Lake Plankton Communities Research Articles

Seasonality of cyanobacteria and eukaryotes in Lake Geneva and the impacts of cyanotoxins on growth of the model ciliate Tetrahymena pyriformis.

Toxic cyanobacteria are likely to be favored by global warming and other human impacts, posing significant threats to aquatic ecosystems. While cyanobacterial blooms in eutrophic lakes are widely investigated, the dynamics of cyanobacteria and the effects of their toxins and bioactive metabolites on the plankton communities in mesotrophic and oligotrophic lakes are less well understood. Here we investigated seasonal dynamics of cyanobacteria, eukaryotic algae and cyanotoxins in oligo-mesotrophic Lake Geneva-the largest and deepest lake in western Europe. High-throughput sequencing of the 16S rRNA genes in 143 samples along a water column revealed that Lake Geneva hosts diverse, co-dominant cyanobacterial genera, including Planktothrix, Cyanobium, Pseudanabaena, and Aphanizomenon. The abundance of the mcyA gene marker for microcystin production was highly correlated with total cyanobacteria abundance, obtained from qPCR of the 16S rRNA genes. Targeted LC-HRMS/MS analysis demonstrated peak concentrations of cyanotoxins in September and December 2021 at the deep chlorophyll-a maximum layer, reaching up to 1474 ng/l for anabaenopeptins and 144 ng/l for microcystins. The toxin peaks did not correlate with the abundance or variations in the cyanobacteria or eukaryote community, but they were correlated in time with seasonal lows in the abundances of ciliates (18S rRNA analysis). Laboratory exposure tests demonstrated that growth of the model ciliate Tetrahymena pyriformis was inhibited by Microcystin-RR and Anabaenopeptin A at environmentally relevant concentrations in the ng/l-range, in natural lake water, synthetic freshwater, and growth media spiked with the cyanotoxins. Our findings suggest that even low concentrations (in the ng/l-range) of microcystins and anabaenopeptins, reduce growth of ciliates such as T. pyriformis and can be expected to have wider impacts on the eukaryote communities.

Changing Patterns and Driving Factors of Plankton Coupling Relationships in Lakes around the Yangtze River, China.

In recent decades, cyanobacterial blooms have intensified in many lakes in China. Algal blooms are closely linked to the predation pressure on phytoplankton, but the changes in the relationship between phytoplankton and their primary predators, zooplankton, remain unclear. To investigate the changing patterns and driving factors of the relationship between plankton, the historical data of plankton from 14 typical freshwater lakes around the Yangtze River were collected from multiple databases. By comparing the structure of plankton communities in typical lakes between the 1990s and the 2010s, it was found that the phytoplankton density was elevated in 79% of all the lakes; on average, it had increased to 3156 times higher than it had been. In contrast, the zooplankton density was elevated in only 57% of these lakes, and this value was only two times higher than it had been. In 11 out of the 14 lakes, the zooplankton density growth rate was lower than that of the phytoplankton. The percentage of cyanobacteria in these lakes increased from 53% to 62%, and the changes in cyanobacteria were significantly negatively correlated with the changes in zooplankton. Eutrophication caused this significant increase in phytoplankton, especially cyanobacteria. Cyanobacterialization, changes in fish community structures, biological invasion, and river-lake relationships impede zooplankton survival. This combination of factors hinders plankton coupling in many lakes. This study attempts to provide new insights for lake ecological management.

Effects of Massive Use of Disinfectants on the Plankton Communities in Lakes from Wuhan

