Bathymetric projection of the South Pacific Ocean with numbered field locations as described in the text. 1, Tonga- Kermadec arc; 2, deep-ocean trenches; (3) mid-plate seamounts of the Louisville Ridge; 4 & 6, Pacific-Antarctic Ridge; 5 & 8, abyssal plains; 7, Southern EPR; 9, Chile margin; 10, Bransfield Strait back-arc basin. doi:10.1371/journal.pone.0023259.g006 

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... to understand better the biodiversity and functioning of deep-sea ecosystems, as well as the connectivity between habitat types. An important goal of INDEEP, as a direct consequence, will be to help meet a pressing need for improved management and conservation of these vulnerable ecosystems. Going forward, it will be critical to (i) evaluate species distributions and differences in community composition and structure in areas that overlap in depth and habitat type; (ii) assess heterogeneous nutrient sources and diverse inputs; and (iii) reveal the genetic relationships among species and populations across diverse deep-ocean habitats. Only then can we expect to understand the formative ecological and evolutionary processes that have shaped current patterns of biodiversity and ecosystem function and serve to sustain deep-sea biodiversity, as well as fisheries-based goods and services in, the face of increasing anthropogenic impacts. One high-priority area in which we recommend that we should seek to address both long-standing and recently-developed hypotheses is the South Pacific Ocean. This deep-ocean basin represents the largest contiguous ecosystem for life on our planet and contains the full range of known seafloor habitats: vast abyssal plains underlying the huge central oligotrophic gyre, eutrophic hotspots underlying equatorial and Antarctic upwelling zones and active and inactive seamount chains that extend from ocean margins into the ocean interior where they intersect mid-ocean ridges. Furthermore, the South Pacific Ocean also contains the world’s most abundant hydrothermal vents, the world’s largest seep sites, oxygen minimum zones adjacent to whale and wood falls and networks of canyons. While the South Pacific provides connectivity between established biodiversity and evolutionary hotspots, in a range of habitat types, however, it also includes some of Earth’s most poorly studied deep-ocean regions juxtaposed directly against those ‘‘hot- spots’’. One of the most striking images from the synthesis activities of the Census of Marine Life (Figure 5) is a plot of Hurlberts First Index (HFI), a sample-size independent proxy for species richness, throughout Earth’s Ocean Basins (www.coml. org). What is particularly notable in the projection shown, focused on the South Pacific, is that ‘‘hot-spot’’ areas of high biodiversity to the west and east are separated by areas where insufficient data exist to assign an HFI value because insufficient biological observations (50 or more) have yet to be conducted, throughout the entire history of deep-ocean research, within any of the ‘‘blank’’ boxes (pixel size: 5 u Latitude 6 5 u Longitude)! In this single ocean basin, all of the habitats present must share a common history and will have interacted, both biologically and geologically, throughout their formative history. What we recommend for a future and concerted effort, therefore, is an internationally coordinated project to investigate the interconnected deep-ocean habitats and ecosystems – from ocean margins to ridge-crests at 2000–3000 m depth, abyssal plains . 3000 m deep and ocean trenches that lie more than 10,000 m below sea level – of the South Pacific Ocean: arguably Earth’s largest and yet least understood deep-ocean basin. Specifically, we recommend a programme that would seek to address the following key questions: 1. How do species richness and community diversity vary across diverse habitat types, latitudes, depths and nutrient supply, both locally and regionally in the South Pacific? 2. Do the deep-ocean fauna of the South Pacific reveal patterns of connectivity via gene flow, or patterns of isolation and endemism to their various specific habitat types? 3. Is the vast oligotrophic abyss beneath the South Pacific gyre a biodiversity sink where food limitation exceeds adaptive limits, yielding a region of depauperate biodiversity? 4. Are the South Pacific abyssal, vent, seep and seamount fauna evolutionarily and functionally distinct from each other and from the fauna in other ocean basins? 5. Do the patterns of diversity and connectivity observed in South Pacific ecosystems render them particularly vulnerable to anthropogenic impact and/or variations in patterns of oceanic productivity that are predicted from climate change models? Our vision is that this programme could be implemented over a period of a decade in this single ocean basin, using international coordination to gain access to ships of multiple nationalities and the most sophisticated deep-submergence capabilities worldwide. Such a South Pacific programme would allow us to investigate a broad range of distinct ecosystems and obtain the samples required to characterise the intersection of inter-connected ecosystems and their seafloor habitats, from microbes to meio-, macro- and megafauna, at key abyssal plain, continental margin, vent, seep, whale and seamount sites located across the length and breadth of the South Pacific Ocean (Figure 6). Specific targets that could be selected from within this region include: the volcanically and tectonically active ocean margins of the Tonga-Kermadec arc (1) and Chile (9), where OMZs, seeps and vents exist in close proximity; (2) deep ocean trenches; (3) mid-plate seamounts of the Louisville Ridge, a hotspot chain that extends from New Zealand to the East Pacific Rise; abyssal plains (5, 8) that underlie some of the most oligotrophic open-ocean waters; and vents along the Pacific-Antarctic Ridge, north and south of the Polar Front (4,6), on the southern East Pacific Rise (Earth’s fastest-spreading ridge) (7), and in the isolated Bransfield Strait back-arc basin (10). The international umbrella for efficient coordination of this work could readily be provided by the INDEEP initiative whose objectives are to promote research in the deep-ocean realm in the areas of: 1) Taxonomy and Evolution; 2) Biodiversity and Biogeography; 3) Population Connectivity; 4) Ecosystem Functioning; and 5) Anthropogenic Impact and Science Policy. We believe that such a programme would have the potential to change, completely, the way we think about, study and train new scientists to understand diverse deep-ocean ecosystems. The project would provide key information for large-scale understanding of the ecology, biogeography, biodiversity inter-connectivity and evolution of the marine biodiversity of the deep South Pacific and allow direct comparisons with other oceans across comparable latitudes. Such a project would also have a strong exploratory component, providing for exciting new discoveries including, almost certainly, the identification and description of novel species and adaptations previously unknown to science. Although the scope and ambition of the project outlined here, across a largely uninvestigated ocean basin, may speak to some of purely academic ‘‘blue skies’’ research, we anticipate that the knowledge to be gained is also likely to be of critical importance for the development of the applied understanding that will be required for the future management and conservation of living and mineral resources in the deep ocean. Finally, the scale and ambition of the project outlined here would almost certainly lend itself to extensive, multi-media forms of outreach with the potential to expose millions of people to both the exciting expeditions and discoveries throughout the South Pacific and the concept of the common heritage of Earth’s deep oceans. In conclusion, the deep ocean has provided some of the most spectacular and paradigm-changing observations and data over the last 40 years. There is no doubt in our minds that the deep sea will continue to challenge scientists to devise ways and means of discovering and analysing its secrets into the future. Just as the discovery of hydrothermal vents could never have been made had scientists restricted their observations to remote sensing of the global mid-ocean ridge crest, it seems inevitable that even more exciting discoveries await as we extend our focus to the deepest seafloor abyssal plains and on, to the very depths of the deep- ocean trenches found at the far end of the plate tectonic cycle, associated with subduction ...