Sediments and Benthic Biota of Bass Strait: an Approach to Benthic Habitat Mapping

The biological data used in this study was collected by Museum Victoria in an extensive survey of the fauna of Bass Strait between 1979 and 1983. Additional sediment sampling and swath mapping of parts of Bass Strait were undertaken on GA Survey 226 and Australian Hydrographic Office Survey HI339, in which Geoscience Australia personnel participated (GA Survey 233). Survey HI339 also collected underwater video footage. Biological material from a range of taxonomic groups was identified as a basis for identification and analysis of biological communities. The results indicate that Bass Strait supports a particularly diverse fauna. A high degree of small-scale variation occurs, with even adjacent samples having low similarity. Video footage from sites to the east of Bass Strait corroborates the high degree of faunal diversity over small spatial scales. Analysis of physical variables, derived from data collected on the original survey and supplemented by more recent data, show that longitude and depth are important factors in explaining the biological diversity. Despite this, overall correlation of faunal composition with physical factors is poor, indicating that other environmental variables influence the composition of benthic assemblages, and that different groups of species react to different environmental variables. It is likely that the biota reflect a series of intergrading assemblages rather than a group of discrete and repeatable species associations. Sediment facies identified can be correlated with facies from the Otway margin (Boreen et al., 1993) and those mapped previously in Bass Strait (Jones and Davies, 1983). Analysis of sediments taken from sites previously targeted by Jones and Davies (1983) indicate that sampling technique has had little impact on retention of fines. Rather, the lack of fines is a reflection of the high energy environment of much of Bass Strait. Examination of the composition of sand and gravel fractions indicates that extensive bioerosion acts in concert with physical processes to produce carbonate mud. Biogenic content in sediments shows little correlation with living communities, due in part to the abundance of soft-bodied organisms in the biota, as well as the strong imprint of post-depositional processes on sediments. The biological patterns identified in this study broadly support the divisions of the current Interim Marine and Coastal Regionalisation of Australia (IMCRA Technical Group, 1998) for Bass Strait. However, the biological assemblages are not consistent enough to be mapped. The lack of relationships between biota and sediments over the scale of the study area may reflect the scale of the study area and limitations of the statistical analyses used.