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.     

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.     

A comparison of natural and human determinants of phytoplankton communities in the Kentucky River basin,USA

Physical, chemical, and biological characteristics of the Kentucky River and its tributaries were assessed for one year to compare effects of seasonal, spatial, and human environmental factors on phytoplankton. Phytoplankton cell densities were highest in the fall and summer and lowest in the winter. Cell densities averaged 1162 (± 289 SE) cells m1^–1. Cell densities were positively correlated to water temperature and negatively correlated to dissolved oxygen concentration and to factors associated with high-flow conditions (such as, suspended sediment concentrations). Chrysophytes, diatoms, and blue-green algae dominated winter, spring, and summer assemblages, respectively. Ordination analyses (DCCA) indicated that variation in taxonomic composition of assemblages was associated with stream size as well as season.Spatial variation in phytoplankton assemblages and effects of humans was investigated by sampling 55 sites in low flow conditions during August. Phytoplankton density increased with stream size. Assemblages shifted in composition from those dominated by benthic diatoms upstream to downstream communities dominated by blue-green algae and small flagellates. Human impacts were assumed to cause higher algal densities in stream basins with high proportions of agricultural or urban land use than in basins with forested/mined land use. While density and composition of phytoplankton were positively correlated to agricultural land use, they were poorly correlated to nutrient concentrations. Phytoplankton diversity changed with water quality: decreasing with nutrient enrichment and increasing with conditions that probably changed species composition or inhibited algal growth. Human impacts on phytoplankton in running water ecosystems were as great or greater than effects by natural seasonal and spatial factors. Our results indicated that phytoplankton could be useful indicators of water quality and ecosystem integrity in large river systems.     

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.     

Temporal variation in plankton assemblages and physicochemistry of Devils Lake, North Dakota

Seasonal and annual variation in biomass and structure of algal assemblages of hyposaline Devils Lake were examined in relation to turbidity, ambient concentrations of major ions, trace elements and nutrients, and the standing crop of herbivores. Lake level declined during the early years of study, but rose markedly in subsequent years as historically large volumes of water flowed into this hydrologically-closed basin. Winter algal assemblages were dominated (in biomass) most years by small, non-motile chlorophytes ( Choricystis minor, Kirchneriella lunaris or Dunaliella sp.), or Euglena sp. in the most saline sub-basin. Spring assemblages were dominated by diatoms (Stephanodiscus cf. minutulus, Surirella peisonis, Cyclotella meneghiniana and Entomoneis paludosa were especially prominent) or chlorophytes ( C. minor) until the lake level rose. C. minor abundances then declined in spring assemblages and diatoms ( Stephanodiscus cf. agassizensis and S. niagarae; E. paludosa in the more saline sub-basins) dominated. The potential for nitrogen-deficient conditions for phytoplankton growth was evidenced most summers and early autumns by consistently high concentrations of reactive-P relative to inorganic-N and blooms of the N-fixing cyanophyte Aphanizomenon flos-aquae; Microcystis aeruginosa typically was a co-dominant (>30% of biomass) in these assemblages. Pulses of diatoms ( S. cf. agassizensis and C. meneghiniana) occurred in summers following unusually prolonged periods of calm weather or large water inflows. Physical (irradiance, turbulence) and chemical (major nutrients) variables were the primary factors associated with phytoplankton growth. Transparency and major nutrient concentrations accounted for more of the annual variation in phytoplankton structure than did salinity. Seasonal abundance patterns of the dominant zooplankton (the copepod Diaptomus sicilis; the cladocerans Ceriodaphnia quadrangula, Chydorus sphaericus, Daphnia pulex and Diaphanosoma birgei; and the rotifers Brachionus spp., Filinia longiseta, Keratella cochlearis and K. quadrata) also indicated variation in algal populations related to grazing. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Composition of inorganic and organic nutrient sources influences phytoplankton community structure in the New River Estuary, North Carolina

