Abstract
AbstractAimMining 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.LocationThe Great Australian Bight (34–36°S, 129–134°E) and south‐eastern (SE) and north‐eastern (NE) Australian continental margins (23–42°S, 149–155°E) in depths of 1,900–5,000 m.MethodsA 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.ResultsMultivariate 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.ConclusionsSignificant 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.
Highlights
Deep seafloors cover over half the planet (Ramirez-Llodra et al, 2010), few studies have examined patterns of biodiversity for the deep sea over large spatial scales
There are plans to mine the deep sea for polymetallic nodules on oceanic abyssal plains, cobalt-rich ferromanganese crusts on seamounts and polymetallic sulphide deposits on volcanically active continental margins and mid-ocean ridges (Miller, Thompson, Johnston, & Santillo, 2018)
Deep-sea sedimentary basins on continental margins are of interest to the oil and gas industry (Zou et al, 2015), while renewable energy and aquaculture increasingly look to offshore areas to dilute environmental and social concern
Summary
Deep seafloors cover over half the planet (Ramirez-Llodra et al, 2010), few studies have examined patterns of biodiversity for the deep sea over large spatial scales. The GAB invertebrate communities' KEF designation was based primarily on a study by Ward, Sorokin, Currie, Rogers, and McLeay (2006), who reported relatively high species richness of epibenthic megafauna on the continental shelf of the GAB (0–200 m) which they attributed to the unusual carbonate sediments and overlapping SW and SE Australian faunas. Over a 3-year period (2015–2017), a number of voyages of the RV “Investigator” collected comparative beam trawl samples from lower bathyal (1,900–3,500 m) and abyssal (3,500–5,000 m) depths from both the GAB (IN2015_C01, IN2015_C02, IN2017_ C01) and off eastern Australia (IN2017_V03) (Figure 1) This provided the opportunity to assess whether (a) the deep-sea benthic diversity of the GAB differed from that of comparable habitats off the east coast, and/or (b) whether the assemblages differed in composition at these spatial scales. These covariates included oceanographic variables such as seafloor water temperature, salinity and dissolved oxygen, carbon flux to the seafloor, mean annual and seasonal variation of net primary productivity at the sea surface, as well as geographical variables latitude, longitude and depth
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