Historical continuity as a determinant of habitat suitability for rare zooplankton in ephemeral wetlands developed on arable land

Abstract Most wetlands in the floodplains of lowland rivers have been lost to agriculture, while those that remain are often inhabited by dense populations of planktivorous fish that exclude large-bodied zooplankton species. Spontaneously occurring ephemeral wetlands on arable land are one of the last fish-free aquatic habitats that have the potential to serve as refugia for regionally rare zooplankton species. We repeatedly sampled zooplankton communities (Cladocera and Copepoda, including benthic species) in 48 ephemeral wetlands on arable land in a predominantly agricultural landscape (South Moravia) during different flood events. We observed a high variability in community composition between different flood events, indicating a higher diversity of dormant than active stages. While the communities consist of generalists, we also recorded species specialized to temporary pools, including regionally rare species (e.g. Daphnia atkinsoni species complex, Wlassicsia pannonica , Hemidiaptomus amblyodon ). Importantly, the number of species and the occurrence of rare zooplankton species increased significantly in wetlands with historical continuity. Our results suggest that ephemeral pools on arable land may serve as surrogate refugia for rare zooplankton species. Measures should be taken to avoid their destruction, prioritizing pools that were wetlands in the past, as they harbour a high diversity of zooplankton, including rare species.