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22

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.