Comparative composition and dynamics of harmful dinoflagellates in Mediterranean salt marshes and nearby external marine waters

The taxonomic structure of phytoplankton populations in two Mediterranean coastal lagoons were compared with those of nearby marine waters (external waters). Mediterranean confined lagoons remain isolated for most the year and concentrate phytoplankton to a very high biomass. Coastal lagoons on the Mediterranean may, therefore, act as accumulators of neritic phytoplankton (including species related to harmful algal blooms). We examined whether coastal lagoons act as concentrators of marine toxic dinoflagellates during confinement periods, and the common environmental factors that favour growth of specific harmful species in the two ecosystems considered: coastal lagoons and external waters. An alternation between the dominance of diatoms and dinoflagellates was observed, coinciding with that described in Margalef's mandala, occurring in external waters as well as in coastal lagoons. Moreover, the temporal patter was different in the two ecosystems. Dinoflagellate species composition and their bloom period were highly variable in time and space, thus, species had to be analysed individually. Most of the dinoflagellate species found in this study were potentially harmful and high biomass producers. Harmful dinoflagellate species performed well in both, external waters and lagoons, but the specific species-dependent affinity to each of these environments determined which organisms bloom there. Thus, expansion of harmful algal blooms (HAB) to inland waters is not likely and some environmental factors such as the oxidised state of available nitrogen, became determinant to the success and bloom of a species in the coastal lagoon ecosystem.     

Winter condition of marine plankton populations in Saanich inlet,B.C., canada. I. Phytoplankton and its surrounding environment

Weekly sampling was carried out in Saanich Inlet, British Columbia throughout the winter of 1975–1976. The surface water column was characterized by exposure to low solar radiation energy (<150 g cal·cm^?2 · day^?1), slight stratification with occasional vertical mixing, and abundant algal nutrients. Phytoplankton were mostly distributed above 5 m in the water column, with a fairly low biomass averaging <1 μgchla·1^?1. Dominant phytoplankton organisms were nanoflagellates occasionally accompanied by dinoflagellates as the second dominant. Centric diatoms, which were dominant in the blooms, were always present but less than a few percentage of the total phytoplankton biomass. Daily photosynthetic productivity was exclusively limited by available radiant energy. Low solar radiation and occasional mixing of the surface zone prohibited the centric diatoms from becoming dominant.     

The effects of nutrients and their ratios on phytoplankton abundance in Junk Bay,Hong Kong

Eutrophication has been considered to be undoubtedly one of the key factors stimulating phytoplankton growth, since it involves the enrichment of a water mass with both inorganic and organic nutrients supporting plant growth. Nutrient enrichment as a result of anthropogenic activity occurs in estuaries and coastal waters as well as in lakes and freshwater impoundments, and blooms of phytoplankton are one of the effects of such an accelerated process of nutrient enrichment. This paper presents the results of a two-year survey of the nutrients and phytoplankton at 3 stations in Junk Bay, Hong Kong, carried out from 1997 to 1998. The relationships between nitrogen, phosphorus, and their ratio, with phytoplankton abundance have been studied. The results show that the highest nitrogen concentration was in Station 2 which is close to a sewage input, whereas the highest phosphorus concentration was in Station 1 which is close to a landfill area. The mean N:P ratios at the three stations were between 8 and 14. The diatoms were the dominant group during most of the year but it seems that diatoms were more sensitive than dinoflagellates and other algal groups to the increase in nutrients.     

Year-to-year variation in the occurrence of some dominant phytoplankton species in Dutch coastal waters, 1973–1984

The surface water layer of a 70 km wide area along the Dutch coast has been sampled monthly from (February) 1973 to (August) 1984, as part of a water quality assessment research. The blooming periods of phytoplankton algae studied, fluctuated from year-to-year, but diatom blooms increased in length in the late 1970s. Dinoflagellates decreased in cell numbers in the same period. The observation of highest cell numbers of some diatoms and dinoflagellates in the lower salinity near coastal waters can be explained by eutrophication effects.     

