Benthic biodiversity of seamounts in the southwest Indian Ocean

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Benthic biodiversity of seamounts in the southwest Indian Ocean Seamounts are centres of biological diversity and are ecological hotspots in the deep ocean but their inaccessibility poses major challenges for research. In consequence, there are conspicuous sampling gaps of which the equatorial regions and most of the Indian Ocean are the most extensive. The southwest Indian Ridge (SWIR) is a major geological feature which extends from the central Indian Ocean to join the Mid-Atlantic Ridge in the Southern Ocean. It is rich in seamounts and supports a productive deep-water fishery yet, in terms of biodiversity and ecosystem functioning, it is one of the least sampled regions of the global ocean. We propose to study the diversity and distribution of benthic assemblages, from meiofauna to megafauna, on seamounts in the central section of the SWIR between 41 degrees S 42 degrees E and 33 degrees S 58 degrees E. The benthos of this region is completely unstudied and is of particular interest in terms of its position in relation to major ocean currents, gradients of primary productivity, and recent predictions as to the global distribution of cold-water corals. The region may be regarded as the most significant gap in our understanding of the seamount fauna globally. By studying the associations between faunal assemblages and habitat types, the genetic relatedness of populations, and the relationships between surface productivity, currents, and benthic distributions, we will enhance understanding of the processes governing the distribution, abundance, diversity and evolution of fauna on oceanic seamounts. A new habitat-suitability model based on environmental niche factor analysis (ENFA) has predicted that hard substrata in the southern Indian Ocean, down to ca. 2,500 m, are prime habitats for cold-water scleractinian corals. We propose to test these predictions by comparing the distributions and abundances of coral species across the study area with modelled distributions. Confirmation of the model predictions would lend support to recent concerns that increases in anthropogenic carbon dioxide emissions are likely to cause range shifts in calcareous marine organisms. A recent initiative from the deep-sea fishing industry working with the United Nations Food and Agriculture Organisation (FAO) has proposed a number of voluntary benthic protected areas (BPAs) on the SWIR in which no bottom trawling will take place: three of these are within the proposed study area. This is an unprecedented event in international waters and presents a unique opportunity to study the effectiveness of BPAs in protecting deep-sea habitats and species in the high seas. Detailed information on fishing effort at the study sites, available through industry collaboration, will allow us to assess the effects of trawling on slow-growing deep-sea benthic assemblages, and to gather baseline information against which the process of recovery following cessation of fisheries can be assessed.