The Beautiful Colors of Coral Reefs |
Coral reefs are underwater structures
made from calcium carbonate secreted by corals. Coral reefs are
colonies of tiny animals found in marine waters that contain few
nutrients. Most coral reefs are built from stony corals, which in turn
consist of polyps that cluster in groups.
The polyps belong to a group of
animals known as Cnidaria, which also includes sea anemones and
jellyfish. Unlike sea anemones, coral polyps secrete hard carbonate
exoskeletons which support and protect their bodies. Reefs grow best in
warm, shallow, clear, sunny and agitated waters.
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Often called "rainforests of the
sea", coral reefs form some of the most diverse ecosystems on Earth.
They occupy less than 0.1% of the world's ocean surface, about half the
area of France, yet they provide a home for 25% of all marine species,
including fish, mollusks, worms, crustaceans, echinoderms, sponges,
tunicates and other cnidarians.
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Paradoxically, coral reefs flourish
even though they are surrounded by ocean waters that provide few
nutrients. They are most commonly found at shallow depths in tropical
waters, but deep water and cold water corals also exist on smaller
scales in other areas.
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Coral reefs deliver ecosystem
services to tourism, fisheries and shoreline protection. The annual
global economic value of coral reefs is estimated between US$ 29.8-375
billion. However, coral reefs are fragile ecosystems, partly because
they are very sensitive to water temperature.
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They are under threat from climate
change, oceanic acidification, blast fishing, cyanide fishing for
aquarium fish, overuse of reef resources, and harmful land-use
practices, including urban and agricultural runoff and water pollution,
which can harm reefs by encouraging excess algal growth.
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samedi 23 août 2014
The Beautiful Colors of Coral Reefs
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