The New River Estuary, NC, is a nutrient-sensitive, eutrophic water body that is prone to harmful algal blooms. High annual loading from the watershed of varying nutrient forms, including inorganic phosphorus and inorganic and organic nitrogen, may be linked to the persistence of algal blooms in the estuary. In order to evaluate phytoplankton response to nutrient inputs, a series of in situ nutrient addition experiments were carried out during June 2010 to July 2011 on water from an estuarine site known to support algal blooms. Estuarine water was enriched with nutrients consisting of individual and combined sources of dissolved inorganic nitrogen, orthophosphate, urea, and a natural dissolved organic nitrogen (DON) addition derived from upstream New River water. The combined inorganic N and P addition most frequently stimulated phytoplankton biomass production as total chlorophyll a. The responses of diagnostic (of major algal groups) photopigments were also evaluated. Significant increases in peridinin (dinoflagellates), chlorophyll b (chlorophytes), and myxoxanthophyll (cyanobacteria) were most frequently promoted by additions containing riverine DON. Significant increases in zeaxanthin (cyanobacteria) were more frequently promoted by inorganic nitrogen additions, while increases in fucoxanthin (diatoms) and alloxanthin (cryptophytes) were not promoted consistently by any one nutrient treatment. Evaluating the impact of varying nutrient forms on phytoplankton community dynamics is necessary in order to develop strategies to avoid long-term changes in community structure and larger-scale changes in ecosystem condition.     

Dynamics of ice algae and phytoplankton in Frobisher Bay

Summary Vertical and seasonal variations of ice algae and phytoplankton were studied in relation to their physico-chemical environments in Frobisher Bay from 1979 to 1986. The biomass, estimated by both chlorophyll a concentrations and cell counts, was greater in the ice algae than in the phytoplankton in the underlying sea-water during winter and spring. Algal distribution in the sea ice varied vertically and seasonally, while in the underlying water column the phytoplankton distribution was much less variable. The ice algal bloom occurred at the bottom of the ice, particularly in the lower 5 cm during late spring, while the phytoplankton bloom took place at depths between 1 and 10 m during early summer after the ice bloom was over. The community structure of the ice algae changed from pennate to centric diatoms as the ice melted. The centrics dominated through the fall, and then decreased as the pennates increased in dominance when the ice formed again in winter. Species diversity and number were greater in the sea ice than in the seawater, but they were similar vertically within each habitat. The evenness of the species distribution did not vary with ice thickness or water depth. Species composition, abundance and dominance of ice algae and phytoplankton continually change both vertically and seasonally. The differential abilities of the species to attain maximal growth rates under various environmental conditions may result in species succession. Evidence is given for the major role of environmental factors regulating the dynamics of ice algae and phytoplankton.     

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.     

The Effect of Artificial Destratification on Phytoplankton in a Reservoir

The effects of artificial destratification on limnological conditions and on phytoplankton were surveyed for 6 years (1995-2000) in Lake Dalbang (South Korea), a water supply reservoir receiving nutrients from agricultural non-point sources. In order to reduce odor problems caused by cyanobacterial blooms, six aerators were installed in 1996 and operated regularly during the warm season. Aeration destratified the water column of the reservoir and produced homogeneous physical and chemical parameters. The maximum surface temperature in summer decreased from 28.9 °C before aeration to 20.0-26.4 °C after aeration, whereas the maximum hypolimnetic temperature increased from 8.0 to 17.0-23.7 °C. Despite these changes, surface water concentrations of total phosphorus (TP) and chlorophyll a(CHLA) and their seasonal patterns did not change with destratification. Phosphorus loading was concentrated in heavy rain events during the summer monsoon, and TP and CHLA reached maximal concentrations in late summer after the monsoon. Because the hypolimnion was never anoxic prior to aeration, internal loading did not seem to be substantial. Cyanobacteria were the dominant phytoplankton in summer before aeration, but diatoms replaced them after operation of the aerator. Cyanobacteria blooms were eliminated. In contrast, total algal biomass in the water column (as CHLA integrated over depth) increased from 190 mg m^–2 in 1995 to 1150, 300, 170, and 355 mg m^–2 in 1997, 1998, 1999, and 2000, respectively. The increased ratio of mixing depth to euphotic depth to 2.5 may have resulted in a net reduction in the amount of underwater irradiance experienced by phytoplankton cells, and this may have favored the switch to diatom dominance. Furthermore, the mixing may have allowed diatoms to flourish in summer by lowering their settling loss that would be critical in stratified water columns. In conclusion, the destratification in this reservoir was effective in preventing cyanobacteria blooms, but not in reducing the total algal standing crop.     

