  117  Table A5. May 1994 size group abundance (cells L' ) of autotrophic nanoflagellates, HF. Total autotrophic nanoflagellates, TANF. SE is standard error of the mean (n=3). 1  P4 Depth 0 2 6 15 25 45 P12 0 3 10 30 50 60 P16 0 5 12 35 70 85 P20 0 3 10 35 50 70 P26-1 0 2 6 25 45 60 P26-2 0 3 9 30 45 65  AF 2-5 nm  Abundance (cells L-l) AF SE 5-10 mn SE  AF 10-20 mn  1.2E+05 1.3E+05 1.3E+05 7.3E+04 1.0E+04 7.7E+04  2.8E+04 7.1E+04 1.1E+05 1.3E+05 2.9E+05 3.4E+04  SE  TANF  4.1E+05 4.9E+05 6.2E+05 5.1E+05 1.2E+06 5.9E+05  6.7E+03 4.8E+03 3.5E+04 3.0E+04 4.8E+04 8.4E+03  2.5E+03 0.0E+00 5.4E+03 2.5E+03 1.5E+04 1.2E+04  SE  2.5E+03 O.OE+00 5.4E+03 2.5E+03 8.5E+03 6.4E+03  4.4E+05 5.6E+05 7.4E+05 6.4E+05 1.5E+06 6.4E+05  7.4E+04 8.5E+04 1.0E+05 7.9E+04 1.9E+05 9.7E+04  3.6E+05 3.1E+05 4.7E+05 4.0E+05 4.4E+05 4.3E+05  5.8E+04 8.3E+04 1.8E+04 8.9E+04 8.9E+04 2.3E+04  2.8E+04 3.3E+04 2.5E+04 6.9E+04 2.7E+04 8.9E+04  1.6E+04 1.0E+04 7.0E+03 2.2E+04 6.8E+02 2.5E+04  0.0E+00 0.0E+00 0.0E+00 0.0E+00 2.2E+03 2.3E+03  0.0E+00 0.0E+00 0.0E+00 0.0E+00 2.2E+03 2.3E+03  3.9E+05 3.4E+05 5.0E+05 4.7E+05 4.7E+05 5.2E+05  6.0E+04 5.5E+04 7.7E+04 6.7E+04 7.5E+04 6.5E+04  5.9E+05 4.0E+05 6.0E+05 4.5E+05 4.4E+05 3.6E+05  1.1E+05 3.7E+04 1.2E+04 5.2E+04 5.8E+04 4.1E+04  5.7E+04 4.9E+04 2.9E+04 6.5E+04 6.4E+04 1.1E+04  1.1E+04 2.2E+04 7.6E+03 6.9E+03 2.0E+04 2.2E+03  0.0E+00 2.3E+03 2.4E+03 O.OE+00 9.3E+03 2.5E+03  0.0E+00 2.3E+03 2.4E+03 0.0E+00 4.7E+03 2.5E+03  6.5E+05 4.5E+05 6.3E+05 5.1E+05 5.1E+05 3.7E+05  9.9E+04 6.4E+04 9.8E+04 7.1E+04 7.0E+04 5.9E+04  1.3E+06 1.3E+06 1.1E+06 1.3E+06 6.3E+05 5.2E+05  9.3E+04 1.9E+05 1.2E+05 1.8E+05 3.1E+04 3.1E+04  6.7E+04 7.8E+04 6.5E+04 1.1E+05 8.8E+04 5.1E+04  9.9E+03 1.6E+04 2.0E+04 1.9E+04 5.2E+03 1.1E+04  0.0E+00 2.5E+03 5.0E+03 7.4E+03 2.5E+03 6.1E+03  0.0E+00 2.5E+03 5.0E+03 4.4E+03 2.5E+03 7.6E+02  1.3E+06 1.4E+06 1.1E+06 1.4E+06 7.2E+05 5.8E+05  2.1E+05 2.2E+05 1.8E+05 2.1E+05 9.8E+04 8.3E+04  1.3E+06 1.3E+06 1.3E+06 1.4E+06 1.8E+06 2.1E+06  1.6E+05 1.3E+05 1.3E+05 1.2E+05 2.4E+05 1.9E+05  5.7E+04 4.8E+04 2.7E+04 5.9E+04 9.6E+04 1.3E+05  2.4E+04 1.8E+04 1.6E+04 2.6E+04 3.7E+04 4.2E+03  0.0E+00 5.0E+03 3.7E+03 0.0E+00 2.1E+04 4.4E+03  0.0E+00 5.0E+03 3.7E+03 0.0E+00 2.1E+04 4.4E+03  1.4E+06 1.3E+06 1.3E+06 1.5E+06 1.9E+06 2.3E+06  2.2E+05 2.1E+05 2.2E+05 2.4E+05 2.9E+05 3.5E+05  1.8E+06 1.8E+06 1.9E+06 2.1E+06 2.2E+06 2.1E+06  1.7E+05 1.0E+04 1.3E+05 4.5E+05 2.9E+05 2.5E+05  2.5E+04 3.0E+04 1.3E+04 1.2E+04 6.9E+03 1.1E+04  1.4E+04 6.1E+03 4.5E+03 9.1E+03 1.4E+04 