Decadal-scale changes of dinoflagellates and diatoms in the anomalous baltic sea spring bloom

The algal spring bloom in the Baltic Sea represents an anomaly from the winter-spring bloom patterns worldwide in terms of frequent and recurring dominance of dinoflagellates over diatoms. Analysis of approximately 3500 spring bloom samples from the Baltic Sea monitoring programs revealed (i) that within the major basins the proportion of dinoflagellates varied from 0.1 (Kattegat) to >0.8 (central Baltic Proper), and (ii) substantial shifts (e.g. from 0.2 to 0.6 in the Gulf of Finland) in the dinoflagellate proportion over four decades. During a recent decade (1995-2004) the proportion of dinoflagellates increased relative to diatoms mostly in the northernmost basins (Gulf of Bothnia, from 0.1 to 0.4) and in the Gulf of Finland, (0.4 to 0.6) which are typically ice-covered areas. We hypothesize that in coastal areas a specific sequence of seasonal events, involving wintertime mixing and resuspension of benthic cysts, followed by proliferation in stratified thin layers under melting ice, favors successful seeding and accumulation of dense dinoflagellate populations over diatoms. This head-start of dinoflagellates by the onset of the spring bloom is decisive for successful competition with the faster growing diatoms. Massive cyst formation and spreading of cyst beds fuel the expanding and ever larger dinoflagellate blooms in the relatively shallow coastal waters. Shifts in the dominant spring bloom algal groups can have significant effects on major elemental fluxes and functioning of the Baltic Sea ecosystem, but also in the vast shelves and estuaries at high latitudes, where ice-associated cold-water dinoflagellates successfully compete with diatoms.     

Structure of the summer under fast ice microbial community near Syowa Station,eastern Antarctica

Temporal variations in the microbial community structure of plankton, which is composed of autotrophic and heterotrophic pico-, nano- and microplankton, were investigated during the austral summer of 2005/2006 under fast ice near Syowa Station, eastern Antarctica. Autotrophic algal populations were composed almost entirely of diatoms followed by phytoflagellates such as autotrophic dinoflagellates and cryptophytes. Among the microbial community, heterotrophic biomass was dominated by heterotrophic dinoflagellates and naked ciliates and finally exceeded autotrophic biomass. Qualitative microscopic analysis revealed that heterotrophic dinoflagellates were ingesting large number of diatoms. Synchronizing fluctuation of naked ciliates with phytoflagellates suggested a predator–prey relationship between them. Our results suggest that the pelagic food webs under the extensive ice-covered areas in coastal Antarctic regions are not short but complex.     

大亚湾澳头水域浮游植物群落结构及周年数量动态

对1997年至1998年广东省大亚湾澳头水域的浮游植物群落进行调查和分析。结果发现浮游植物65属198种;硅藻在种类组成和数量上都比甲藻占有优势,存在春季和秋季高峰,主要优势类群依次是角毛藻、骨条藻、拟菱形藻等;甲藻只存在春季高峰,代表种类有裸甲藻、原甲藻等。主要优势种类的生长与调查水域的盐度没有明显关系,但全年水温的季节性变化对优势种类的消长影响显著。Simpson多样性指数、Shannon-Weaver多样性指数、均匀度的年平均值分别是0.611、2.107、0.557,多样性指数没有明显的季节变化规律和水平分布规律。       

Downwelling and dominance of autochthonous dinoflagellates in the NW Iberian margin: The example of the Ría de Vigo

