Sediment migrations drive the dynamic of macrobenthic ecosystems in subtidal sandy bedforms.

A traditional taxonomic approach coupled to a biological traits analysis was conducted in order to provide a new insight into macrobenthic communities associated with subtidal sandy environments. Results suggest that the macro-scale distribution of benthic communities is mainly driven by the migration rate of bedforms (sandbank, barchan dune and transversal dune) which changes the sediment grain size and reduces macrobenthic diversity. A classic scheme of species/traits succession was also observed from less to more physically disturbed areas. Finally, the high frequency of migration events homogenized macrobenthic communities between the troughs to the crest of bedforms. As bedforms areas are targeted for the commissioning of offshore windfarms the information provided by the present paper will be particularly useful to implement the environmental impact assessment required for such activities at sea.

Environmental control on fish and macrocrustacean spring community-structure, on an intertidal sandy beach.

The inter-annual variability of the fish and macrocrustacean spring community on an intertidal sandy beach near the Canche estuary (North of France) was studied from 2000 to 2013 based on weekly spring sampling over an 11-year period. Twenty-eight species representing 21 families were collected during the course of the study. The community was dominated by a few abundant species accounting for > 99% of the total species densities. Most individuals caught were young-of-the-year indicating the importance of this ecosystem for juvenile fishes and macrocrustaceans. Although standard qualitative community ecology metrics (species composition, richness, diversity, evenness and similarity) indicated notable stability over the study period, community structure showed a clear change since 2009. Densities of P. platessa, P. microps and A. tobianus decreased significantly since 2009, whereas over the period 2010-2013, the contribution of S. sprattus to total species density increased 4-fold. Co-inertia and generalised linear model analyses identified winter NAO index, water temperature, salinity and suspended particular matter as the major environmental factors explaining these changes. Although the recurrent and dense spring blooms of the Prymnesiophyte Phaeocystis globosa is one of the main potential threats in shallow waters of the eastern English Channel, no negative impact of its temporal change was detected on the fish and macrocrustacean spring community structure.