Using Artificial Mimics of a Subtidal Pinnid Bivalve to Enhance Coastal Benthic Biodiversity

Abstract Global declines of bivalves have resulted in losses to ecosystem functions and services in marine habitats. In New Zealand, the pinnid bivalve Atrina zelandica (hereafter Atrina ) is a key subtidal structure-forming species in soft-sediment habitats that has become functionally extinct in many coastal regions over the past two decades. The emergent shells of Atrina enhance the structural complexity and vertical relief of benthic soft-sediments, influencing biodiversity. Because of the extremely low numbers of live Atrina now available for experimentation and transplantation, we trialled a novel structural restoration approach using mimics. Four artificial reef plots (4 m 2 ) comprised of individual concrete Atrina mimics (at densities of 20 ind. m − 2 ) were deployed for 17 months in Tauranga Harbour, New Zealand. We evaluated how the enhancement of the emergent physical structure (created by the shell mimics) alters local community structure and diversity in nekton, macrofauna and attached epibiota. Overall, our results indicate that the addition of habitat complexity by Atrina mimics generally enhanced biodiversity relative to bare sediment habitats. A substantial increase in nekton was observed within artificial reefs compared to bare sediment habitats, alongside diverse epibiont assemblages colonising the surfaces of the Atrina mimics, composed primarily of sessile species. Macrofaunal abundance was similar across habitats, with Atrina mimics supporting a distinct community composition and lower species richness. This study indicates that restoring pinnid structures may be a valuable restoration tool for enhancing biodiversity and facilitating ecological recovery of degraded soft-sediment habitats where restoration of live shellfish is no longer possible.