Long-term changes of the Seine estuary suprabenthos (1996-2012)

The freshwater discharge into the Seine estuary decreased between 1996 and 2012 and no discharge > 1200 m3 s− 1 has occurred after 2001. The suprabenthic community in the navigational channel of the Seine estuary was characterised in 1996 by high abundances and biomass of mysids and the decapod Palaemon longirostris, which were among the highest in the world for transitional waters during a period of high discharge of the Seine River. A recent sampling (2011-2012) of the suprabenthos in new hydrological conditions (i.e., low river discharge) showed subsequent changes of the quantitative composition of the community with both decreases of abundance and biomass. Such long-term changes were probably due to the combination of hydrological changes, and anthropogenic modifications of the entrance of the Estuary, the Port 2000 construction, and supplementary dredging in the navigational channel of the Rouen harbour. The changes of the suprabenthic community encompassed an important impact in the estuarine trophic chain, which was essential to fish juveniles, such as sea bass and flat fish.