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Coral reefs are marine ridges or mounds, which have formed
over millennia as a result of the deposition of calcium carbonate
by living organisms, predominantly corals, but also a rich diver-
sity of other organisms such as coralline algae and shellfish.
Coral reefs provide a unique habitat able to support a high di-
versity and density of life. They occur globally in two distinct
marine environments; deep, cold water (3–14ºC) coral reefs, and
shallow, warm water (21–30ºC) coral reefs in tropical latitudes.
Cold-water corals have been recorded in 41 countries world-
wide (Freiwald
et al
., 2004), but they are most likely distrib-
uted throughout the World’s oceans. They occur wherever the
environmental conditions (cold, clear, nutrient-rich waters) are
present, from Norwegian fjords in 39 meters depth to several
thousand metres in the deep-sea. Living mostly in perpetual
darkness, cold-water corals do not possess symbiotic, single-
celled algae, and rely solely on zooplankton and detritus, which
CORAL REEFS
they capture with their tentacles. Some species, such as
Lophelia
,
can form large, complex, 3-dimensional reef structures several
metres in height. The largest reef so far was discovered in 2002
is the Rost reef off the Norwegian coast. It spans twice the size
of Manhattan, is part of the
Lophelia
reef belt stretching all along
the eastern Atlantic continental shelf and slopes from within the
Arctic Circle to the coast of South Africa. Other soft corals living
in colder waters such as
Gorgonia
species do not form reefs but
large ‘gardens’, covering vast areas for example around the Aleu-
tian island chain in the North Pacific. The ecological functions
of such reefs and gardens in the deeper waters are very similar
to tropical reefs: they are biodiversity hotspots and home, feed-
ing and nursery grounds for a vast number of other organisms,
including commercial fish and shellfish species.
Living in highly productive areas, cold-water coral reefs and
gardens are threatened by bottom fishing, especially with trawls
and dredges. Observations with submersibles and remotely
Figure 7. Distribution of coldwater and tropical coral reefs.
The coldwater reefs are highly susceptible to deep-sea
trawling and ocean acidification from climate change, which has its greatest impacts at high latitudes, while tropical
reefs will become severely damaged by rising sea temperatures.