The outbreak of COVID-19 led to the extensive use of disinfectants in urban areas. These disinfectants, along with disinfection by-products (DBPs), eventually enter waters and affected the aquatic organisms. But little information could be obtained on disinfectants threatening aquatic ecosystems. This study was conducted to obtain insight into the effects of massive use of disinfectants on freshwater ecosystems, DBPs, phytoplankton, and zooplankton in nine urban and two country lakes in Wuhan during the COVID-19 pandemic; in addition, the residual chlorine in the South Lake (one of the urban lakes), was investigated. The concentration of residual chlorine in the South Lake ranged from 0.000 mg L−1 to 0.427mg L−1, with an average concentration of 0.092 mg L−1. The total concentrations of DBPs (halogenated aliphatic DBPs and aromatic halogenated DBPs) detected in the urban and country lakes ranged from 4.22 μg L−1 to 16.59 μg L−1 and 5.92 μg L−1 to 7.84 μg L−1, respectively. There was no significant difference in DBPs content between urban lakes and country lakes (p < 0.05). Mann–Whitney U tests showed no significant differences in plankton cell density, biomass, and alpha diversity indexes between urban and country lakes, except for the Shannon−Wiener diversity index of phytoplankton. Beta diversity demonstrated that plankton communities at different sampling stations in urban and country lakes were not significantly separated into two groups, but rather intersected each other. Variance partitioning analysis revealed that the composition of plankton communities was primarily influenced by other plankton organisms and community stability under the conditions of the investigated factors. Results indicated that the detected plankton communities in urban lakes from Wuhan were not significantly affected by the use of disinfectants. It could be deduced that the massive use of disinfectants in this outbreak had no significant impact on the plankton communities.

Summer dynamics of cyanobacteria in an oligo-mesotrophic temperate lake in Northwest Ireland

Despite the potential adverse consequences they can impart on biotopes, cyanobacteria are an understudied component of lake plankton communities in Ireland. This study, in summer 2019, examined cyanobacterial diversity and associated environmental variables in a lake previously impacted by algal blooms, in north-west Ireland. Vertical profiling showed that photosynthetic pigment concentrations were spatially heterogenous for the majority of the survey. However, water column homogeneity was observed towards the end of the survey, coinciding with increases in pigment concentrations. Sunshine hours, nutrient concentrations and wind speed were stable throughout the survey. Spatial homogeneity in pigments was attributed to an increase in minimal temperatures observed in the water column. PCR-DGGE analysis identified patterns in community composition, indicating a rise in cyanobacterial richness concomitant to increase in temperature and photosynthetic pigments. Band sequencing analysis identified phylotypes similar to the toxigenic species Microcystis sp. These were prominent at the end of the survey and coincided with the presence of the mcyE gene and low levels of microcystins, as indicated by real time PCR and ELISA analyses. The summer background presence of toxigenic cyanobacteria with potential bloom-forming capacity highlights the importance of annual lake cyanotoxin monitoring to inform resource management to protect human and animal health.

Stoichiometric constraints in plankton communities of Patagonian lakes. Implications for Parabroteas sarsi distribution and conservation

The Patagonian region, from the Andes to the steppe, includes a profuse hydrographic network with deep and shallow lakes. Here, we analyze the stoichiometric constraints for the large predaceous copepod Parabroteas sarsi in fish and fishless lakes. For this purpose, we examined previous literature data on the composition of the zooplankton community in different Patagonian lakes with and without fish (mainly introduced in the XX century) and own laboratory and field experiments. The ecological stoichiometry theory predicts that consumers need to attain specific elemental ratios to achieve maximum growth, and the geometric framework of nutrition proposes that consumers may need to combine food items to fulfill nutrient requirements. We show that the predaceous copepod does not necessarily encounter prey that fulfills their stoichiometric requirements, thus growth is impaired. However, through the combination of different prey, this predator can fulfill its requirements. In the presence of fishes, food webs change towards smaller-sized zooplankton species with the loss of low C:nutrient ratio species. In this sense, we demonstrate the direct and indirect impact of fish introduction on the stoichiometric balances and the disappearance of this invertebrate predator in lacustrine food webs.

Diversity of plankton communities of chloride lakes of Southeastern Transbaikalia

Saline lakes as an extreme type of ecosystems are the object of intensive multidisciplinary research. The few chloride water bodies are unique in their own way and are of great interest to researchers. Their morphometric, hydrological, physical and hedrochemical characteristics are subject to significant changes, which are caused by cyclic climatic fluctuations. These lakes periodic fill and dry up. Most chloride lakes are localized on relatively level surfaces. The depth and area of the lakes vary depending on meteorological conditions. They are fed by surface runoff water and atmospheric precipitation. The surveyed water bodies are part of the Onon-Borzya group of lakes, located in the Onon River valley in the south-eastern Transbaikalia. The region is characterized by a cryoarid climate. Organisms adapted to living in mineral lakes combine wide physiological tolerance to changing salinity with rather strong dependence on other features of the habitat. We aim is to research the diversity of algae and plankton invertebrates in shallow chloride lakes (Gorbunka, Dabasa-Nur, Hilganta). This work presents the results of primary studies conducted in March and July 2021. Plankton samples were collected and processed according to methods generally accepted in hydrobiology. Taxonomic composition, abundance and biomass of planktonic organisms were revealed. The composition of algae and the ratio of the divisions in the plankton of the surveyed chloride water bodies are typical for water bodies with increased salinity, where cyanobacteria and green algae prevail. In zooplankton one species, rotifer Brachionus plicatilis, which is a cosmopolitan, halobiont and typical inhabitant of inland mineral lakes, was found. Quantitative indices varied within a wide range, which is probably connected with hydrochemical indices and different level of filling of lakes.

