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Cyanobacterial blooms have a strong impact on the food web structure, interactions and ecosystem functioning. The aim of this study was to describe the seasonal changes in composition and abundance of heterotrophic nanoflagellates, ciliates, rotifers, and crustaceans in relation to algae and nutrients in a shallow eutrophic lake (north-eastern Poland) dominated by cyanobacteria and exposed to the strong impact of cormorants. Our results showed that algae accounted for a small part of the total phytoplankton abundance (9–40%) and biomass (10–21%) and were dominated by diatoms and cryptophytes. All of the studied groups of planktonic organisms were quite rich in species (95 algal, 79 ciliate, 44 rotifer and 25 crustacean species) and relatively abundant. Copepods formed a substantial part (45–83%) of the total zooplankton biomass during all seasons. Relatively low algal to zooplankton biomass ratio (0.8–1.1) suggests that during spring, summer, and winter algae were not sufficient food resources for metazooplankton, which supplemented its diet with protists (heterotrophic nanoflagellates and ciliates). In a shallow lake dominated by cyanobacteria, winter (ice-covered period) may be a more favourable period for the growth of some groups of algae, ciliates and rotifers than other seasons due to decreasing abundance of cyanobacteria. [ABSTRACT FROM AUTHOR]

Soft-water lakes are valuable natural habitats and an important aquatic ecosystems. Lobelia lakes, which are classified based on the occurrence of isoetids, are the most characteristic of this group. The aim of our research was to assess the species richness and structure of pelagic zooplankton communities in the epilimnion of 45 Polish soft-water lakes. The lakes analyzed included a wide range of trophic states from oligotrophic to eutrophic. We noted 79 species of zooplankton, including 49 rotifer, 23 cladoceran, and seven copepod species. The species composition of epilimnetic zooplankton communities in these soft-water lakes was poor, and the species richness and zooplankton biomass were low. In these lakes, the species with the highest frequencies accounted for an important part of the total zooplankton biomass of the zooplankton communities, but the species occurring at lower frequencies differed among the lakes. The most common rotifer taxa were: Keratella cochlearis, Keratella cochlearis var. hispida, Polyarthra euryptera, Gastropus stylifer , and Trichocerca similis. The most important crustacean species in the soft-water lakes were: Macrocyclops albidus, Ceriodaphnia quadrangula , and Eudiaptomus sp. The major factors influencing rotifer species richness were total phosphorus, conductivity, and the trophic state of the lakes. Cladoceran species richness was positively related to lake area and pH, while the species richness of copepod communities was negatively related to chlorophyll a concentrations. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the species composition and structure of zooplankton and fish communities in lakes with similar ecological conditions that are connected by periodic streams. This was done by assessing the relative importance of local biotic and abiotic interactions associated with the species composition and structure of the zooplankton and fish communities. The study was conducted in three small, soft water lobelia lakes located in the source area of the Brda River, which were characterized by low trophic statuses and similar depths. A total of 15 Rotifera taxa, 18 Cladocera taxa, and nine Copepoda taxa were identified in the lakes analyzed. The lake zooplankton communities differed in species richness, total density, and biomass, while the Shannon–Wiener diversity indexes of the zooplankton communities were similar. Of the three lakes analyzed, the faunal similarity index was the highest in Lake Smołowe. Comparisons of the three lakes indicated there was greater similarity in the pelagic (42.7–50.0%) than in the littoral (20.1–26.8%) zones. The fish community of the three lakes consisted of eight species, and species richness ranged from two to eight fish species. Only perch (Perca fluviatilis L.) and pike (Esox lucius L.) were present in all three lakes. The fish groups also differed in terms of density and biodiversity indicators. Faunal similarity indicators showed significant similarity in the dominance structure of the fish communities. [ABSTRACT FROM AUTHOR]

The structure and abundance of winter planktonic communities are limited by environmental conditions that are unfavorable to life, but do not stop biological processes. The aim of the study was to test the hypothesis that the abundance of planktonic groups of organisms in temperate lakes can be higher during winter under ice cover than during the ice‐free seasons. Physical (ice/snow cover, temperature), chemical (organic carbon, chlorophyll a, phosphorus, nitrogen) and biological parameters (phytoplankton, protozooplankton, zooplankton) were investigated in three eutrophic lakes during two consecutive years in winter, spring, summer and autumn. The results of this study showed that in all lakes chlorophyll a concentrations were usually lower in winter than in other seasons, while total nitrogen concentrations were higher in winter than in autumn. All groups of planktonic organisms were able to reach similar or even higher abundances in winter under‐ice than in other ice‐free periods, depending on the lake morphometry and the year of the study. Winter taxonomic structure of phytoplankton was similar to the spring (medium‐sized Lake Dgał Wielki with the dominance of cryptophytes), summer (small‐sized Lake Dgał Mały with cyanobacteria as a dominant group) or autumn (the shallow lake with the dominance of diatoms) structure, depending on the lake. In all lakes, the structure of the ciliate community was the most similar to that of the spring with the clear dominance of Oligotrichida. Our results show that some species among all the studied groups of organisms can lead an active and dynamic life under the ice cover. [ABSTRACT FROM AUTHOR]

