Influence of temperature on zooplankton emergence from a riverbank and floodplain sediments of a regulated temperate river

Context River regulation has altered the timing and magnitude of hydrological connectivity between rivers and their floodplains, with potential consequences for zooplankton that persist by diapausing eggs in sediment ‘egg banks’. Aims We examined how water temperature and recent inundation history of riverbank v. floodplain sediments influence emergence, diversity and community composition of zooplankton. Methods Dry riverbank and floodplain sediments from the lower Lachlan River (New South Wales, Australia) were rewetted and incubated in temperature-controlled cabinets at 10°C (winter) and 21°C (spring). Emerging zooplankton were sampled repeatedly over 6 weeks and identified to the lowest feasible taxonomic level. Key results Greater abundance of zooplankton emerged at warmer temperatures, and floodplain sediments supported a greater abundance and diversity of emerging zooplankton, whereas differences in community composition between habitats were minor, perhaps because all collected sediments had been recently inundated by large-scale flooding. Conclusions Seasonal timing and the extent of floodplain inundation jointly govern activation of sediment egg banks and zooplankton emergence dynamics in this regulated lowland river–floodplain system. Implications Management that maintains lateral river–floodplain connectivity, particularly during warmer periods, is likely to support high zooplankton abundance with potential flow-on effects for the riverine food webs.