Coral requires a narrow range of conditions to properly grow: clear water less than 330 feet deep and warmer than 68 degrees F. Anything which interferes with this environment either stops coral growth or kills the living coral. The only living Northern Hemisphere reef is located in the Florida Keys, but coral reefs around the world face threats from pollution daily. Pollution both blocks out the light need by coral reefs but it also adds nutrients to the water which kill coral. The coral reefs require low amounts of nutrients in the water to be able to grow without competition from seaweed and other ocean plants that need more nutrients in the water. Water pollution kills the greatest amount of coral each year.
Natural causes and Air Pollution
Hurricanes batter the coral in shallow waters through the wave action, and large patches of coral can be killed with a passing hurricane. A great variety of fauna exists in coral reefs; 25 percent of ocean species live in coral reefs even though the reefs only take up 2 percent of the ocean floor. This fauna feeds off the coral. Fish, snails, sea worms and starfish nibble away daily at the living coral. Dying coral reefs cannot replace the coral eaten off by fauna, hastening the rate of destruction of the reef.
Air pollution from carbon dioxide also affects the lifespan of reefs. Excessive carbon dioxide from air pollution affects the growth of coral reefs in two ways: decreasing the pH of the ocean and warming water temperature through global warming. The increase in water temperature causes the coral to turn white (bleach) by releasing zooxanthellae which makes food for the coral through photosynthesis. Without the zooxanthellae, the coral loses its source for 80 percent of its energy and unless reversed, bleached coral dies.
Other Manmade Causes
Sediment washing off of the land into the reefs clouds the shallow waters. This prevents the zooxanthellae from being able to get enough sunlight to undergo photosynthesis. The coral cannot get the energy it needs from the zooxanthellae to properly grow and reproduce.
Fishing practices such as dynamite, poisons, spear-fishing and overfishing both physically damage the coral and disrupt the delicate food web of the coral reef.
Coastal development, tourism and mining by humans also destroy coral reefs by increasing pollution, sediments and physical damage to the coral reefs.
- Photo Credit Mikhail Rogov/wikicommons.org,KeithH/wikicommons.org, Mila Zinkova/wikicommons.org, Patrickneil/wikicommons.org
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