Organic-walled Dinoflagellate Cyst Production, Composition and Flux in the Central Strait of Georgia (BC, Canada): a Sediment Trap Study
by
Svetlana Esenkulova
B.Sc., Udmurt State University, 2004 A Thesis Submitted in Partial Fulfillment of the
Requirements for the Degree of MASTER OF SCIENCE
in the School of Earth and Ocean Sciences
© Svetlana Esenkulova, 2009 University of Victoria
All rights reserved. This dissertation may not be reproduced in whole or in part, by photocopying or other means, without the permission of the author.
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Organic-walled Dinoflagellate Cyst Production, Composition and Flux in The Central Strait of Georgia (BC, Canada): a Sediment Trap Study
by
Svetlana Esenkulova
B.Sc., Udmurt State University, 2004
Supervisory Committee
Dr. Vera Pospelova, Supervisor (School of Earth and Ocean Sciences)
Dr. Sophia C. Johannessen, Departmental Member (Department of Geography)
Dr. Tom Pedersen, Departmental Member (School of Earth and Ocean Sciences)
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Supervisory Committee
Dr. Vera Pospelova, Supervisor (School of Earth and Ocean Sciences)
Dr. Sophia C. Johannessen, Departmental Member (Department of Geography)
Dr. Tom Pedersen, Departmental Member (School of Earth and Ocean Sciences)
ABSTRACT
To study the ecology of organic-walled dinoflagellate cysts, the changes in species composition, diversity, and seasonal variations of cyst flux in the sediment trap deployed in the Strait of Georgia (BC, Canada) were examined. The cyst production rate varied from ~600 to 336,200 cysts m-2 day-1, with an average of 20,000 cysts m-2 day-1. Throughout the study period (March, 1996 - January, 1999), cyst assemblages were mostly dominated by cysts produced by heterotrophic dinoflagellates, such as Protoperidineaceae (Brigantedinium spp., Quinquequspis
concreta, and cysts of Protoperidinium americanum). Cysts produced by heterotrophic
dinoflagellates peaked in June each year, whereas cysts produced by autotrophic taxa were most abundant during August-September. The total annual dinoflagellate cyst flux was higher in 1996 than in 1997 and 1998, being enhanced by the bloom of Alexandrium spp. The warmer sea-surface temperature in 1998 had a positive effect on the production of both autotrophic and heterotrophic dinoflagellates, as inferred from the cyst fluxes.
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TABLE OF CONTENTS
SUPERVISORY COMMITTEE ...ii
ABSTRACT ...iii
TABLE OF CONTENTS ...iv
LIST OF TABLES ...vi
LIST OF FIGURES ...vii
ACKNOWLEDGEMENTS ...viii
1 INTRODUCTION ...1
2. MATERIALS AND METHODS ...6
2.1 Regional setting...6
2.2. Sediment trap location and collection of samples...8
2.3. Palynological sample preparation...12
2.4. Dinoflagellate cyst analysis...13
2.5. Environmental data...15
3. RESULTS...16
3.1. Dinoflagellate cyst compositions and relative abundance in sediment trap samples...16
3.2 Dinoflagellate cyst flux and concentration...20
3.3 Sedimentary records of dinoflagellates producing toxic components...26
3.4 Other palynomorphs...27
3.5 Dinoflagellate cysts in core sediment sample...27
4. DISCUSSION...30
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4.2. Seasonal and annual variability of dinoflagellate cyst flux...31
4.3 Comparison of cyst flux from the Strait of Georgia with other sediment trap studies…...34
4.4 Sedimentary records of potentially toxic dinoflagellates...35
4.5 Sediment core sample...38
4.6 Other palynomorphs...40
5. CONCLUSIONS...42
REFERENCES...44
PLATE AND PLATE DESCRIPTIONS...59
APPENDIX 1: Taxonomic listing...75
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LIST OF TABLES
Table 1. Taxonomic citation of dinoflagellate cysts used in this study. Thecate equivalents are taken from Head (1996), Zonneveld (1997), Head et al. (2001), and Pospelova and
Head (2002)………..….14 Table 2. Daily average cyst flux (cysts m-2 day-1) for individual taxa recovered at
GSCM-3 mooring. Flux of Lingulodinium machaerophorum, Namatosphaeropsis
labirinthus, Islandinium brevispinosum, Pheopolykrikos hartmanii, and Protoperidinium
type 1 were not calculated due to a very low (<5 specimens) occurrence during the
deployment period……….17 Table 3. The relative abundance (%) of dinoflagellate cysts from sediment trap GSCM-3
and the core sediment sample CM-3. The asterix (*) indicates that cysts of Alexandrium
spp. are not included in the calculations………...21 Table 4. Total annual dinoflagellate cyst flux (cysts x 106 m-2 year-1) and biogenic Silica
(g x 104 m-2 year-1). The asterix (*) indicates that cysts of Alexandrium spp. are not included in the calculations…………...………...22 Table 5. Annual dinoflagellate cyst fluxes (cysts x 103 m-2 year-1) for the most common taxa. Arrows indicate noticeable changes (increase or decrease) in the cyst flux compared to the flux in 1996...25
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LIST OF FIGURES
Figure 1. Map showing location of sediment trap GSCM-3, buoy 46146, lighthouse Active Pass in the Strait of Georgia, and the direction (the arrow) to Hope
station (49°22'50", 121°27'05")……….10 Figure 2. Mooring layout for station GSCM-3………..11 Figure 3. Three year time-series of A. Species richness and relative abundance of cysts produced by autotrophic taxa; B. Total dinoflagellate cyst concentration, flux, and individual fluxes of cysts produced by autotrophic and heterotrophic taxa, as well as flux of cysts of Alexandrium spp.; C. Monthly average sea surface temperature and salinity along with daily Fraser River discharge; D. Flux of sediments, biogenic silica, and organic carbon (adapted from Johannessen et al., 2005)………...19 Figure 4. Average daily cyst flux for the most common taxa, with
cell content and without cell content……….24 Figure 5. Average daily flux of selected aquatic palynomorphs …...28
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ACKNOWLEDGEMENTS
I am genuinely thankful to my supervisor Dr. Vera Pospelova for her exceptional mentoring, encouragement, and kindness. Without her enthusiasm and support this work would not have been possible. Special thanks to Dr. Sophia C. Johannessen who gave friendly advice while members of my advisory Committee. I am grateful to Dr. Robie W. Macdonald, Dr. Sophia C. Johannessen and Mary C. O’Brien for providing sediment trap samples and allowing me access to their data. I also thank Dr. Jim Gower for sharing his data on monthly averaged values of sea surface temperature from buoy 46146. Additional thanks go to Dr. Mike Foreman and Dr. John Morrison for their help with obtaining data on Fraser River flow.
Captain Brown and crew of the marine sciences vessel John Strickland are thanked for the cruise to collect core sediment samples for this research. Work study students and also paleolab friends - Alanna Krepakevich and Kirsten Kennedy, are thanked for assistance with some aspects of this project.
I want to express my deepest gratitude to my family for their priceless moral support during my studying: Vincent J. Negrin, Joseph F.J. Negrin, and Tatiana Esenkulova.
Financial assistance was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC) through Discovery and Shiptime grants to Dr. Vera Pospelova and by the University of Victoria Fellowship to Svetlana Esenkulova.
1. INTRODUCTION
Dinoflagellates are primarily singled–celled organisms (protists) that occur as motile cells with two flagella and characteristic nuclei (Dale, 1996; Fensome et al., 1996). They comprise the most diverse group of phytoplankton in coastal/estuarine environments and are one of the most important primary producers (Taylor, 1987). About half of modern dinoflagellate species are autotrophic and half are heterotrophic (Taylor, 1987; Jacobson and Andersen, 1996). The distribution of autotrophic dinoflagellates is mostly controlled by sea surface temperature (SST), sea surface salinity (SSS), and availability of dissolved nutrients, whereas heterotrophic dinoflagellates are highly dependant on prey availability (mostly diatoms) (Taylor, 1987, Dale, 1996).
During their life cycle many dinoflagellate species produce resting cysts in the process of sexual reproduction (Pfiester and Anderson, 1987; Taylor, 1987). Resting cysts represent non-motile, immobile cells that lack flagella and in which metabolic processes are greatly reduced (e.g. Taylor, 1987). Cysts sink to the seafloor in the same way as fine particles (Dale, 1983) and have mandatory resting periods after which they re-establish a motile population (Anderson, 1997). Organic walls of resting cysts are highly resistant to physical, chemical, and biological degradation, and are subject to fossilisation (Fensome et al., 1996).
During the last several decades palynologists have been intensively developing an application of dinoflagellate cysts as paleoenvironmental indicators. Cyst assemblages in Quaternary sediments may provide information on such environmental signals as sea-surface temperature, salinity, marine productivity, coastal eutrophication, and pollution (de Vernal et al., 1993; Dale, 1996; de Vernal et al., 1997; Rochon et al., 1999; Matsuoka, 1999; de Vernal et al.,
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2001, 2005; Marret and Zonneveld, 2003; Pospelova et al., 2002, 2004, 2005; Radie and de Vernal, 2004; Radie et al., 2007; Holzwarth et al., 2007; Marret et al., 2008; Pospelova et al., 2008). These applications are based on a wealth of knowledge of dinoflagellate cyst distributions in modern sediments in relation to environmental parameters (e.g. Wall et al., 1977; Dale, 1983; Harland, 1983; Dale, 2009). However, cyst assemblages from core sediment samples are deposited over many years and many ecological signals are averaged out (Zonneveld et al., 1997). Thus, standard seafloor surface samples provide insufficient information on year-to-year cyst ecology and do not answer important questions of seasonal patterns and rates of dinoflagellate cyst production. Ultimately, this limits the application of dinoflagellate cysts as bio-indicators of environmental conditions in the past and present (Pospelova et al., 2006).
