Biological surveys of inshore soft-bottom communities in Tasmania

Abstract

Benthic invertebrates were sampled from seagrass, sand and mud habitats around Tasmania from three coastal environment types, Georges Bay, Norfolk Bay and the Tamar River. Seasonal sampling was undertaken at a selected number of sites in each area and a snapshot survey conducted to examine invertebrate assemblages over a broader geographical range. The habitat study revealed no large differences in densities or diversities between environment types. Vegetated sites generally had highest densities and diversity, although not at all sites in all areas. Hence, in order to maximise invertebrate abundance and diversity both vegetated and shallow and deep unvegetated habitats should be included within a marine reserve system. A distinct assemblage occurred at sandy beach sites, while the remaining sites showed a gradation of assemblage change from deep unvegetated to shallow vegetated with assemblages showing little habitat specificity. No consistent seasonal trend was apparent in invertebrate densities or diversity. Autumn assemblages were markedly different at four out of nine sites indicating that autumn is the least appropriate season to undertake soft-bottom invertebrate surveys. However, it is not known if the temporal shifts in relationships are truly seasonal or resulted from variability between different sets of samples. In general, the snapshot survey revealed no trend in densities or diversity with regard to geographic location with highest densities and diversity at the most marine dominated vegetated sites. Species assemblages showed little similarity by habitat, or between both near and geographically separated sites. Hence, the habitat and snapshot survey indicate that to cover the range of inshore soft-bottom assemblages, marine reserves should encompass sandy beach habitats, and mud and seagrass habitats covering a broad range of environmental conditions.