Abstract
In this study we aim to provide a basic description and comparison of the spatial distribution and population structure of the common intertidal mollusc species, sampled within a single winter along a latitudinal gradient of diVerent soft-sediment areas spanning 8° of latitude (46°-54°N) and 900 km of dis- tance in northwest Europe. Sediment samples were collected from December 2003 to early March 2004 in the Wadden Sea (The Netherlands), the Wash (United Kingdom), Mont Saint-Michel Bay (France) and two bays on the central French Atlantic coast in south of Brittany. Core-sampling over 250 m grids allowed us to cover 3-30 km² at nine separate intertidal subsites, with a grand total of 2,103 points visited. Among the 15 bivalve and 8 gastropod species collected, we focused on the four most common and abundant bivalve spe- cies (Cerastoderma edule, Macoma balthica, Scrobicu- laria plana and Abra tenuis) that together represented 96% of all collected bivalves, and on the mudsnail Hydrobia ulvae that comprised 99% of all collected gastropods. C. edule and M. balthica were the most widespread bivalves, with higher densities occurring at higher latitudes. S. plana and A. tenuis were more abundant at southern sites, both with a clear prefer- ence for muddy sediments. The mudsnail H. ulvae occurred commonly and in comparable densities at all study sites, except in Mont Saint-Michel Bay where it was very rare. Mean sizes of the common molluscs were highly variable between sites, without clear north-south gradients. The mollusc distribution pat- terns at the Wve intertidal areas and nine subsites were predominantly site-speciWc. Mollusc community com- position showed greater similarity within than between the regions north and south of the Brittany peninsula.
Published Version
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