Dinoflagellate blooms in coastal upwelling systems are restricted to times and places with reduced exchange and mixing. The Rías Baixas of Galicia are four bays in the NW Iberian upwelling with these characteristics where harmful algal blooms (HABs) of dinoflagellates are common. These blooms are especially recurrent at the end of the upwelling season, when autumn downwelling amplifies accumulation and retention through the development of a convergence front in the interior of Rías. Because oceanic water enters the Rías during downwelling, it has been hypothesised that dinoflagellate blooms originate by the advection and subsequent accumulation of allochthonous populations. To examine this possibility, we studied the microplankton succession in relation to hydrographic variability in the Ría de Vigo (one of these four bays) along an annual cycle making use of a high sampling frequency. The results indicated that upwelling lasted from May to August, with downwelling prevailing in winter. Microplankton during upwelling, although dominated by diatoms, evidenced a progressive increase in the importance of dinoflagellates, which achieved maximum abundance at the end of the upwelling season. Thus, diatoms characterised the spring bloom, while diatoms and autochthonous dinoflagellates composed the autumn bloom. Diatoms dominated during the first moments of the autumn downwelling and dinoflagellates were more abundant later, after stronger downwelling removed diatoms from the water column. Since the dinoflagellates selected by downwelling belonged to the local community, it is concluded that advection of alien populations is not required to explain these autumn blooms.     

A global satellite observation of phytoplankton taxonomic groups over the past two decades

Marine phytoplankton fuel the oceanic biotic chain, determine the carbon sequestration levels, and are crucial for the global carbon cycle and climate change. In the present study, we show a near-two-decadal (2002–2022) spatiotemporal distribution of global phytoplankton abundance, proxy as dominant phytoplankton taxonomic groups (PTGs), with a newly developed remote sensing model. Globally, six chief PTGs, namely chlorophytes (~26%), diatoms (~24%), haptophytes (~15%), cryptophytes (~10%), cyanobacteria (~8%), and dinoflagellates (~3%), explain most of the variation (~86%) in phytoplankton assemblages. Spatially, diatoms generally dominate high latitudes, marginal seas, and coastal upwelling zones, whereas chlorophytes and haptophytes control the open oceans. Satellite observations reveal a gentle multi-annual trend of the PTGs in the major oceans, indicative of roughly “unchanged” conditions on the total biomass or compositions of the phytoplankton community. Jointly, “changed” status applies to a short-term (seasonal) timescale: (1) Fluctuations of PTGs exhibit different amplitudes among different subregions, together with a general rule-more intense vibration in the Northern Hemisphere and polar oceans than other zones; (2) diatoms and haptophytes vary more dramatically than other PTGs in a global-scale scope. These findings provide a clear picture of the global phytoplankton community composition and can improve our understanding of their state and further analysis of marine biological processes.     

The role of phytoplankton diversity metrics in shallow lake and river quality assessment

Ecological water quality problems are frequently connected to increment of phytoplankton productivity and overdominance of some phytoplankton species. Metrics that show monotonously increasing or decreasing tendencies along stressor gradients is recommended for ecological state assessment. Diversity metrics are influenced by various physical disturbances and show high within-year variability; thus, there is no agreement on the usefulness of these metrics as state indicators.To test the usefulness of phytoplankton diversity in ecological state assessment we investigated the productivity–diversity relationships for lakes and rivers in the Carpathian Basin (Hungary). We demonstrated that the shape of productivity–diversity relationship depends on the investigated water body type. Regarding lakes, hump-shaped relationship was found for all computed metrics. Parallel with the increase in phytoplankton productivity values, diversity metrics showed monotonously increasing tendencies in rhithral and decreasing tendencies in large potamal rivers. We found no systematic relationship in the case of small lowland rivers.Changes of diversity metrics calculated for species and functional groups showed similar tendencies within the types, only the slopes of regression lines differ each other.The use of diversity metrics as ecological state indicators should be restricted to water body types where diversity decreases or increases monotonously with phytoplankton biomass. Regarding the lakes the use of diversity metrics is not recommended for ecological state assessment. In rhithral and large potamal river assessment, application of diversity metrics should be strongly considered. We demonstrated that diversity metrics can be useful components of multimetric indices proposed to use by the Water Framework Directive.     

