Regional-scale patterns of deep seafloor biodiversity for conservation assessment

Aim Mining and petroleum industries are exploring for resources in deep seafloor environments. Lease areas are often spatially aggregated and continuous over hundreds to thousands of kilometres. Sustainable development of these resources requires an understanding of the patterns of biodiversity at similar scales, yet these data are rarely available for the deep sea. Here, we compare biodiversity metrics and assemblage composition of epibenthic megafaunal samples from deep-sea benthic habitats from the Great Australian Bight (GAB), a petroleum exploration zone off southern Australia, to similar environments off eastern Australia. Location The Great Australian Bight (34-36 degrees S, 129-134 degrees E) and south-eastern (SE) and north-eastern (NE) Australian continental margins (23-42 degrees S, 149-155 degrees E) in depths of 1,900-5,000 m. Methods A species-sample matrix was constructed from invertebrate and fish megafauna collected from beam trawl samples across regions at lower bathyal (1,900-3,200 m) and abyssal (>3,200 m) depths, and analysed using multivariate, rarefaction and model-based statistics. We modelled rank abundance distributions (RAD) against environmental factors to identify drivers of abundance, richness and evenness. Results Multivariate analyses showed regional and bathymetric assemblage structure across the region. There was an almost complete turnover of sponge fauna between the GAB and SE. SE samples had the highest total faunal abundance and species richness. RAD models linked total abundance and species richness to levels of carbon flux. Evenness was associated with seasonality of net primary production. Conclusions Significant assemblage structure at regional scales is reported for the first time at lower bathyal and abyssal depths in the southern Indo-Pacific region along latitudinal and longitudinal gradients. The GAB fauna was distinct from other studied areas. Relatively high species richness, previously reported from the GAB continental shelf, did not occur at lower bathyal or abyssal depths. Instead, the abundance, richness and evenness of the benthic fauna are linked to surface primary production, which is elevated off SE Australia.