Biogeography and ecology of the first known deep-sea hydrothermal vent site on the ultraslow-spreading Southwest Indian Ridge

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This proposal is for a short extension to a NERC research cruise to obtain a missing piece of a global jigsaw puzzle of deep-sea life, thereby advancing our understanding of the patterns of biodiversity in the Earth's largest ecosystem. The proposal is to visit a site on the Southwest Indian Ridge (SWIR) where deep-sea vents were recently observed for the first time, but not sampled, by a Chinese research cruise. In 2011/12, a NERC cruise will be visiting undersea mountains in the Indian Ocean just 110 km away with Isis, the UK's remotely-operated vehicle (ROV). This proposal is therefore to visit the nearby vent site with the ship, and undertake the first ever ROV dives at a deep-sea vent on this mid-ocean ridge. Deep-sea vents support lush colonies of marine life, ultimately nourished by chemicals gushing from the seafloor. Investigations of vents over the past three decades have found hundreds of new animal species, revolutionised ideas about how ecosystems can be supplied with energy, and even provided clues to the origins of life. But we have yet to understand what controls the global distribution of species in these island-like extreme environments on the ocean floor. Thirty years of investigations have so far revealed six provinces of animal life at vents, where different species are found at vents in different regions. These provinces are akin to terrestrial continents - e.g. lions living in Africa and tigers in India - but unlike such patterns of life on land, the origin and maintenance of these provinces are not yet understood. Deep-sea vents are dotted along the mid-ocean ridge, a 65000 km chain of undersea volcanoes. Some sections of the mid-ocean ridge are more volcanically active than others. The SWIR is an ultraslow-spreading ridge, where there is less volcanic activity and the plates of the Earth's crust are moving apart more slowly than in other regions. The spacing of deep-sea vents along the mid-ocean ridge decreases with its volcanic activity. At fast-spreading ridges, such as in the Eastern Pacific, vents are less than tens of kilometres apart. On less active slow-spreading ridges, such as the Mid-Atlantic Ridge, vents are hundreds of kilometres apart. This difference may influence which species are found at vents, as the larvae of some species are more capable than others of dispersing long distances between vents. But this idea has yet to be thoroughly tested and the species that live on ultraslow-spreading ridges are largely unknown, despite such ridges forming proportionally the greatest length of the global mid-ocean ridge system. The international Census of Marine Life has therefore identified the SWIR as a priority target to understand what shapes global patterns of life at deep-sea vents. As much of what we know about the dispersal of deep-sea species in general comes from studying these systems, this will advance our understanding of patterns of biodiversity in the deep ocean. Undertaking the first ROV dives at a deep-sea vent on this ultraslow-spreading ridge will determine whether its fauna differ from other ridges. Seafloor images from the Chinese expedition suggest that some species may be similar to those recently discovered at vents in the Southern Ocean by a NERC Consortium. The samples and data collected by the ROV will therefore test the hypothesis that there is a new province of vent biology in the southern hemisphere. The project will also collect samples of novel organisms for the marine biotechnology sector, and share its discoveries with the public through outreach activities. Given the costs of mounting a research cruise in the Indian Ocean, this unique opportunity to extend an existing cruise to visit the first-known deep-sea vent on the SWIR represents exceptional value for NERC science. By answering a key question in deep-sea ecology, this proposal also addresses NERC's goal of delivering world-class research at the frontiers of knowledge.