The study of dinoflagellate cysts, derived from sediment trap material, can provide unique ecological information (Dale and Dale 1992; Heiskanen, 1993; Montresor et al., 1998; Matsuoka and Fukuyo, 2000). It may answer the following questions: when and how many cysts of a certain species are produced? Can cyst production be correlated directly with water properties? What is the relationship between cyst production and cyst accumulation in underlying sediments? Quantitative measurements from sediment traps may be limited by resuspension of bottom material, trap efficiency that depends on configuration, and other factors (e.g. Larsson et al., 1986; Gardner, 2000). Nevertheless, sediment traps provide the most reliable tool for qualitative analysis of cyst production (Matsuoka and Fukuyo, 2000).
To date, field based information on dinoflagellate cyst production is limited (Dale and Dale, 1992; Montresor et al., 1998; Harland and Pudsey, 1999; Zonneveld and Brumer, 2000; Godhe et al., 2001; Tanimura and Shimada, 2004; Susek et al., 2005; Fujii and Matsuoka, 2006). Most of the existing sediment trap studies of dinoflagellate cysts were of short duration and only
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a few exceed nine months (Montresor et al., 1998; Zonneveld and Brummer, 2000; Harland and Pudsey, 1999; Fujii and Matsuoka, 2006; Susek et al., 2005). Among long term studies, only two had sediment traps deployed in a coastal marine environment: the Gulf of Naples in the Mediterranean Sea (Montresor et al., 1998) and Omura Bay in the West Pacific (Fujii and Matsuoka, 2006). Both studies covered a two year period.
Despite scarcity of sediment trap studies and non-uniformity of study approaches (there is no standardized design of sediment trap and procedures of setting) such studies have made a significant contribution to dinoflagellate cyst ecology. They have clearly demonstrated seasonal trends of cyst production that are dependent on oceanographic settings. Indeed, it is now clear that dinoflagellate cyst diversity and fluxes demonstrate very strong sensitivity to regional environmental conditions, implying that the ecology of each particular taxon should be further investigated at the regional scale. It is obvious that more long-term sediment trap studies are needed, in particular studies of cyst production from coastal sites. Current study is the first study of dinoflagellate cyst production from Pacific coastal waters of North America.
This work is also motivated by the lack of long term biological observations of dinoflagellate species that produce toxins and cause harmful algal blooms (HABs) in the Strait of Georgia. Along the East Pacific coast, the major toxic syndromes caused by HABs are paralytic shellfish poisoning (PSP) and diarrhetic shellfish poisoning (DSP) (Trainer, 2002; Taylor and Horner, 1994). Since the beginning of the PSP monitoring program in the late 1940s, toxicity has been detected on the British Columbia coast every year (Taylor and Harrison, 2002), sometimes related to dinoflagellate blooms genus Alexandrium (Prakash and Taylor, 1966). Gaines and Taylor (1985) found cyclical patterns in British Columbia of about five - seven years in PSP intensity that often correspond with El Niño events. DSP may very occasionally occur in BC
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coastal waters and are caused by blooms of the dinoflagellate genus Dinophysis (Taylor and Horner, 1994; Taylor et al., 1994). Toxins and phytoplankton monitoring alone can not reveal all toxic dinoflagellate taxa and do not provide sufficient information on their year-to-year occurrence.
Decadal and sub-decadal global climate variability, including in particular the El Niño - Southern Oscillation phenomenon, to a certain extent can be considered as a natural experiment with strong changes in SST, SSS, and availability of nutrients in the ocean. Biological communities are highly affected by such environmental changes with the strongest response in the lower trophic level communities. Studying effects of El Niño on primary producers helps to understand natural adaptations of phytoplankton groups to climatic and environmental change. There is a vital need for a consistent direct comparison of trends in primary producers with variations of physical parameters. The present work is the first in situ study of the response of dinoflagellate cyst production to a major El Niño event.
El Niño 1997-98 was one of the strongest El Niños of 20th century (Fact sheet of Fisheries and Oceans Canada, 2003). In the open coastal waters of British Columbia (BC) this event was characterised by higher than usual SST, lower nutrient concentrations (Whitney and Welch, 2002), reduced summer coastal upwelling (Beamish and Neville, 1999; Whitney and Welch, 2002), lower rates of primary production, as well as distinct changes in phytoplankton, zooplankton and higher trophic level communities (Whitney and Welch, 2002; Harrison et al., 2004). The semienclosed Strait of Georgia was affected by less variability due to its sheltered location. Nevertheless it was subject to distinct El Niño - associated ecological changes. The waters in the central Strait of Georgia in 1997 were fresher due to increased fluvial input (Water Survey Canada) and in 1998 warmer than usual (Gower, 2002).
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This Thesis is designed to test the hypothesis that changes of the cyst flux in the central Strait of Georgia, Canada are closely associated with fluctuations of the major environmental parameters of the water column. For this purpose, a high resolution (bi-weekly scale) investigation of three years of dinoflagellate cyst flux was conducted. The primary goal was to document the composition, diversity, abundance, and seasonal succession of dinoflagellate cysts, including toxic and potentially toxic taxa. Another major goal was to study seasonal and inter-annual changes of cyst flux in relation to changes SST, SSS, freshwater input, and examine the link between the cyst flux and the 1997-98 El Niño climatic event. Finally, this work compared cyst assemblages from sediment trap material and core sediments at the same site. The ultimate objective of this study was to provide new information on organic-walled cyst ecology from a coastal site in the North Pacific.
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2. MATERIALS AND METHODS 2.1. Regional setting
The Strait of Georgia is a semi-enclosed basin on the west coast of Canada (Fig. 1). It is a narrow passage of the eastern North Pacific between the Vancouver Island and the mainland of British Columbia. The Strait is approximately 220 km long and 28 km wide, with a total surface area of 6800 km2. The average water depth is 155 m, with the maximum depth of 420 m in the central part of the Strait (Thomson, 1981; Thomson, 1994). At its northern end, the Strait of Georgia terminates in narrow channels that connect to the open ocean through very small cross sections. Most of the exchange with the Pacific Ocean occurs through Juan de Fuca Strait to the south (Waldichuk, 1957), and the basin-water properties (nutrients, O2, T, S) and influenced by those observed on the continental shelf (Johannessen and Macdonald, 2009).
The coastal zone of British Columbia has one of the warmest climates in Canada, with average air temperatures of 12-18 ºC in July and 4-6 ºC in January (Thomson, 1994). The seasonal variation in SST in the Strait of Georgia has a limited range of 7 ºC (Thomson, 1994). The water column is highly stratified. The top 50 m is characterised by strong seasonal variation in SST and SSS, which is affected by its proximity to the Fraser River. On average, the SST in the Strait of Georgia is 13-16 ºC in August and 6-7 ºC in February; SSS in the central Strait of Georgia ranges from 22 to 30 (Masson, 2006; Thomson, 1981). The layer bellow 50 m is nearly uniform with respect to temperature (~ 8 ºC) and salinity (~30.5) over the entire basin. Precipitation is ~ 600 mm year-1 (Thomson, 1994). The photic zone is ~ 20 m deep (John et al., 1992). The water is the clearest (with the secchi depth up to 11 m) at the end of summer and beginning of fall (Parsons, 1979). The dominant winds in the exposed areas of the Strait of
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Georgia are from the northwest in the summer and from the southeast in winter. The mixed tidal system is characterised by combination of diurnal and semi-diurnal tides (Thomson, 1981).
Water circulation in the Strait of Georgia is dominated by a seasonally modulated estuarine circulation, which is directly related to the amount and patterns of Fraser River discharge (Thomson, 1994). The upper portion of the water column is characterized by seaward outflow and is driven mainly by the Fraser River outflow which peaks in early summer. The subsurface layer flows landwards, carrying saline and nutrient rich ocean water. This pattern is enhanced in summer when deep, nutrient rich water wells up and mixes with brackish Fraser River water (Thomson, 1994). Winds and tidal currents modulate these typical circulation patterns (Masson, 2002).
Of the numerous rivers and creeks that discharge into the Strait of Georgia, the Fraser River is the most significant source of fresh water (75%) and has a major influence on the surface water properties. Its annual flow is ~ 140 km3, with a maximum discharge at the beginning of summer that reflects snowmelt, and a minimum during the winter (Mosher and Thomson, 2002). The Fraser River delivers 65-80% of the particulate matter (30 x 109 kg year-1) that enters Strait of Georgia (Johannessen et al., 2003). Also, the river supplies approximately half of the dissolved and particulate organic carbon in the Strait (6 x 108 kg year-1), while the reminder of the carbon is derived mainly from in situ primary production (Johannessen et al., 2003). Fraser River flow is affected by large-scale climate shifts, as surface air temperature affects snow accumulation and snow melt (Moore, 1991; Morrison et al., 2002).
The Strait of Georgia is naturally a very nutrient rich environment (Masson, 2002). Estimates of primary production in the Strait vary from 120 to 340 gC m− 2 year− 1 (Parsons et al.,
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1981; Harrison et al., 1983; Antoine et al., 1996; Johannessen et al., 2003). Chlorophyll a concentration ranges from <1 mg m-3 in the winter to >15 mg m-3 in spring/early summer (Parsons et al., 1981). The most marked changes in chlorophyll a occur in the proximity of the Fraser River plume where chlorophyll a abundance can be as high as 20 mg m-3 (Antoine et al., 1996).
