The Role of Temperature in the Termination of Dormancy in Zooplankton

Abstract

Organisms in systems with seasonality require adaptations that enable them to endure harsh conditions and to emerge again at an optimal time to start a new period of production. One such adaptation is dormant eggs in zooplankton. While there is much information on the cues leading to the production of dormant eggs, less is known about the termination and hatching of these eggs, especially among marine zooplankton. Our results from a combined laboratory and field study at a coastal Baltic Sea site showed that hatching in some overwintering copepods was temperature-dependent, with a threshold-like initiation between 6°C and 9°C. In contrast, overwintering rotifers hatched in comparable abundances in all temperatures, once a similar amount of degree-days had been accumulated. The field study demonstrated that nauplii started to appear when temperatures increased above 6.8°C and were more abundant close to the sediment than in surface water in early spring, matching the hatching threshold found in the laboratory. Various rotifers increased in abundance at different times during the spring phenology, but without any differences in abundance between deep and surface waters. Hence, the hatching of zooplankton dormant eggs in this system is temperature-dependent, likely taxa-specific, and continued climate change is predicted to have implications for the plankton phenology, mismatches, and food web composition.