Soft-sediment benthic biodiversity on the continental shelf in relation to environmental variability

Abstract

Soft-sediment macrobenthos data for the Norwegian continental shelf (61°N, 1 to 2°E) was used to examine species distributions, community structure and community differences, and how different measures of biodiversity are related to environmental variability. Water depth at 35 sites ranged from 115 to 331 m over a spatial sampling scale of ca. 45 km × 60 km, and there was consid- erable variation in sediment characteristics. Of a total of 508 recorded species, 39% were restricted to 1 or 2 sites, whereas only 3 species spanned the entire sampling area. Polychaetes were the most common and widespread taxonomic group; crustaceans and echinoderms were more restricted in their distributions than the other dominant groups. Whittaker's beta diversity measure ( βW, extent of change in species composition among sites) was highest for those groups with the highest proportion of restricted-range species. The number of shared species, the complementarity (biotic distinctness), and the Bray-Curtis similarity between all pairwise combinations of sites (3 beta diversity measures) were more strongly related to change in environment (notably depth, followed by median grain size and silt-clay content) than to spatial distance between sites. Likewise, a multivariate analysis (BIO- ENV) identified these factors as the major environmental variables influencing the faunal patterns, whereas univariate measures of diversity were not related to depth or median grain size. Univariate measures of diversity, beta diversity measures, and BIO-ENV analyses showed that molluscs, followed by polychaetes, were most highly related to environmental variables. In this study, alpha, beta and gamma diversity were higher than in a study of a single soft-sediment habitat type in the southern part of the Norwegian continental shelf.