Winter Phytoplankton Communities Research Articles

Community Structure and Toxicity Potential of Cyanobacteria during Summer and Winter in a Temperate-Zone Lake Susceptible to Phytoplankton Blooms.

Cyanobacterial blooms are increasingly common during winters, especially when they are mild. The goal of this study was to determine the summer and winter phytoplankton community structure, cyanotoxin presence, and toxigenicity in a eutrophic lake susceptible to cyanobacterial blooms throughout the year, using classical microscopy, an analysis of toxic cyanometabolites, and an analysis of genes involved in biosynthesis of cyanotoxins. We also assessed whether cyanobacterial diversity in the studied lake has changed compared to what was reported in previous reports conducted several years ago. Moreover, the bloom-forming cyanobacterial strains were isolated from the lake and screened for cyanotoxin presence and toxigenicity. Cyanobacteria were the main component of the phytoplankton community in both sampling times, and, in particular, Oscillatoriales were predominant in both summer (Planktothrix/Limnothrix) and winter (Limnothrix) sampling. Compared to the winter community, the summer community was denser; richer in species; and contained alien and invasive Nostocales, including Sphaerospermopsis aphanizomenoides, Raphidiopsis raciborskii, and Raphidiopsis mediterranea. In both sampling times, the blooms contained toxigenic species with genetic determinants for the production of cylindrospermopsin and microcystins. Toxicological screening revealed the presence of microcystins in the lake in summer but no cyanotoxins in the winter period of sampling. However, several cyanobacterial strains isolated from the lake during winter and summer produced anabaenopeptins and microcystins. This study indicates that summer and winter blooms of cyanobacteria in the temperate zone can differ in biomass, structure, and toxicity, and that the toxic hazards associated with cyanobacterial blooms may potentially exist during winter.

Phytoplankton Community Patterns in the Northeastern South China Sea: Implications of Intensified Kuroshio Intrusion During the 2015/16 El Niño

AbstractKuroshio intrusion into the South China Sea (SCS) varies seasonally and interannually under different climatic conditions. To characterize the intensity of the climate‐driven Kuroshio intrusion and its impact on the phytoplankton community in the northeastern South China Sea (NESCS), two cruises were conducted during the 2015/16 El Niño event. In situ observations and remote sensing data showed that the Kuroshio strongly intruded into the SCS in both summer and winter. The summer phytoplankton community was dominated by cyanobacteria (Trichodesmium erythraeum), associated with high surface temperature, shallower mixed layer depth, and low nutrient concentrations. The winter phytoplankton community was mainly dominated by cosmopolitan diatoms (Thalassiosira diporocyclus, Thalassionema nitzschioides, and Chaetoceros socialis), associated with low surface temperature, deeper mixed layers, and relatively higher nutrient concentrations. Meanwhile, the elevated abundance of T. erythraeum coupled well with the Kuroshio intrusion index during the El Niño summer. The phytoplankton network was unstable in summer but not in winter, induced by the Kuroshio intrusion. Our findings show that intensified Kuroshio intrusion during the El Niño event was a vital driving force for reshaping phytoplankton community dynamics of the NESCS through lateral advection and affecting temperature, mixed layer depth, and nutrient supply.

Small phytoplankton dominate western North Atlantic biomass

The North Atlantic phytoplankton spring bloom is the pinnacle in an annual cycle that is driven by physical, chemical, and biological seasonality. Despite its important contributions to the global carbon cycle, transitions in plankton community composition between the winter and spring have been scarcely examined in the North Atlantic. Phytoplankton composition in early winter was compared with latitudinal transects that captured the subsequent spring bloom climax. Amplicon sequence variants (ASVs), imaging flow cytometry, and flow-cytometry provided a synoptic view of phytoplankton diversity. Phytoplankton communities were not uniform across the sites studied, but rather mapped with apparent fidelity onto subpolar- and subtropical-influenced water masses of the North Atlantic. At most stations, cells < 20-µm diameter were the main contributors to phytoplankton biomass. Winter phytoplankton communities were dominated by cyanobacteria and pico-phytoeukaryotes. These transitioned to more diverse and dynamic spring communities in which pico- and nano-phytoeukaryotes, including many prasinophyte algae, dominated. Diatoms, which are often assumed to be the dominant phytoplankton in blooms, were contributors but not the major component of biomass. We show that diverse, small phytoplankton taxa are unexpectedly common in the western North Atlantic and that regional influences play a large role in modulating community transitions during the seasonal progression of blooms.

