Sponge gardens of Ningaloo Reef (Carnarvon Shelf, Western Australia) are biodiversity hotspots

During a multi-agency Australian Government initiative sponges were sampled at three areas from Carnarvon Shelf, NW Australia. Sponges were identified to lowest possible level, largely as morphospecies (84%). A searchable and interactive taxonomic catalogue was created and is publicly accessible through the Ningaloo Atlas collated by the Australian Institute for Marine Science. The sponge gardens on Carnarvon Shelf are patchily distributed but highly diverse and occasionally extremely dense. We examined 754 specimens and distinguished 261 species belonging to 112 genera. Species accumulation curves indicate that this species number does not represent local sponge biodiversity, which is projected to reach up to 840 species with additional sampling. Many observed species appear to be new to science, 81% occurred only at one of the three areas, about 56% were singletons, and 76% had a wet weight of ≤500 g. Detailed spatial analyses were difficult due to sampling design, but general trends could be detected. The northern areas, where the Australian continental shelf is narrowest, favour sponges with a higher content of inorganic skeleton and growth forms able to withstand the strong tidal currents and exposure typical for this area. Sponges were most abundant at the shelf edge, where massive forms dominated. While the central and northern areas are protected by zoning regulations, the southern area had the highest species diversity, the largest individuals and the densest distributions, suggesting additional conservation measures may be required. Western Australia is clearly an important, but under-studied bioregion for sponges, and future research foci are proposed.