The phytoplankton composition in the Strait of Georgia is typical for cold temperate, coastal waters with some estuarine influence. Dinoflagellates, particularly heterotrophic species, are the second most abundant group of phytoplankton, following diatoms (Harrison et al, 1983; Radi et al., 2007). There are at least 88 dinoflagellate species in British Columbia’s coastal waters, of which 21 are recorded to produce organic-walled cysts (Buchanan, 1961). The phytoplankton bloom in the Strait of Georgia usually develops in the Strait in early March (Harrison et al., 1983) with dinoflagellates generally achieving greatest abundance in summer (Cattell, 1969). Heterotrophic species of dinoflagellates are most abundant next to diatom blooms, in early summer (Taylor, unpublished observations, in Harrisson et al., 1983). Hydrographic conditions of the Strait of Georgia, nutrient concentrations, and phytoplankton components show considerable seasonal and inter-annual fluctuations (Harrison et al., 1983; Masson 2002).
2.2. Sediment trap location and collection of samples
Sediment samples for this study were collected by Institute of Ocean Sciences (IOS), Sidney with a Baker-Milburn sequential sediment trap (Baker and Milburn, 1983), composed of a broad funnel with a collecting jar at the bottom that collects organic and inorganic matter
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falling towards the sea bed. This material is commonly used in chemical, physical, and biological lines of marine research (Honjo, 2001).
The GSCM -3 trap was deployed in the central part of the Strait of Georgia, 49°06´31´´ N, 123°29´44´´ W (Fig. 1) at 150 m water depth, which is 200 m above the seafloor (Fig. 2). The particular details of the GSCM-3 sediment trap, their deployment, field sampling methods, sample handling, and geochemical analyses are provided elsewhere (O’Brien et al., 2000; Johannessen et al., 2005). The sampling period covered a three year record from March, 1996 to January, 1999 with collection intervals of 8 - 16 days, averaging at 11 days. There were two gaps throughout the deployment period. The sample 08-113 (deployment period: 21 – 31 May 1998) was lost due to complications with recovery from the trap, and the sample 08-91 (deployment period: 26 August – 08 September 1997) was lost during palynological treatment.
Samples were sieved through a 500 µm mesh to remove zooplankton, and one half of each < 500 µm sample was analysed for total carbon, organic carbon, total nitrogen, carbonate carbon, and biogenic silica as well as stable isotopes of carbon and nitrogen (Johannessen et al., 2005). The other half of each sample was preserved with HgCl2, stored in plastic cups in the dark at 4 C° (O’Brien et al., 2000), and then used for this study.
Core sediment material was obtained from the location of the GSCM-3 mooring. Surface sediments were collected with a small gravity core in March, 2008. The sediment core sample was taken from a core depth of 28-30 cm which approximately represents the depth of material deposited during years of the sediment trap mooring, based on the sedimentation rate at this site, ~ 2.8 cm year-1 (Johannessen et al., 2003). However, surface sediments in the Strait of
V ANC OUV E R IS LAND US A
Strait of Georgia
C ANADA G S C M-3 Fraser river 124 W 49 N o o o o V ancouver B uoy 46146 Lighthouse Active P ass 0 10 km C ANADA 123 WoFig. 1. Map showing location of sediment trap GSCM-3, buoy 46146, lighthouse Active Pass in the Strait of Georgia, and the direction (the arrow) to Hope station (49°22'50", 121°27'05").
Fig. 2. Mooring layout for station GSCM-3.
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Georgia are affected by bioturbation (Burd et al., 2008) therefore core sample might correspond to years other than 1996-98.
2.3. Palynological sample preparation
Sediment were rinsed several times with distilled water to remove HgCl2, centrifuged, oven-dried at 40 °C, and weighed with an analytical balance. The samples were subsequently soaked with distilled water for a night, centrifuged, and then processed with the standard palynological technique (Pospelova et al., 2005). Marker-grains of a known number of
Lycopodium clavatum spores were added in order to calculate the absolute concentrations (cyst
g-1 dry sediments) (Stockmarr, 1971). Sediment samples were treated with cold 10% HCl for 5 minutes in order to remove carbonates. After rinsing with distilled water, the samples were sieved through 125 µm and 15 µm mesh sieves to eliminate coarse and fine material. Additions of cold 48% HF for up to 5 days removed the siliceous particles. The residue was treated with cold 10% HCl, rinsed twice with distilled water, and sonicated for between 0.2 and 0.8 minutes. The final fraction was collected on 15 µm mesh sieves and transferred to 1.5 ml tubes. Samples were centrifuged after each step of the described technique. No oxidation was applied in order to prevent loss of the more fragile protoperidinoid cysts (Dale, 1976; Zonneveld, 1997).
Aliquots of final homogenized residue were mounted in glycerine gel between glass microscope slide and cover slip. Slides were sealed to preserve the samples from drying. Dinoflagellate cysts and other organic palynomorphs were identified and counted using light microscopy on a Nikon Eclipse 80i at 60X and 100X oil objectives. A total of 89 samples were examined for the cysts of dinoflagellates and other palynomorphs.
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2.4. Dinoflagellate cyst analysis
The paleontological taxonomy system is used throughout this paper following Fensome et al. (1993), Lentil and Williams (1993), Head (1996), Zonneveld (1997), Matsuoka and Cho (2000), Head et al. (2001), and Pospelova and Head (2002). Taxonomic listing of dinoflagellate cysts recovered in this study is provided in Appendix 1, the cyst-theca nomenclature is provided in Table 1.
On average, 300 cysts per sample were counted, however due to limited amount of sediment trap material the count for eight samples did not exceed 200 cysts per sample. Each cyst was distinguished as either with cell content (recently produced) or without cell content (remains of cysts that hatched).
Cysts were identified to the species level, whenever possible. Some of dinoflagellate cyst taxa were grouped together on the basis of morphological similarities. In particular,
Brigantedinium simplex and B. cariacoense are grouped into Brigantedinium spp. because
archeopyles often were not observed. Cysts of Polykrikos schwarzii and P. kofoidii are grouped in cysts P. schwartzii/kofoidii according to Matsuoka and Cho (2000).
Species richness (SR) reflects the total number of cyst taxa identified in a trap over the investigated period and was used as a measure of dinoflagellate cyst diversity (Pospelova et al., 2002). Relative abundance (%) of cyst species in an individual sample was calculated by dividing the number of cysts of a certain species by the number of all cysts in the sample. Mean relative abundance over annual cycles was calculated taking into account the collecting intervals. The cyst assemblage over the three year deployment period is referred to in the text as the total
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Cyst species Dinoflagellate theca
(paleontological name) (biological name)
AUTOTROPHIC Gonyaulacaceae
--- Alexandrium spp.
Lingulodinium machaerophorum Lingoludinium polyedrum
Nematosphaeropsis spp. Gonyaulax spinifera complex
Protoceratium reticulatum
Spiniferites ramosus Gonyaulax spinifera complex
Spiniferites spp. Gonyaulax complex
Protoperidiniaceae
--- Pentapharsodinium dalei
HETEROTROPHIC Diplopsalidaceae
Dubridinium spp. Diplopsalid group
Polykrikaceae
--- Pheopolykrikos hartmanii
--- Polykrikos schwarzii/kofoidii
Protoperidiniaceae
Brigantedinium spp. ? Protoperidinium spp.
Brigantedinium cariacoense Protoperidinium avellanum
Brigantedinium simplex Protoperidinium conicoides
Echinidinium aculeatum Protoperidinium sp.indet.
Echinidinium delicatum Protoperidinium sp.indet.
Echinidinium granulatum Protoperidinium sp.indet.
Echinidinum spp. Protoperidinium sp.indet.
Islandinium? minutum Protoperidinium sp.indet.
Islandinium? minutum var. cesare Protoperidinium sp.indet.
Islandinium brevispinosum Protoperidinium sp.indet.
--- Protoperidinium americanum
Quinquecuspis concreta Protoperidinium leonis
Selenopemphix nephroides Protoperidinium subinerme
Selenopemphix quanta Protoperidinium conicum
Votadinium calvum Protoperidinium oblongum
Votadinium spinosum Protoperidinium claudicans
Operculodinium centrocarpum sensu Wall & Dale 1966
Table 1. Taxonomic citation of dinoflagellate cysts used in this study. Thecate equivalents are taken from Head (1996), Zonneveld (1997), Head et al. (2001), and Pospelova and Head (2002).
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cyst assemblage, while the cyst assemblage over an annual cycle is referred as the annual assemblage. Concentrations of dinoflagellate cysts were calculated by dividing total number of cysts by weight of dry sediment sample. Cyst fluxes were calculated by dividing the number of cysts collected per square metre in the investigated period by the number of collecting days (cysts m-2 day-1). The total annual cyst flux is a sum of fluxes multiplied by the number of days in a sampling interval. Concentrations and fluxes for other palynomorphs were calculated accordingly. Detailed formulas are listed in Appendix 2.
2.5. Environmental data
The monthly average values of sea surface temperature (SST) from buoy 46146 (Fig. 1) were provided by J.F.R. Gower. Information on the methodology of measurements, accuracy and compilation of the in situ measurements is documented by Gower (2002). Data on Fraser River flow were obtained from the Archived Hydrometric Data HYDAT (Water Survey of Canada) with daily discharge measured at Hope station (Fig. 1). Data on sea surface salinity, measured daily at Active Pass lighthouse (Fig. 1), were obtained from the British Columbia Lighthouse data archive (Fisheries and Oceans, Canada).