Key Drivers of Seasonal Plankton Dynamics in Cyclonic and Anticyclonic Eddies off East Australia

Mesoscale eddies in the south west Pacific region are prominent ocean features that represent distinctive environments for phytoplankton. Here we examine the seasonal plankton dynamics associated with averaged cyclonic and anticyclonic eddies (CE and ACE, respectively) off eastern Australia. We do this through building seasonal climatologies of mixed layer depth and surface chlorophyll-a for both CE and ACE by combining remotely sensed sea surface height (TOPEX/Poseidon, Envisat, Jason-1, and OSTM/Jason-2), remotely sensed ocean colour (GlobColour) and in situ profiles of temperature, salinity and pressure from Argo floats. Using the CE and ACE seasonal climatologies, we assimilate the surface chlorophyll-a data into both a single (WOMBAT), and multi-phytoplankton class (EMS) biogeochemical model to investigate the level of complexity required to simulate the phytoplankton chlorophyll-a. For the two eddy types, the data assimilation showed both biogeochemical models only needed one set of parameters to represent phytoplankton but needed different parameters for zooplankton. To assess the simulated phytoplankton behavior we compared EMS model simulations with a ship-based experiment that involved incubating a winter phytoplankton community sampled from below the mixed layer under ambient and two higher light intensities with and without nutrient enrichment. By the end of the 5-day field experiment, large diatom abundance was four times greater in all treatments compared to the initial community, with a corresponding decline in pico-cyanobacteria. The experimental results were consistent with the simulated behavior in CE and ACE, where the seasonal deepening of the mixed layer during winter produced a rapid increase in large phytoplankton. Our model simulations suggest that CE off East Australia are not only characterized by a higher chlorophyll-a concentration compared to ACE, but also by a higher concentration of large phytoplankton (i.e. diatoms) due to the shallower CE mixed layer. The model simulations also suggest the zooplankton community is different in the two eddy types and this behavior needs further investigation.

Phytoplankton composition under contrasting oceanographic conditions: Upwelling and downwelling (Eastern Australia)

Phytoplankton abundance and distribution along the east coast of Australia are driven primarily by the southward flowing East Australian Current (EAC), which transports tropical water masses to temperate latitudes. The Solitary Islands Marine Park (SIMP, ~30°S) is located north of the EAC separation point (~32°S) in this tropical–temperate transition zone. In this study, we describe the oceanographic context (wind, current and nutrient load) during a wind-driven downwelling and a current-driven upwelling event, both sampled in austral winter only ten days apart. We investigate the effect of these contrasting oceanographic conditions on phytoplankton abundance, composition and distribution along a cross-shelf transect. During downwelling we find a cross-shelf transition in microphytoplankton composition from an offshore- to an inshore-community associated with nutrient gradients (nitrate and silicate). Strong vertical mixing leads to increased occurrences of benthic diatoms in near-shore surface waters. During upwelling conditions, elevated nutrient availability results in maximum microphytoplankton abundances (mainly oceanic diatoms) and increased species richness on the mid-shelf. An increase in dinoflagellates and silicoflagellates (mid-shelf) and the appearance of tropical phytoplankton (especially picoplankton and dinoflagellates, offshore) signals a strong impact of the EAC across all shelf communities. Nanoplankton are a major part of the winter phytoplankton community during both oceanographic regimes (~40–50% of TChl a). Our findings provide evidence of EAC-driven, nutrient-rich, slope water intrusion in the SIMP as expressed by cross-shelf phytoplankton variability. We suggest that rapid (~weekly) changes in phytoplankton composition along the east Australian coast are likely to be enhanced by the climate change-induced warming/strengthening of the EAC.

Unique picoeukaryotic algal community under multiple environmental stress conditions in a shallow, alkaline pan

Winter phytoplankton communities in the shallow alkaline pans of Hungary are frequently dominated by picoeukaryotes, sometimes in particularly high abundance. In winter 2012, the ice-covered alkaline Zab-szék pan was found to be extraordinarily rich in picoeukaryotic green algae (42-82 × 10(6) cells ml(-1)) despite the simultaneous presence of multiple stressors (low temperature and light intensity with high pH and salinity). The maximum photosynthetic rate of the picoeukaryote community was 1.4 μg C μg chlorophyll a (-1) h(-1) at 125 μmol m(-2) s(-1). The assimilation rates compared with the available light intensity measured on the field show that the community was considerably light-limited. Estimated areal primary production was 180 mg C m(-2) d(-1). On the basis of the 18S rRNA gene analysis (cloning and DGGE), the community was phylogenetically heterogeneous with several previously undescribed chlorophyte lineages, which indicates the ability of picoeukaryotic communities to maintain high genetic diversity under extreme conditions.

