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| Titel |
Deep, diverse and definitely different: unique attributes of the world's largest ecosystem |
| VerfasserIn |
E. Ramirez-Llodra, A. Brandt, R. Danovaro, B. Mol, E. Escobar, C. R. German, L. A. Levin, P. Martinez Arbizu, L. Menot, P. Buhl-Mortensen, B. E. Narayanaswamy, C. R. Smith, D. P. Tittensor, P. A. Tyler, A. Vanreusel, M. Vecchione |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 7, no. 9 ; Nr. 7, no. 9 (2010-09-22), S.2851-2899 |
| Datensatznummer |
250004973
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| Publikation (Nr.) |
 copernicus.org/bg-7-2851-2010.pdf |
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| Zusammenfassung |
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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