Hyperbenthos in the upper reaches of the Scheldt estuary (Belgium): Spatiotemporal patterns and ecological drivers of a recovered community

Monthly monitoring data between 2013 and 2018 are used to investigate and document the recovery of the hyperbenthic community in the Sea Scheldt, the Belgian part of the Scheldt estuary after a long-lasting state of hypoxia, and to identify ecological drivers of the current community. Hyperbenthos was present in all studied salinity zones and was taxonomically dominated by juvenile fish, Amphipoda, mysids and decapod shrimps. Species richness and guild diversity were comparable to that of other European estuaries. Variation in community composition was primarily governed by salinity zone and seasonality. In addition, hyperbenthos densities related negatively to recent river discharge, likely through flush effects or marinisation. Hyperbenthos abundance was positively affected by particulate organic matter density and was higher near neap tide. Seasonal migrations and changes in age and size distributions illustrate that the upper Scheldt estuary resumed its functions as spawning, nursery and feeding area. Given the observed rapid recolonization, we speculate that estuarine resident taxa may have persisted in refuges within the estuary from which recolonization could occur. Evidence is given of the contribution of the freshwater tidal zone to the estuarine food production and biodiversity maintenance functions, justifying maintenance and restoration of these rare habitats.