Molluscan assemblages on intertidal platform reefs demonstrate importance of including multiple locations of similar habitat type in marine protected areas

The intertidal coastline of Perth, Western Australia is dominated by faunally depauperate sand beaches broken up by small, biodiverse intertidal limestone platform reefs. Many platforms are in Marine Protected Areas (MPAs), but there is little quantitative information on the biological communities present. We compared mollusc assemblages on three metropolitan platforms to determine what variation exists between platforms. Each platform was divided into habitats seaward from the shore, based on the dominant algae present. Transects were made in each habitat and molluscs collected from quadrats in the transects. Forty-two species were recorded, but 12 comprised 93 % of total mollusc density. While only one or two individuals of 11 species were recorded, all are widespread with ranges extending well outside the Perth region. There were significant differences between the three platforms, demonstrating that including a single platform in an MPA would not meet the "Comprehensive, Adequate, and Representative" (CAR) requirements of an MPA system. The current MPA network and planned expansion of Marmion Marine Park meets the objectives for conservation of intertidal platform reef communities, using molluscs as the indicator. Lessons from this study are widely applicable and demonstrate importance of including multiple locations of similar habitat type in MPAs.