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3. RESULTS
3.1. Dinoflagellate cyst compositions and relative abundance in sediment trap samples
The sediment trap samples contain well preserved organic-walled dinoflagellate cysts (Plates I -VII) and other organic palynomorphs (Plate VIII). Dinoflagellate cysts were recovered from all sediment trap samples. In this work, 30 dinoflagellate cyst taxa were identified, of which seven were produced by autotrophic and 23 by heterotrophic taxa (Table 1, 2, Appendix 1). The number of dinoflagellate cyst taxa in an individual sample varied from eight to 25, with an average of 18. The highest values of species richness were usually recorded during spring and summer (Fig. 3A).
The total cyst assemblage was dominated by cysts of Alexandrium spp. (Plate I/1,2),
Brigantedinium spp. (Plate III/5), Quinquecuspis concreta (Plate V/3,4) and cysts of Protoperidinium americanum (Plate V/1,2) which constituted 51.2%, 22.8%, 8.8% and 4.7%,
respectively (Table 3). The dominance of cysts of Alexandrium spp. was due to the outbreak in spring and summer 1996 when its annual relative abundance comprised 78.8%. Cysts of
Alexandrium spp. constituted only 4.7% and 3.0% in 1997 and 1998. Total annual assemblages
in 1997 and 1998 were strongly dominated by heterotrophic taxa that represented 90.1% and 93.1% respectively. In general, the majority of recorded cysts in the samples belong to the order Protoperidiniales.
The relative abundance of dinoflagellate cysts varied considerably from year to year with the greatest fluctuation occurring in 1996 where cysts of Alexandrium spp. had the highest values (Fig. 3B). The highest relative abundance of the other autotrophic taxa (Table 1) was observed in the end of summer 1997, when it increased up to 33.7% (Fig. 3A). The composition of
Uvic I D Star ting date C los ing date In te rv al d ay s C ys t of A lexandr ium s pp. Oper culodinium centr ocar pum Cy st s o f P entaphar sodinium daleii Sp in if eri te s ra m osu s Spinife rite s s pp. Is landinium ? minutum Is landinium ? minutum var . ces ar e B rigantedinium s pp. B rigantedinium car iacoens e B rigantedinium s implex Dubr idinium s pp. E chinidinium aculeatum E chinidinium delicatum E chinidinium gr anulatum E chinidinum s pp. Cy st s o f P rotoper idinium amer icanum Quinquecus pis concr eta Cy st s o f P oly kr ik os s chw ar tz ii/k ofoidii Selenopemphix nephr oides
Selenopemphix quanta Votadinium calvum Votadinium s
pinos um C ys t type A C ys t type Y Spiny br own T otal cys t count 08_46 04-Mar-96 14-Mar-96 10.5 291 171 17 17 0 0 0 1608 34 34 137 17 0 0 34 564 770 17 120 0 17 17 0 0 51 230 08_47 14-Mar-96 25-Mar-96 10.5 225943 167 24 24 24 72 48 3801 311 287 215 0 72 0 502 1315 2008 24 72 0 0 0 0 0 143 995 08_48 25-Mar-96 04-Apr-96 10.5 324662 146 36 36 36 182 1237 5494 109 218 400 73 146 0 182 910 1710 73 218 109 36 0 0 36 146 1316 08_49 04-Apr-96 15-Apr-96 10.5 92008 110 110 55 0 55 55 4500 0 165 329 55 220 165 549 1262 4775 55 220 110 55 0 110 823 110 747 08_50 15-Apr-96 25-Apr-96 10.5 14216 213 128 0 43 43 128 3574 85 85 298 43 85 0 298 851 6722 43 213 170 128 0 0 170 128 435 08_51 25-Apr-96 06-May-96 10.5 10880 490 82 41 82 41 123 2247 123 82 409 41 41 41 245 531 5719 204 82 163 41 0 0 327 41 422 08_52 06-May-96 16-May-96 10.5 6366 155 67 0 0 22 0 1754 0 111 155 22 155 22 244 777 888 89 67 0 0 0 0 178 67 382 08_53 16-May-96 27-May-96 10.5 84695 195 195 0 49 486 49 1459 0 97 49 0 243 49 292 535 1070 49 97 0 0 0 49 292 438 725 08_54 27-May-96 06-Jun-96 10.5 19390 81 61 0 0 0 0 1152 40 20 222 0 61 0 101 344 1900 20 0 0 40 0 61 0 101 464 08_55 06-Jun-96 17-Jun-96 10.5 9000 170 170 0 0 85 42 2544 85 42 594 42 170 0 170 1102 1611 0 85 42 42 42 2332 254 170 294 08_56 21-Jun-96 29-Jun-96 8.0 31389 70 70 0 0 1265 211 8876 70 70 492 4921 1406 0 1125 703 4358 0 211 70 281 70 703 844 422 518 08_57 29-Jun-96 07-Jul-96 8.0 11679 77 155 77 0 77 0 3326 0 155 1083 774 387 0 541 6188 1392 155 309 77 155 0 232 464 155 298 08_58 07-Jul-96 15-Jul-96 8.0 7873 0 138 0 0 0 69 5520 345 276 276 1104 207 138 483 7038 1242 276 0 69 69 0 0 207 276 361 08_59 15-Jul-96 23-Jul-96 8.0 20403 196 98 0 65 0 0 3296 98 98 359 196 131 0 65 1175 653 33 98 33 0 0 0 65 65 302 08_60 23-Jul-96 31-Jul-96 8.0 10879 282 71 0 35 71 71 3919 35 35 353 106 106 35 318 530 1059 0 35 106 0 0 0 0 106 298 08_61 31-Jul-96 08-Aug-96 8.0 5091 466 155 0 0 155 155 7770 155 311 3963 155 777 78 389 2720 466 78 78 155 78 0 78 0 389 301 08_62 08-Aug-96 16-Aug-96 8.0 158 316 39 0 0 0 0 4739 118 671 276 0 395 0 39 2054 197 0 0 0 39 0 0 0 39 230 08_63 16-Aug-96 24-Aug-96 8.0 1699 442 68 0 0 68 0 4689 34 68 238 0 476 34 680 1019 272 0 0 0 34 0 102 306 374 297 08_64 13-Sep-96 28-Sep-96 15.8 390 779 195 0 0 0 22 2750 173 0 0 0 22 0 130 779 736 0 173 0 22 0 22 130 368 309 08_65 28-Sep-96 14-Oct-96 15.8 2328 135 202 0 0 0 0 3003 0 67 34 101 202 34 405 3037 641 34 67 0 0 0 101 337 67 320 08_66 14-Oct-96 30-Oct-96 15.8 1473 0 87 0 0 0 0 2533 0 0 262 0 568 44 349 3275 437 131 0 0 0 0 131 742 218 233 08_67 30-Oct-96 15-Nov-96 15.8 566 0 0 0 23 0 0 2156 23 92 138 0 206 0 69 1308 619 0 69 0 0 23 0 0 0 223 08_68 15-Nov-96 30-Nov-96 15.8 463 191 54 0 0 0 27 2233 163 82 490 0 109 27 82 1035 1117 27 82 54 54 0 27 272 136 247 08_69 30-Nov-96 16-Dec-96 15.8 727 101 20 0 0 0 0 2107 41 61 284 0 0 0 41 851 405 0 142 20 41 20 0 20 81 229 08_70 16-Dec-96 01-Jan-97 15.8 166 12 0 0 0 0 0 1434 12 25 137 0 0 0 0 598 287 12 50 0 0 0 0 12 12 216 08_71 01-Jan-97 17-Jan-97 15.8 397 20 10 0 0 0 0 1394 30 99 297 40 49 0 20 564 485 10 69 10 0 0 10 0 40 345 08_72 17-Jan-97 01-Feb-97 15.8 257 97 0 0 0 0 0 1882 16 32 322 0 80 16 16 611 965 32 0 16 16 0 0 0 64 275 08_73 01-Feb-97 17-Feb-97 15.8 686 69 0 0 0 0 0 1071 69 27 206 41 69 14 14 357 673 14 69 0 0 0 0 14 41 244 08_74 21-Feb-97 02-Mar-97 9.4 58 10 0 0 0 0 0 301 0 0 29 0 0 0 0 58 87 0 10 0 0 0 0 0 0 57 08_75 02-Mar-97 12-Mar-97 9.4 88 28 14 0 0 0 0 1451 0 0 405 0 28 14 42 307 419 0 42 0 0 0 0 0 42 239 08_76 12-Mar-97 21-Mar-97 9.4 423 141 28 0 28 0 0 4345 113 141 564 0 28 28 56 395 1777 0 113 0 0 0 0 0 56 292 08_77 21-Mar-97 31-Mar-97 9.4 115 44 9 0 0 0 0 480 0 0 79 0 0 0 0 122 113 0 35 0 9 0 0 0 9 114 08_78 31-Mar-97 09-Apr-97 9.4 106 17 8 0 0 0 34 498 0 0 51 0 0 0 0 93 135 0 0 0 0 0 8 0 0 113 08_79 09-Apr-97 18-Apr-97 9.4 764 42 64 0 85 42 1805 1847 42 42 531 21 0 21 42 212 531 0 170 0 0 0 21 0 85 300 08_80 18-Apr-97 28-Apr-97 9.4 1192 140 0 0 0 210 2315 18587 281 140 281 140 140 0 140 772 421 70 0 0 140 70 70 210 70 366 08_81 28-Apr-97 07-May-97 9.4 801 133 67 0 0 33 200 5605 33 33 867 0 267 0 67 133 2402 0 67 0 133 0 33 0 133 341 08_82 07-May-97 16-May-97 9.4 568 142 114 0 0 85 14 1335 0 28 256 0 71 0 85 241 2357 0 0 43 71 0 99 28 99 399 08_83 16-May-97 26-May-97 9.4 694 391 217 0 0 0 87 3428 0 87 1085 0 0 0 130 87 6510 0 174 434 174 0 0 0 130 314 08_84 31-May-97 12-Jun-97 12.5 324 81 0 0 81 81 0 9407 0 81 4703 1865 730 162 811 1541 3000 1054 649 243 81 0 243 0 1216 325 08_85 12-Jun-97 25-Jun-97 12.5 170 73 73 0 0 24 0 2528 0 0 1191 802 583 122 389 194 9943 340 97 49 24 0 365 0 1118 753 08_86 25-Jun-97 07-Jul-97 12.5 760 152 95 38 38 19 0 2451 19 57 95 76 57 19 209 247 646 114 57 57 19 19 95 19 380 303 08_87 07-Jul-97 20-Jul-97 12.5 168 84 324 24 36 0 36 1273 12 12 96 24 36 0 72 156 552 72 60 0 0 0 144 0 468 306 Table 2. Daily average cyst flux (cysts m-2 day-1) for individual taxa recovered at GSCM-3 mooring. Flux of Lingulodinium machaerophorum , Namatosphaeropsis labirinthus , Islandinium brevispinosum , Pheopolykrikos hartmanii , and Protoperidinium type 1 were not calculated due to a very low (<5 specimens) occurrence during the deployment period.