Seasonal Si:C ratios in Lake Erie diatoms — Evidence of an active winter diatom community

Recent investigations of Lake Erie in the winter have demonstrated the occurrence of substantial phytoplankton communities largely consisting of the diatom Aulacoseira islandica (O. Müller) Simonsen. To assess the activity of this diatom community, multiple measures of production, both general and diatom-specific, were undertaken. We measured oxygen (O2) evolution as proxy for carbon (C)-fixation and 2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl) methoxy)-phenyl)oxazole (PDMPO) incorporation as a measure of silica (Si) deposition. The latter demonstrated conclusively that diatoms were active during winter months and confirmed that diatoms are the primary drivers of winter productivity. The stoichiometric relationship between carbon and silica in the winter Lake Erie phytoplankton assemblage was further compared to the activity of the summer community. Although the winter phytoplankton community was observed to be active, it was less active than the summer community, with lower measured rates of O2 evolution and Si deposition. These findings provide a new and expanded understanding of the biological carbon production in Lake Erie.

동계 광양만에서 식물플랑크톤 군집구조의 수평적 분포특성과 성장에 미치는 영양염 제한 특성

To estimate the effects of limitation nutrients for phytoplankton growth and its influences on short-term variations of a winter phytoplankton community structure, we investigated the abiotic and biotic factors of surface and bottom waters at 20 stations of inner and offshore areas from 6 to 7 February in Gwangyang Bay, Korea. Also, several algal bio-assay studies were conducted to identify any additional nutrient effects on phytoplankton assemblage using surface water for the assay. The dominant species in the bay was diatom Skeletonema costatum, which occupied more than 70% of total species in most stations (St.1-16) of the inner bay. According to a cluster and multidimensional scaling (MDS) analysis based on phytoplankton community data from each station, the bay was divided into three groups. The first group included stations from the south-western parts of Myodo lsland, which can be characterized as a semienclosed eutrophic area with high phytoplankton abundance. The second group included most stations from the north-eastern part of Myodo lsland, influenced indirectly by surface water currents from offshore of the bay. The standing phytoplankton crops were lower than those of the first group. The other cluster was restricted to samples collected from offshore of the bay. In the bay, silicon (Si) and phosphorus (P) were not a major limiting factor for phytoplankton production. However, since the DIN: DIP and DSi: DIN ratios clearly demonstrated that there were potential stoichiometric N limitations, nitrogen (N) was considered as a limiting factor. Based on the algal bio-assay, in vivo fluorescence values in N (+) added experiments were higher compared to control and P added experiments. Our results suggested that nitrogen may act as one of the most important factors in controlling primary production during winter in Gwangyang Bay.

Seasonal diatom cycle in Anegada Bay, El Rincón estuarine system, Argentina

Seasonal variations in the composition and carbon biomass of diatoms and other phytoplankton groups were analyzed over two years, from December 1996 to January 1999, at a fixed station in Anegada Bay, within the El Rincón estuarine system (38–41°S). Phytoplankton communities characterizing the different seasons were identified by classification and detrended correspondence analyses. Diatom communities were highly speciose, with 117 species recorded during the two-year study. Three diatom species are new records for the Argentinean Sea (i.e., Minidiscus trioculatus (F.J.R. Taylor) Hasle, M. decoratus Chrétiennot-Dinet & Quiroga and Thalassiosira tealata Takano). Phytoplankton taxonomic composition and carbon biomass showed a strong seasonality, with two carbon (C) biomass maxima occurring in summer and winter (maximum concentration: 193 μ g C L−1). Summer blooms were mainly dominated by tychoplanktonic diatom species (Paralia sulcata (Ehrenberg) Cleve, Rhaphoneis amphiceros (Ehrenberg) Ehrenberg and Delphineis surirella (Ehrenberg) Andrews), probably resuspended from the sediments, and by the pelagic diatom T. hendeyi Hasle & Fryxell. The winter phytoplankton community was characterized by a high number of diatom species and a high carbon biomass of diatom resting spores. The occurrence of the winter bloom seems to be closely associated with the inoculation of the water column by diatom resting spores. Maximum diatom carbon biomass corresponded to periods of increased freshwater inflow, whereas seasonal variations in diatom taxonomic composition may be explained by the life-cycle strategies of the species. The taxonomic composition and temporal succession of phytoplankton communities in Anegada Bay are comparable with previous studies in Blanca Bay, suggesting relatively uniform phytoplankton seasonality over shoals in the El Rincón estuarine system.

