Responses of a Northern Adriatic Ampelisca–Corbula community to seasonality and short-term hydrological changes in the Po river

During the 20th century, increased nutrient inflow has increased the frequency and intensity of eutrophicationevents in the North-western Adriatic Sea. More recently, evidence of a reduction in the Po riverflow and a recovery of the benthic environment were reported. We examined the role played by Po riverregime and seasonality in determining the temporal pattern of macrozoobenthos variation: samples werecollected from a site located 10–12 km off Cesenatico during two years from October 2004 to September2006, when the mean Po discharge remained exceptionally low. 88 taxa were found, and the communitywas dominated by few species: Ampelisca diadema, Lumbrineris latreillii, Corbula gibba, Aricidea claudiae,Levinsenia gracilis and Nucula nucleus account for about 80% of total abundances. The density of these speciesexhibited a marked seasonal variability. Moreover, the total abundance and the density of the sensitivespecies, A. diadema, were negatively affected by several disturbance events (hypoxic conditions,frequent storms and an anomalous winter flood) that occurred between November 2005 and March2006. The reduction of C. gibba and the increase of A. diadema densities observed in the investigated period,and verified recently by other authors could be related to the reduction in river inputs as a consequenceof climatic changes.