The deep sea begins at the edge of the
continental shelf, which is usually at depths over 200m.
Just like in shallower areas, there can be
various kinds of deep-sea bed, including bedrock, limestone
pavements, boulders, gravel, sand and mud.
There are some unique deep-sea bed types
too, including manganese nodules, in which minerals such as nickel
and copper as well as manganese, build up like the rings of an
onion around a shell fragment or other hard particle. Past
interest in mining these nodules has yet to lead to significant
exploitation, due primarily to the expense of extracting the
nodules from such great depths.
Unique biological seabeds include
‘bioherms’, which are mounds or reefs of rock formed from the
remains of marine organisms, and embedded within mineral rock.
Living deep-sea reefs are formed by
cold-water corals. They can extend for several kilometers and be
more than 20m high. Much of the deep-sea bed is barren and
inhospitable, so the cold water coral reefs form oases, in which
the number of different species can be three times as high as on
the surrounding soft seabed.
Large colonies of sponges can also be found
in the deep-sea.
For the official habitat definition please
see the documents listed below.
Large areas of the Atlantic Ocean are
deep-sea bed. Areas of the Mediterranean Sea which are deeper
than 200 metres, are included as deep-sea habitat, but the Baltic,
being a shelf sea, is not.
Official habitat definition
EUNIS habitat A6
JNCC EUNIS habitat correlations table