Table 2 (continued ) Uvic I D Star ting date C los ing date In te rv al d ay s C ys t of A lexandr ium s pp. Oper culodinium centr ocar pum Cy st s o f P entaphar sodinium daleii Sp in if eri te s ra m osu s Spinife rite s s pp. Is landinium ? minutum Is landinium ? minutum var . ces ar e B rigantedinium s pp. B rigantedinium car iacoens e B rigantedinium s implex Dubr idinium s pp. E chinidinium aculeatum E chinidinium delicatum E chinidinium gr anulatum E chinidinum s pp. Cy st s o f P rotoper idinium amer icanum Quinquecus pis concr eta Cy st s o f P oly kr ik os s chw ar tz ii/k ofoidii Selenopemphix nephr oides
Selenopemphix quanta Votadinium calvum Votadinium s
pinos um C ys t type A C ys t type Y Spiny br own T otal cys t count 08_88 20-Jul-97 01-Aug-97 12.5 49 94 85 0 26 51 9 752 0 0 60 0 0 0 17 111 299 0 17 0 0 0 0 0 316 220 08_89 01-Aug-97 14-Aug-97 12.5 39 711 96 0 96 0 0 807 19 38 96 19 0 0 19 38 96 0 38 19 0 0 0 0 1863 211 08_90 14-Aug-97 26-Aug-97 12.5 212 2307 80 0 0 53 0 743 0 80 27 0 27 0 0 106 690 0 0 186 27 0 345 0 2413 275 08_91 26-Aug-97 08-Sep-97 12.5 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 08_92 08-Sep-97 20-Sep-97 12.5 109 150 105 0 0 0 0 1274 15 30 90 0 0 0 0 45 1094 0 75 0 0 0 45 0 150 212 08_93 20-Sep-97 03-Oct-97 12.5 405 256 85 21 64 0 21 2198 21 0 21 64 21 0 64 299 1921 0 64 21 0 0 128 43 299 282 08_94 06-Oct-97 18-Oct-97 12.8 276 221 0 0 22 0 0 1698 0 66 66 0 22 0 0 176 1698 0 66 0 243 0 132 0 154 219 08_95 18-Oct-97 31-Oct-97 12.8 636 397 238 0 0 0 0 3418 0 159 0 0 79 0 0 79 4690 0 318 0 79 0 636 0 1669 156 08_96 31-Oct-97 13-Nov-97 12.8 58 115 19 0 0 0 0 1344 0 38 38 0 0 0 19 58 826 0 38 0 0 0 38 0 134 142 08_97 13-Nov-97 26-Nov-97 12.8 87 158 32 0 0 0 0 1418 0 16 126 0 16 0 32 126 930 0 32 16 16 0 32 0 268 209 08_98 26-Nov-97 08-Dec-97 12.8 285 522 47 0 0 0 0 3844 0 237 237 0 47 0 142 427 3702 0 380 47 0 0 0 0 285 215 08_99 08-Dec-97 21-Dec-97 12.8 216 259 47 0 71 0 0 2027 0 71 94 0 0 24 47 353 1225 0 212 24 47 0 0 0 212 209 08_100 21-Dec-97 03-Jan-98 12.8 159 583 243 0 340 0 0 3447 97 146 243 243 49 0 146 1068 2525 49 146 49 0 0 0 0 437 205 08_101 03-Jan-98 16-Jan-98 12.8 135 158 26 79 26 0 0 3107 0 26 369 0 26 0 26 211 1106 0 26 26 0 0 0 0 132 208 08_102 16-Jan-98 28-Jan-98 12.8 254 175 32 32 16 16 0 1590 16 32 159 0 16 0 16 509 445 0 32 16 16 0 16 0 48 215 08_103 28-Jan-98 10-Feb-98 12.8 575 874 328 109 546 328 0 13212 109 546 983 437 764 109 546 1529 6115 0 546 437 0 0 0 0 764 266 08_104 14-Feb-98 24-Feb-98 10.8 176 410 117 20 0 20 0 2208 59 156 274 20 0 0 59 528 801 20 98 59 0 0 0 0 20 258 08_105 24-Feb-98 07-Mar-98 10.8 193 618 309 309 39 0 0 7725 77 154 116 0 39 0 39 1815 5832 39 270 39 39 0 0 0 502 470 08_106 07-Mar-98 18-Mar-98 10.8 204 560 255 51 51 0 0 7132 509 306 917 51 102 0 204 1834 3311 102 458 153 51 51 0 0 306 326 08_107 18-Mar-98 29-Mar-98 10.8 1465 200 266 0 0 0 0 11457 133 133 133 0 67 0 67 866 3597 133 67 133 67 67 200 0 133 288 08_108 29-Mar-98 08-Apr-98 10.8 210 559 0 0 70 0 70 17475 0 0 280 0 0 0 70 909 1817 0 70 0 70 0 0 0 210 26 08_109 08-Apr-98 19-Apr-98 10.8 186 139 46 0 0 0 0 7984 93 0 371 46 0 0 46 557 1671 0 232 0 46 46 0 46 139 312 08_110 19-Apr-98 30-Apr-98 10.8 218 364 146 73 0 0 0 13539 0 0 510 0 946 0 510 1965 3931 218 146 218 0 0 0 801 291 252 08_110 30-Apr-98 11-May-98 10.8 614 511 205 205 0 0 0 26074 205 0 716 102 614 0 511 2761 1841 0 205 205 0 0 0 102 307 328 08_112 11-May-98 21-May-98 10.8 125 313 438 125 63 0 0 10633 0 0 375 0 500 0 438 3753 438 0 188 375 0 0 0 0 250 344 08_113 21-May-98 31-May-98 9.8 N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 08_114 02-Jun-98 14-Jun-98 12.3 2586 431 1149 575 144 0 0 25001 0 0 1149 144 1293 0 1293 575 6753 144 431 1437 144 0 4742 862 862 347 08_115 14-Jun-98 26-Jun-98 12.3 86 68 136 0 34 0 68 4645 0 0 373 0 34 0 68 203 1322 0 68 34 68 0 136 0 136 220 08_116 26-Jun-98 08-Jul-98 12.3 177 38 13 0 0 0 0 937 13 13 139 13 0 0 0 215 152 0 13 13 0 0 0 0 63 142 08_117 08-Jul-98 21-Jul-98 12.3 1283 55 109 0 55 0 0 3110 55 109 491 0 0 0 0 982 1200 0 55 0 55 0 55 0 109 139 08_118 21-Jul-98 02-Aug-98 12.3 273 23 23 0 0 0 0 682 23 0 91 0 45 0 91 227 341 0 23 0 0 0 0 0 45 83 08_119 02-Aug-98 14-Aug-98 12.3 282 71 71 0 0 0 71 2679 0 141 212 776 5288 71 1199 564 846 0 71 0 0 71 212 635 846 200 08_120 14-Aug-98 26-Aug-98 12.3 34 237 135 0 34 0 0 3753 0 169 135 169 1082 0 101 2028 372 0 34 0 68 0 34 101 710 272 08_121 26-Aug-98 08-Sep-98 12.3 83 62 62 0 0 0 0 1538 0 42 42 104 270 0 104 291 249 0 21 42 21 0 42 62 208 218 08_122 08-Sep-98 20-Sep-98 12.3 92 46 276 46 92 138 0 5061 46 46 184 552 828 0 1150 276 736 230 138 1058 276 0 184 322 552 268 08_123 20-Sep-98 02-Oct-98 12.3 122 44 88 0 0 132 0 3296 88 44 396 220 88 0 220 1143 264 88 44 88 88 44 132 88 220 222 08_124 04-Oct-98 14-Oct-98 10.8 36 35 53 18 18 18 18 1806 18 0 53 159 35 18 35 744 266 0 0 18 53 0 18 0 177 203 08_125 14-Oct-98 25-Oct-98 10.8 37 37 19 0 19 19 0 2680 19 19 354 93 130 0 37 503 168 19 0 0 19 19 37 0 74 231 08_126 25-Oct-98 05-Nov-98 10.8 121 19 19 0 19 0 0 2223 19 19 261 19 19 0 19 448 486 19 37 19 0 0 19 0 75 204 08_127 05-Nov-98 16-Nov-98 10.8 80 94 94 0 0 0 0 2294 47 70 281 0 23 0 47 866 702 23 0 23 0 0 0 0 117 203 08_128 16-Nov-98 26-Nov-98 10.8 263 124 35 18 0 0 0 1308 35 18 194 18 35 18 124 689 318 0 35 0 18 0 35 0 212 200 08_129 26-Nov-98 07-Dec-98 10.8 204 18 12 0 12 6 12 542 0 6 73 6 6 0 6 134 152 6 6 6 6 0 0 0 43 201 08_130 07-Dec-98 18-Dec-98 10.8 105 84 42 0 21 42 21 1787 0 42 168 42 42 21 84 357 925 42 63 42 21 0 147 0 84 200 08_131 18-Dec-98 29-Dec-98 10.8 67 54 41 0 0 14 0 1256 14 27 216 0 0 0 0 176 608 0 14 27 14 0 0 0 54 209 08_132 29-Dec-98 08-Jan-99 10.8 28 28 55 0 0 55 0 3280 55 55 551 0 55 28 28 689 1130 0 83 0 28 0 0 0 28 224 08_133 08-Jan-99 19-Jan-99 10.8 266 345 115 0 58 58 0 5988 230 58 749 58 403 0 115 173 2361 58 173 0 173 0 58 0 173 201
60 1110
0
20 Relative abundance of cysts of autotrophic taxa*
5 10 15
20 Sea surface temperature
15 20 25 30
Sea surface salinity
60 1110
0 50 100
Total sediment flux
M J S D M J S D M J S D
Fraser River discharge
1110 1110
Organic carbon flux 0
5000
10000 Total cyst concentration*
0 25000 50000
Total cyst flux*
0
Flux of autotrophic cyst taxa*
0 175000 350000
Cyst flux of Alexandrium spp.
