<?xml version="1.0" ?>
<EFGs>
   <EFG code="M3.6" update="2020-12-11" version="v2.0">
      <Realms>
         <Realm>Marine</Realm>
      </Realms>
      <Biome>M3. Deep sea floors biome</Biome>
      <Name>M3.6 Hadal trenches and troughs</Name>
      <Short-name>M3.6 Hadal</Short-name>
      <Contributors>
         <contributor>E Ramirez-Llodra</contributor>
         <contributor>AA Rowden</contributor>
         <contributor>AJ Jamieson</contributor>
         <contributor>IG Priede</contributor>
         <contributor>DA Keith</contributor>
         <map-contributor>DA Keith</map-contributor>
         <map-contributor>JR Ferrer-Paris</map-contributor>
      </Contributors>
      <Short-description>The deepest ocean trenches, up to 11 km beneath the surface, are the least explored marine ecosystems.  They are also one of the most extreme, with no sunlight, low temperatures, nutrient scarcity and hydrostatic pressures of 600 to 1100 atmospheres, extending beyond the limits to vertebrate life. The major sources of nutrients and carbon are fallout from upper layers, drifts of fine sediment and landslides. Most organisms are scavengers and detrivores, like the supergiant amphipod, with abundance of predatory fish and crustaceans diminishing with depth.</Short-description>
      <Ecological-traits updated="2020-05-28 10:18:36">Hadal zones are the deepest ocean systems on earth and among the least explored. They are heterotrophic, with energy derived from the fallout of particulate organic matter through the water column, which varies seasonally and geographically and accumulates in the deepest axes of the trenches. Most organic matter reaching hadal depths is nutrient-poor because pelagic organisms use the labile compounds from the particulate organic matter during fallout. Hadal systems are therefore food-limited, but particulate organic matter flux may be boosted by sporadic pulses (e.g. whale falls and wood falls) and sediment transported by advection and seismically induced submarine landslides. Additional energy is contributed by chemosynthetic bacteria that can establish symbiotic relationships with specialised fauna. These are poorly known but more are expected to be discovered in the future. Hadal trophic networks are dominated by scavengers and detritivores, although predators (including through cannibalism) are also represented. Over 400 species are currently known from hadal ecosystems, with most metazoan taxa represented including amphipods, polychaetes, gastropods, bivalves, holothurians, and fish. These species possess physiological adaptations to high hydrostatic pressure, darkness, low temperature, and low food supply. These environmental filters, together with habitat isolation, result in high levels of endemism. Gigantism in amphipods, mysids, and isopods contrasts with the dwarfism in meio-fauna (e.g. nematodes, copepods, and kinorhynchs).</Ecological-traits>
      <Key-ecological-drivers updated="2020-05-28 10:18:37">The hadal benthic zone extends from 6,000 to 11,000 m depth and includes 27 disjoint deep-ocean trenches, 13 troughs, and 7 faults. Sunlight is absent, nutrients and organic carbon are scarce, and hydrostatic pressure is extremely high (600–1,100 atmospheres). Water masses in trenches and troughs are well oxygenated by deep currents and experience constant, low temperatures (1.5–2.5°C). Rocky substrates outcrop on steep slopes of trenches and faults, while the floors comprise large accumulations of fine sediment deposited by mass movement, including drift and landslides, which are important sources of organic matter. Sediment, organic matter and pollutants tend to be &quot;funnelled&quot; and concentrated in the axis of the trenches.</Key-ecological-drivers>
      <Distribution updated="2020-05-28 10:18:36">A cluster of isolated trenches in subduction zones, faults, and troughs or basins, mostly in the Pacific Ocean, as well as the Indian and Southern Oceans, accounting for 1–2% of the total global benthic area.</Distribution>
      <Map code="M3.6.web.orig" version="v1.0">Major occurrences of Hadal trenches and troughs was based on the ‘hadal’ and ‘trenches’ geomorphic units of Harris et al. (2014b). Occurrences were converted to 30 arc second spatial resolution.</Map>
      <References>
         <Reference name="Harris PT et al. 2014">Harris PT, Macmillan-Lawler M, Rupp J, Baker EK  (2014) Geomorphology of the oceans Marine Geology 352: 4-24 DOI:10.1016/j.margeo.2014.01.011</Reference>
         <Reference name="Jamieson A, Fujii T, Mayor DJ, Solan M, Priede IG  2010">Jamieson A, Fujii T, Mayor DJ, Solan M, Priede IG  (2010) Hadal trenches: the ecology of the deepest places on Earth Trends in Ecology and Evolution 25: 190-197 DOI:10.1016/j.tree.2009.09.009</Reference>
         <Reference name="Stewart HA, Jamieson AJ  2018">Stewart HA, Jamieson AJ  (2018) Habitat heterogeneity of hadal trenches: considerations and implications for future studies Progress in Oceanography 161: 47-65 DOI:10.1016/j.pocean.2018.01.007</Reference>
      </References>
   </EFG>
</EFGs>