Carbon:chlorophyll <Emphasis Type="Italic">a</Emphasis> ratio,assimilation numbers and turnover times of Lake Kinneret phytoplankton

Carbon to chlorophyll a (C:Chl) ratios, assimilation numbers (A.N.) and turnover times of natural populations of individual species and taxonomic groups were extracted from a long-term database of phytoplankton wet-weight biomass, chlorophyll a concentrations, and primary production in Lake Kinneret, Israel. From a database spanning more than a decade, we selected data for samples dominated by a single species or taxonomic group. The overall average of C:Chl was highest for cyanophytes and lowest for diatoms, while chlorophytes and dinoflagellates showed intermediate values. When converting chlorophyll a to algal cellular carbon this variability should be taken into account. The variability in C:Chl within each phylum and species (when data were available) was high and the variability at any particular sampling date tended to be greater than the temporal variability. The average chlorophyll a-normalized rate of photosynthetic activity of cyanophytes was higher and that of the dinoflagellates lower than that of other phyla. Turnover time of phytoplankton, calculated using primary productivity data at the depth of maximal photosynthetic rate, was longest in dinoflagellates and shortest in cyanophytes, with diatoms and chlorophytes showing intermediate values. The more extreme C:Chl and turnover times of dinoflagellates and cyanobacteria in comparison with chlorophytes and diatoms should be taken into consideration when employed in ecological modeling.     

Seasonal phytoplankton responses to N:Si:P enrichment ratio in the Bizerte Lagoon (southwestern Mediterranean)

This study investigated the role of N, P and Si enrichments on phytoplankton in the Bizerte Lagoon (southwestern Mediterranean Sea, Tunisia) during March, June, August, October and December 2004. Polycarbonate bottles were enriched with different nutrients according to four treatments N:Si:P ratios [+NSi/-P (40:40:1), +P/-NSi (20:20:2,5), +NP/-Si (16:0:1) and +Si/-NP (16:32:1)] and incubated in situ during six days. Chl a and carbon biomass of phytoplankton varied significantly during the course of months, with the highest levels recorded in summer (4-4.4 microg Chl a L(-1) or 1126-1721 microg C L(-1)). Dinoflagellates dominated the initial phytoplankton communities, except in August, when diatoms represented a high fraction of microalgae (48%). Enrichment experiments induced significant increases in Chl a and in the final phytoplankton carbon biomasses. In summer (June/August), Si was the main limiting element for phytoplankton. Diatoms strongly responded to +Si/-NP and +NSi/-P enrichments and dominated the final phytoplankton communities (52-61%) in both treatments. Si played the most important role in the growth and development of diatoms. The biomasses and growth rates of dinoflagellates were significantly stimulated by +P/-NSi and +NP/-Si enrichments. After 6 days, dinoflagellates represented more than 70% of the total phytoplankton biomass in samples subjected to these treatments. Moreover, the addition of +P/-NSi increased the biomasses of several dinoflagellates. This suggests that dinoflagellates were mostly controlled by P availability. Unlike diatoms and dinoflagellates, flagellates showed weak responses to nutrient treatments during only some months of the year. The results showed that phytoplankton dynamics in the lagoon were influenced by nutrients in different manners.     