Light as a controlling factor of winter phytoplankton in a monomictic reservoir

Factors affecting the seasonal succession of plankton communities in freshwater temperate lakes have been thoroughly studied for decades. However, there are still relatively few data describing the winter season patterns in detail, as the focus has been mostly on spring to autumn conditions. Ice cover is often the crucial factor limiting light availability for winter phytoplankton, but in warm monomictic lakes is usually lacking and the gradually increasing solar radiation should, theoretically, drive phytoplankton growth. In this study conducted in 2002–2010, we documented regular sharp increases in phytoplankton chlorophyll a, starting just after the winter solstice and lasting throughout the total circulation and/or unstable inverse stratification period in the monomictic Slapy reservoir (Czechia). Chlorophyll a concentrations analysed in one-week intervals reached their yearly minimum of 0.2–0.8 µg L−1 in the solstice period, and the spring peak occurred before the onset of stable thermal stratification. The regular pattern was slightly disrupted in some years, associated with short periods of ice cover. Winter phytoplankton were species poor and dominated by diatoms, cryptophytes, green algae, and cyanobacteria. Using semiparametric regression approach, we aimed to test if selected environmental parameters had a significant effect on the observed winter trend. The resulting model revealed that solar radiation and water temperature positively influenced log chlorophyll a concentrations, whereas water age had a significant negative effect. On the other hand, zooplankton density and ice cover effects were not significant. The shapes of the marginal effects of water temperature and solar radiation were nonlinear, and the interaction of these two major factors was significant. The model-based estimated chlorophyll a concentrations showed a shift from radiation dominance to temperature-positive effects along the temperature gradient. This might represent as yet neglected pattern of phytoplankton seasonal development in warm monomictic lakes worldwide.

Balancing ecosystem integrity and cultural values at sacred Lake Hora, Ethiopia: The need for conservation of wetland vegetation

AbstractAlthough macrophytes represent important habitats for the plankton communities of shallow lakes and ponds, the role of littoral macrophyte patches in deep crater lakes is not well described. The objective of the present study was to investigate the role of littoral macrophyte vegetation in structuring phytoplankton and zooplankton communities and, therefore, sustaining ecological integrity in a deep tropical crater lake (Hora Lake, Ethiopia). The lake has a surface area of 1.03 km2 and a mean depth of 16.5 m. The area surrounding the lake is a prime location for the celebration of the Oromo thanksgiving festival (Irreecha), which is inscribed by the United Nations Educational, Scientific and Cultural Organization (UNESCO) as an intangible cultural heritage, and also considered sacred by the Oromo people. Measurements of physical, chemical and biological parameters were conducted at fifteen sampling sites in both the littoral and central parts of the lake during the dry and wet seasons in 2017. A total of 28 phytoplankton and 19 zooplankton genera were identified. The phytoplankton and zooplankton communities were dominated by cyanobacteria and rotifers, respectively, at the open water sites. The wetland vegetation was found to be important in reducing potentially toxic and unsightly cyanobacteria. The submerged and emergent vegetation also served as refugia for zooplankton during the wet and dry seasons, respectively. Crustaceans accounted for about 30–45% of the total zooplankton abundance within the vegetation fringes. Their abundance decreased to 5% in the non‐vegetated areas, wherein the community was dominated by rotifers. As the population around the lake, particularly during the festival, may damage the aquatic vegetation, their access to the shoreline should be regulated for conservation and sanitary reasons (e.g. to reduce cyanobacteria growths).

