The influence of geomorphology and sedimentary processes on benthic habitat distribution and littoral sediment dynamics: Geraldton, Western Australia

Understanding of the processes regulating sediment transport, accumulation and erosion requires an appropriate mapping of coastal geomorphology, seabed sediments and benthic habitat distribution to allow management issues to be identified, understood and addressed. In this study multibeam echo-sounder data were used to map shallow water geomorphological features and the spatial distribution of benthic habitats, with the support of underwater imagery for ground truthing the acoustic data. At Geraldton, sediment analyses have revealed a dominant biogenic nature, with modern carbonate sedimentation linked to the seagrass and macroalgal carbonate factories colonising these shallow (< 30 m) coastal embayments. Whilst seagrasses are common on sheltered hardgrounds blanketed by fine sand, macroalgae were found on high energy limestone reefs. The distribution of sand bar and sheet systems is regulated by wave induced sediment transport with the influence of pre-existing seabed topography. Exposure to wave energy, seabed geomorphology and sediment characteristics is closely related to the distribution of benthic habitats and sand substrates, highlighting the value of an integrated analysis of these parameters. The capability of multibeam echo-sounder backscatter data to discriminate between seagrass meadows, macroalgal communities and sandy substrates was also evaluated and the acoustic response from the seabed was better explained by considering together seafloor geomorphology and biota type, as both these parameters influence backscatter strength.