Effects of Spring Temperature on Seasonal Dynamics of a Freshwater Zooplankton Community

ABSTRACT With climate change and rising temperatures, the timing of spring is advancing in many parts of the world. Such environmental changes may have immediate effects on species communities, but also carry‐over effects into later seasons. However, little is known about the extent of such carry‐over effects for communities consisting of short‐lived species with multiple life cycles in a year. We used a 26‐year dataset to explore the immediate and carry‐over effects of spring temperature on freshwater zooplankton communities consisting of three taxonomic groups (Rotifera, Cladocera and Copepoda), sampled at three locations in a lake in central Norway. We first described the seasonal dynamics of zooplankton community abundance and species richness, as well as the ratio between abundance and species richness, using generalised additive mixed models (GAMM). Next, we used a sliding window analysis to identify the most important time during spring for which temperature affected community abundance and species richness, and the impact of this window on different parts of the seasonal curve of abundance and species richness of the community. This allowed us to explore whether spring temperature affected overall abundance and species richness, whether there were seasonal differences in the strength of the effect, how any effects varied between the three phyla, and whether they were consistent among the three localities. Cladocera and Rotifera roughly followed the expected seasonal pattern, with a peak in total abundance. Copepoda, on the other hand, showed lower abundance in the middle of the sampling season. The shape of the curve also varied between localities. Spring air temperature affected the overall abundance, species richness, and abundance: species richness ratio throughout the season. In some cases, models with an interaction between spring temperature and Julian day were the best, indicating that the effect of spring temperature varied temporally in strength and direction. Given the short life cycles of most zooplankton species present in our dataset, it is surprising that effects of spring temperature are visible throughout the summer and into early autumn. This implies that pulse disturbances may have long‐lasting, multigenerational effects even in communities of short‐lived species. Our study also illustrates how different zooplankton groups may vary in their response to temperature variations.