Geoscience Australia undertook seabed mapping surveys in the eastern Bonaparte Gulf in 2009/2010 to deliver integrated information relevant to marine biodiversity conservation and offshore infrastructure development. The survey objectives were to characterise the physical, chemical and biological properties of the seabed, document potential geohazards and to identify unique or sensitive benthic habitats and collect baseline information on these habitats. Different clustering methods were applied to a 124 sample dataset comprising 74 physical and geochemical variables which describe organic matter (OM) reactivity/quantity/source and geochemical processes relevant to biodiversity. Infauna data were used to assess different groupings because they are an important food source for epibenthic crustaceans and fish and purveyors of ecosystem services including nutrient cycling and mineralisation. Clusters based on physical/geochemical data discriminated infauna better than geomorphic features. Major variations amongst clusters included grainsize and a cross-shelf transition in from authigenic-Mn /As enrichments (inner shelf) to authigenic-P enrichment (outer shelf) which relate to energy levels and sediment oxygen status. Groups comprising raised features had the highest reactive OM concentrations (e.g. based on low chlorin indices and C:N-ratios, and high k) and benthic algal -13C signatures. Surface area normalised OM concentrations higher than continental shelf norms were observed in association with: (i) low -15N, inferring Trichodesmium input; and (ii) pockmarks. The pockmarks are shown to impart bottom-up controls on seabed chemistry and cause inconsistencies between bulk and pigment OM pools. The geochemical data and clustering methods provide insight into ecosystem processes which influence biodiversity patterns in the region. Low Shannon-Wiener diversity occurred in association with low porewater pH and evidence for low sediment redox status and high energy levels, while the highest beta-diversity was observed at euphotic depths. Pair-wise ANOSIM results for infauna are brought together in a summary model which highlights the influence of the clusters on beta diversity.
Abstract presented at GEOHAB 5-9 May 2014 Lorne, Australia
