Soft-bottom community responses in a marine area influenced by recurrent dumping activities and freshwater discharges

The results of a 3 years monitoring program to assess the effects associated with recurrent dredged spoil disposal activity in a naturally stressed subtidal coastal area subjected to estuarine inputs are described. Changes observed through time in environmental and anthropogenic variables have been analyzed using cumulated sums and compared to macrobenthic community structure. Results revealed a scarce impact of the recurrent dumping activities, with faunal assemblages derived from the main “Tellina-venus community”. The magnitude of estuarine influence appeared indeed greater on the soft-bottom community than the putative changes due to anthropogenic activities. Through a combination of high energetic conditions, structural changes were observed and ascribed to a flushing action of the highly channeled estuary. Finally, an exceptional flood was recorded over the monitoring period, resulting in a short-term spatial homogenization of the benthic community with an abundance burst of A. alba. Origins of this main new species are discussed. •Short term spatial homogenization of the subtidal benthic communities following an exceptional flood event•Marginal effect of recurrent dumping activities on macrobenthic communities•Hydrodynamic conditions as key descriptors for the local distribution of benthic communities•A four-month recovery time observed for these soft-bottom communities exposed to multiple natural and anthropogenic disturbances