太湖西北湖区2003-2012年间氮磷浓度及浮游植物主要类群变化趋势分析

基于2003-2012年太湖竺山湖和西部沿岸区水体理化指标与浮游植物丰度的逐月监测数据,分析了两个湖区氮磷营养盐状态和浮游植物丰度以及浮游植物主要类群的年际变化趋势及季节变化特征,探讨了浮游植物群落变化与水温及营养盐指标间的关系。结果表明：10年间两个湖区氮磷营养盐浓度总体呈下降趋势,以竺山湖TN、NH₃-N浓度和西部沿岸区NO₃-N浓度下降最为显著;浮游植物丰度总体呈上升趋势,蓝藻在群落结构中日益占据绝对优势;季节变化上,氮营养盐浓度表现为春冬季节高于夏秋季节,TP浓度和浮游植物丰度呈相反的变化趋势。Pearson相关分析显示,水温、NH₃-N浓度和TN/TP是影响蓝藻丰度及其在浮游植物群落中所占比例的主要因素。在温度和营养盐结构的共同作用下,10年间两个湖区蓝藻水华暴发时间逐渐提前,而消退时间逐渐滞后,水华持续时间逐年上升。在全球变暖背景下,太湖水华治理需执行更加严格的氮磷限制阈值,且在重污染的西北湖区控磷依然是关键。     

Responses of spring phytoplankton communities to their habitats in the Xiangxi Bay of Three Gorges Reservoir,China

Since the water storage was initiated in 2003, the environment of Three Gorges Reservoir (TGR) has changed significantly. Algal blooms and eutrophication have been a frequent occurrence, with serious eutrophication in the tributary bays. To provide some theoretical evidence for the prevention and control of algal blooms, the goal of this study is to elucidate factors that influence algal blooms at different sections of the Xiangxi Bay (XXB). Using field data from the XXB, the responses of phytoplankton communities to their habitats were investigated from March to May, 2010. The results indicated a significant spatial and temporal heterogeneity in phytoplankton composition, cellular abundance, and habitats in the spring. Fifty-four genera representing 6 phyla were monitored. Redundancy analysis indicated that the variation in water temperature and relative water column stability (RWCS) contributed greatly to the succession of spring phytoplankton. Due to different physiological adaptabilities and mechanisms of competition among the algae species, significant succession of the community structure had been observed. The predominant species appears to have changed from those adapted to low temperatures and strong mixing (dinoflagellates and diatoms) to those adapted to high temperatures and weak mixing (green algae and cyanobacteria). The lack of silicate resulted in the succession from diatoms to green algae. Due to the influence of the Yangtze River, there is a low potential for algal blooms at lower reaches of the bay because of frequent water exchange. In contrast, the potential is high at middle and upper reaches where the water temperature increases gradually. The hierarchical status of the two sections is significantly different. Precipitation would inhibit algal blooms somewhat, and heavy rainfall would eliminate algal blooms throughout the bay. Phytoplankton are sensitive to their changing habitat in XXB. For a bloom to occur, sufficient nutrients, a lower flow velocity, and appropriate temperature and light conditions are necessary. As an artificial regulating reservoir, proper ecological regulation could not only significantly affect the dynamic conditions of the water body tributaries, but it could also change the transfer characteristics of light and heat, abolishing the algae habitats and thereby inhibiting the water bloom.     

DO PHYSICAL FACTORS REGULATE PHYTOPLANKTON DISTRIBUTION PATTERNS IN LARGE, SHALLOW LAKES?

Factors that regulate phytoplankton dynamics in shallow, productive lakes are poorly understood, due to their predisposition for frequent algal blooms and sediment resuspension events. In Lake Apopka, greatest phytoplankton biomass reflects wind-induced resuspension of algae (meroplankton) that exists on the aphotic lake bottom in a layer approximately 5 cm thick; this assemblage is dominated by diatoms (>60% of total biomass) that can occur in resting stages. Once exposed to moderate light, meroplankton are capable of growth and photosynthetic rates comparable with surface populations. In Lake Okeechobee, remote sensing was used to assess the basin-wide distribution of suspended particles. Satellite reflectance values agreed well with in situ particle densities at 20 in-lake stations (average r²; LANDSAT = 0.81, AVHRR = 0.53), and maps of algal blooms (r² = 0.79, p ≤ 0.01). The greatest chlorophyll concentrations occurred in the vicinity of tributary nutrient inputs at the lake's perimeter, while turbidity increased towards the center of the lake reflecting predominant water circulation patterns. These results underscore the importance of physical-biological interactions in lakes.     