4.5E+04  O.OE+00 O.OE+00 4.5E+03 0.0E+00 0.0E+00 0.0E+00  O.OE+00 5.0E+03 3.7E+03 O.OE+00 2.1E+04 4.4E+03  1.8E+06 2.1E+06 2.1E+06 1.1E+06 2.2E+06 1.8E+06  3.0E+05 3.5E+05 3.5E+05 2.2E+05 3.7E+05 2.9E+05  Table A6. May 1993 size group biomass (as carbon) (ug C L' ) of heterotrophic nanoflagellates, HF; autotrophic nanoflagellates, AF, and Cyanobacteria. SE is standard error of the mean (n=3). 1  Biomass: ng/L P12 Depth H.F. 0 43.0 2 42.0 5 44.0 20 41.0 30 38.0 40 23.8 P16 5 43.0 10 34.0 20 48.0 40 47.0 50 55.0 P20 0 57.3 2 66.0 5 52.0 17 25.0 40 23.0 55 10.9 P26-1 0 22.0 3 29.0 7 30.0 20 48.0 30 52.0 50 22.0 P26-2 0 39.0 2 28.0 7 28.0 16 22.2 30 28.0 45 7.7  S.E. 3.0 4.0 6.0 4.0 17.0 0.9  A.F. 47.0 51.0 65.0 68.0 53.0 48.0  S.E. 13.0 5.0 8.0 18.0 7.0 2.0  Oyanobacteria 4.7 3.5 7.0 5.5 5.7 5.2  S.E. 0.1 0.0 2.0 0.9 1.0 0.1  2.0 8.0 2.0 5.0 3.0  39.0 34.0 37.0 28.0 26.0  3.0 8.0 7.0 4.0 3.0  6.7 4.0 5.0 8.0 7.0  0.2 3.0 1.0 1.0 1.0  0.2 66.0 7.0 10.0 8.0 0.5  26.7 62.0 29.0 27.0 31.0 75.0  0.3 62.0 2.0 0.0 3.0 6.0  7.0 4.0 7.1 6.2 6.9 2.0  2.0 4.0 0.0 0.5 0.3 0.1  7.0 4.0 2.0 4.0 5.0 3.0  19.7 18.0 18.0 39.0 37.0 59.0  0.7 3.0 2.0 1.0 6.0 7.0  0.5 0.6 0.4 1.0 0.9 0.9  0.1 0.0 0.1 0.1 0.2 0.1  1.0 4.0 3.0 0.8 3.0 0.2  36.0 37.0 33.0 34.9 48.2 48.0  3.0 6.0 1.0 0.5 0.5 5.0  1.3 1.2 1.2 1.1 1.2 0.9  0.1 0.3 0.2 0.1 0.1 0.1  119  Table A7. February 1994 size group biomass (as carbon) (ug C L" ) of heterotrophic nanoflagellates, HF; total heterotrophic nanoflagellates, THNF. SE is standard error of the mean (n=3). 1  P4 Depth 0 3 12 35 55 75  HF 2-5 mn 0.5 0.6 0.3 0.7 1.5 0.6  0.2 0.3 0.1 0.1 0.2 0.1  HF 5-10 nm 1.0 0.4 0.3 1.0 0.3 0.4  0 2 10 35 60 75  0.4 1.1 0.5 0.4 1.2 0.4  0.0 0.1 0.1 0.2 0.5 0.0  0 2 10 35 60 75  2.1 1.1 2.0 1.1 1.9 2.0  3 3 0 7 15 35 55 75  0.1 0.1 0.1 0.1 0.1 0.1  HF 10-20 mn 0.2 0.7 0.0 0.4 0.3 0.1  0.6 0.7 0.3 1.4 0.9 1.0  0.2 0.4 0.1 0.8 0.3 0.2  0.2 0.2 0.2 0.1 0.7 0.1  0.1 0.0 0.2 0.6 0.7 0.4  1.6 1.4  0.1 0.2  4.0 3.4 2.4 1.3 1.1 0.6  0.1 0.4 0.1 0.1 0.0 0.1  SE  P12  SE  SE 0.0 0.2 0.0 0.3 0.0 0.1  THNF 1.7 1.7 0.6 2.0 2.1 1.1  0.5 0.6 0.6 0.2 0.3 0.2  0.3 0.3 0.1 0.0 0.1 0.2  1.5 2.3 6.3 11.0 10.4 13.1  0.5 0.9 4.8 1.0 1.3 0.5  0.1 0.0 0.1 0.1 0.2 0.2  0.2 0.1 0.0 0.2 0.1 0.1  0.0 0.1 0.0 0.1 0.1 0.0  2.4 1.2 2.2 1.9 2.7 2.5  0.3 0.2 0.3 0.1 0.3 0.3  0.68 0.08  0.07 0.05  0.5 0.4  0.3 0.2  2.8 1.8  0.2 0.2  0.3 0.6 0.7 0.4 0.2 0.2  0.1 0.2 0.2 0.1 0.1 0.1  2.0 0.9 1.4 0.3 0.3 0.1  0.9 0.3 0.5 0.1 0.3 0.1  6.5 5.2 4.8 2.3 1.8 0.9  0.6 0.5 0.3 0.2 0.1 0.1  P16  P20  P23a  SE 0.1 0.1 0.1 0.1 0.2 0.1  Table A7. February 1994 size group biomass (as carbon) (ug C L') of heterotrophic nanoflagellates, HF; total heterotrophic nanoflagellates, THNF. SE is standard error of the mean (n=3).  