Biodiversity of a continental shelf soft-sediment macrobenthos community

Soft-sediment macrobenthos data from the southern part of the Norwegian continental shelf was used to study faunal patterns and spatial variability, and to evaluate different measures of marine biodiversity. Water depth and sediment characteristics were remarkably uniform over the spatial sampling scale of 130 x 70 km, and relations between measured environmental variables and community structure were weak. Out of 175 recorded species, 10 % spanned the entire sampling area (16 sites), while 27 % were restricted to a single site. The number of rare species was positively correlated with species richness. Common species were widely spatially distributed, while species of low abundance had strongly compressed range sizes. The distribution of species varied among the 4 dominant taxonomic groups: the polychaetes, crustaceans, molluscs, and echinoderms, Polychaetes were the most common taxonomic group and had the highest proportion of widespread species. Whittaker's beta diversity measure (beta (W), extent of change in species composition among sites) varied among the dominant taxonomic groups and was highest for crustaceans, followed by molluscs. Neither the number of shared species nor the complementarity (biotic distinctness) between all pairwise permutations of sites was linked to spatial distance. However, the Bray-Curtis similarity between all pairwise combinations of sites was a function of spatial arrangement and was the most sensitive measure of beta diversity. Faunal pattern changed across the study area, despite the uniform habitat. Furthermore, faunal pattern and variability changed with scales. The measurement of biodiversity is therefore dependent on spatial scale, and cross-scale studies are important. The abstract concept of biodiversity as the 'variety of life' cannot be encapsulated by a single measure, Distributions of species and community differences should be taken into account in addition to species diversity when measuring marine biodiversity and planning conservation areas, and more than 1 taxonomic group should be studied in a system.