Seasonality in Environmental Conditions Drive Variation in Plankton Communities in a Shallow Tropical Lake

Factors influencing the spatio-temporal dynamics of plankton communities in small tropical lakes are not well-understood. This study assessed plankton communities in response to spatial (six sampling sites) and seasonal (wet vs. dry seasons) changes in environmental variables in Lake Kanyaboli, a small satellite lake on the northern shores of Lake Victoria, Kenya. Water quality variables, including pH, conductivity (EC), dissolved oxygen (DO), temperature, Secchi depth (SD), nitrates (NO3-), nitrites (NO2-), ammonium (NH4+), soluble reactive phosphorus (SRP), total nitrogen (TN), total phosphorus (TP), and chlorophyll-a(Chl-a), were monitored monthly at six sites spread throughout the lake for 1 year. Phytoplankton and zooplankton samples were collected and analyzed for taxon composition and abundance. Two-way ANOVA showed no significant interaction between site and season for all variables. Likewise, there were no significant spatial differences for all variables except Chl-a. At-test showed significant seasonal differences in SD, DO,NH4+,NO3-,NO2-, and TN. Thirty phytoplankton genera were identified belonging to Bacillariophyceae, Chlorophyceae, Cryptophyceae, Cyanophyceae, Euglenoidae, Trebouxiophyceae, and Zygnematophyceae, with Chlorophyceae being the most dominant (42.30%). Zooplankton comprised of 15 genera, belonging to Copepoda (55.4%), Rotifera (27.9%), and Cladocera (16.7%). Two-way ANOVA for plankton abundance showed no significant interaction between site and season, but there were significant differences in community composition between the wet and dry seasons. Canonical correspondence analysis identified water clarity (Secchi depth) and concentrations of dissolved fractions of nitrogen and phosphorus as the major water quality variables driving variation in the composition of plankton communities in the lake. This study showed that seasonality was a major driver of changes in plankton community composition between dry and wet seasons through changes in the concentrations of nutrients (NH4+,NO3-,NO2-, TN, and TP). Lake Kanyaboli's phytoplankton community indicated a non-equilibrial state, perhaps due to short residence times of water, especially during the wet season, and dense macrophytes fringing the lake that increase nutrient uptake and limit the dominance of select phytoplankton species. This study shows the importance of long-term studies covering dry and wet seasons to understand the dynamics of plankton communities and their drivers in small tropical waterbodies to inform management and conservation.

Lake ecosystem on the Qinghai–Tibetan Plateau severely altered by climatic warming and human activity

Modelling, monitoring, and experimental data have shown that global climate change can impact aquatic phytoplankton communities directly, through the effects of warming on primary producers, as well as indirectly through cascading effects from higher trophic levels. Although both concepts are common in modern limnological studies, it remains unclear whether the ‘top-down’ effects from higher trophic levels on phytoplankton exert strong effects in natural systems over long (centennial) timescales. Here, we use multiproxy data including pigments, zooplankton remains, nutrient concentrations, and paleoclimate indicators from a sediment core in Dagze Co, Central Tibet (a two-trophic level lake) to reconstruct algal production, zooplankton community, nutrient and salinity changes. Our results show that top-down effects of higher trophic levels offset effects from warming and nutrient addition on algal growth. Warming enhanced glacial meltwater inflow to the lake, and intensive human activities increased nutrient inputs. Changes in lake salinity and N:P ratios coincided with zooplankton community shifts during the past 600 years, and Daphnia tibetana replaced the brine shrimp, Artemia tibetiana, after the relocation of a town to upstream of the lake in the 1980s led to overharvesting of the brine shrimp. These shifts contributed strongly to changes in algal communities, with changes in zooplankton leading to strong top-down effects that decreased algal production through increasing grazing pressure despite increasing nutrient concentrations. Our results suggest that the typical external drivers (climate and nutrients) of lake ecosystems may be suppressed by internal shifts in plankton communities in lakes.

