The influence of spring warming and food chain length on plankton phenology in subtropical shallow lakes: a mesocosm study

Numerous studies have shown that warming advances spring phenology in various ecosystems. However, few studies explicitly consider the effect of food web structure, e.g. food chain length (FCL), and most studies have focused on temperate systems. We investigated the effect of vernal warming on the spring phenology of a key herbivore, Daphnia galeata (hereafter Daphnia), and its prey, phytoplankton, in subtropical shallow aquatic mesocosms in the presence and absence of the planktivorous fish Aristichthys nobilis, simulating food chains with two or three trophic levels. The warming effect on the timing of the spring phytoplankton peak varied with the FCL. Warming led to the disappearance of the phytoplankton peak in the 2-level systems but resulted in an extensive, delayed phytoplankton peak in the 3-level systems. Irrespective of the FCL, warming did not significantly advance the timing of the Daphnia peak, although Daphnia recruited earlier under warm conditions. Both warming and FCL significantly reduced the size of the Daphnia peak. Our study suggests that spring warming affects the plankton spring phenology in subtropical shallow lakes, but the response patterns depend on the food web structure.