Suspended sediment grain size and mineralogy across the continental shelf of the Great Barrier Reef: Impacts on the physiology of a coral reef sponge

Declining water quality associated with increased suspended sediments has been closely linked to the reduced health status of benthic marine ecosystems and their associated organisms, including marine sponges. The mechanisms driving the impacts of elevated suspended sediments on marine sponges are poorly investigated. This study elucidates spatial and temporal variations in sediment size and mineralogy of inorganic suspended sediments within sponge habitats (reef environments) across the continental shelf of the central Great Barrier Reef (GBR), North-eastern Australia. Inshore sponge habitats were dominated (>80%) by fine-grained suspended sediments consisting of both terrigenous (clay and quartz) and biogenic material (carbonates) with grain sizes <100 μm. In contrast, mid- and outer-shelf sponge habitats were dominated by carbonate material with grain sizes >100 μm. The abundance and distribution of the common coral reef sponge Rhopaloeides odorabile across the GBR shelf shows a clear correlation between habitat and the distinct patterns in suspended sediment size and mineralogy. Experimental exposure of R. odorabile to clay and carbonate sediments in this study provides the first evidence that the metabolic demand (respiration) of coral reef sponges increases (up to 40%) in response to fine terrigenous (clay) sediments. This physiological response supports sediment load, size, and mineralogy as key factors affecting the distribution and abundance patterns of R. odorabile across the continental shelf of the central GBR.