Lake Sediments Exposed Under Warmer Temperatures Hatched a Lower Diversity of Microfauna From the Egg Bank

ABSTRACT Dormant structures produced by aquatic microorganisms are ecologically important for restoring ecosystems after extreme climatic events. Among these events, heat waves cause the desiccation of environments and expose sediments to high temperatures, which reduce the viability of dormant propagules. Here, we measured the richness and species composition of the dormant aquatic microfauna (ciliates, rotifers, cladocerans, copepods and ostracods) hatched from sediments heated under a gradient of increasing temperatures. Sediment samples were collected from a temporary lake in the Upper Paraná River floodplain, Brazil. The material was exposed at temperatures of 25°C, 30°C, 40°C, 50°C, and 60°C. They were subsequently inundated and kept in mesocosms at 25°C with a 12‐h light/dark photoperiod for 8 weeks. Hatched organisms were harvested weekly. Increasing drying temperature significantly reduced the richness of hatching aquatic microfauna and led to significant differences in species composition between temperature treatments, although these trends were less linear for microcrustacean. Temperatures above 50°C (not uncommon for dried sediments exposed to direct sun in humid tropical areas) negatively affected community richness and promoted biotic homogenization of the communities hatched from the egg bank. Therefore, increased sediment temperatures in dry wetlands are a potential threat to dormant microfauna through biotic homogenization and species loss. Mitigation measures may be needed to conserve wetland egg banks.