Deep, diverse and definitely different: unique attributes of the world's largest ecosystem

Type Article
Date 2010
Language English
Author(s) Ramirez-Llodra E.1, Brandt A.2, Danovaro R.3, De Mol B.4, Escobar E.5, German C. R.6, Levin L. A.7, Arbizu P. Martinez8, Menot LenaickORCID9, Buhl-Mortensen P.10, Narayanaswamy B. E.11, Smith C. R.12, Tittensor D. P.13, Tyler P. A.14, Vanreusel A.15, Vecchione M.16
Affiliation(s) 1 : CSIC, Inst Ciencias Mar, E-08003 Barcelona, Spain.
2 : Biocentrum Grindel & Zool Museum, D-20146 Hamburg, Germany.
3 : Polytech Univ Marche, Dept Marine Sci, I-60131 Ancona, Italy.
4 : Univ Barcelona, Parc Cient Barcelona, GRC Geociencies Marines, E-08028 Barcelona, Spain.
5 : Univ Nacl Autonoma Mexico, Inst Ciencias Mar & Limnol, Mexico City 04510, DF, Mexico.
6 : Woods Hole Oceanog Inst, Woods Hole, MA 02543 USA.
7 : Univ Calif San Diego, Scripps Inst Oceanog, Integrat Oceanog Div, La Jolla, CA 92093 USA.
8 : Deutsches Zentrum Marine Biodiversitatsforsch, D-26382 Wilhelmshaven, Germany.
9 : Ifremer Brest, DEEP LEP, F-29280 Plouzane, France.
10 : Inst Marine Res, N-5817 Bergen, Norway.
11 : Scottish Marine Inst, Scottish Assoc Marine Sci, Oban PA37 1QA, Argyll, Scotland.
12 : Univ Hawaii, Dept Oceanog, Honolulu, HI 96822 USA.
13 : Dalhousie Univ, Dept Biol, Halifax, NS, Canada.
14 : Univ Southampton, Natl Oceanog Ctr, Southampton SO14 3ZH, Hants, England.
15 : Univ Ghent, B-9000 Ghent, Belgium.
16 : Natl Museum Nat Hist, NMFS Natl Systemat Lab, Washington, DC 20013 USA.
Source Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2010 , Vol. 7 , N. 9 , P. 2851-2899
DOI 10.5194/bg-7-2851-2010
WOS© Times Cited 227
Abstract The deep sea, the largest biome on Earth, has a series of characteristics that make this environment both distinct from other marine and land ecosystems and unique for the entire planet. This review describes these patterns and processes, from geological settings to biological processes, biodiversity and biogeographical patterns. It concludes with a brief discussion of current threats from anthropogenic activities to deep-sea habitats and their fauna. Investigations of deep-sea habitats and their fauna began in the late 19th century. In the intervening years, technological developments and stimulating discoveries have promoted deep-sea research and changed our way of understanding life on the planet. Nevertheless, the deep sea is still mostly unknown and current discovery rates of both habitats and species remain high. The geological, physical and geochemical settings of the deep-sea floor and the water column form a series of different habitats with unique characteristics that support specific faunal communities. Since 1840, 28 new habitats/ecosystems have been discovered from the shelf break to the deep trenches and discoveries of new habitats are still happening in the early 21st century. However, for most of these habitats the global area covered is unknown or has been only very roughly estimated; an even smaller - indeed, minimal - proportion has actually been sampled and investigated. We currently perceive most of the deep-sea ecosystems as heterotrophic, depending ultimately on the flux on organic matter produced in the overlying surface ocean through photosynthesis. The resulting strong food limitation thus shapes deep-sea biota and communities, with exceptions only in reducing ecosystems such as inter alia hydrothermal vents or cold seeps. Here, chemoautolithotrophic bacteria play the role of primary producers fuelled by chemical energy sources rather than sunlight. Other ecosystems, such as seamounts, canyons or cold-water corals have an increased productivity through specific physical processes, such as topographic modification of currents and enhanced transport of particles and detrital matter. Because of its unique abiotic attributes, the deep sea hosts a specialized fauna. Although there are no phyla unique to deep waters, at lower taxonomic levels the composition of the fauna is distinct from that found in the upper ocean. Amongst other characteristic patterns, deep-sea species may exhibit either gigantism or dwarfism, related to the decrease in food availability with depth. Food limitation on the seafloor and water column is also reflected in the trophic structure of heterotrophic deep-sea communities, which are adapted to low energy availability. In most of these heterotrophic habitats, the dominant megafauna is composed of detritivores, while filter feeders are abundant in habitats with hard substrata (e. g. mid-ocean ridges, seamounts, canyon walls and coral reefs). Chemoautotrophy through symbiotic relationships is dominant in reducing habitats. Deep-sea biodiversity is among of the highest on the planet, mainly composed of macro and meiofauna, with high evenness. This is true for most of the continental margins and abyssal plains with hot spots of diversity such as seamounts or cold-water corals. However, in some ecosystems with particularly "extreme" physicochemical processes (e.g. hydrothermal vents), biodiversity is low but abundance and biomass are high and the communities are dominated by a few species. Two large-scale diversity patterns have been discussed for deep-sea benthic communities. First, a unimodal relationship between diversity and depth is observed, with a peak at intermediate depths (2000-3000 m), although this is not universal and particular abiotic processes can modify the trend. Secondly, a poleward trend of decreasing diversity has been discussed, but this remains controversial and studies with larger and more robust data sets are needed. Because of the paucity in our knowledge of habitat coverage and species composition, biogeographic studies are mostly based on regional data or on specific taxonomic groups. Recently, global biogeographic provinces for the pelagic and benthic deep ocean have been described, using environmental and, where data were available, taxonomic information. This classification described 30 pelagic provinces and 38 benthic provinces divided into 4 depth ranges, as well as 10 hydrothermal vent provinces. One of the major issues faced by deep-sea biodiversity and biogeographical studies is related to the high number of species new to science that are collected regularly, together with the slow description rates for these new species. Taxonomic coordination at the global scale is particularly difficult, but is essential if we are to analyse large diversity and biogeographic trends. Because of their remoteness, anthropogenic impacts on deep-sea ecosystems have not been addressed very thoroughly until recently. The depletion of biological and mineral resources on land and in shallow waters, coupled with technological developments, are promoting the increased interest in services provided by deep-water resources. Although often largely unknown, evidence for the effects of human activities in deep-water ecosystems - such as deep-sea mining, hydrocarbon exploration and exploitation, fishing, dumping and littering - is already accumulating. Because of our limited knowledge of deep-sea biodiversity and ecosystem functioning and because of the specific life-history adaptations of many deep-sea species (e. g. slow growth and delayed maturity), it is essential that the scientific community works closely with industry, conservation organisations and policy makers to develop robust and efficient conservation and management options.
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Ramirez-Llodra E., Brandt A., Danovaro R., De Mol B., Escobar E., German C. R., Levin L. A., Arbizu P. Martinez, Menot Lenaick, Buhl-Mortensen P., Narayanaswamy B. E., Smith C. R., Tittensor D. P., Tyler P. A., Vanreusel A., Vecchione M. (2010). Deep, diverse and definitely different: unique attributes of the world's largest ecosystem. Biogeosciences, 7(9), 2851-2899. Publisher's official version : https://doi.org/10.5194/bg-7-2851-2010 , Open Access version : https://archimer.ifremer.fr/doc/00017/12816/