Temporal dynamics of estuarine phytoplankton: A case study of San Francisco Bay

Detailed surveys throughout San Francisco Bay over an annual cycle (1980) show that seasonal variations of phytoplankton biomass, community composition, and productivity can differ markedly among estuarine habitat types. For example, in the river-dominated northern reach (Suisun Bay) phytoplankton seasonality is characterized by a prolonged summer bloom of netplanktonic diatoms that results from the accumulation of suspended particulates at the convergence of nontidal currents (i.e. where residence time is long). Here turbidity is persistently high such that phytoplankton growth and productivity are severely limited by light availability, the phytoplankton population turns over slowly, and biological processes appear to be less important mechanisms of temporal change than physical processes associated with freshwater inflow and turbulent mixing. The South Bay, in contrast, is a lagoon-type estuary less directly coupled to the influence of river discharge. Residence time is long (months) in this estuary, turbidity is lower and estimated rates of population growth are high (up to 1–2 doublings d^–1), but the rapid production of phytoplankton biomass is presumably balanced by grazing losses to benthic herbivores. Exceptions occur for brief intervals (days to weeks) during spring when the water column stratifies so that algae retained in the surface layer are uncoupled from benthic grazing, and phytoplankton blooms develop. The degree of stratification varies over the neap-spring tidal cycle, so the South Bay represents an estuary where (1) biological processes (growth, grazing) and a physical process (vertical mixing) interact to cause temporal variability of phytoplankton biomass, and (2) temporal variability is highly dynamic because of the short-term variability of tides. Other mechanisms of temporal variability in estuarine phytoplankton include: zooplankton grazing, exchanges of microalgae between the sediment and water column, and horizontal dispersion which transports phytoplankton from regions of high productivity (shallows) to regions of low productivity (deep channels).Multi-year records of phytoplankton biomass show that large deviations from the typical annual cycles observed in 1980 can occur, and that interannual variability is driven by variability of annual precipitation and river discharge. Here, too, the nature of this variability differs among estuary types. Blooms occur only in the northern reach when river discharge falls within a narrow range, and the summer biomass increase was absent during years of extreme drought (1977) or years of exceptionally high discharge (1982). In South Bay, however, there is a direct relationship between phytoplankton biomass and river discharge. As discharge increases so does the buoyancy input required for density stratification, and wet years are characterized by persistent and intense spring blooms.     

Phytoplankton distribution and production along a wide environmental gradient in the South-West Atlantic off Uruguay

We investigated phytoplankton biomass, assemblage structure and production along an environmental gradient to evaluate if chlorophyll-a (as proxy for biomass) and primary production peaked under conditions hypothesised to favour phytoplankton growth. During Spring 2003, a wide area from shallow estuarine waters to the shelf slope off the Río de la Plata was sampled and routine measurements included CTD profiles, nutrients, chlorophyll-a, phytoplankton composition and abundance, seston and organic matter loads, downwelling light and, at selected stations, production versus irradiance experiments. Spatial differences in abiotic variables suggested distinct hydrographic zones that differed in phytoplankton biomass and productivity. Chlorophyll-a was highest under estuarine influence and peaked at low salinity when strong stratification developed in the outer estuary, and was minimum at the shelf break and slope. In that area, however, relatively high chlorophyll-a was associated to oceanographic fronts and to the occurrence of Sub Antarctic water within the photic depth range. Productivity was maximum in shallow waters, but biomass-specific productivity peaked at the outer shelf in oceanographic fronts or in upwelled Sub Antarctic waters. Over shelf and slope waters productivity and biomass were not tightly coupled, as indicated by situations of high biomass and low productivity (Station 9), low biomass and high productivity (Station 10), or both high biomass and productivity (Station 22). Ordination analysis of phytoplankton taxa suggested that assemblages changed gradually along the environmental gradient and correlated to abiotic variables defining geographic zones. Overall results were consistent with an interpretation that phytoplankton biomass and growth were modulated by light in estuarine and coastal waters, and by hydrographic processes on the continental shelf and slope. Handling editor: Luigi Naselli-Flores     

Responses of Phyto- and Zooplankton Communities to Prymnesium polylepis (Prymnesiales) Bloom in the Baltic Sea

