Life-history traits of lake plankton species may govern their phenological response to climate warming

A prominent response of temperate aquatic ecosystems to climate warming is changes in phenology - advancements or delays in annually reoccurring events in an organism's life cycle. The exact seasonal timing of warming, in conjunction with species-specific life-history events such as emergence from resting stages, timing of spawning, generation times, or stage-specific prey requirements, may determine the nature of a species' response. We demonstrate that recent climate-induced shifts in the phenology of lake phytoplankton and zooplankton species in a temperate eutrophic lake (Muggelsee, Germany) differed according to differences in their characteristic life cycles. Fast-growing plankton in spring (diatoms, Daphnia) showed significant and synchronous forward movements by about 1 month, induced by concurrent earlier ice break-up dates (diatoms) and higher spring water temperature (Daphnia). No such synchrony was observed for slow-growing summer zooplankton species with longer and more complex life cycles (copepods, larvae of the mussel Dreissena polymorpha). Although coexisting, the summer plankton responded species specifically to seasonal warming trends, depending on whether the timing of warming matched their individual thermal requirements at decisive developmental stages such as emergence from diapause (copepods), or spawning (Dreissena). Others did not change their phenology significantly, but nevertheless, increased in abundances. We show that the detailed seasonal pattern of warming influences the response of phyto- and zooplankton species to climate change, and point to the diverse nature of responses for species exhibiting complex life-history traits.