Shifts in phytoplankton communities in response to water parameters and large branchiopod filter feeders in kettle hole ponds of farmland landscape.

Temporary ponds in agricultural landscapes, highly vulnerable to anthropogenic pressure and climatic variation, constitute unique habitats for microalgae and endangered filter feeders (large branchiopods). Such ponds play a crucial role in the functioning of farmland ecosystem, yet they remain largely understudied. Our study is the first to examine changes in phytoplankton communities in temporary kettle hole ponds in relation to rapid shifts in biotic (large branchiopods) and physical and chemical parameters of water. We conducted our research over a three-year cycle (in nine ponds in western Poland), with sampling starting in spring when inundation usually occurs, and continuing until the ponds dried out. Among 406 phytoplankton taxa (mainly euglenoids, but also diatoms and chlorophytes), locally rare species (e.g. Desmatractum indutum) were noted. When branchiopods occurred in the ponds, the phytoplankton communities shifted towards unicellular chlorophytes. Furthermore, nitrogen forms, temperature, conductivity, and pH were the abiotic factors altering the studied communities. Surprisingly, the diversity of phytoplankton species did not decrease with increasing temperature, which is inconsistent with the trend observed in permanent water bodies. The study identified specific drivers of phytoplankton community structure and dynamics, underscoring their ecological significance and management implications. These insights will be valuable for future conservation strategies of temporary ponds, crucial in sustaining biodiversity in farmland areas.