P4 Depth  HF 2-5 u m  0 3 12 35 55 75  0.5 0.6 0.3 0.7  HF 5-10 u m  SE  1.5  0.2 0.3 0.1 0.1 0.2  0.6  0 2 10 35 60 75  1.0 0.4  HF 10-20 u m  SE  0.3 1.0 0.3  0.1 0.1 0.1 0.1 0.1  0.2 0.7 0.0 0.4 0.3  0.1  0.4  0.1  0.4 1.1 0.5 0.4 1.2 0.4  0.0 0.1 0.1 0.2 0.5 0.0  0.6 0.7 0.3 1.4 0.9 1.0  0 2 10 35 60 75  2.1 1.1 2.0 1.1 1.9 2.0  0.2 0.2 0.2 0.1 0.7 0.1  3 3  1.6 1.4  0 7 15 35 55 75  4.0 3.4 2.4 1.3 1.1 0.6  THNF  SE  0.0 0.2  SE  0.0 0.3 0.0  1.7 1.7 0.6 2.0 2.1  0.1 0.1 0.1 0.1 0.2  0.1  0.1  1.1  0.1  0.2 0.4 0.1 0.8 0.3 0.2  0.5 0.6 0.6 0.2 0.3 0.2  0.3 0.3 0.1 0.0 0.1 0.2  1.5 2.3 6.3 11.0 10.4 13.1  0.5 0.9 4.8 1.0 1.3 0.5  0.1 0.0 0.2 0.6 0.7 0.4  0.1 0.0 0.1 0.1 0.2 0.2  0.2 0.1 0.0 0.2 0.1 0.1  0.0 0.1 0.0 0.1 0.1 0.0  2.4 1.2 2.2 1.9 2.7 2.5  0.3 0.2 0.3 0.1 0.3 0.3  0.1 0.2  0.68 0.08  0.07 0.05  0.5 0.4  0.3 0.2  2.8 1.8  0.2 0.2  0.1 0.4 0.1 0.1 0.0 0.1  0.3 0.6 0.7 0.4 0.2 0.2  0.1 0.2 0.2 0.1 0.1 0.1  2.0 0.9 1.4 0.3 0.3 0.1  0.9 0.3 0.5 0.1 0.3 0.1  6.5 5.2  0.6 0.5 0.3 0.2 0.1 0.1  P12  P16  P20  P23a  4.8 2.3 1.8 0.9  121  Table A8. February 1994 size group biomass (as carbon) (ug C L"*) of autotrophic nanoflagellates, AF; total autotrophic nanoflagellates, TANF. SE is standard error of the mean (n=3).  P4 Depth  AF 2-5 urn  AF 5-10 u.m  SE  0 3 12 35 55 75  10.7 3.4 4.5 10.3 10.0 1.9  0.5  0 2 10 35 60 75  2.9 8.0 6.2 2.4 0.6 2.3  0 2 10 35 60 75  0.7 0.2 0.5 1.0 1.0  1.7 1.4 0.9 0.9  AF 10-20 um  SE  1-9 0.3  0.1 0.4 0.4 0.1 0.4  0.1 0.4 0.1 0.7 0.0  0.1  0.2 0.7 0.2 0.2 0.1 0.1  1.0 1.6 0.7 0.1 0.2 0.2  22.7 8.6 9.1 13.0 9.0 4.8  0.1 0.2 0.5 1.0 1.0 0.1  3 3  11.9 13.7  0 7 15 35 55 75  16.3 20.7 5.9 14.6 6.0 6.7  SE  TANF  SE  12.5 5.2 5.4 11.9 11.6 2.2  1.7 0.5 0.7 1.6 1.5  0.1  0.1 0.2 0.1 0.4 0.0 0.1  0.1 0.3 0.4 0.1 0.1 0.0  0.0 0.7 0.1 0.2 0.2 0.2  0.0 0.2 0.1 0.1 0.1 0.0  4.0 10.3 5.4 0.8 0.5 0.6  0.1 1.0 2.1 0.2 0.2 0.1  1.2 1.2 1.6 1.1 1.3 0.4  0.4 0.1 0.3 0.2 0.3 0.2  0.2 0.4 0.3 0.1 1.8 0.5  0.1 0.2 0.3 0.1 0.1 0.3  24.1 9.9 10.8 14.1 11.9 5.7  3.7 1.3 1.4 2.1 1.3 0.7  0.7 1.5  1.5 1.3  0.3 0.3  1.9 2.6  0.7 1  16.2 15.3  1.7 2.0  0.7 1.5 0.4 0.1 0.9 0.1  1.6 3.4 0.8 0.6 11.4 0.4  0.6 0.6 0.1 0.0 6.8 0.1  2.0 1.1 0.6 1.3 1.3 0.6  0.6 0.2 0.3 0.9 0.3 0.3  20.0 25.2 7.2 16.5 18.7 7.6  2.5 3.2 0.9 2.3 3.3 1.0  P12  P16  P20  P23a  0.3  Table A9. May 1994 size group biomass (as carbon) (ug C L"') of heterotrophic nanoflagellates, HF; total heterotrophic nanoflagellates, THNF. SE is standard error of the mean (n=3).  