Development of phytoplankton in Lake Pääjärvi (Finland) during under-ice convective mixing period

The development of winter phytoplankton communities was studied in both shallow and deep areas of Lake Paajarvi, southern Finland, during the final 2 weeks of winter ice cover. Phytoplankton was mainly composed of diatoms, cryptophytes and chrysophytes. The diatoms Aulacoseira and Rhizosolenia were always uniformly distributed with depth, initially probably due to mixing induced by heat flux from the sediment and later due to thermal convection. Motile Rhodomonas cryptophytes and Chrysococcus chrysophytes were most abundant near the ice showing that, despite their small size, they were partly able to resist mixing by convection. Their ability to stay in more illuminated water layers was reflected in net rates of increase about an order of magnitude higher than those of diatoms in the middle of the lake. Given the low temperatures and convection, the observed net rates of increase of motile taxa were very high compared to growth rates reported in the literature. The gradual increase in light availability following melting of ice led to a consistent increase in the abundances of major phytoplankton taxa irrespective of deep convective circulation. It is suggested that those algae most abundant at the time of ice break have a competitive advantage in the following open water conditions when nutrients are abundant but deep water circulation limits light availability. The results emphasize that in lakes which cool below the maximum density of water before freezing, apparently small differences in temperature and light conditions can cause important changes in the circulation patterns that impact on phytoplankton development.

Winter phytoplankton communities in different depths of three mesotrophic lakes (Łęczna-Włodawa Lakeland, Eastern Poland)

AbstractPhytoplankton samples were collected from three mesotrophic lakes: Piaseczno, Rogóźno and Krasne during winter seasons (from January to March). The samples were analyzed for species analysis and abundance of planktonic algae in relation to different depths of water column (0–7 m). Selected water physical-chemical parameters were also measured. Abundance of phytoplankton depended strongly on the thickness of snow and ice cover or mixing conditions. The maximal phytoplankton total number reached about 5 × 106 ind. L−1 beneath the clear ice in the Krasne Lake, minimal numbers were recorded under the thick snow and ice layers in the Piaseczno Lake (2 × 103 ind. L−1). The winter phytoplankton communities were dominated by flagellates principally cryptomonads (Cryptomonas spp. Rhodomonas minuta), euglenophytes (Trachelomonas volvocina, T. volvocinopsis), dinoflagellates (Peridinium bipes, Gymnodinium helveticum) and chrysophytes (Mallomonas elongata, M. akrokomos, Dinobryon sociale) or non-motile small species of blue-green algae (e.g. Rhabdoderma lineare, Limnothrix redekei), diatoms (Stephanodiscus spp., Asterionella formosa), and green algae (e.g. Scenedesmus spp., Monoraphidium spp.). Phytoplankton abundance and structure showed differentiation during the winter season and along the water column as well.

Ecophysiological growth characteristics and modeling of the onset of the spring bloom in the Baltic Sea

The onset of spring bloom in temperate areas is a transition period where the low productive, winter phytoplankton community is transformed into a high productive spring community. Downwelling irradiance, mixing depth and the ability of the phytoplankton community to utilize the light, are key parameters determining the timing of the onset of the spring bloom. Knowing these parameters would thus provide tools for modeling the spring bloom and enhance our knowledge of ecophysiological processes during this period. Our main objective with this study was to provide data for the growth characteristics of some key species forming the spring bloom in the Gulf of Finland, and to apply those results in a simple dynamic model for the onset of the spring bloom, in order to test if the timing of the spring bloom predicted by the models corresponds to field observations. We investigated the photosynthetic characteristics of three diatoms and two dinoflagellates ( Chaetoceros wighamii, Melosira arctica, Thalassiosira baltica, Scrippsiella hangoei and Woloszynskia halophila), at low temperatures (4–5 °C). All of these species are common during spring bloom in the Baltic Sea. Cultures of these species were acclimated to different irradiance regimes prior to measurements of photosynthesis, respiration, pigment concentration and light absorption. We did not find a positive relationship between respiration and growth rate, and we hypothesize that this relationship, which is well established at higher temperatures, is negligible or absent at low temperatures (< 10 °C). Photosynthetic maximum ( P m), and maximum light utilization coefficient ( α) was lowest and respiration ( R) highest in the dinoflagellates. We made a model of the onset of the spring bloom in the western part of Gulf of Finland, using the obtained data together with monitoring data of mixing depth and water transparency from this area. Model results were compared to field observations of chlorophyll- a (Chl- a) concentration. There was a good agreement between the model predictions and the observed onset of the spring bloom for the diatoms. S. hangoei, however, was not able to reach positive production in the model, and W. halophila had the similar growth characteristics as S. hangoei. Consequently, these species must have other competition strategies enabling them to exist and grow during spring bloom.