The role of environmental, geographical, morphometric and spatial variables on plankton communities in lakes of the arid Patagonian plateaus

Abstract Species diversity is one of the most informative community metrics and is influenced by regional and local factors. We studied the spatial patterns of taxonomic and functional phyto- and zooplankton diversity in 33 lakes from two basaltic plateaus of the arid Patagonia. The aims of our study were to evaluate α, β and γ taxonomic diversity of phyto- and zooplankton; to assess the influence of environmental, spatial, geographical and morphometric factors on phyto- and zooplankton communities and to compare the influence of these variables on the taxonomic and functional composition. β1-diversity (within plateaus) was the major component for phytoplankton, rotifers and microcrustaceans taxonomic regional diversities. Planktonic communities were mainly constrained by macrophytes, fish, conductivity, dissolved organic carbon, altitude and spatial factors. The high dispersion of small individuals within plateaus tends to homogenize these communities, as indicated by null model results and the high explanation of fine-scale spatial factors in variation partitioning. This knowledge contributes to explaining the diversity patterns of planktonic communities of these valuable environments and to develop conservation strategies, considering both environmental heterogeneity and spatial effects.

Long-term data on plankton communities in Torey lakes, a shallow saline lakes, Transbaikalia, Russia

This study aims to investigate dynamics of environmental and plankton parameters during the drying and initial filling phases of Torey lakes. These lakes located in the South-East Transbaikalia are shallow saline fluctuating lakes. We conducted our studies during different water level phases of the hydrological cycle, including three periods for Zun-Torey Lake: high (1999 and 2003), intermediate (2007, 2011) and low (2014 and 2016) lake levels and two periods for Barun-Torey: high water level (1999 and 2003) and the initial filling phase (2014, 2016, 2018). Fluctuations in water level and environmental conditions (TDS, pH, dissolved oxygen content, water temperature) changes due to dilution and concentration have influence on phyto- and zooplankton structure. Fluctuations of plankton communities are different for each lake and conform the phases of the hydrological cycle. We have identified four stages in changes of plankton community for Zun-Torey Lake as the deeper and slowly drying, and three stages for Barun-Torey Lake as a shallower and rapidly drying.

The El Niño Southern Oscillation (ENSO) is the main source of variation for the gamma diversity of plankton communities in subtropical shallow lakes

We determined the variation in the composition of plankton communities (zooplankton, phytoplankton, and ciliates) in subtropical lakes at different temporal scales, in relation to the seasons (dry and rainy seasons), as well as at finer (among months) and broader (ENSO—among El Nino, La Nina, and normal climate events) scales. Using a 16-year time-series dataset, we tested the hypothesis that seasonal variation would explain most of the gamma diversity of these plankton communities. We also investigated the environmental and temporal factors responsible for the variations in composition and species turnover. The scale related to dry and rainy seasons explained a considerable percentage of the gamma diversity and variation partitioning, showed that compositional changes occurred mainly over broader temporal scales. Environmental factors varying among seasons and ENSO events explained changes in composition, although some communities did not respond to the environment. Our results suggest that niche and stochastic processes operating at temporal scales correlated with ENSO climate events contributed to changes in species composition. Hence, climate anomalies might be important to maintain diversity in areas with reduced or loss of the natural variations in environmental conditions. Our results also suggest that, although communities show similar patterns of variation in composition, they might respond in a different degree to environmental and temporal factors. Thus, while niche-associated (environment) and stochastic (time) processes drove the phytoplankton, stochastic processes were more important for zooplankton, whereas neither were important for ciliates.

Altered food-web dynamics under increased nitrogen load in phosphorus deficient lakes

Atmospheric nitrogen deposition predominantly influences ecosystems by shifting their available nutrient budgets towards excess nitrogen conditions. In temperate lakes nitrogen is often naturally in excess and phosphorus is deficient, when compared with the optimal Redfield ratio of 16:1. To investigate effects of future increasing nitrogen conditions on lake plankton communities, we performed mesocosm experiments in three different nitrogen rich lakes, all characterised by high nitrogen to phosphorus ratios. In order to determine functional responses to increased nitrogen loading, we conducted six nitrogen fertilization treatments. Nitrogen fertilization was based upon existing nitrate and ammonium concentrations in natural wet deposition and multiple loadings of these concentrations. Despite the initial conditions of excess nitrogen, removal of additional nitrogen by the plankton community was observed in all of the lakes. In one lake, an increasing phosphorus limitation became visible in seston stoichiometry. Over all of the lakes and within each lake’s experimental nitrogen gradient, we found evidence for decreased mesozooplankton due to nitrogen enrichment. The negative responses of mesozooplankton to N enrichment were mainly restricted to cladocerans and nauplii. The results indicate that nitrogen enrichment within the magnitudes of projected future atmospheric nitrogen depositions may lead to a long-term reduction of mesozooplankton in phosphorus deficient lakes. The transfer of nitrogen enrichment effects on lower food-web dynamics could have consequences for higher trophic levels, such as fish.

