Subtidal shellfish reefs as fish habitats within urban coastal seascapes of Gulf St. Vincent, South Australia

Interest in coastal management is increasing globally, particularly in urbanised temperate regions where cumulative stressors have degraded biogenic habitats. This includes renewed shellfish reef conservation efforts including restoration and fish habitat management. However, fish-habitat interactions within and across shellfish reefs and habitat types, including taxonomic, behavioural and trait variability is understudied. Here, we investigated subtidal shellfish reef fish assemblages in Gulf St. Vincent near metropolitan Adelaide, South Australia, from restored oyster (Ostrea angasi) and natural pinnid (Pinna bicolor) reefs, in comparison to seagrass and bare sediment habitats. Fishes were surveyed with unbaited video stations and were analysed using multiple assemblage metrics. All habitats were found to support distinct fish assemblage compositions, with the highest fish abundances associated with seagrass meadows. Across structural habitats of shellfish reef and seagrass habitats, fish assemblages shared similar traits, behaviours and higher species richness compared to bare sediment habitats. These findings indicate that both restored and natural shellfish reefs can support distinct fish assemblages and reaffirms the fish habitat value of structural habitats. By investigating fish-habitat interactions using multiple fish assemblage metrics, we demonstrate an approach that expands knowledge of shellfish reef fish monitoring that is applicable to other restoration and seascape management efforts.