The continental margin of northwestern Australia hosts a complex and poorly understood deep-sea environment shaped by interacting geomorphological and oceanographic processes. This study characterises the morphology, substrate composition, and mobile bait-attending fauna of the Gascoyne Marine Park (GMP), a large offshore marine park spanning continental shelf, slope, and abyssal depths. Using an integrated approach that combines geomorphic mapping, substrate classification, and biological observations, we examine how physical seabed structure influences patterns of biodiversity across the region.
A compiled bathymetric dataset for the GMP was generated by integrating multiple expeditions, while substrate types were characterised using multi-platform imagery from landers, towed camera systems, and remotely operated vehicles (ROVs), encompassing a total of 84 sites. These data provide a consistent and spatially comprehensive basis for geomorphological interpretation and seabed substrate classification. The biological component is based on 45 baited lander deployments (1026–5099 m water depth). A total of 754 individuals (summed MaxN) across 45 taxa were recorded. Decapod crustaceans dominated both abundance and occurrence, with Cerataspis monstrosus, Heterocarpus tricarnatus, and Heterogenys sp. 1 comprising the most abundant taxa, while C. monstrosus and Heterogenys sp. 1 were also the most widespread. Assemblage structure varied with both depth and seabed geomorphology, with upper slope communities (1000–2000 m) dominated by mobile decapods, macrourids, and halosaurs associated with relatively higher food availability and more stable soft-sediment habitats. In contrast, the incised lower slope (2000–3500 m), characterised by canyons and gully-incised terrain that enhances hydrodynamic focusing and organic matter transport, supported high abundances of Antimora rostrata and Aristeidae spp. Deeper abyssal plain communities (>3500 m), occupying flat, sediment covered and food-limited environments, were dominated by specialised deep-sea taxa including Cerataspis monstrosus, Benthesicymus crenatus, and Barathrites iris, which are adapted to extreme pressure, low temperatures, and oligotrophic conditions.
Observed shifts in species dominance with depth and seabed morphology are consistent with global patterns and likely reflect ecological processes such as resource partitioning and physiological constraints driven by pressure, temperature, and nutrient availability. These findings highlight the strong coupling between geomorphology, substrate heterogeneity, and faunal distribution in the GMP. By linking physical habitat characteristics with biological assemblages across a broad depth gradient, this study provides critical baseline knowledge for understanding deep-sea ecosystem structure and supports the conservation and management of Australia’s offshore marine environments.