Impact of enhanced summer temperatures on the distribution and structure of zooplankton communities in the heated stratified lakes: Implications for climate change.

Abstract Long-term studies demonstrated that temperature increases of 3–6 °C above natural levels caused reduction in zooplankton biomass. We hypothesized that large-bodied species would respond more strongly to temperature increases than small-bodied species because they are less adapted to high temperatures. Studies were conducted in three similar stratified meso-eutrophic lakes with different thermal regimes. Enhanced temperature, migrations, food abundance and dissolved oxygen concentrations were analyzed as potential factors that could affect zooplankton biomass. The warmest lake differed from the other lakes by lower total biomass of zooplankton less abundance of large-bodied zooplankton species, smaller population body sizes of abundant cladoceran species and higher food concentrations. Day and night abundances of zooplankton did not differ between the vertical strata and between the pelagic and littoral zones in the three study lakes suggesting that zooplankton did not vertical or horizontal migrations. We suggest that decreases of dissolved oxygen below the epilimnion prevented zooplankton from vertically migrating. As a result, zooplankton accumulated in the epilimnion where temperatures were higher than in the lower strata. Regression analysis showed that temperature had a significant negative impact on the total biomass of zooplankton in the epilimnion of the warmest study lake. Therefore, our results are in accordance with the ecological Bergmann's and James' rules dealing with the temperature-size relationships. [ABSTRACT FROM AUTHOR]