Synergistic effects of warming and eutrophication alert zooplankton predator-prey interactions along the benthic-pelagic interface.

Contemporary evidence suggests that climate change and other co-occurring large-scale environmental changes, such as eutrophication, will have a considerable impact on aquatic communities. However, the interactions of these environmental changes on trophic interactions among zooplankton remain largely unknown. Here we present results of a mesocosm experiment examining how a couple of zooplankton predator and prey taxa with different life-history strategies respond to the combined effect of an increase in temperature (4.5°C) and in eutrophication (phosphorus addition), during the crucial recruiting and growing season. We show that the addition of phosphorus alone significantly weakened the top-down effects by the cyclopoid copepod predators on their rotifer prey. In contrast, warming strengthened the top-down effects from the predator, leading to a reduction in the abundance of the rotifer prey. These effects of warming were enhanced by phosphorus addition. Together, our results demonstrate that warming made plankton prey organisms more susceptible to top-down effects from predators, but reduced their sensitivity to nutrient enrichment. In terms of the phenological effects, warming advanced the termination of diapause for both rotifers and cyclopoid copepods by about 2 weeks, but these temporal shifts, akin for both groups, resulted in no apparent trophic mismatch. Hence, from a future perspective, cyclopoid copepods are likely to benefit more from the combination of nutrient enrichment and climate warming to the detriment of their rotifer prey.