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What are corals?
Coral reefs are among the best-known marine ecosystems because of their incredible biological productivity and their diverse and beautiful organisms. But what is a coral reef? A reef is an aggregation of tiny colonial animals (called coral polyps) that live symbiotically with photosynthetic algae. Over time, calcium-rich coral skeletons are built up, creating reefs, atolls and islands. Such structures are essential for protecting shorelines and providing much-needed shelter for countless species of fish, worms, crustaceans and other life forms.
Where do reefs form? Reef-building corals live where water is shallow and clear enough for sunlight to reach the photosynthetic algae. They need warm (but not too warm) water, and are not able to survive where concentrations of nutrients are too high or when runoff from the land creates dense layers of algae, fungi or sediment.
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An Ecosystem In Danger
Coral reefs are among the most endangered ecosystems in the world. Destructive fishing practices can damage or destroy coral communities. In addition, polluted urban runoff, trash, sewage and industrial effluent, sediment from agriculture, and unsustainable forestry are smothering coral reefs along coastlines that have high human populations. Introduced pathogens and predators also threaten many reefs.
Perhaps the greatest threat to reefs is global warming. Elevated water temperatures cause coral bleaching, in which corals expel their algal partner and then die. Also contributing to coral bleaching are high light and UV levels, low salinity and high turbidity from coastal runoff events or heavy rain, exposure to air during very low tides.
The third UNESCO Conference on Oceans, Coasts and Islands in 2006 reported that one-third of all coral reefs have been destroyed, and that 60 percent are now degraded and may be dead by 2030.
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The Cost of Coral Bleaching
Coastal and island communities along coral reefs find substantial economic rewards through the tourism industry. Thousands, perhaps millions, of scuba divers, snorkelers, and fishing enthusiasts make their way to the ocean each year in order to recreate around the world’s most diverse living ecosystem. However, increased coral bleaching is indeed taking a toll on these areas – which are often in poor, otherwise struggling economies where the government is unable to offer the financial resources to protect the dying reefs.
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What can we do?
Experts advise that reducing the overall stress of the reef will help slow the bleaching process. Coral management programs should find ways to shade reefs, cool water temperatures, improve water quality and reduce overfishing.
To learn more about how to protect coral reefs, check out the Coral Reef Alliance.