122  P4 Depth  HF 2-5 u,m  HF 5-10 um  SE  HF 10-20 um  SE  THNF  SE  SE  0 2 6 15 25 45  5.0 3.0 7.0 2.3 3.9 0.7  1.0 0.5 2.0 0.3 0.4 0.2  2.0 0.2 4.3 1.7 5.1 0.4  0.3 0.1 0.9 0.4 0.8 0.1  0.2 0.2 0.0 0.7 0.5 0.3  0.2 0.1 0.2 0.2 0.3 0.0  6.9 3.3 10.9 4.7 9.5 1.3  0.7 0.5 1.0 0.3 0.7 0.1  0 3 10 30 50 60  1.0 0.6 0.6 0.3 0.2 0.4  0.2 0.1 0.1 0.1 0.0 0.0  0.5 0.1 0.3 0.3 0.4 0.4  0.3 0.1 0.1 0.1 0.1 0.1  0.5 0.1 0.0 0.2 0.4 0.5  0.3 0.1 0.2 0.2 0.2 0.3  2.0 0.8 0.9 0.9 1.0 1.3  0.2 0.1 0.1 0.1 0.1 0.1  0 5 12 35 70 85  0.4 0.5 0.2 0.3 0.3 0.1  0.0 0.0 0.0 0.1 0.1 0.0  0.6 0.1 0.4 0.5 0.2 0.1  0.1 0.1 0.0 0.3 0.0 0.0  0.7 0.2 0.0 0.2 0.5 0.2  0.3 0.1 0.2 0.2 0.0 0.1  1.6 0.8 0.6 0.9 0.9 0.4  0.1 0.1 0.1 0.1 0.0 0.0  0 3 10 35 50 70  1.5 0.7 0.5 0.4 0.2 0.2  0.3 0.2 0.1 0.1 0.0 0.0  2.6 0.8 1.2 0.6 0.2 0.2  0.4 0.4 0.4 0.2 0.1 0.1  2.5 1.4 0.0 1.5 0.6 0.3  0.7 0.7 0.3 0.9 0.3 0.1  6.6 2.9 1.8 2.6 1.0 0.6  0.3 0.3 0.2 0.3 0.1 0.0  0 2 6 25 45 60  0.8 0.9  0.3 0.1 1.0 1.3 1.0 1.0  0.1 0.1 0.2 0.1 0.1 0.3  0.1 0.3 0.0 0.4 0.2 0.1  0.1 0.2  1.5 1.9 2.3 3.1  0.1 0.0 0.3 0.2 0.9 0.4  0.1 0.4 0.1 0.1  1.1 1.2 2.5 3.6 3.5 4.2  0.1 0.1 0.2 0.3 0.4 0.5  0 3 9 30 45 65  1.3 0.6 0.6 0.3 2.4 1.3  0.1 0.1 0.2 0.2 0.5 0.3  0.3 0.1 0.4 0.1 1.7 0.4  0.2 0.1 0.1 0.1 0.4 0.1  0.1 0.1 0.0 0.0 0.0 0.5  0.1 0.1 0.0 0.0 0.0 0.1  1.7 0.7 1.0 0.5 4.1 2.1  0.2 0.1 0.1 0.1 0.4 0.2  P12  J  '  P16  P20  P26-1  P26-2  Table A10. May 1994 size group biomass (as carbon) (ug C L") of autotrophic nanoflagellates, AF; total autotrophic nanoflagellates, TANF. SE is standard error of the mean (n=3). 1  123  P4 Depth  AF 2-5 um  AF 5-10 um  SE  0 2 6 15 25 45  3.1 5.0 7.0 2.4 13.9 2.8  1.0 1.0 0.3 0.1 0.4  0 3 10 30 50 60  4.0 1.5 2.2 3.0 3.3 3.2  0 5 12 35 70 85  0.9  0.5  AF 10-20 um  SE  TANF  SE  SE  ^3.0 2.7 9.0 0.8  0.1 0.1 1.0 0.6 2.0 0.2  0.1 0.0 0.2 0.1 0.7 0.3  0.1 0.0 0.2 0.1 0.4 0.2  2.6 10.7 7.1 3.8 21.7 4.2  0.5 0.9 1.1 0.5 2.0 0.4  0.7 0.4 0.1 0.7 0.7 0.2  1.1 0.9 0.4 1.2 0.7 4.0  0.6 0.3 0.1 0.4 0.0 1.0  0.0 0.0 0.0 0.0 0.1 0.1  0.0 0.0 0.0 0.0 0.1 0.1  5.1 3.1 2.4 5.3 3.8 6.2  0.7 0.3 0.3 0.5 0.5 0.6  4.4 3.0 6.8 3.3 3.3 2.7  0.8 0.3 0.1 0.4 0.4 0.3  2.0 1.8 1.6 3.0 8.0 0.9  0.4 0.8 0.4 0.3 2.0 0.2  0.0 0.1 0.2 0.0 0.5 0.2  0.0 0.1 0.2 0.0 0.2 0.2  4.6 4.9 8.6 5.8 7.6 3.0  0.7 0.5 1.0 0.6 1.2 0.4  0 3 10 35 50 70  14.0 6.3 5.0 9.0 