SummaryThis paper analyzes whether physicochemical properties significantly influence the occurrence of zooplankton in a brackish reservoir. The studies were carried out on the Vistula Lagoon in August and September from 2006 to 2009 at 32 research sites. The environmental conditions in the Vistula Lagoon varied widely. At the time of the investigation, 17 species of rotifers, six species of Cladocera, and ten species of Copepoda were noted, and the total density of plankton fauna ranged from 145 to 765ind.dm−3. Statistical analysis demonstrated a significant correlation between the occurrence of some zooplankton species and certain environmental parameters, whereas the sampling sites were grouped according to study years. The zooplankton systems recorded at the research sites in 2006 constitute the most disparate group. Thus, it can be concluded that physicochemical properties might significantly impact both individual species (depending on their environmental demands) and entire zooplankton clusters

The aim of this study was to evaluate a procedure of weighing live fish larvae and to determine its impact on the survival and growth rates based on the example of ide Leuciscus idus(L.). The platform with larvae was then dried on the blotting paper and next weighed together with larvae. The weight of the larvae was calculated by deducting the weight of the platform from the total weight recorded. After weighing, the fish were returned to the rearing tank. Fish from the control group were not manipulated during the whole experiment. No significant differences were recorded in larvae survival, weight and length (91.33±4.73%; 41.69±10.70 mg; 17.56±1.44 mm and 94.00±4.00%; 49.40±10.79 mg; 18.41±1.24 mm in E group and C group, respectively). Significant differences were recorded in case of SGR that reached 15.80±0.29 in C group and 14.60±0.17 in E group. The described method may be a useful tool for determining fish larvae weight. Although it requires conducting further researches in order to establish the influence of accompanying factor such as e.g. kind and concentration of anaesthetic.

The objective of the study was to identify seasonal changes in phytoplankton taxonomic structure and development rates to characterize phytoplankton communities as determinants of the trophic and ecological conditions of Lake Kortowskie in northeast Poland which has been undergoing restoration with selective hypolimnetic withdrawal. The lake was designated as being of high trophic state and bad ecological status based on intense phytoplankton growth, the strong dominance and persistent occurrence of blue-green algae, and seasonal modifications in phytoplankton taxonomic structure and assemblage growth rates. The ecological status of the lake assessed in 2011 corresponds to that determined in 1987-1990 and 1999 and indicates that eutrophication in Lake Kortowskie is progressing.

Zooplankton are an important link between trophic levels in aquatic ecosystems, and their response to organic carbon is likely to have broad implications for lake food webs. The main objective of the research was to determine variations in zooplankton communities against the background of the structural heterogeneity of the lake and to link the observed patterns to the organic carbon content of the lake water. Spatial differences were noted in the organic carbon content of the lake water. Higher total organic carbon (TOC) and dissolved organic carbon (DOC) concentrations were recorded in the vegetated littoral area than in the lake pelagic zone. Zooplankton distribution and response to organic carbon content varied among habitats. At sites covered by plants, DOC and the bacterial sized fraction of particulate organic carbon were positively correlated with zooplankton biomass. In reeds, the grazing pressure by zooplankton on bacterial sized organic carbon was particularly strong. This implied that the microbial carbon link could be an important food web component providing carbon to higher trophic levels in areas covered by plants. This assumption corresponded well with the results of redundancy analysis (RDA).

Restoring lakes with hypolimnetic withdrawal can severely threaten water quality and biocenosis downstream. The objective of this study was to evaluate the effect of lake restoration on riverine zooplankton during a period of intense hypolimnion water inflow. Zooplankton density and biomass were determined in water samples. The water samples were also analyzed to determine the following physicochemical parameters: flow rate, dissolved oxygen, hydrogen sulphide, sulphate, ammonium nitrogen, nitrate nitrogen, total phosphorous, soluble reactive phosphorus, total organic carbon, and temperature. The results of multiple regression indicated that water flow was the most significant variable and was the best predictor of total zooplankton and rotifer density. Soluble reactive phosphorous was the main predictor of copepod biomass and density. Our study showed that hypolimnetic withdrawal disturbed the natural process of planktic community transformation, which was linked to the environmental shift from lacustrine to riverine. During the study, zooplankton density and biomass were low, but not as low as when the pipeline was operating at maximum output. At present, this lake restoration method has become more sustainable, because the adverse effects of hypolimnetic withdrawal on the recipient river have been minimized and limited to several weeks.

Knowledge and management of aquatic ecosystems (formerly Bulletin Français de la Pèche et de la Pisciculture), an international journal on freshwater ecosystem