Depth, sediment type, biogeography and high species richness in shallow-water benthos

Abstract

Until recently, quantitative data on the benthic fauna along the coast of Victoria, south-east Australia, were restricted to those few areas (potentially) receiving commercial and industrial effluent. Collectively, studies in these areas covered ~50 to 60 km of a coastline that extends for 1000 km. Recently, samples were taken from depths of 10, 20 and 40 m along the entire coast, and analysis of these made it possible to examine benthic community structure throughout the region. Species richness is high along the entire length of the coast, supporting the argument that species richness in temperate areas is not always higher in the deep sea than in shallow water. The major factor influencing species richness was depth. Although slightly more individuals were collected from stations at 10-m depth than from stations at 40-m depth, almost three times as many species were found at the deeper stations. Sediment type also influenced species richness. For the stations at 40-m depth, species richness was ~25% higher in medium and coarse sands than in fine sand. Pattern analysis suggested some bioregionalisation of the fauna, but the effect of geographical location on affinities among sample stations was much less than the effects of depth and sediment type.