4.7 3.9  1.0 0.9 0.6 1.0 0.2 0.2  2.7 2.0 1.2 2.0 2.3 2.1  0.4 0.4 0.4 0.3 0.1 0.4  0.0 0.0 0.0 0.0 0.1 0.2  0.0 0.0 0.0 0.0 0.1 0.0  14.1 6.9 6.1 11.6 7.3 5.4  2.2 1.0 0.8 1.5 0.7 0.6  0 2 6 25 45 60  6.3 6.1 9.9 3.9 8.0 10.1  0.7 0.6 1.0 0.3 1.0 0.9  1.0 1.0 0.5 1.2 1.9 2.7  0.4 0.4 0.3 0.5 0.7 0.1  0.0 0.1 0.2 0.0 0.0 0.2  0.0 0.1 0.2 0.0 0.0 0.2  5.2 7.0 11.8 3.8 9.3 14.7  1.0 1.0 1.6 0.6 1.3 1.5  0 3 9 30 45 65  4.9 2.9 5.7 1.6 10.3 8.1  0.5 0.0 0.4 0.6 1.4 1.2  0.5 0.2 0.1 0.2 2.8 2.0  0.3 0.1 0.1 0.2 0.6 1.3  0.0  0.0  0.1 0.0 0.0 0.0  0.1 0.0 0.0  5.8 3.2 6.4 1.8 13.7 15.0  0.8 0.5 0.9 0.3 1.6 1.3  C  2  1  P12  P16  P20  P26-1  P26-2  Table A l l . February and May 1994 abundance (cells L"') biomass (as carbon) (ug C L"') of cyanobacteria, Cyano. SE is standard error of the mean (n=3).  124  P4 Depth 0 3 12 35 55 75 P12 0 2 10 35 60 75 P16 0 2 10 35 60 75 P20 3 3  P23a 0 7 15 35 55 75  Abundance Feb. 1994 Cyano.  Biomass SE  Cyano.  SE  1.29E+07 1.48E+07 1.32E+07 1.32E+07 1.50E+07 7.12E+05  1.36E+06 1.04E+06 1.08E+06 4.06E+06 1.04E+06 2.64E+04  3.0 3.0 3.0 2.8 3.0 0.2  1.0 2.0 1.0 0.6 2.0 0.1  6.18E+06 6.72E+06 5.38E+06 5.86E+06 7.57E+06 5.87E+06  7.51E+05 6.24E+05 8.23E+05 3.84E+05 1.68E+06 2.18E+05  1.3 1.4 1.1 1.2 1.6 1.2  0.7 0.7 0.8 0.6 0.7 0.7  6.91E+06 7.35E+06 8.04E+06 7.95E+06 7.38E+06 4.11E+06  7.72E+05 1.20E+06 8.16E+05 3.24E+05 1.49E+06 5.00E+05  1.5 1.5 1.7 1.7 1.5 0.9  0.2 0.3 0.2 0.1 0.3 0.1  8.20E+06 3.02E+05 8.73E+06 4.78E+05  1.7 1.8  0.9 1  8.88E+06 8.24E+06 8.57E+06 8.14E+06 9.16E+06 7.05E+06  1.9 1.7 1.8 1.7 1.9 1.5  0.2 0.2 0.2 0.2 0.2 0.5  9.67E+05 9.45E+05 7.44E+05 7.52E+05 9.50E+05 2.49E+06  P4 Depth 0 2 6 15 25 45 P12 0 3 10 30 50 60 P16 0 5 12 35 70 85 P20 0 3 10 35 50 70 P26-1 0 2 6 25 45 60 P26-2 0 3 9 30 45 65  Abundance May-94 Cyano.  Biomass SE  Cyano.  SE  1.71E+07 1.63E+07 1.92E+07 1.88E+07 3.56E+07 7.88E+06  2.05E+06 5.09E+06 4.46E+06 1.02E+06 4.34E+06 2.17E+05  4.0 3.0 4.0 4.0 7.0 1.7  2.0 3.0 2.0 2.0 4.0 0.9  1.63E+07 1.41E+07 1.84E+07 6.47E+06 1.81E+07 5.17E+06  3.80E+06 1.51E+06 1.85E+06 6.02E+05 5.41E+05 4.12E+05  3.0 3.0 4.0 1.4 4.0 1.1  2.0 2.0 2.0 0.8 2.0 0.5  9.63E+06 6.95E+06 8.47E+06 9.22E+06 2.38E+06 1.01E+06  7.94E+05 1.04E+06 2.47E+06 9.53E+05 1.62E+05 6.04E+04  2.0 1.5 2.0 2.0 0.5 0.2  1.0 0.9 2.0 1.0 0.3 0.1  1.57E+07 1.31E+07 1.47E+07 2.17E+07 6.41E+06 5.31E+06  1.14E+06 3.27E+06 7.32E+05 7.14E+05 1.28E+06 1.69E+04  3.0 3.0 3.0 5.0 1.0 1.1  2.0 1.0 2.0 3.0 1.0 0.6  1.39E+07 1.52E+07 1.45E+07 1.46E+07 1.48E+07  3.08E+06 2.00E+06 3.53E+06 2.60E+06 7.25E+05  0.0 2.9 3.2 3.1 3.1 3.1  0.0 0.6 0.4 0.7 0.5 0.2  1.82E+07 1.67E+07 1.67E+07 1.86E+07 1.97E+07 2.04E+07  1.18E+06 1.55E+06 1.22E+06  3.8 3.9 4.3  0.3 0.4 0.3  1.65E+06 5.33E+06  2.3 2.0  0.4 1.1  125 Table A12. Heterotrophic bacterial abundance and production (pM TdR incorporated h' ), BP, in May 1993 and February 1994. 