Oceanographic influences on reef fish assemblages along the Great Barrier Reef

Abstract

Along the Great Barrier Reef, multi-year fish and oceanographic data were integrated to determine the shelf-scale relationship between oceanographic and environmental variables with reef fish assemblage structure. We used data from long-term monitoring of reef fishes sourced from underwater visual surveys and baited remote underwater video stations, combined with a regional hydrodynamic model, multi-year mooring observations, and surface drifting buoy trajectories. Multivariate analyses revealed distinct latitudinal splits in reef fish assemblages, which aligned spatially with the lagoonal branch of the East Australian Current. This lagoonal current flows onto the continental shelf in the central Great Barrier Reef (∼18-19°S), moves poleward within the lagoon, and exits out the Capricorn Channel (∼23°S). We used oceanographic data to characterize the lagoonal current and its seasonal variability, showing that the current reached its maximum strength during the peak reef fish spawning period in austral spring and summer. The shelf-scale structure in reef fish assemblages was best explained by the orientation angle from reef fish sites to the lagoonal current. The results indicate that the prevailing oceanographic patterns may enhance or restrict larval dispersal and contribute to maintaining distinct mesoscale reef fish communities. These findings provide insights for managing marine populations, and we consider how climate projections could influence large-scale ocean currents and environmental gradients and impact broad-scale reef fish community structure.