Razor clam (Pinna bicolor) structural mimics as drivers of epibenthic biodiversity; a manipulative experiment

Shellfish ecosystems facilitate important ecological functions and communities, but overexploitation and mismanagement have contributed to their decline worldwide. Within recent decades, coastal management efforts have increasingly sought to understand and reinstate valuable ecological functions provided by habitat-forming bivalves including oysters, mussels and pinnids. However, many bivalve species are critically understudied, limiting restoration and ecological engineering opportunities. Pinnids, specifically, are an underappreciated bivalve group, with razor clams (Pinna bicolor) forming dense aggregations, and potentially supporting important ecological functions. This study, conducted in an urban Australian estuary, was a manipulative experiment that investigated whether artificial razor clam shells could facilitate beneficial ecological functions through the provision of structural habitat. Specifically, we investigated the influence of intertidal benthic structures, including the micro-habitat influences of surface structure associated with mortality status (open or closed shell), and the short-term response of the benthic and epifaunal communities. Within 12 weeks, the structural razor clam mimics rapidly changed the aboveground ecological community, relative to the bare habitat controls. Both open and closed artificial shells provided a settlement surface for epiphytic organisms and supported enhanced epifaunal biodiversity. Contrastingly, the artificial structures did not significantly alter sediment characteristics or infaunal macroinvertebrate composition in the surrounding benthos. These results provide important insights into the rapid ecological response to the installation of intertidal pinnid structures in dynamic estuarine ecosystems. Furthermore, we provide a case study for understanding the ecological functions of an understudied habitat-forming species, which could be used to inform future restoration and management efforts.