Wave energy drives biotic patterns beyond the surf zone: Factors influencing abundance and occurrence of mobile fauna adjacent to subtropical beaches

Management of beach ecosystems often focuses on geomorphic and socio-economicissues. Yet understanding patterns and processes affecting fishes and invertebratesin this dynamic inshore environment will better inform ecosystem management. We used Baited Remote Underwater Video (BRUVs) to survey fish and mobile invertebrate assemblages immediately beyond the surf zone (in 5–8 m depth) across 12 beaches of varying energy and geomorphology, to assess drivers of abundance and occurrence. These beaches in subtropical eastern Australia were categorised based on various morphological, energy, connectivity and management characteristics. Characteristics associated with wave energy (aspect, exposure, modal value) were the strongest drivers of assemblages and functional groups overall. Patterns were strongest for crabs, with high relative abundance of Diogenid crabs (hermit crabs) at low energy beaches, and high relative abundance of Matutid crabs (moon crabs) at higher energy beaches. Bony fish and elasmobranchs were also predominantly influenced by energy characteristics, but these patterns were highly variable. This habitat beyond the surf zone was richer in species relative to adjacent deeper unconsolidated habitats, especially for elasmobranchs. It included target fished species and was a juvenile nursery for several Carangid species. These patterns and values should be considered when management actions are undertaken.