Sediment grain size and bedform morphology and dynamics shape benthic community heterogeneity in submarine dune fields.

The distribution of benthic communities is governed by a multitude of interacting ecological processes. Among these factors, sediment grain size is generally considered as a key structuring factor for benthic communities in the eastern English Channel. However, grain size often oversimplifies the true complexity of the substrate, as the presence of bedforms such as submarine dunes adds another layer of complexity to this relationship. This study utilizes bathymetric, grain size, and macrofauna benthic data collected during four surveys conducted between 2014 and 2016 at the planned site of the Dieppe-Le Tréport offshore wind farm. The significance of these sedimentary characteristics for benthic community structure was examined through multivariate analyses and trophic group studies. The results revealed significant heterogeneity in the benthic communities within dune fields. The troughs and adjacent nondune areas, which are primarily composed of coarse sediments (gravels), support a diverse community dominated by deposit feeders and filter feeders. In contrast, the stoss and lee sides of the dunes present a much less diverse community dominated by predators and scavengers. The mechanisms driving this structuring are discussed, with an emphasis on sediment dynamics and trophic processes.