0 25000 50000 Flux of heterotrophic cyst taxa 1110 1110
Flux of biogenic silica 1.5 0.7 1.0 0.5 10000 5000 0 0 0 cysts g -1 cysts m day -2 -1 m s 3 -1 C o g m day -1 -2 % 40 30 18 6
* cysts of Alexandrium spp. are not included in calculations
Species richness B A D C 1996 1997 1998 sample is missing 2000 4000 19
Fig. 3. Three year time-series of A. Species richness and relative abundance of cysts
produced by autotrophic taxa; B. Total dinoflagellate cyst concentration, flux, and individual fluxes of cysts produced by autotrophic and heterotrophic taxa, as well as flux of cysts of
Alexandrium spp.; C. Monthly average sea surface temperature and salinity along with daily
Fraser River discharge; D. Flux of sediments, biogenic silica, and organic carbon (adapted from Johannessen et al., 2005).
20
dinoflagellate cyst assemblages, relative abundance of dinoflagellate cyst taxa, and the relative abundance of cysts produced by autotrophic and heterotrophic species are provided in Table 3.
3.2 Dinoflagellate cyst flux and concentration
During the three year deployment period the flux of organic walled dinoflagellate cysts range over three orders of magnitude. The total dinoflagellate cyst flux varied from 5 x 102 cysts m-2 day-1 (February 1997) to 3 x 105 cysts m-2 day-1 (April 1996), with an average of 2 x 104 cysts m-2 day-1. Due to the outbreak of cysts of Alexandrium spp. in 1996, the total annual cyst flux was about five times higher in 1996 then in 1997 and three times higher than in 1998. The total annual cyst flux of other autotrophic taxa was only half as high in 1996 as in 1997 and 1998 (Table 4, Fig. 3B). The total flux in 1997 and 1998 was strongly dominated by cysts produced by heterotrophic species (Table 4, Fig. 3A, 3B). Due to a decrease in cyst flux of heterotrophic taxa, the minimum value of total annual flux was recorded in 1997. The highest values for the total fluxes heterotrophic taxa over the studied period were observed in 1998. Total annual fluxes of dinoflagellate cyst taxa over the three year period are provided in Table 4.
The flux of cysts of Alexandrium spp. was up to 3 x 105 cysts m-2 day-1 in spring and summer 1996 (Fig. 3B). Cyst flux of Alexandrium spp. drastically declined in 1997-98 with the highest values of the flux, also recorded during spring and summer, reaching only 3 x 103 cysts m-2 day-1 (Table 2). Cyst flux of other autotrophic taxa demonstrated marked variability and did not have stable seasonal patterns. Cyst flux of autotrophic taxa, excluding cysts of Alexandrium spp., varied from 23 to 2 x 103 cysts m-2 day-1 during 1996, with highest values recorded in September. In winter 1996-97, this flux was extremely low (not exceeding 1 x 102 cysts m-2 day -1). During 1997 the highest values were recorded in August and were twice as high as the
21 Core Core* Mar. 1996-D ec. 1996 Jan. 1997-D ec. 1997 (Mar. -D ec. ) Jan. 1998-D ec. 1998 (Mar. -D ec. ) Mar. 1996-Jan. 1999 ~ 1996-98 Mar. 1996-D ec. 1996 Jan. 1997-D ec. 1997 (Mar. -D ec. ) Jan. 1998-D ec. 1998 (Mar. -D ec. ) Mar. 1996-Jan. 1999 ~ 1996-98 Cyst of Alexandrium spp. (78.8) 4.7 (4.2) 3.0 (3.1) 51.2 0.5
Cyst of Pentapharsodinium dalei (0.2) 1.0 (1.1) 1.3 (1.3) 0.6 1.3 (1.0) 1.1 (1.1) 1.3 (1.4) 1.2 1.3
Operculodinium centrocarpum (0.5) 3.7 (3.9) 1.8 (1.4) 1.2 4.6 (2.2) 3.9 (4.0) 1.9 (1.4) 2.5 4.6
Spiniferites spp. (S . ramosus & S . spp) (0.05) 0.4 (0.5) 0.9 (0.6) 0.3 2.7 (0.2) 0.5 (0.5) 0.9 (0.6) 0.6 2.7 Total Brigantedinim (8.2) 38.0 (38.2) 54.0 (55.3) 22.8 41.8 (38.4) 40.1 (39.6) 55.6 (57.1) 46.8 42.0 Cyst type A (0.3) 1.2 (1.3) 1.8 (1.2) 0.8 0.3 (1.6) 1.3 (1.4) 1.8 (2.2) 1.6 0.3 Cyst type Y (0.5) 0.1 (0.1) 0.9 (0.1) 0.5 N/A (2.5) 0.1 (0.1) 0.9 (1.1) 1.1 N/A Cyst of Polykrikos schwartzii/kofoidii (0.1) 0.9 (0.9) 0.3 (0.4) 0.3 1.9 (0.6) 0.9 (1.0) 0.3 (0.4) 0.5 1.9 Cyst of Protoperidinium americanum (3.7) 4.5 (3.8) 7.8 (7.9) 4.7 3.2 (17.5) 4.7 (3.9) 8.1 (8.2) 9.7 3.2
Dubridinium spp. (0.9) 5.8 (5.7) 3.0 (2.9) 2.1 0.8 (4.4) 6.1 (5.9) 3.1 (3.0) 4.3 0.8
Echinidinium aculeatum (0.5) 1.7 (1.8) 0.9 (0.9) 0.8 0.3 (2.6) 1.8 (1.8) 0.9 (0.9) 1.6 0.3
Echinidinium delicatum (0.5) 1.2 (1.1) 3.6 (4.1) 1.3 0.5 (2.5) 1.2 (1.2) 3.7 (4.2) 2.7 0.5
Echinidinium granulatum (0.1) 0.2 (0.2) 0.1 (0.1) 0.1 N/A (0.3) 0.2 (0.2) 0.1 (0.1) 0.2 N/A
Echinidinum spp. (0.6) 1.3 (1.3) 2.1 (2.3) 1.0 1.3 (3.0) 1.3 (1.4) 2.1 (2.3) 2.1 1.3
Islandinium ? minutum (0.2) 0.3 (0.3) 0.2 (0.1) 0.2 0.5 (1.0) 0.3 (0.3) 0.2 (0.2) 0.5 0.5
Islandinium ? minutum var. cesare (0.2) 1.7 (1.9) 0.1 (0.1) 0.4 0.3 (0.9) 1.8 (2.0) 0.1 (0.1) 0.8 0.3
Quinquecuspis concreta (3.7) 24.4 (24.8) 13.5 (11.4) 8.8 34.3 (17.5) 25.6 (25.9) 13.9 (11.7) 18.1 34.5
Selenopemphix nephroides (0.2) 1.5 (1.5) 1.0 (0.8) 0.6 1.6 (1.1) 1.5 (1.6) 1.0 (0.9) 1.2 1.6
Selenopemphix quanta (0.1) 0.6 (0.6) 1.3 (1.4) 0.4 1.9 (0.5) 0.6 (0.6) 1.3 (1.4) 0.9 1.9 Spiny brown (0.4) 6.2 (6.6) 2.2 (2.2) 1.6 1.6 (1.8) 6.5 (6.8) 2.3 (2.2) 3.2 1.6
Votadinium calvum (0.1) 0.5 (0.5) 0.3 (0.4) 0.2 0.5 (0.4) 0.5 (0.5) 0.3 (0.4) 0.4 0.5
Votadinium spinosum (0.02) 0.04 (0.04) 0.1 (0.1) 0.03 N/A (0.1) 0.04 (0.1) 0.1 (0.1) 0.1 N/A
Lingulodinium machaerophorum <0.01 <0.01 <0.01 <0.01 N/A <0.01 <0.01 <0.01 <0.01 N/A
Namatosphaeropsis labirinthus <0.01 <0.01 <0.01 <0.01 N/A <0.01 <0.01 <0.01 <0.01 N/A
Islandinium ? brevispinosum <0.01 <0.01 <0.01 <0.01 N/A <0.01 <0.01 <0.01 <0.01 N/A
Pheopolykrikos hartmanii <0.01 <0.01 <0.01 <0.01 N/A <0.01 <0.01 <0.01 <0.01 N/A
Protoperidinium type 1 <0.01 <0.01 <0.01 <0.01 N/A <0.01 <0.01 <0.01 <0.01 N/A Total autotrophic taxa 79.5 9.9 (9.6) 6.9 (6.4) 53.3 9.1 3.4 5.4 (5.7) 4.1 (3.4) 4.3 8.6 Total heterotrophic taxa 20.5 90.1 (90.4) 93.1 (93.6) 46.7 90.9 96.6 94.6 (94.3) 95.9 (96.6) 95.7 91.4
Sediment trap Sediment trap*
Table 3. The relative abundance (%) of dinoflagellate cysts from sediment trap GSCM-3 and the core sediment sample CM-3. The asterix (*) indicates that cysts of Alexandrium spp. are not included in the calculations.
