Assessing functional diversity in marine benthic ecosystems: a comparison of approaches

Two methods traditionally employed to investigate functional diversity in marine benthic ecosystems are relative taxon composition analysis, which interprets changes in the distribution of taxa in terms of the characteristics they exhibit, and trophic group analysis, which investigates differences in feeding mechanisms between assemblages. An alternative approach, biological traits analysis, considers a range of biological traits expressed by organisms to assess how functioning varies between assemblages. This study compares biological traits analysis to the relative taxon composition and trophic group approaches. Biological trait scores were assigned to a range of epibenthic invertebrate taxa from the southern North Sea and eastern English Channel and differences in the relative proportions of these traits were investigated using multivariate methods. The traits important in differentiating stations were attachment, flexibility, body form, mobility, feeding method and life habit. Such assemblages were spatially heterogeneous and there was no obvious distinction between different geographical sectors. This contrasted with the results of the relative taxon composition approach, which showed broad patterns in assemblage distribution in the eastern English Channel and southern North Sea. The biological traits approach provided information on a larger variety of ecological functions than the other techniques and revealed very different relationships between assemblages. It highlighted a greater diversity of assemblage types and was resistant to large-scale biogeographic variations Therefore, it is potentially more useful than the traditional approaches for assessing ecosystem functioning on both large and small scales in benthic environments.