Endangered Species Handbook

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Aquatic Ecosystems

Coral Reefs

     The beautiful and diverse coral reefs of the world are today more threatened than they have been for many millions of years.  A survey in the 1980s found that damage had occurred in coral reefs in 93 of the 109 countries where these rich ecosystems are found (Wells and Hanna 1992).  At least 10 percent of coral reefs around the world had been damaged beyond repair, while 30 percent were in critical condition and expected to disappear within 10 to 20 years; another 30 percent were expected to die by 2050 (Carter 1997).  Research in 1999 found further damage:  one-third of all coral reefs were dead and 90 percent degraded to some extent.
     In the Maldive Islands in the Indian Ocean, all the coral around inhabited islands has been excavated.  This limestone material has been fashioned into houses.  An estimated 95 percent of these reefs are dead or dying (Zuckoff 2000b).  The result has been lowland flooding by the sea because these protective barriers were destroyed.  Because of the growing numbers of tourists, tour boats, scuba divers and spear fishers, many ancient reefs are declining in species diversity or dying out altogether.  In some areas, hotels are often built with inadequate pollution and erosion controls near coral reefs.  Even touching a coral can harm the delicate outer layer, which can take 100 years to recover.
     Dynamiting and poisoning reefs to obtain fish are methods banned throughout Asia, yet they regularly occur.  David Doubilet (1999) has spent much of his life photographing coral reefs and has witnessed such activities.  On one occasion while diving in the Philippines, he saw large areas of coral reefs reduced to white rubble.  The cause was nearby boatmen who lobbed bottles of homemade explosives into the sea (Doubilet 1999).  They were chased off by a marine official who fired a pistol round over the poachers' heads, but on inspecting the results in the coral reef, Doubilet saw fish spinning aimlessly in convulsions or belly-up amidst the craters of blast sites (Doubilet 1999).   Beginning in the 1960s, Philippine fishermen pumped cyanide poison into 33 million coral heads at a rate of 330,000 pounds yearly (Chadwick 1999).  Approximately 95 percent of the reefs of the Philippines have been destroyed from the combined effects of sewage pollution, dynamiting and the use of cyanide to obtain tropical fish for the pet trade (Chadwick 1999).  These fish usually die within weeks from the cyanide (Wells and Hanna 1992).  In the rich reefs surrounding Indonesia, a recent trade has begun for live fish which are kept in aquariums to be consumed in restaurants in Hong Kong and other major cities; the fish are stunned by small amounts of poison and the coral often dies after being sprayed (see Trade, Fisheries). 
     Seashell and pearl harvests have depleted many reefs of species important in controlling reef predators.  The Crown-of-Thorns starfish of the western Pacific was once preyed on and kept in check by 12-inch giant triton mollusks, a species collected heavily for the shell trade.  The fish that controlled populations of Crown-of-Thorns starfish have been killed off by fishing, further causing imbalance to reefs.  Sewage or agricultural runoff promotes the growth of plankton that also encourages these starfish to multiply to pestilential levels, killing off large portions of coral (Chadwick 1999). 
     Siltation runoff from clear-cutting forests near shore and agricultural plowing has become major factors in the death of 95 percent of Philippine reefs and the dying of reefs in the Florida Keys and elsewhere.  When silt comes to rest on live coral, the coral is smothered.  Fertilizers and sewage encourage the growth of bacteria, viruses and diseases, such as aspergillosis, that have devastated hundreds of coral reefs in the Caribbean (Chadwick 1999). 
     Coral bleaching, in which colorful corals turn white and die, is affecting a growing number of reefs.  Even a slight rise in ocean temperature can kill off the symbiotic algae living in the coral. The algae gives coral color and without it, the coral animals die.  Global warming has been mainly responsible for gradually raising ocean temperatures, and should it continue, the majority of the world's reefs will die out.  Household bleach, used by fishermen to stun fish, can also cause bleaching.  UV radiation from ozone depletion may play a major role, as well by killing off the symbiotic algae (Chadwick 1999).  In some cases, coral bleaching can be temporary, and corals can recover if water temperatures cool before too much time has passed or if the corals are not also being attacked by pollutants, pesticides or a different type of algae produced from fertilizer nutrients in the water.    
     The Great Barrier Reef has incurred die-offs of coral in many areas.   This massive reef is considered one of the great natural wonders of the world, with a great diversity of fish and corals.  Coral bleaching has killed various parts of the reef in recent years, and in 1998, the warmest year ever recorded, large sections of the reef died, leaving white skeletons in place of dazzling fish and colorful corals (Zuckoff 2000b).  Some reefs recovered when temperatures cooled, but most did not.  Scientists meeting at the fourth meeting of the International Coral Reef Symposium in 2000 warned that global warming and other threats must be stopped if the world's coral reefs are to be saved (Zuckoff 2000b).  At the present rate of destruction, one scientist estimated that coral reefs will be gone in 30 to 50 years (Zuckoff 2000b).  Global warming is not being arrested, however, as countries, led by the United States, the largest producer of greenhouse gases, continue to pollute the atmosphere.

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