Interannual changes in the benthic and pelagic communities of the Shark Bay World Heritage Area

Effective conservation of marine biodiversity requires a strong understanding of how marine systems change over time. Connections between coastal benthic and pelagic systems mean that additional insight may be gained from surveying both habitats alongside each other to investigate if interannual trends are similar. We utilised a multiyear dataset of both seabed and midwater baited remote underwater video systems (BRUVS) deployments from the Shark Bay World Heritage Area to investigate interannual changes in broad metrics of abundance, richness, biomass, and length, as well as composition for neighbouring pelagic and demersal communities. In total, 297 taxa were recorded, 272 from seabed surveys and 47 from midwater surveys. Between four surveys across a 5-year period, patterns in benthic and pelagic habitats differed, but both showed significant shifts in community composition between each survey. Benthic communities were broadly stable in biomass, fork length, and abundance. Pelagic communities increasingly favoured larger abundances of smaller fishes which may be indicative of excessive fishing pressure. Several vulnerable species were recorded including multiple young of the month shortfin mako sharks ( Isurus oxyrinchus ). The Shark Bay World Heritage Area was found to be an area of high biodiversity undergoing significant interannual change in both its pelagic and demersal communities, which should inform current and future conservation approaches.