Zooplankton hatching from dormant eggs in a large Pampean shallow lake

Dormancy is an essential component of the life cycle for populations that disappear from the plankton during winter. The hatching of resting eggs is the main mechanism for restoring active population components. Here, we analyzed the hatching dynamics of zooplankton from sediments of a shallow lake as affected by temperature. Sediment samples collected every other month were incubated at in situ temperatures and at 20 degrees C. The highest number of individual's hatchings was observed for copepod nauplii, the cladoceran Bosmina sp., and the rotifer Brachionus havanaensis. Temperature showed a positive significant effect on the hatchlings of B. havanaensis. Other zooplankton species were less affected by temperature, and there was no relationship between their emergence from the incubated sediments and occurrence in the water column. We also tested the effect of short-term (6 and 12 weeks) and long-term (a year) storage duration on hatching success. The hatching success of B. havanaensis was not affected by the storage time. In contrast, the hatchlings of Bosmina sp. and nauplii increased after short storage time. The evidence collected here suggests that many zooplankters were not affected by temperature, while for B. havanaensis temperature turned out to be a master variable that links planktonic and passive phases.