Cascading effect of exotic fish fry on plankton community in a tropical Andean high mountain lake: a mesocosm experiment

<p>Fishless Andean high mountain lakes may be vulnerable to fish invasion because they tend to be small, oligotrophic and contain low zooplankton diversity. During the first decades of the twentieth century, rainbow trout, <em>Oncorhynchus mikiss</em>, was introduced in South America, and stocking of juvenile stages (fry) in lakes continues today. However, their effect on plankton in these lakes has been little studied. We performed a mesocosms experiment to assess effects of trout of different ontogenetic stages on zooplankton and phytoplankton in a tropical-Andean high mountain lake. The presence of trout fry resulted in declines in several large zooplankton taxa, increases in chlorophyll <em>a</em> and dissolved inorganic nitrogen (DIN). Our results showed that small fry consume large copepods (<em>Colombodiaptomus brandorffi</em>) at a faster rate than larger fry, and also consumed medium sized copepods (<em>Tropocyclops prasinus</em>) that are not affected by the larger trout fry. Fish of both sizes consumed <em>Ceriodaphnia quadrangula</em>, a midsize cladoceran. Fish predation had weak effect on the phytoplankton biomass, but we found a correlation between zooplankton biomass and phytoplankton richness, and significantly larger cell of the alga <em>Peridinium</em> in the presence of fish. Our results indicate that trout introduction produces cascading ecological and phenotypic effects on the plankton communities of tropical mountain lakes, similar to those observed in temperate latitudes.</p>

Mesocyclops and Thermocyclops (Copepoda, Cyclopidae) in the major Visayas Islands (central Philippines)

Our knowledge of the freshwater cyclopid copepods of the Visayas Islands remains poor as compared to other terrestrial and aquatic fauna. This study focuses on two genera,MesocyclopsandThermocyclops, which are common components of lake plankton communities. This study included specimens collected from 59 sampling sites found in major islands (Panay, Negros, Cebu, Bohol, Leyte and Samar) and a small island (Pacijan) in the Visayas region. Four species ofMesocyclopsand three species ofThermocyclopswere identified. This includes the first record ofMesocyclops woutersiin the Philippines, which was so far unknown from insular SE Asia. The endemicMesocyclops microlasius, previously reported from Luzon Island, was also found in Lake Danao (Pacijan Island). An identification key to Philippine species ofMesocyclopsandThermocyclopsis herein provided. Geographic distribution and possible causes of the low number of species observed and their implications for further faunal studies are also discussed.

The effect of fish stocking on mountain lake plankton communities identified using palaeobiological analyses of bottom sediment cores

The artificial introduction of fish into a naturally fishless lake can effectively modify the food web and trophic status of that lake. We observed changes in the zooplankton community after stocking fish in Przedni Staw Polski, an oligotrophic mountain lake in the Tatra Mountains (Poland). Results were compared with observations about a stocked lake that naturally contained fish (Morskie Oko), and with two fishless lakes that served as reference sites. The main change observed in the cladoceran community of Przedni Staw Polski was the elimination of large-bodied Daphnia ~10 years after stocking fish. The introduction of fish also affected the phytoplankton community and resulted in an increase in diatom species related to higher trophic state, most likely due to the fish-induced alteration of the phosphorus cycle. Moreover, all of the studied lakes have been influenced by global and regional climatic and environmental changes, including intensive tourism and acid deposition. Changes in diatom communities were observed after fish stocking even in the lake with a natural fish population, while the zooplankton did not reflect higher fish density. These findings suggest that the natural balance between fish and phytoplankton was destroyed by fish stocking, and although it caused eutrophication in the lake, the higher fish density did not strongly modify the species composition of Cladocera.