Seasonal variation in composition and production of planktonic communities in the lower River Rhine

1. The composition and activity of phytoplankton, zooplankton and bacterioplankton in the lower River Rhine were measured in 1990 as part of an international biological inventory of the river. A seasonal study was carried out on two stations: one in the river mouth (km 1019) and one at the German/Dutch border (km 863). 2. High densities of phytoplankton (with up to 140 μg chlorophyll a 1-^?1) and occasional depletion of dissolved silicate were observed at the upstream station. Phosphate concentrations were also lowered during blooms. 3. Phytoplankton blooms, dominated by a few species of centric diatoms, declined one order of magnitude during downstream transport. During non-bloom conditions (low) algal densities were maintained during transport, or increased slightly, indicating the suitability of the river reach for algal growth. 4. Bacterial cell number and production (measured by the ³H-thymidine method) showed a broad summer maximum with activity peaks (0.5 nK < M thymidine h^?1) coincident with declining phytoplankton blooms. Winter values of bacterial production (0.02–0.05 n < Mh^?1) were substantial, probably as a result of allochthonous input of organic matter. 5. Rotifers and crustaceans made up the greater part of the zooplankton biovolume, but at the upstream station the contribution of Dreissena larvae and rhizopods was also substantial. High zooplankton biovolumes, of over 500 × 10⁶μm³1-^?1, were observed only during the phytoplankton spring bloom. 6. Quantitative relationships between the high phytoplankton production (2.1–3.4 gCm^?2 day^?1), the high bacterial substrate uptake (0.5–1gCm^?2 day^?1), and grazing were analysed for the growing season 1990. Algal grazing by metazoan herbivores was substantial only during spring, while the role of phagotrophic microplankton and cell lysis were indicated as major factors responsible for the downstream decline of phytoplankton blooms in the lower Rhine.     

深澳湾浮游植物群落特征及其多样性研究

2007年1月～2008年12月对汕头深澳湾进行的浮游植物周年调查表明,深澳湾共有浮游植物64属178种。其中硅藻为最大的优势类群,共57属154种,占总种数的86.03%;甲藻5属23种;其它浮游植物类群2属2种。2007年和2008年浮游植物总丰度年均值分别为5.47×10⁷ cells·m^-3和2.26×10⁸ cells·m^-3。周年变动模式为单峰型(2007年和2008年的高峰分别位于7月和8月)。2007年和2008年多样性指数与均匀度指数范围分别是0.435～2.490、0.118～0.825和0.211～2.632、0.059～0.820,且夏季的多样性指数和均匀度指数都是最低的。中肋骨条藻Skeletonema costatum是该湾的全年优势种,其2007年和2008年优势指数与优势度年均值分别是55.17%、0.489与68.65%、0.652。中肋骨条藻的绝对占优已在很大程度上改变了该湾浮游植物的群落结构,并使中肋骨条藻赤潮的发生机率大大增加。深澳湾浮游植物的分布与水文、营养盐、滤食生物的摄食等均有一定的关系。     

Successional pattern of phytoplankton (>55 microm) in Lekki lagoon, Nigeria

Lagoons are dominant features along large stretches of the West Africa coast. These freshwater environments are very valuable areas where phytoplankton constitute the basis of aquatic food webs. In order to know the effects of environmental variables on phytoplankton, a study of the successional pattern of phytoplankton in Lekki lagoon was carried out monthly for two years (June 2003-May 2005). Phytoplankton samples were collected from 12 stations using a plankton net of 55 microm mesh, and samples preserved in 4% unbuffered formalin. Besides, surface water samples were taken for physico-chemical analysis. For each year, the seasonal distribution and succession of dominant phytoplankton followed different patterns. Phytoplankton abundance was higher during the dry season (November-April) for the two annual cycles. The diatoms (Aulacoseira granulata and A. granulata var angustissima) and blue green algaes, Microcystis aeruginosa, Merismopedia tennuissima and Trichodesmium lacustre showed this trend by being the abundant species in some of these months. For the rainy season, the green alga Mougeotia sp. dominated. The replacement of one form by another throughout seasonal cycles was probably controlled by the changes in environmental variables such as rainfall, nitrate-nitrogen and phosphate-phosphorus.     

