Coral reefs and corals
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The Pompeys complex in the southern Great Barrier
Reef.
Photo: GBRMPA |
Coral reefs are one of the most diverse and beautiful natural environments
on earth. Australia's Great Barrier Reef is the largest of the world's
reef systems, extending 2,500 km along Australia's eastern coastline,
and containing around 2,900 individual reefs.
The Great Barrier Reef World Heritage Area supports a diverse fauna and
flora, including around 400 coral species, 4,000 molluscs (shells), 1,500
fish species and 23 species of marine mammal.
Coral reefs are extraordinary living geological structures. They are
highly diverse and productive, but grow best in oceanic waters with very
low levels of nutrients. Coral reefs can form only in relatively clear,
warm waters, where water temperature rarely falls below 18° C.
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| Healthy coral. Photo: GBRMPA |
Coral reefs are massive structures; kilometres in diameter, and tens
to hundreds of metres deep. However, the living reef is only a thin veneer
on the outside of a structure formed by the remains of dead corals and
algae.
Coral reefs are largely confined to shallow waters because the corals
on which reefs rely contain small algae, called zooxanthellae. These algae
help to supply food to the coral, and they, like other plants, require
light to survive. Where water temperature varies from the preferred temperature,
or environmental conditions are otherwise unfavourable, coral
bleaching and death may occur.
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