Photosynthetic and fatty acid acclimation of four phytoplankton species in response to light intensity and phosphorus availability

Photosynthetic acclimation of phytoplankton to lower irradiation can be met by several strategies such as increasing the affinity for light or increasing antenna size and stacking of the thylakoids. The latter is reflected by a higher proportion of polyunsaturated fatty acids (PUFAs). Additionally, photosynthetic capacity (Pmax), respiratory losses, and proton leakage can be reduced under low light. Here we consider the effect of light intensity and phosphorus availability simultaneously on the photosynthetic acclimation and fatty acid composition of four phytoplankters. We studied representatives of the Chlorophyceae, Cryptophyceae and Mediophyceae, all of which are important components of plankton communities in temperate lakes. In our analysis, excluding fatty acid composition, we found different acclimation strategies in the chlorophytes Scenedesmus quadricauda, Chlamydomonas globosa, cryptophyte Cryptomonas ovata and ochrophyte Cyclotella meneghiniana. We observed interactive effects of light and phosphorus conditions on photosynthetic capacity in S. quadricauda and Cry. ovata. Cry. ovata can be characterized as a low light-acclimated species, whereas S. quadricauda and Cyc. meneghiniana can cope best with a combination of high light intensities and low phosphorus supply. Principal component analyses (PCA), including fatty acid composition, showed further species-specific patterns in their regulation of Pmax with PUFAs and light. In S. quadricauda and Cyc. meneghiniana, PUFAs negatively affected the relationship between Pmax and light. In Chl. globosa, lower light coincided with higher PUFAs and lower Pmax, but PCA also indicated that PUFAs had no direct influence on Pmax. PUFAs and Pmax were unaffected by light in Cry. ovata. We did not observe a general trend in the four species tested and concluded that, in particular, the interactive effects highlight the importance of taking into account more than one environmental factor when assessing photosynthetic acclimation to lower irradiation.

High diversity of protistan plankton communities in remote high mountain lakes in the European Alps and the Himalayan mountains.

We analyzed the genetic diversity (V4 region of the 18S rRNA) of planktonic microbial eukaryotes in four high mountain lakes including two remote biogeographic regions (the Himalayan mountains and the European Alps) and distinct habitat types (clear and glacier-fed turbid lakes). The recorded high genetic diversity in these lakes was far beyond of what is described from high mountain lake plankton. In total, we detected representatives from 66 families with the main taxon groups being Alveolata (55.0% OTUs97%, operational taxonomic units), Stramenopiles (34.0% OTUs97%), Cryptophyta (4.0% OTUs97%), Chloroplastida (3.6% OTUs97%) and Fungi (1.7% OTUs97%). Centrohelida, Choanomonada, Rhizaria, Katablepharidae and Telonema were represented by <1% OTUs97%. Himalayan lakes harbored a higher plankton diversity compared to the Alpine lakes (Shannon index). Community structures were significantly different between lake types and biogeographic regions (Fisher exact test, P < 0.01). Network analysis revealed that more families of the Chloroplastida (10 vs 5) and the Stramenopiles (14 vs 8) were found in the Himalayan lakes than in the Alpine lakes and none of the fungal families was shared between them. Biogeographic aspects as well as ecological factors such as water turbidity may structure the microbial eukaryote plankton communities in such remote lakes.

The effects of local, buffer zone and geographical variables on lake plankton metacommunities

Lake plankton metacommunities are affected by their surrounding multidimensional landscape. Hence, understanding mechanisms shaping lake plankton communities requires considering not only local or geographical drivers, but also drivers at buffer zone level, indicating fluxes of nutrients and organic compounds. We investigated the effects of local, buffer zone (characterised via remote sensing) and geographical level variables on the phyto- and zooplankton community composition in 100 lakes distributed over five watersheds in Finland. We examined the community variation at two spatial scales using redundancy analysis with variation partitioning. Among watersheds, phyto- and zooplankton showed a small spatial imprint in their metacommunity structure, suggesting weak dispersal limitation. Environmental drivers explained negligible shares of the community variation, indicating weak species sorting. However, within single watersheds, larger fractions of the variation in communities were explained by the effects of multi-scale variables, suggesting that communities may be structured by species sorting and mass effects. Groups of variables exerted a relatively equal influence on the community composition. Including buffer zone variables into models increased the explained community variation by one-third. Due to the unique effects of the buffer zone on plankton composition, remotely sensed buffer zone variables may serve as useful proxies in analyses of lake plankton metacommunities.