A large bloom of Prymnesium polylepis occurred in the Baltic Sea during the winter 2007 – spring 2008. Based on numerous reports of strong allelopathic effects on phytoplankton exerted by P. polylepis and its toxicity to grazers, we hypothesized that during this period negative correlations will be observed between P. polylepis and (1) main phytoplankton groups contributing to the spring bloom (i.e., diatoms and dinoflagellates), and (2) zooplankton growth and abundance. To test these hypotheses, we analyzed inter-annual variability in phytoplankton and zooplankton dynamics as well as growth indices (RNA∶DNA ratio) in dominant zooplankton in relation to the Prymnesium abundance and biomass. Contrary to the hypothesized relationships, no measurable negative responses to P. polylepis were observed for either the total phytoplankton stocks or the zooplankton community. The only negative response, possibly associated with P. polylepis occurrence, was significantly lower abundance of dinoflagellates both during and after the bloom in 2008. Moreover, contrary to the expected negative effects, there were significantly higher total phytoplankton abundance as well as significantly higher winter abundance and winter-spring RNA∶DNA ratio in dominant zooplankton species in 2008, indicating that P. polylepis bloom coincided with favourable feeding conditions for zooplankton. Thus, primary consumers, and consequently also zooplanktivores (e.g., larval fish and mysids), may benefit from haptophyte blooms, particularly in winter, when phytoplankton is scarce.     

Phytoplankton structure in the White Sea after summer bloom: Spatial variability in relation to hydrophysical conditions

The species composition and phytoplankton biomass, concentrations of chlorophyll “a” (Chl) and nutrients, concurrent hydrophysical conditions were studied in the south part of the White Sea in July 10–15, 2012 during chlorophyll “a” decrease after summer peak. The water column stability varied, the concentration of dissolved silicon in upper mixed layer was closed to the range favorable for diatoms with exception of areas of intensive tide mixing and areas influenced by waters of Severnaya Dvina River. In surface layer the dinoflagellates dominated excepting of areas with intensive tide mixing where diatoms prevailed. Diatoms provided major contribution to biomass in different stations above, in and under pycnocline and in deep waters out of photic zone. Structural analysis has revealed three phytoplankton communities that corresponded to different depths: communities of photic zone, intermediate and deep layers. Extension of layers inhabited by different communities depended on water column stability and on genesis of water masses. Integrated values of phytoplankton biomass and Chl varied from 250 to 1188 mg С/m², and from 22 to 51 mg/m², correspondently.     

Influence of water-column stability on phytoplankton size and biomass succession patterns in the central Cantabrian Sea (Bay of Biscay)

The seasonal cycle of phytoplankton biomass in the CantabrianSea (Bay of Biscay) is characterized by peaks produced duringthe spring blooms, as in most temperate seas. Although stratificationand light intensity variabilities were high throughout the year,only a small range of low water-column stability and light intensitywas associated with the biomass maximum. Out of this range,accumulations of biomass would be limited primarily by highturbulence and low light intensities in winter, and low nutrientconcentrations, sedimentation and grazing in summer. Associatedwith these periods six seasonal stages have been identifiedusing particle size distributions (PSD). These stages correspondedto three different spring types, and summer, fall and wintertypes. Most of the variability of the PSD was associated withthe maximum of biomass during the spring blooms. During theseblooms the distributions were dominated either by small, largeor by several sizes of particles. In summer the PSD were polymodal,while in winter the biomass was uniformly distributed withinthe considered particle size range. The transition between PSD types was paralleled by similar changesin phytoplankton species composition. The seasonal cycle ofphytoplankton species abundance was characterized by the alternanceof diatoms in water-mixing periods and dinoflagellates in stratificationperiods. However, microflagellates were abundant in diverseconditions throughout the year. As a result of microflagellateabundance and the formation of cell chains and aggregates, particlesize composition during the bloom period resulted largely unpredictableusing water-column stability data.     

