Intertidal molluscan and echinoderm diversity at Althorpe Island and Innes National Park, South Australia

Species inventory data provide the first step towards understanding local marine communities. Here I apply rapid biodiversity assessment to ten intertidal sites, with two levels of habitat complexity: rock platform with and without boulder fields. Five sites were located in Althorpe I., with a further five reefs in and around the Innes National Park on Yorke Peninsula. One hour time-search surveys were used to determine the species richness and rarity of macromolluscs and echinoderms. In total 82 molluscan species were found, but only eight echinoderms. A large proportion of species was found to be numerically rare (site) or spatially rare (only observed at one or two sites). Reefs with boulder fields supported the highest species richness, and overall more species were found on Althorpe I. (66) than the mainland (59). Multivariate analyses revealed that different molluscan communities occur on rock platforms with and without significant boulder habitat. Different molluscan communities also appear to occur on Althorpe I. when compared to the mainland sites. This, a comprehensive marine reserve system should include representation from these two distinct intertidal rocky reef habitats, at both offshore and coastal locations on Yorke Peninsula.