1  May-93 Depth P4  BP  SE  0 2 5 20 30 P12  2.09 2.37  40  Bacteria Feb-94 1.00E+10 Depth (cells/L) P4 0 1.17 0.21 1.47 3 1.21 U 0.14 0.93 35 0.84 55 75  0 2 5 20 30  3.26  0.46  1.1  0.21  40 P16  0  5 10 20  0.74  40  0.61  0.21  0.13  1.24 P12 loop 0.95 return 1.14 0.87 P16 0.65 loop return 0.91 0.76 P20 loop 0.59 return 0.41 P23  50 P20  0  1 0.91 0.74 0.94  2 5 17  1.05 1.09  0.09 0.14  40 55  0.76 0.17  0.08 0.11  0.62  0  1.08  0.12  0.89  0.97  0.24  0.47  0.07  P26-1 3 7 20 30 50  1.14 1.17 0.89 0.81 0.43  2 7 15 35 55 75  BP 1.01 0.78 0.42  Bacteria 1.00E+10 SE (cells/L) 0.87 0.05 0.74 0.89 0.1 0.55 0.68 0.1 0.31  SE  0.95 0.56  0.17 0.09  0.59 0.49  0.13 0.07  0.94 0.74  0.17 0.07  0.64 0.7  0.21 0.09  1.25 1.18  0.1 0.14  0.91 0.74  0.13 0.06  0.86  0.11  0.79  0.14  0.76  0.22  0.72 0.84 0.58 0.71 0.8 0.62  0.11 0.1 0.19 0.09 0.04 0.09  126  Table A13. Heterotrophic bacterial abundance and production (pM TdR incorporated h"), BP, In May 1993 and February 1994. 1  P4 Depth 0 2 6 15 25 45 P12 0 3 10 30 50 60 P16 0 5 12 35 70 85 P20 0 3 10 35 50 70 P26-1 0 2 6 25 45 60  Bacteria 1.00E+10 (cells/L) SE  May-94 BP SE 1.72  0.21  1.13  1.64  0.23  1.17 0.94  0.19  0.05  0.59  0.44  0.07  0.35  0.06  0.79 0.84 0.54 0.64  0.11  0.03  0.31  0.07  0.43  0.1  0.09  0.05  0.28  0.05  0.35  0.21  0.23  0.06  0.77  0.18  0.71  0.11  0.49  0.07  0.49 0.61 0.71 0.84 0.77 0.43 0.51 0.71 0.74 0.61 0.5 0.59  0.84 0.79 0.89 0.61 0.5 0.51  0.11 0.06  0.1  Cells*10 L 9  1  Cells * 1 0 L 9  0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6  i 2.10  1 2.17  1 2.24  r  1 2.31  2.38  pM Tdr incorporated hour  0.6 0.7 0.8 0.9 1.0 1.1 J  I  I  1  0.00 0.17 0.34 0.51 0.68  0.60  0.64  0.68  0.85  0.72  0.76  pM Tdr incorporated hour  1.2  1.3  L  1  0.63 0.70 0.77 0.84 0.91 0.98 1.05 J 1—_J 1 1 -L#-  10 H E 20  H  §•30-1 Q 40 50  i—i—i—i—i—n—r 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 pM Tdr incorporated hour  1  0.0  i  i  i  0.5  1.0  1.5  1 2.0  r 2.5  pM Tdr incorporated hour  3.0 1  Figure A l . Heterotrophic bacterial abundance and production at stations a) P4, b) P12, c) P16, and d) P20 in May 1993. Error bars are standard error of the mean (n=3).  