Assessing the Efficacy of a Bouchot-Style Shellfish Reef as a Restoration Option in a Temperate Estuary

Abstract

Shellfish reefs around the world have become degraded, and recent efforts have focused on restoring these valuable habitats. This study is the first to assess the efficacy of a bouchot-style reef, where mussels were seeded onto wooden stakes and deployed in a hypereutrophic estuary in Australia. While >60% of translocated mussels survived one month, after ten months, only 2% remained alive, with this mortality being accompanied, at least initially, by declining body condition. Mussel survival, growth, body condition and recruitment were greater on the top section of the stake, implying that the distance from the substrate was important. More fish species inhabited the reefs (31) than unstructured control sites (17). Reefs were also colonised by a range of invertebrate species, including 11 native and six non-indigenous species. However, the number of individuals declined from 4495 individuals from 14 species in December 2019 to 35 individuals representing 4 species in March 2021, likely due to hypoxic bottom water conditions following unseasonal rainfall. Although the bouchot-style reefs were unable to sustain mussels and other invertebrates over sequential years, this approach has the potential to be successful if deployed in shallow water or intertidal zones, which are largely exempt from biotic and abiotic stressors characteristic of deeper waters in microtidal estuaries.