Update on the soft-bottom benthic habitats in the Belgian Part of the North Sea, with new functional information

Soft-bottom macrobenthic habitats are an essential part of the marine ecosystem and so their healthy status is strived for. Previously, four soft-bottom macrobenthic habitats were distinguished in the Belgian part of the North Sea: the coastal Macoma balthica and Abra alba habitats, and the offshore Nephtys cirrosa and Ophelia borealis habitats. The current study provides a revision, based on an enlarged dataset with 10 more years of data (1994-2012) and an increased spatial coverage. In addition, the habitats are also described functionally by means of biological traits. The structural characteristics in the muddy Macoma balthica, fine muddy sand Abra alba, and well sorted medium sand Nephtys cirrosa habitats showed no obvious changes compared to previous studies. However, a new coastal fine muddy sand Magelona-Ensis directus habitat is described, with low diversity values and a dominance of alien species Ensis directus. Also, the offshore Ophelia borealis habitat, previously characterized by low diversity and abundance, is now renamed as Hesionura elongata, still characterized by medium to coarse sands, but now showing high diversity and moderate abundances. Functionally, the most remarkable differences were observed between the coastal and the offshore habitats. In the relative coarser, permeable sands in the offshore area, we find more free living, mobile polychaetes and crustaceans, whilst the finer sand habitats have more sessile, tube building and burrow dwelling species. This is apparent in differing trait values for living habit, feeding mode, mobility and bioturbation. This study
illustrates how an appropriate spatial and temporal coverage within a baseline dataset is required as a proper starting point to assess the structural and functional state of an area.