22
Jan.1997-Dec.1997 Jan.1998-Dec.1998 (Mar.1996-Dec.1996) (Mar.1997-Dec.1997) (Mar.1998-Dec.1998)
Days of deployment (298) 355 (299) 364 (304)
Autotrophic taxa (9.16) 0.26 (0.24) 0.32 (0.25)
Autotrophic taxa* (0.08) 0.14 (0.14) 0.18 (0.13)
Heterotrophic taxa (2.36) 2.26 (2.10) 4.16 (3.49)
Total cyst flux (11.53) 2.34 (2.52) 4.47 (3.74)
Total cyst flux* (2.45) 2.41 (2.24) 4.34 (3.62)
Total flux of biogenic Silica (8.60) 14.66 (13.39) 12.26 (10.85)
Table 4. Total annual dinoflagellate cyst flux (cysts x 106 m-2 year-1) and biogenic Silica (g x 104 m-2 year-1). The asterix (*) indicates that cysts of Alexandrium spp. are not included in the calculations.
23
highest values of the previous year. The cyst flux was high during winter 1997-98, and the following spring 1998, with values from 2 x 102 cysts m-2 day-1 to 2 x 103 cysts m-2 day-1. From June to December 1998, the flux was low (Fig. 3B).
The fluxes of cysts produced by heterotrophic taxa showed consistent seasonal patterns, peaking in spring and the beginning of summer during all three years (Fig. 3B), with highest always in June. In June 1996 and 1998, the maximum cyst flux (up to ~ 0.5 x 105 cysts m-2 day-1) was twice as high as in June 1997. Cyst production, reflected by flux, was prolonged during 1998, compared to both 1996 and 1997 (Fig. 3B). The lowest values of cyst flux were observed in the winter, with the exception of winter 1997-98 when cyst flux was relatively high (up to 3 x 104 cysts m-2 day-1).
Fluxes of individual taxa varied seasonally (Fig. 4) and annually (Table 5). The most abundant taxon Brigantedinium spp., had decreased in 1997 and significantly increased in1998 (more than doubling the flux), compared to 1996. Q concreta showed slight increase in 1997 compared to 1996 and 1998. P. americanum showed a marked decline in 1997 compared to 1996, recovering almost completely in 1998. Islandinium? minutum, Echinidinium aculeatum, and cysts type Y (Plate VI/6) had significantly suppressed their fluxes in both 1997 and 1998. E.
delicatum, Echinidinium spp., and cysts type A (Plate VI/5) had higher fluxes in 1996 and 1998
compared to 1997. Operculodinium centrocarpum, Islandinium? var. cesare, and cysts of
Polykrikos schwarzii/kofoidii considerably increased in flux in 1997. Cysts of Pentapharsodinium dalei, Spiniferites spp., and Selenopemphix quanta had increased their
highest fluxes in 1997, reaching the highest values in 1998. Daily average fluxes for the most common species are provided in Table 2 and illustrated in Figure 4.
0 1.5 3.0
Operculodinium centrocarpum 0
1.5 Cysts of Pentapharsodinium dalei
0 1.5 Spiniferites spp. Brigantedinium spp. 0 5.0 10.0 Quinquecuspis concreta 0 3.5 7.0
Cysts of Protoperidinium americanum
0 4.5 9.0 Selenopemphix nephroides 0 0.9 1.8 Islandinium? minutum 0 3.5 7.0 Echinidinium aculeatum 0 0.9 1.8 Echinidinum spp. 0 0.9 1.8 Cyst type Y 0 3.5 7.0 Echinidinium delicatum 0 3.5 7.0 Cyst type A 0 1.5 3.0
Islandinium? minutum var. cesare
0 0.9 1.8
Cysts of Polykrikos schwarzii/kofoidii 0 3.5 7.0 Dubridinium spp. 0 1.5 Selenopemphix quanta 0 15.0 30.0 M J S D M J S D M J S D 1996 1997 1998
Fig. 4. Average daily cyst flux for the most common taxa - with cell content - without cell content.
cysts x 10 m day
3
-2
-1
25
Mar.1996-Dec.1996 Jan.1997-Dec.1997 (Mar.-Dec.) Trend Jan.1998-Dec.1998 (Mar.-Dec.) Trend
Cyst of Alexandrium spp. (9078) 118 (96) ↓ 137 (121) ↓
Cyst of Pentapharsodinium dalei (24) 26 (26) 63 (53) ↑
Operculodinium centrocarpum (54) 106 (103) ↑ 78 (51)
Spiniferites spp. (S. ramosus , and S . spp) (6) 12 (12) ↑ 40 (26) ↑
Brigantedinium (B . simplex , B . cariacoense ,
and B . spp.) (940) 953 (877) ↓ 2408 (2059) ↑
Cyst type A (40) 33 (32) ↓ 102 (102) ↑
Cyst type Y (61) 3 (3) ↓ 41 (41) ↓
Cyst of Polykrikos schwartzii/kofoidii (11) 22 (21) ↑ 13 (13)
Cyst of Protoperidinium americanum (429) 111 (86) ↓ 343 (289) ↓
Dubridinium spp. (107) 143 (129) ↑ 130 (107) Echinidinium aculeatum (63) 42 (40) ↓ 37 (31) ↓ Echinidinium delicatum (61) 29 (26) ↓ 158 (148) ↑ Echinidinium granulatum (7) 5 (5) 3 (2) ↓ Echinidinum spp. (74) 31 (30) ↓ 95 (86) ↑ Islandinium ? minutum (23) 7 (7) ↓ 10 (5) ↓
Islandinium ? minutum var. cesare (22) 43 (43) ↑ 3 (3) ↓
Quinquecuspis concreta (429) 610 (575) ↑ 592 (423)
Selenopemphix nephroides (27) 37 (35) ↑ 44 (32) ↑
Selenopemphix quanta (12) 15 (15) 64 (57) ↑
Spiny brown (43) 167 (165) ↑ 97 (79) ↑
Table 5. Annual dinoflagellate cyst flux (cysts x 103 m-2 year-1) for the most common taxa. Arrows indicate noticeable changes (increase or decrease) in the cyst flux compared to flux in 1996.
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Dinoflagellate cyst concentration ranged from 66 to 29,448 cysts g-1, with an average of ~2,600 cysts g-1. Highest cyst concentrations were recorded in the end of spring and in the summer of 1996 due to the cyst outbreak (up to ~ 28,400 cysts g-1) of Alexandrium spp. The average dinoflagellate cyst concentration, not including cysts of Alexandrium spp. was ~1,500 cysts g-1 (Fig. 3B). Concentration of cysts produced by the rest of the autotrophic species varied from 7 to ~590 cysts g-1 with prominent peaks between August and September. The concentration of cysts produced by heterotrophic species varied from 57 to 8,984 cysts g-1 with highest values during summer. The lowest total concentrations for both autotrophic and heterotrophic taxa occurred during the winters (Fig. 3B).
3.3 Sedimentary records of dinoflagellates producing toxic components
Toxic and potentially toxic dinoflagellate cysts and organic remains of the motile dinoflagellates were recorded in the sediment trap samples. These cysts included Alexandrium spp., Lingulodinium machaerophorum (biological name - L. polyedrum), O. centrocarpum (biological name - Protoceratium reticulatum), Dinophysis acuminata, and D. acuta.
The cysts of Alexandrium spp. (Plate I/1, 2) were recorded in very high concentrations in the spring of 1996. For that year, the cysts of Alexandrium spp. comprised ~78% of the assemblage (Table 3). After the outbreak in 1996 (Fig. 3B), these cysts were found in almost all samples during the study period (Table 2) with an average flux of 5 x 102 cysts m-2 day-1. Only three specimens of L. machaerophorum (Plate I/3), observed in May 1996 samples, were found over the three year period. In contrast, O. centrocarpum was commonly found with the highest associated fluxes during the end of summer and beginning of fall. The flux of O. centrocarpum peaked to 2 x 103 cysts m-2 day-1 in August 1997.
27
Thecae of D. acuminate (Plate VIII/5, Fig. 5) were observed mostly in summer samples. In 1997, the flux of D. acuminate noticeably increased reaching its highest values up to 2 x 105 thecae m-2 day-1. Thecae of D. acuta (Plate VIII/6, Fig. 5) were common during the summers of 1996 and 1997, with its highest values (up to ~ 4 x 104 thecae m-2 day-1) recorded at the end of summer. The flux of D. acuta declined in 1998.
