Optimising estuarine management with ecologically validated habitat maps in the Scheldt Estuary

Van Braeckel Alexander; Speybroeck Jeroen; Vanoverbeke Joost; Plancke Yves & Van den Bergh Erika Optimising estuarine management with ecologically validated habitat maps in the Scheldt Estuary Over the last decades the Scheldt Estuary has been altered by anthropogenic measures such as channel widening and enhanced wastewater treatment. At the same time, macrobenthic invertebrate abundance decreased whereas hyperbenthic (including mysid, shrimps, and decapod shrimps) and fish species reappeared in the upstream freshwater part. To assess effects of future modifications (maintain accessibility, dumping,...) on benthic species and their communities, a better understanding of the relation with hydro- and morphodynamics is necessary. Combining hydrodynamic and ecological modelling, we have investigated the relation of benthic species and communities with morphological and hydrodynamic variables in subtidal habitats of the freshwater and brackish water parts of the Scheldt. Flow velocities, derived from 2D hydrodynamic modelling, water depth, sediment characteristics and organic matter are used to explain community composition and species densities. Firstly, a multivariate analysis allowed for a distinction of a brackish and freshwater subtidal macrobenthic community. Secondly, within these salinity zones, maximum flood velocity explains the changes in the benthic species and communities. This is reflected in a typical high and low dynamic subtidal benthic community. Additionally hyperbenthic species preferred flood dominant areas within high dynamic areas. Based on a threshold analysis taking into account the most relevant variables, benthic and hyperbenthic community composition, a new habitat typology is proposed. This typology provides an improved, ecologically validated instrument for monitoring, evaluation and impact assessment of management measures and infrastructure works, such as dredging, dumping and sand extraction. As such, abiotic data can allow to define mitigation measures to minimize the ecological impact of these measures.