Increased blooms of a dinoflagellate in the NW Atlantic

Sampling by the Continuous Plankton Recorder (CPR) over the NW Atlantic from 1960 to 2000 has enabled long-term studies of the larger components of the phytoplankton community, highlighting various changes, particularly during the 1990s. Analysis of an index of phytoplankton biomass, the Phytoplankton Colour Index (PCI) has revealed an increase over the past decade, most marked during the winter (December to February) months. Examination of the structure of the community using multiple linear-regression models indicates that the winter phytoplankton community composition has changed markedly in the 1990s compared to the 1960s. One phytoplankter, the dinoflagellate Ceratium arcticum (Cleve), has undergone dramatic changes in abundance during this period, with pronounced large winter blooms and decreased autumnal levels, and its contribution to the Phytoplankton Colour index values has increased significantly. Other dominant species in the phytoplankton community, both diatoms and dinoflagellates, did not show the same variations over the examined time period. It is suggested that the response of C. arcticum is probably a result of previously reported changes in stratification in the NW Atlantic, due to dynamic hydro-climatic (freshening and cooling) events.

Winter phytoplankton community structure in three shallow temperate lakes during ice cover

The general model of seasonal phytoplankton succession in temperate lakes suggests that winter phytoplankton growth is minimal under ice-cover. However, some studies have found diverse phytoplankton communities during winter. The primary objectives of this study were to determine the species composition and the changes in the winter phytoplankton community structure under the ice. For 2 consecutive winters, phytoplankton samples were collected under ice-cover at 4 sites on 3 lakes in Arrowwood National Wildlife Refuge (ANWR), near Pingree, North Dakota. Ninety taxa were identified and enumerated. Densities of several of these taxa frequently exceeded 106 cells l−1. The winter phytoplankton communities in these lakes were dominated by flagellates, principally cryptomonads, a synurophyte (Synura uvella), small chrysophytes (Chrysococcus spp., Kephyrion spp.) and a dinoflagellate (Peridinium aciculiferum), as well as non-flagellate microchlorophytes (Monoraphidium spp., Ankistrodesmus spp., and Pseudodictyosphaerium sp.), a cyanobacterium (Gloeocapsa aeruginosa) and centric diatoms (Stephanodiscus minutulus, S. parvus and Cyclotella meneghiniana).

Sensitivity of winter phytoplankton communities from Andean lakes to artificial ultraviolet-B radiation

Durante julio de 1999 se realizaron muestreos en cinco lagos Andinos con el objetivo de determinar la sensibilidad de comunidades fitoplanctonicas invernales a la radiacion ultravioleta-B (UV-B, 280-320 nm). Los lagos estudiados, Moreno, El Trebol, Nahuel Huapi, Gutierrez y Morenito, estan ubicados la region Patagonica (41° S, 71° W, 800 m de altitud) y tienen coeficientes de atenuacion variables entre 0,36 m-1 (Lago Moreno) y 2,8 m-1 (Lago Morenito). Las muestras se inocularon con carbono marcado (NaH14CO3) y se incubaron en una camara iluminada (UV-B = 0,35 W m-2, UV-A [320-400 nm] = 1,1 W m-2, y PAR [400-700 nm] = 10,8 W m-2) a 10° C. El fitoplancton se expuso a PAR (radiacion fotosinteticamente activa) + radiacion UV (tubos de cuarzo), y a PAR + UV-A (tubos de cuarzo recubiertos con Mylar-D). La duracion total de los experimentos fue de 4 h y se retiraron dos muestras de cada tratamiento cada 1 h. En los Lagos Moreno, El Trebol, Nahuel Huapi y Gutierrez la inhibicion fotosintetica aumento en forma linear con la dosis de UV-B, mientras que en el Lago Morenito esta relacion fue debil. Despues de recibir una dosis de 1,25 kJ m-2 (UV-B), el fitoplancton del Lago Morenito tuvo la mayor inhibicion fotosintetica acumulada (44 %), mientras que en los Lagos Moreno, Trebol, Nahuel Huapi y Gutierrez la inhibicion fue de 22, 11, 5 y 1 %, respectivamente. Sin embargo, al final de la incubacion, y luego de recibir una dosis de 5 kJ m-2, el fitoplancton mas inhibido fue aquel del Lago Moreno (70 %), y el mas resistente aquel del Lago Gutierrez (27 %). La cinetica de inhibicion fue distinta para cada lago, registrandose una mayor velocidad en los lagos mas transparentes y con mayor proporcion de celulas grandes. Los resultados sugieren que, ante un aumento de UV-B (e.g., producto de una disminucion de ozono estratosferico), el microplancton de lagos mas claros sera el mas afectado mientras que el pico- y nanoplancton de lagos menos transparentes sera el mas resistente

