Shell Death and Density Influences Habitat Use of Intertidal Pinnid (Pinna bicolor) Ecosystems

Extensive bivalve aggregations, including shellfish reefs and beds, influence the structure and functions of coastal environments. In soft-bottom habitats, bivalves contribute consolidated structures which can influence species distributions, often long after bivalve death. Understanding this process is essential to inform habitat management and conservation efforts. Here, we describe how intertidal razor clams Pinna bicolor (Pinnidae) influence fish and invertebrate assemblages within a temperate Australian estuary. Specifically, we assessed how pinnid mortality status (dead and alive) and density influenced assemblage habitat use. Assemblages were assessed using a combination of shell scrapings, infauna cores, sweep nets, unbaited video stations, and squidpops. Evidence from multiple methods demonstrated that pinnids underpinned structural and faunal species diversity in an otherwise homogenous benthic environment. Fauna species abundances varied with pinnid mortality status and density. Pinnid aggregations provided settlement surfaces, refugia, and trophic resources that facilitated a range of sessile and mobile organisms. This benefited fisheries-targeted fish and decapod species which used this habitat for foraging based on video monitoring and predation assays. Additionally, densities of > 10 pinnids m⁻² optimised the facilitation of benthic and epifaunal habitat functions. Further studies of Pinnidae ecosystems, incorporating broader seascape assessments, will improve knowledge of their habitat use by mobile species. Our results illustrate how Pinna bicolor aggregations can influence intertidal species assemblages, and identified opportunities for improved Pinnidae ecosystem management.