Differences in recruitment and life-history strategy alter zooplankton spring dynamics under climate-change conditions.

In recent decades temperature elevation has been the focus of many studies on climate change, including effects on planktonic communities, but few studies have examined the effects of increased water color ("brownification"). Since these changes are likely to occur simultaneously, it is important to investigate their potential interactive effects. Accordingly, we performed a mesocosm experiment where we combined a 3°C increase in temperature with a doubling in water color to study how these factors affect zooplankton. In particular, we looked at recruitment of cladocerans and copepods from the sediment in spring, as well as their establishment in the water column. Our results show that an elevated temperature will have considerable effects on recruitment as well as on pelagic abundances of both cladocerans and copepods, whereas increases in water color will have less effects on the recruitment and pelagic establishment. But more importantly, the proportion of cladocerans in the water column, relative to copepods, increased at higher temperature, suggesting that cladocerans benefit more from elevated temperatures than copepods do. Overall, these results likely stem from the combined effect of changes in recruitment and differences in life history between copepods and cladocerans. Taking a wider outlook, this suggests that future climate warming will change the dominance pattern of zooplankton communities in spring, and, in accordance with the experimental data, we here show that cladocerans are more abundant than copepods in natural lake ecosystems during warmer rather than cooler years