128  P12: February 1994 Cells*10 L6  0.0  Cells*10 L  1  5  0.2 0.4 0.6 0.8 1.0  Cells*10 L" 4  1  0.0 0.3 0.6 0.9 1.2 1.5 1.8  1  Figure A2. HNF and ANF abundance at Station P12 in Febrary 1994, a) cells 2-5 urn, b) cells 5-10 urn, c) cells 10-20 um, d) total HNF and ANF. Symbols and error bars as in Figure 4.  129  P12 February 1994  ug C/L  ug C/L  Figure A4. HNF arid ANF biomass (as carbon) at Station P12 in Febrary 1994, a) cells 2-5 um, b) cells 5-10 jim, c) cells 10-20 urn, d) total HNF and ANF. Symbols and error bars as in Figure 4.  130  Figure A4. HNF and ANF biomass (as carbon) at Station P12 in Febrary 1994, a) cells 2-5 um, b) cells 5-10 um, c) cells 10-20 urn, d) total HNF and ANF. Symbols and error bars as in Figure 4.  131  P16 February 1994 ng C/L  ngC/L  Figure AS. HNF and ANF biomass (as carbon) at Station P16 in Febrary 1994, a) cells 2-5 um, b) cells 5-10 um, c) cells 10-20 um, d) total HNF and ANF. Symbols and error bars as in Figure 4.  Cells*"! 0 L 6  1  Figure A6. Cyanobacterial abundance (cells L ) in February 1994 at P16. Error bars are standard (n=3). 1  Figure A7. HNF and ANF abundance (cells L a t Station P12 in May 1994, a) cells 2-5 um, b) cells 5um, c) cells 10-20 urn, d) total HNF and ANF. Symbols and error bars as in Figure 4.  134  P16: May 1994 Cells*10 L6  0.0  1  0.2 0.4 0.6 0.8 1.0  Cells*10 L5  1  0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7  Figure A8. HNF and ANF abundance (cells L"') at Station P16 in May 1994, a) cells 2-5 um, b) cells 5-10 um, c) cells 10-20 um, d) total HNF and ANF. Symbols and error bars as in Figure 4.  135  P20: May 1994 Cells*10 L6  0.0  Cells*10 L-  1  5  0.3 0.6 0.9 1.2 1.5  CeIls*10 L 4  1  2  1  0.0  0.3 0.6 0.9  Cells*10 L-1 6  3  Figure A9. HNF and ANF abundance (cells L"') at Station P20 in May 1994, a) cells 2-5 um, b) cells 5-10 urn, c) cells 10-20 um, d) total HNF and ANF. Symbols and error bars as in Figure 4.  136  P26-1: May 1994 Cells'lO !.6  0.0  1  0.5 1.0 1.5 2.0 2.5 3.0  Cells*10 L6  1  0.00 0.04 0.08 0.12  Figure A10. The first vertical profile of HNF and ANF abundance (cells L"') at Station P26 in May 1994, a) cells 2-5 um, b) cells 5-10 um, c) cells 10-20 um, d) total HNF and ANF. Symbols and error bars as in Figure 4.  