Naturally occurring hydrocarbon content and baseline condition of deep-sea benthic fauna from the Great Australian Bight

The deep sea (> 500 m) of the Great Australian Bight (GAB) has not been well studied even though it is believed to have high conservation values as evidenced by large marine reserves, and where adjacent (continental shelf) waters support important commercial fisheries and large populations of marine mammals. Recent interest in developing the region's deep-sea hydrocarbon resources has drawn attention to this sparsity of data and the need to characterise the region's benthic ecology in order to detect and understand any potential impacts linked to a developing oil and gas industry. To that end, we measured the naturally occurring hydrocarbon content and baseline condition of a variety of benthic fishes and invertebrates collected during two surveys of the continental slope and seabed geological features. A total of 225 individuals, representing 15 species (7 invertebrates and 8 fishes) were analysed for (i) polycyclic aromatic hydrocarbons (PAH) body burdens or biliary PAH metabolites; (ii) 7-Ethoxyresorufin O-deethylase (EROD), a commonly used oil exposure biomarker; and (iii) lipid profiles and histology. Hydrocarbon concentrations, although measurable at some sites, did not indicate any anthropogenic contamination or unequivocal hydrocarbon seepage. PAH body burdens in the invertebrate species were below the levels of detection, and phenanthrene metabolites showed differences between species of fish surveyed, but were consistently low relative to oil exposed fish. EROD levels varied between species but also did not indicate exposure to oil. Lipid levels were highly variable between individuals and sites, suggesting that a lipid-related metric would not be suitable for monitoring organism health. Histological analysis indicated no gross deformity or infection in either the liver, gill, kidney or spleen. Pathologies identified were of minimal pathological important and likely to be recoverable. Liver exhibited varying levels of lipid accumulation across all fish species. These results, obtained before the commencement of oil and gas industry activity, can be used as a part of a baseline benthic ecosystem characterisation to guide future ecological monitoring programs.