. Deep-sea biodiversity and ecosystems - a scoping report on their socio-economy, management and governance. UNEP-WCMC Biodiversity Series 28. Three-dimensional map of the seafloor off the Atlantic coast of the Iberian Peninsula, showing various submarine canyons cut into the continental shelf. ABYSSAL PLAINS Abyssal plains, commonly occurring in water depths of about 3 000-6 000 metres, constitute approximately 40 per cent of the ocean floor and 51 per cent of the Earth's area. They are generally flat or very gently sloping areas formed by new oceanic crust spreading from mid-oceanic ridges a
. Deep-sea biodiversity and ecosystems - a scoping report on their socio-economy, management and governance. UNEP-WCMC Biodiversity Series 28. Three-dimensional map of the seafloor off the Atlantic coast of the Iberian Peninsula, showing various submarine canyons cut into the continental shelf. ABYSSAL PLAINS Abyssal plains, commonly occurring in water depths of about 3 000-6 000 metres, constitute approximately 40 per cent of the ocean floor and 51 per cent of the Earth's area. They are generally flat or very gently sloping areas formed by new oceanic crust spreading from mid-oceanic ridges at a rate of 20 to 100 millimetres per year. The new volcanic seafloor near these ridges is very rough, but soon becomes covered in most places by layers of fine-grained sediments, predominantly clay, silt and the remains of planktonic organisms, at a rate of appromimately two to three centimetres per thousand years. The main characteristics of abyssal plain ecosystems are (1) low biomass, |2) high species diversity, |3] large habitat extension and (4) wide- scale, sometimes complex topographic and hydrodynamic features. Species consist mostly of small invertebrate organisms living in or burrowing through the seabed (Gage, 1996], as well as an undiscovered plethora of micro- organisms. Given the relative homogeneity of abyssal plains, small organisms (larvae, juveniles and adults! can drift over long distances. The percentage of endemic species found on abyssal plains may therefore not be as high as elsewhere in the deep sea. In certain areas, special conditions are found on the abyssal plains, which support a distinct community of organisms. Cadavers of large marine mammals (for example, whale falls) or fish sinking to the bottom of the abyss attract a succession of specialized organisms that feed on these carcasses over months to years. Polymetallic. For over four years, the bones of this 35-tonne gray whale have rested on the seabed at 1 670 metres depth in the Santa Cruz Bas
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