137  26-2: May 1994 Cells* 10 L6  Cells*10,6 LI -1  1  6  0.0 0.5 1.0 1.5 2.0 2.5 3.0  0.00 0.02 0.04 0.06 0.08  0 10 20 -  E  30 -  §• 40 H Q 50 60 70 -  70 Cells*10 L3  0.0 0.5 1.0 1.5 2.0 2.5 3.0  Figure A l l . The first vertical profile of HNF and ANF abundance (cells L' ) at Station P26 in May 1994, a) cells 2-5 um, b) cells 5-10 um, c) cells 10-20 um, d) total HNF and ANF. Symbols and error bars as in Figure 1  138  Figure A12. HNF and ANF biomass (jig C L') at Station P4 in May 1994, a) cells 2-5 um, b) cells 5-10 um, c) cells 10-20 um, d) total HNF and ANF. Symbols and error bars as in Figure 4.  139  P12 May 19942 jig C/L  ug C/L  Figure A13. "HNF and ANF biomass (ug C L"*) at Station P12 in May 1994, a) cells 2-5 um, b) cells 5-10 um, c) cells 10-20 um, d) total HNF and ANF. Symbols and error bars as in Figure 4.  P1 May 19946  Figure A14. HNF and ANF biomass (ug C L"*) at Station P16 in May 1994, a) cells 2-5 um, b) cells 5-10 c) cells 10-20 um, d) total HNF and ANF. Symbols and error bars as in Figure 4.  141  P26-1 May 1994 ugC/L  pig C/L  Figure A15. First vertical profile of HNF and ANF biomass (ug C L") at Station P26 in May 1994, a) cells 25 um, b) cells 5-10 um, c) cells 10-20 um, d) total HNF and ANF. Symbols and error bars as In Figure 4. 1  Figure A16. Second vertical profile of HNF and ANF biomass (ug C L' ) at Station P26 in May 1994, a) cells 2-5 um, b) cells 5-10 um, c) cells 10-20 um, d) total HNF and ANF. Symbols and error bars as in Figure 4. 1  143  P4 May 1994 Cells*10 L9  0.0  0.5  1.0  1.5  Cells*10 L"  1  7  2.0  2.5  pico M Tdr incorporated hour  1  3.0 1  P12 May 1994 0.0  0.3  0.0  0.6  0.2  0.9  1.2  0.3  1.5  1.8  0.4  pico M Tdr incorporated hour  0.0  0.8  1.6  2.4  3.2  4.0  0.5 1  Figure A17. Heterotrophic bacterial production and abundance in May 1994 at Staions a) P4, and c) P12. Cyanobacterial abundance at Stations b) P4, and d)P12.  144  P16 May 1994 Cells*10 L 9  0.0 0.4 0.8  1.2  I  I  i 0.0 0.1  m  I  CellS*10 L"  1  6  1.6 2.0 2.4 2.8 I  I  L  1 1 1 1 r 0.2 0.3 0.4 0.5 0.6 0.7  pico M Tdr incorporated hour  1  P20 May 1994 o 10 20 30 40 xz 50 o Q. Q 60 70 80 90  0.0 -  0.4 0.8 1.2 ' \ I DM  i 0.1  1  1 0.2  1.6 2.0 2.4 2.8 1 1 L  Cells*10 L" 7  1  0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 J I ilA I I I I I  1 1 1 r 0.3 0.4 0.5 0.6 0.7  pico M Tdr incorporated hour  1  Figure A18. Heterotrophic bacterial production and abundance in May 1994 at Staions a) P16, and c) P20. Cyanobacterial abundance at Stations b) P16, and d) P20.  P26 May 1994  Figure A19. Heterotrophic bacterial abundance and production in May 1994 at Station P26.  146  148  •ST  149  150  151  152  153  154  155  i  157  158  159  160  162  165  166  167  168  169  

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