Lipid biomarkers and trophic linkages between phytoplankton, zooplankton and anchovy (Engraulis encrasicolus) larvae in the NW Mediterranean

Identification and quantification of the main fatty acids inphytoplankton, zooplankton and Engraulis encrasicolus larvaewere used to study the relationship among the different trophiclevels. Three northwestern Mediterranean sea areas were studiedas representative of potentially heterogeneous environments.HPLC pigment analysis was performed to assess the contributionof different phytoplankton groups to total chlorophyll biomass.In spite of the physical variability, a homogeneous patternin phytoplankton composition among areas was found, with thePrymnesiophyceae representing more than half of the phytoplanktonchlorophyll biomass. This homogeneous spatial pattern was alsoreflected in the phytoplankton fatty acid proportions. Thus,significant amount of 14:0, 18:1(n-9) and 18:4(n-3) could berelated to the dominance of the prymnesiophytes; the low proportionof fatty acid markers of diatoms and dinoflagellates agreedwith the low abundances of those phytoplankton groups. Zooplanktonfatty acids also showed homogeneous proportions in the studiedareas, with a preferential accumulation of 16:1(n-7) and 20:5(n-3),and 22:6(n-3). This observation may indicate a preferentialgrazing on diatoms and dinoflagellates. Anchovy larvae displayeddiffering fatty acids contributions related to size. Large larvaecontained a higher proportion of polyunsaturated fatty acid(PUFA). Small larvae showed a high percentage of 18:1(n-9) and18:4(n-3) fatty acids, considered Prymnesiophyceae biomarkers.These results suggest an additional food resource for the anchovythat is complementary to a zooplankton diet, but probably ofprotozoan origin (i.e. microzooplankton). Significant logarithmicrelationships were found between dry mass and 20:5(n-3) and22:6(n-3) fatty acid proportions in E. encrasicolus larvae.These PUFA are considered essential for the fish-larvae development.     

Nutrient and phytoplankton dynamics in the Queen Charlotte Islands (Canada) during the summer upwelling seasons of 2001-2002

The Queen Charlotte Islands, Canada, lie at the northern extremeof the coastal upwelling system of the eastern North PacificOcean (51–54°N). In this study, the first observationsof spatial and inter-annual patterns in nutrient inventories,chlorophyll (Chl) a and phytoplankton assemblages are reportedand related to oceanographic conditions in near-shore watersof the island archipelago. Stronger and more persistent upwellingin 2002 coincided with higher nutrient and Chl a standing stockscompared to 2001 and a higher proportion of diatoms. Dinoflagellateswere more prevalent in 2001, including several potentially harmfulspecies. At sub-seasonal scales, Chl a concentrations were greatestduring downwelling conditions and smallest during upwellingconditions. On the west coast, weak water column stratification,high relative proportions of diatoms and large nutrient inventoriesaccompanied upwelling-favourable conditions, whereas on theeast coast, there was no direct relationship between the BakunUpwelling Index and water column stability. According to redundancyanalysis, variability in species composition was best explainedby sea surface temperature, the depth of the euphotic zone andnutrient inventories. The east coast supported blooms of coccolithophoreswithin protected bays, confirming previous satellite observationsthat showed bright patches in these areas. The data illustratethat moderate upwelling can have an important influence on near-shorealgal standing stocks and species composition at the northernextreme of the upwelling system off the west coast of NorthAmerica, and that topographical complexity may be importantfor the development of phytoplankton blooms.     

Taxonomy and palaeoecology of dinoflagellate cysts from Upper Oligocene freshwater sediments of Lake Enspel, Westerwald area, Germany

Freshwater dinoflagellates play an important role as primary producers in the lacustrine environment. A new species of dinoflagellates, Cleistosphaeridium lacustre, is described from Upper Oligocene sediments of palaeo-lake Enspel. They are associated with other phytoplankton, such as diatoms, chrysophytes, green algae and benthic cyanobacteria. Mass occurrences of this species are interpreted as algal blooms and may partly reflect seasonal successions. This phenomenon was controlled by volcanic activities in the depositional area, which led to an increase in nutrient supply.