This paper discusses the problem of the occurrence of non-native fish species in a strongly transformed aquatic ecosystem. The changes in this ecosystem are caused by warm water discharges from two electric power plants. Twelve non-native fish species are confirmed to occur in the system of five heated lakes located in central Poland. In total, 30% of the total number of non-native species confirmed in Polish inland waters were noted. Aquaculture and fisheries are the primary sources of non-native species in these lakes. Among the species identified, most reached the lakes or canals by escaping from farming facilities or through commercial stocking. Four species have established stable populations. Pseudorasbora parva (Temminck & Schlegel), Carassius gibelio (Bloch), and Carassius auratus (L.) are invasive species that occur abundantly in all the lakes, while Cyprinus carpio L. reproduces irregularly and only in the most heated lakes. The remaining species do not reproduce in the heated lakes system, or anywhere else in Poland; still, the threat these species pose must not be underestimated. [ABSTRACT FROM AUTHOR]

The objective of this study was to analyze variations in the planktonic rotifer community in a lake subjected to hypolimnetic withdrawal. The present study is also the first attempt to estimate the effects of changes in hypolimnion water withdrawal rates on the zooplankton community. The lake is located in northeastern Poland. Zooplankton were sampled in 1986, 2004 and 2013. Standard protocols of zooplankton sampling and elaboration were applied. Rotifer abundance, wet biomass, community structure, and species diversity were studied at different intensities of hypolimnetic water withdrawal. Trophic state indices based on rotifer abundance and species structure were used to evaluate changes in the trophic state of the lake. Our results showed increased planktonic rotifer species diversity over a period of years, which was a positive outcome of the restoration measures. Lower hypolimnetic withdrawal rates seemed to favor the development of a diverse rotifer community. Conversely, qualitative changes in zooplankton structure and a zooplankton-based assessment of the lake trophic state indicated that water eutrophication was progressing. Despite modifications to the operation of the pipeline, no significant differences in rotifer abundance or biomass were detected between the sites in each year or among years at each site. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms are tightly related to increasing trophic conditions of lakes and climate warming. Abiotic and biotic parameters were studied in a shallow lake, in which the island with the largest cormorants colony in north-eastern Poland is situated. We hypothesized that the strongest cyanobacterial blooms will persist near the cormorant's island and will decrease with an increasing distance from it. Filamentous cyanobacteria (Pseudanabaena, Planktolyngbya, Limnothrix, Planktothrix) were the main phytoplankton components during summer and autumn. Their strongest blooms (up to 66 mg L−1) were recorded near the roosting area. The content of nutrients and chlorophyll a, and the biomass of phytoplankton (primarily cyanobacteria) and zooplankton, decreased gradually with the increasing distance from the island. The changes from hypertrophic to eutrophic conditions were confirmed by a decrease in values of the trophic state index from 72 (site 1) to 58 (site 5). This all suggests that cormorants might have a significant impact on the deterioration of water quality (at distance to 1.6 km) and can contribute to faster water eutrophication. Our results suggest that protection of breeding sites for many waterbirds, such as cormorants, becomes a real threat for the functioning of aquatic ecosystems due to a large load of nutrients. [ABSTRACT FROM AUTHOR]

Winter conditions in lakes of temperate climatic zones, especially the duration and thickness of ice and snow cover, are strongly influenced by climate changes. The aim of this study was to follow the dynamics of abiotic (organic carbon, total phosphorus, total nitrogen) and biotic (chlorophyll a , cyanobacteria, algae, nanoflagellates, ciliates, rotifers, crustaceans) parameters during two consecutive winters in three eutrophic lakes of different mixing regime (northeastern Poland). Our results showed that dissolved organic carbon was highly stable during both winters and practically did not differ among the studied lakes. Total phosphorus and chlorophyll a concentrations differed significantly between the dimictic and meromictic lakes. The concentrations of nutrients and chlorophyll a and the biomass of phytoplankton, protists, rotifers and crustaceans reached higher values in late winter than in early winter, depending on the lake type (morphometry, mixing regime) and the year of the study. The composition of phytoplankton and ciliates was more or less similar throughout the study in all lakes during both years, but the share of individual groups in the total biomass differed between early and late winter. A high cyanobacterial biomass in January under the ice in the meromictic lake was probably a legacy of the summer/autumn community. Small prostomatid ciliates were the most important group in late winter in the shallow lake. Cladocerans (Bosmina coregoni and B. longispina) were an important component of winter crustacean community on some occasions, especially in the shallow lake. Phosphorus was the major factor determining phytoplankton biomass. Heterotrophic nanoflagellates and rotifers were negatively related to ice cover, while ciliates were positively related to the water temperature. Our study demonstrated that the dynamics, abundance, and structure of the phytoplankton and zooplankton communities in eutrophic lakes changed from one winter to the next despite similar environmental conditions. • Cyanobacterial bloom under ice was probably a continuation of summer/autumn bloom. • Cladocerans were occasionally an important component of crustaceans during winter. • Ice cover was a factor determining the abundances of nanoflagellates and rotifers. • Winter dynamics of the food web components changed from one winter to the next. [ABSTRACT FROM AUTHOR]