Fishing disturbance and marine biodiversity: role of habitat structure in simple soft-sediment systems

Broad-scale anthropogenic disturbances that reduce the density of epifauna and homogenise surficial sediments can have important consequences for seaf loor biodiversity, We investigated the habitat structure and macrofaunal di versity of relatively simple soft-sediment habitats over a number of spatia l scales (cm to km) to identify the role of habitat structure in influencin g macrobenthic diversity and to assess the validity of using habitat struct ure as a surrogate measure for biodiversity. We sampled 10 locations with d ifferences in habitat structure using a sampling design that nested macrobe nthic core samples within videoed transects of the seafloor. This allowed u s to determine relationships between observable habitat structure and macro benthic diversity at a number of spatial scales. We characterised elements of habitat structure based on direct counts of surficial sediment character istics and the presence of other immobile features, many of which were biog enic in origin. We also used multivariate measures (the relative multivaria te dispersion, the mean and range of the Bray-Curtis dissimilarity along th e transects) to characterise habitat structure at the transect scale. We de veloped regression models based on measures of habitat structure that expla ined 74 to 86% of the variance in macrobenthic diversity. This result sugge sts that removal of habitat structure in relatively low-structure soft-sedi ment systems will significantly decrease their biodiversity, and consequent ly that of the wider marine ecosystem.