3.4 Other palynomorphs
In addition to dinoflagellate cysts, other palynomorphs (organic-walled microfossils of a size ranging from 5 - 120 µm) were distinguished and counted. Palynomorph type 1 (Plate VIII/13, 14), with fluxes up to 2 x 106 specimens m-2 day-1 in August 1997 (Fig. 5), was most abundant. Radiosperma corbiferum and palynomorph types 1, 2, and 3 significantly increased in abundance in summer of 1997. The flux of Tintinnid? lorica type 2 considerably decreased during 1997. The flux of Tintinnid? lorica type 1, Rhizopoda, and palynomorph type 4 all increased in the summer and fall of 1998. The flux of copepod eggs declined in both 1997 and 1998. All of these organic palynomorphs were found in the sediment sample with the exception of D. acuta, D. acuminate, and palynomorph type 4.
3.5 Dinoflagellate cysts in core sediment sample
The cyst composition and relative abundance of dinoflagellate cyst taxa in this assemblage are provided in Table 3. Twenty two dinoflagellate cyst taxa were identified in the sediment core samples, of which five were produced by autotrophic and 18 by heterotrophic taxa. Cysts produced by autotrophic taxa contributed ~9% of the mean relative abundance, the rest comprising heterotrophic taxa. Brigantedinium spp. and Q. concreta strongly dominated the assemblage contribution 42% and 34%, respectively. Cysts of Alexandrium spp. constituted
0 0.1 0.2 Radiosperma corbiferum 0 10 20 Dinophysis acuminata 0 2.5 5.0 Dinophysis acuta 0 100 200 Palynomorph type 1 0 1 2 Palynomorph type 2 0 0.06 Hexasterias problematica 0 6 12 0 0.2 0.4 Rhizopoda 0 75
150 Tintinnid? lorica type 1
0 3 6 Palynomorph type 4 0 0.1 Palynomorph type 3 0 0.7 1.5 Copepod eggs M J S D M J S D M J S D 0.2
Tintinnid? lorica type 2 0.03
1996 1997 1998
Fig. 5. Average daily flux of some selected aquatic palynomorphs.
speciments x 10 m day
-2
-1
4
29
~0.5% of the mean relative abundance. The total cyst concentration in sediment was comparable (~2,000 cysts g-1) to the concentration found in sediment trap samples.
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4. DISCUSSION
The dinoflagellate cysts caught in sequential sediment traps deployed over a three-year period at 150 m in the Strait of Georgia have provided one of the most detailed temporal records of cyst flux published to date. The resolution of approximately 11 days per sample provides an opportunity to compare changes in cyst fluxes and composition of cyst assemblages with the seasonal changes of major surface water parameters (SST, SSS, freshwater input). These data also provide an opportunity to evaluate changes in dinoflagellate cyst fluxes into the traps that accompany a very strong El Niño event.
4.1. Composition of dinoflagellate cyst assemblages and relative abundance
The organic-walled dinoflagellate cysts that accumulated in the sediment trap form a diverse assemblage, with the most cysts belonging to widely distributed neritic cold-temperate to temperate taxa (Wall et al., 1977; Dale, 1996). All of the taxa have previously been identified in bottom marine sediments from the Strait of Georgia (Radi et al., 2007). Also contained within the trap collections were dinoflagellate species that had not previously been reported from this area in their planktonic/motile stages. Cysts of P. dalei and P. americanum were common in sediment trap samples and surface sediments (Radi et al., 2007); but their motile stages are virtually absent in plankton samples collected from the water column in the Strait of Georgia (see, e.g. Buchanan, 1961; Catell, 1969; Taylor, 1996 for records of dinoflagellates in the water column). It is commonly the case that planktonic species are encountered for the first time in sediment traps rather than water samples (Dale, 1976; Montresor et al., 1998; Godhe et al., 2001) because the former efficiently integrate sampling over time.
31
4.2. Seasonal and annual variability of dinoflagellate cyst flux
Sediment trap data clearly showed seasonal trends in dinoflagellate cyst production (reflected by the cyst flux) and differences between species in their encystment patterns. In general, the total cyst flux was lowest during winter, increased in early spring and reached its maximum at the end of the three springs or the beginning of summers (Fig. 3B). This pattern agrees with the general trend of abundance of dinoflagellate planktonic stages in the Strait of Georgia, given that motile stages contribute substantially to the spring bloom and achieve greatest abundance in summer (Catell, 1969). This pattern is also consistent with previous results on dinoflagellate cyst production seasonality, where it has been shown that a dinoflagellate bloom is terminated with cyst formation in temperate and cold-temperate environments (Dale, 1976; Heiskanen, 1993; Montresor et al., 1998; Godhe et al., 2001; Tamelander and Heiskanen, 2004).
Cysts produced by autotrophic and heterotrophic dinoflagellates had different seasonal patterns and annual variations in fluxes. Autotrophic taxa - O. centrocarpum, cysts of P. dalei, and Spiniferites spp. - were present in the samples throughout the year (multivoltine reproduction). Although O. centrocarpum and cysts of P. dalei were recorded all year round, the highest flux for O. centrocarpum was recorded at the end of summer and for P. dalei in spring (Fig. 4). Heterotrophic cyst taxa had more temporally restricted production patterns (univoltine reproduction). The most common heterotrophic cyst taxa with fairly regular seasonal patterns were assigned to the following groups: spring taxa - Islandinium? minutum var. cesare; spring and summer taxa - Brigantedinium spp., Q. concreta, Dubridinium spp.; summer taxa - E.
aculeatum, cyst type A; taxa with two peaks in production in fall and spring: P. americanum, E. delicatum, Echinidinium spp., Selenopemphix quanta; winter taxa - S. nephroides (Fig. 4).
32
The cyst taxa that occurred almost always with cell content were cysts of Alexandrium spp., E. aculeatum, E. delicatum, Islandinium? minutum, Islandinium? minutum var. cesare (Fig. 4). In contrast, S. quanta and S. nephroides were found mostly without cell content (Fig. 4). The remaining taxa had varying ratios of cysts with and without cell content. Interpretation of these patterns is limited, as collection intervals were uneven (from 8 to 16 days).
Annual variability of dinoflagellate cyst fluxes contains the imprint of the El Niño 1997-98. Here, 1996 is considered to be a normal year followed by two years impacted by the El Niño 1997-98. In 1997, the Strait of Georgia was characterized by a significantly earlier and higher Fraser River flow (Water Survey of Canada), lower SSS in the summer, and slightly higher SST (Fig. 3). The winter 1997-98 was warm (Foreman et al., 2001), which resulted in noticeable positive deviations in SST (Fig. 3C). Fraser River flow is affected by large-scale climate shifts, as surface air temperature affects snow accumulation and snow melt (Moore, 1991). In 1998 the Fraser River experienced one of the lowest discharges ever recorded due to low snow accumulation during the preceding El Niño winter (Foreman et al., 2001). As a consequence of the low discharge, the summer SSS in 1998 was higher than in 1996 and 1997 (Fig. 3C). Nutrient supply in the Strait of Georgia is affected by variations in Fraser River flows (Harrison et al., 1994) and upwelling (Mackas and Harrison, 1997). Compared to 1996, the total annual dinoflagellate cyst flux in years affected by El Niño decreased by five and three times, in 1997 and 1998, respectively (Table 4). If the bloom of Alexandrium spp. is excluded, the total flux in 1997 was slightly lower than in 1996, followed by a substantial increase in 1998 (Table 4). The total cyst flux completely recovers in 1998, driven mostly by an increase in the production of heterotrophic taxa. This increase is most likely related to the increase in SST and the early warm spring in 1998, resulting in an expanded production season of dinoflagellates and diatoms.
33
The exact linkage between annual changes in dinoflagellate cyst flux at the species level and physical parameters in the Strait is difficult to establish. Phytoplankton production, including dinoflagellates, depends on the number of biotic and abiotic factors such as light, nutrients, salinity, temperature, turbulence, and grazing (Harris, 1986). Moreover, in many cases these factors interact with each other (Harrison et al., 1983) and such interactions become particularly complicated in estuarine systems. Our data yield some insight into this rather complicated issue. Table 5 summarizes main annual trends in cyst fluxes of the most common dinoflagellate cyst taxa. The observed significant drop in the cyst fluxes of Protoperidinium americanum,
Brigantedinium spp., Alexandrium spp., Echinidinum spp., E. aceulatum, E. delicatum, I. minutim, cyst type A and Y during 1997 (Fig. 4, Table 5) could be related to the prolonged
period of reduced SSS (six months with SSS below 25) adversely affecting these taxa. Another factor that might affect phytoplankton is the reduced light penetration related to a many-fold increase in the total sediment flux related to the Fraser River discharge (Harrison et al., 1991). An opposite trend is exhibited by O. centrocarpum, Spiniferites spp. Q. concreta, S. nephroides,
Dubridinium spp., I.? minutum var. cesare, spiny brown cysts and cysts of Polykrikos schwarzii/kofoidii that have an enhanced cyst production during the spring-fall of 1997 (Fig. 4,
Table 5). These taxa are known to be tolerant to lower SSS (Marret and Zonneveld, 2003). Autotrophic taxa Spiniferites spp., cysts of P. dalei and heterotrophic Echinidinium spp., E.
delicatum, S. nephroides, S. quanta and cyst type A exhibit increased production during winter
1997-98 and spring 1998 (Fig. 4, Table 5). The increased flux of these taxa might be associated with increased SST during the prolonged early spring of 1998.
The fluxes of heterotrophic Brigantedinium spp., Q. concreta and cysts of P. americanum have similar patterns with the diatom flux, inferred from the biogenic silica flux (Fig. 3D). Both
