Effects of zebra mussels on cladoceran communities under eutrophic conditions

The purpose of this study was to determine how zebra mussels affected cladoceran community structure under eutrophic conditions. We conducted a mesocosm study where we manipulated the presence of zebra mussels and the presence of large-bodied Daphnia (Daphnia magna and Daphnia pulicaria). We also conducted a complimentary life-table experiment to determine how water from the zebra mussel treatment affected the life history characteristics of the cladoceran species. We anticipated that small- and large-bodied cladoceran species would respond differently to changes in algal quality and quantity under the effects of zebra mussels. Large-bodied Daphnia successfully established in the zebra mussel treatment but failed to grow in the control. We did not observe positive relationships between food concentrations and cladoceran abundances. However, the phosphorus content in the seston indicated that food quality was below the threshold level for large-bodied cladocerans at the beginning of the experiment. We believe that zebra mussels quickly enhanced the phosphorus content in the seston due to the excretion of inorganic phosphorus, thus facilitating the development of large-bodied Daphnia. In conclusion, our results suggest that zebra mussels can alter the phosphorus content of seston in lakes and this can affect the dynamics of crustacean zooplankton

Data Descriptor : A European Multi Lake Survey dataset of environmental variables, phytoplankton pigments and cyanotoxins

Under ongoing climate change and increasing anthropogenic activity, which continuously challenge ecosystem resilience, an in-depth understanding of ecological processes is urgently needed. Lakes, as providers of numerous ecosystem services, face multiple stressors that threaten their functioning. Harmful cyanobacterial blooms are a persistent problem resulting from nutrient pollution and climate-change induced stressors, like poor transparency, increased water temperature and enhanced stratification. Consistency in data collection and analysis methods is necessary to achieve fully comparable datasets and for statistical validity, avoiding issues linked to disparate data sources. The European Multi Lake Survey (EMLS) in summer 2015 was an initiative among scientists from 27 countries to collect and analyse lake physical, chemical and biological variables in a fully standardized manner. This database includes in-situ lake variables along with nutrient, pigment and cyanotoxin data of 369 lakes in Europe, which were centrally analysed in dedicated laboratories. Publishing the EMLS methods and dataset might inspire similar initiatives to study across large geographic areas that will contribute to better understanding lake responses in a changing environment.Peer reviewe

Stratification strength and light climate explain variation in chlorophyll a at the continental scale in a European multilake survey in a heatwave summer

To determine the drivers of phytoplankton biomass, we collected standardized morphometric, physical, and biological data in 230 lakes across the Mediterranean, Continental, and Boreal climatic zones of the European continent. Multilinear regression models tested on this snapshot of mostly eutrophic lakes (median total phosphorus [TP] = 0.06 and total nitrogen [TN] = 0.7 mg L−1), and its subsets (2 depth types and 3 climatic zones), show that light climate and stratification strength were the most significant explanatory variables for chlorophyll a (Chl a) variance. TN was a significant predictor for phytoplankton biomass for shallow and continental lakes, while TP never appeared as an explanatory variable, suggesting that under high TP, light, which partially controls stratification strength, becomes limiting for phytoplankton development. Mediterranean lakes were the warmest yet most weakly stratified and had significantly less Chl a than Boreal lakes, where the temperature anomaly from the long-term average, during a summer heatwave was the highest (+4°C) and showed a significant, exponential relationship with stratification strength. This European survey represents a summer snapshot of phytoplankton biomass and its drivers, and lends support that light and stratification metrics, which are both affected by climate change, are better predictors for phytoplankton biomass in nutrient-rich lakes than nutrient concentrations and surface temperature

Summer food of juvenile turbot, Psetta maxima (L.) and flounder, Platichthys flesus (L.), at Świętouść, Pomeranian Bay

Summer food of 0- and I-age group turbot and flounder utilizing shallow, inshore nursery ground at Świętouść, Pomeranian Bay were examined. Juvenile turbot fed mostly on mysid. Neomysis integer, Pisces and Crangon crangon. Amphipod Bathyporeia pilosa was of little importance. Juvenile flounder fed on polychaete, Nercis diversicolor, and amphipod Bathyporeia pilosa and Gammarus spp. Tiny bottom-stages of Mollusca were of minor importance. Shifts in diet preferences as a function of fish size were observed in both species. Owing to differences in diet composition practically no diet-overlap was found between larger turbot and flounder, from age group I. Between 0-group fish, of these species, diet-overlap high as 36% for two food items shared, Calanoida and Bathyporeic pilosa, occurred

Factors of dynamics of plankton crustacean communities under eutrophic conditions.

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Показано, что основным драйвером динамики обилия ветвистоусых и веслоногих ракообразных в эвтрофных условиях являются хищничество (рыбы), количество или качество пищи, выражаемое в содержании эйкозапентаеновой кислоты, фосфора и азота в сестоне. В результате исследований по динамике обилия веслоногих и ветвистоусых ракообразных в присутствии и отсутствии рыбы в экспериментальных мезокосмах с эвтрофными условиями установлено, что рыбы в эвтрофных условиях не влияют на количество и качество пищевых ресурсов для ракообразных. Однако во второй половине наших экспериментов наблюдался переход доминирования от веслоногих к ветвистоусым ракообразным. Это было связано не с влиянием рыбы, а с улучшением качества пищи для ветвистоусых ракообразных, определяемое соотношением углерода к фосфору в сестоне. Рыбы в эвтрофных условиях понижали биомассу как ветвистоусых, так и веслоногих ракообразных, не меняя соотношение между ними