Physical Surrogates for Benthic Organisms in the Southern Gulf of Carpentaria, Australia: Testing and Application to the Northern Planning Area

The characterisation of benthic habitats based on their abiotic (physical and chemical) attributes remains poorly defined in the marine environment, but is becoming increasingly central in the development of marine management plans in Australia and elsewhere in the world. In this report, I test the link between physical and biological datasets for the southern Gulf of Carpentaria, Australia, and then apply these results to whole of the Northern Planning Area (NPA). The results presented are based on a range of physical factors, including the sediment composition (grain size and carbonate content), sediment mobility, water depth and organic carbon flux. The relationship of these physical parameters is tested against the distribution and diversity of benthic macrofauna. The results reveal the importance of process-based indices, such as sediment mobility, in addition to factors such as the percent mud and gravel, the seabed morphology and water depth in explaining the distribution of benthic marcofauna. Species-environment relationships observed at the small scale of this study are consistent with broader associations observed for other organisms within the Gulf of Carpentaria, allowing extrapolation to the wider NPA. Uncertainties in the extrapolation of the physical relationships across broader gradients than those tested need to be recognised in the application of these results to marine planning. In this report I seek to address the uncertainties associated with both the spatial prediction of habitats and the classification of seabed habitats through statistical procedures such as cluster analysis.