Community-Level and Species-Specific Associations between Phytoplankton and Particle-Associated Vibrio Species in Delaware's Inland Bays

Vibrio species are an abundant and diverse group of bacteria that form associations with phytoplankton. Correlations between Vibrio and phytoplankton abundance have been noted, suggesting that growth is enhanced during algal blooms or that association with phytoplankton provides a refuge from predation. Here, we investigated relationships between particle-associated Vibrio spp. and phytoplankton in Delaware''s inland bays (DIB). The relative abundances of particle-associated Vibrio spp. and algal classes that form blooms in DIB (dinoflagellates, diatoms, and raphidophytes) were determined using quantitative PCR. The results demonstrated a significant correlation between particle-associated Vibrio abundance and phytoplankton, with higher correlations to diatoms and raphidophytes than to dinoflagellates. Species-specific associations were examined during a mixed bloom of Heterosigma akashiwo and Fibrocapsa japonica (Raphidophyceae) and indicated a significant positive correlation for particle-associated Vibrio abundance with H. akashiwo but a negative correlation with F. japonica. Changes in Vibrio assemblages during the bloom were evaluated using automated ribosomal intergenic spacer analysis (ARISA), which revealed significant differences between each size fraction but no significant change in Vibrio assemblages over the course of the bloom. Microzooplankton grazing experiments showed that losses of particle-associated Vibrio spp. may be offset by increased growth in the Vibrio population. Moreover, analysis of Vibrio assemblages by ARISA also indicated an increase in the relative abundance for specific members of the Vibrio community despite higher grazing pressure on the particle-associated population as a whole. The results of this investigation demonstrate links between phytoplankton and Vibrio that may lead to predictions of potential health risks and inform future management practices in this region.     

Strong spatial differentiation of N and P deficiency,primary productivity and community composition between Nyanza Gulf and Lake Victoria (Kenya,East Africa) and the implications for nutrient management

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Winter blooms of centric diatoms in the River Danube and in its side-arms near Budapest (Hungary)

Although the phytoplankton in large eutrophic rivers is often abundant, data on winter populations are scarce. Phytoplankton has been sampled since 1979 in the main arm of the River Danube at Göd (20 km north from Budapest), and also from two side-arms, upstream and downstream of Budapest. Analysis of winter samples has shown high population densities of phytoplankton blooms on several occasions. In general centric diatoms (20 taxa determined) were abundant and dominant during the blooms. The most abundant taxon in November was Stephanodiscus hantzschii f. tenuis, and in February S. minutulus. The most important factors in forming winter blooms of Centrales are rich nutrient supply, slow current speed and high transparency.Massive phytoplankton blooms occurred several times between November and March in the small side-arm at Göd. In the large side-arm downstream of Budapest (Soroksári-Dung) large blooms of centric diatoms were found in winter (often under ice, which was covered by snow in many cases). Here S. hantzschii f. tenuis and S. minutulus were the most abundant species.     

Coupling of autotrophic and heterotrophic processes in a Baltic estuarine mixing gradient (Pomeranian Bight)

This paper presents the results of a long-term survey of the hydrography, nutrients and phytoplankton in Tolo Harbour carried out between 1982 and 1992. Some nutrients such as total inorganic nitrogen, ammonia and total phosphorus increased during the 10 year period, but chlorophyll a, which indicated algal biomass, did not show an increasing trend. The phytoplankton of Tolo Harbour consisted largely of diatoms. Dinoflagellates and minor algal groups such as cryptomonads and small flagellates constituted a smaller fraction of the phytoplankton population. Densities of diatoms and minor algal groups increased in some stations, but the density of dinoflagellates remained relatively unchanged during the study period. Most nutrient variables were negatively correlated with densities of diatom and total phytoplankton, and positively correlated with densities of minor algal groups. While dinoflagellate densities were positively correlated with total nitrogen in some stations, no correlation existed between dinoflagellate density and most of the nutrient variables. Our results show that there is a gradual change in phytoplankton community in Tolo Harbour,most notably in the nutrient-rich inner harbour waters, with the smaller algae assuming increasing abundance. Thus there was a net increase in density of total phytoplankton even though chlorophyll a concentrations did not increase. No evidence was found in this study to show that increased nutrient loading would inevitably lead to increase in densities of dinoflagellates in Tolo Harbour. Instead, dinoflagellate densities showed stronger correlations with physical variables such as temperature, pH and salinity. This revised version was published online in August 2006 with corrections to the Cover Date.