Effects of Ca (OH)2 additions on phytoplankton communities under ice cover in eutrophic hardwater lakes

The effects of Ca(OH) 2 treatment during the open-water season on phytoplankton communities under ice cover were examined for up to three winters (Nov. Apr.) in three eutrophic hardwater lakes in central Alberta. Phytoplankton communities were compared between treated and untreated lakes, and between pre- and posttreatment periods within a treatment lake. In all study lakes, phytoplankton biomass tended to be high at ice-on, decrease after November, and remain low (<2mg/L) from January to early March, when light conditions and water temperatures were also low. After late March to early April, phytoplankton biomass started to increase exponentially because of higher light conditions and water temperature. Most phytoplankton species that were common under ice also occurred during the open-water season. Although phytoplankton species composition was diverse under ice, the biomass of most species, except for flagellates, did not increase before mid-March. Species composition and biomass of some phytoplankton groups varied without clear trends among winters in treated and untreated lakes. Therefore, Ca(OH) 2 treatment during the open-water season did not appear to affect winter phytoplankton communities.

Winter limnology: a comparison of physical, chemical and biological characteristics in two temperate lakes during ice cover

The winter dynamics of several chemical, physical, and biological variables of a shallow, polymictic lake (Opinicon) are compared to those of a deep, nearby dimictic lake (Upper Rock) during ice cover (January to early April) in 1990 and 1991. Both lakes were weakly inversely thermally stratified. Dissolved oxygen concentration was at saturation (11–15 mg l−1) in the top 3 m layer, but declined to near anoxic levels near the sediments. Dissolved oxygen concentrations in the deep lake were at saturation in most of the water column and approached anoxic levels near the sediments only. Nutrient concentrations in both lakes were fairly high, and similar in both lakes during ice cover. Total phosphorus concentrations generally ranged between 10–20 µg l−1, NH4-N between 16–100 µg l−1, and DSi between 0.9–1.9 mg l−1; these concentrations fell within summer ranges. NO3-N concentrations were between 51–135 µg l−1 during ice cover, but occurred at trace concentrations (<0.002 µg l−1) during the summer. The winter phytoplankton community of both lakes was dominated by flagellates (cryptophytes, chrysophytes) and occasionally diatoms. Dinoflagellates, Cyanobacteria and green algae were poorly represented. Cryptophytes often occurred in fairly high proportions (20–80%) throughout the water column, whereas chrysophytes were more abundant just beneath the ice. Zooplankton population densities were extremely low during ice cover (compared to maximum densities measured in spring or summer) in both lakes, and were comprised largely of copepods.

Winter phytoplankton communities of Utah Lake, Utah, USA

Phytoplankton samples were collected from ice-covered Utah Lake during February and March, 1979 in order to characterize the winter algal flora. These samples were analyzed for presence and abundance of diatoms and non-diatom algae as well as selected water chemical parameters. A total of 159 diatom taxa and 20 non-diatoms was found in the water column under the ice. The flagellates Carteria stellifera, Euglena gracilis and Chlamydomonas globosa dominated the winter non-diatom flora while Stephanodiscus cf. dubius, Cyclotella meneghiniana, Navicula minima, Fragilaria construens var. venter, and Melosira granulata var. angustissima dominated the winter diatom flora. Species richness and abundance were elevated in the major bays of the lake.