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Anthrosphere
Coral reefs can live only in a delicate, balanced marine environment. They require lots of light and oxygen. They also need clear water, low nutrients, a steady temperature, and stable salt content, or salinity. With all these needs then, it's not surprising that human activities threaten coral reefs. There are a number of ways we humans can damage such a delicate environment. Among them are deforestation, fishing methods, overfishing, pollution, careless recreation, and nutrient runoff.
Deforestation All the dirt, silt, sand, and human runoff, such as fertilizers and sewage, settle at the bottom of the ocean. That runoff causes water to be cloudy, or what we call turbid, as those materials work their way down to the ocean floor. As a result, the coral can't get enough light and finds itself smothered. Fishing Methods
Overfishing Grouper is a very popular fish to eat. However, their removal in some cases has led to an increase in damselfish, which groupers feed upon. Damselfish, in turn, create pockets in coral. That's where the algae the damselfish feed upon grow. In time, these algae can take over a reef, essentially smothering it. Overfishing of herbivorous (plant-eating) fish can also lead to high levels of algal growth. Photo: Damselfish add to the destruction of coral reef as they create holes in the coral to eat. Algae then grows in those holes and eventually smother the coral. Photo courtesy of NOAA/Department of Commerce and Dr. James P. McVey.
Pollution Of course, a more obvious pollution problem is oil spills. The oil makes survival difficult for many forms of aquatic life. For more information on the Red Sea reefs, check out the Space Station Science Picture of the Day for May 20, 2003. Nutrient Runoff Sometimes algal blooms are important in the nitrogen and carbon cycles. For example, an algal bloom occurs each year off the west coast of India for two months beginning near the end of February. However, when an algal bloom occurs near a coral reef, it may smother parts of the coral reef. The algae block the sunlight required by the zooxanthellae in the coral to complete photosynthesis. This has been a problem in the Caribbean and the Florida Keys. In addition to agricultural nutrient runoff, municipal wastes, septic tank seepage, and other sewageall high in nitrogenfind their way into the sea.
This problem has struck the coral reefs off Australia and Thailand too. Apparently excess nutrients resulted in the growth of plants favored by the crown of thorns starfish. The starfish soon multiplied there. The presence of a large number of them can destroy a reef in a relatively short time span. Photo:
The crown of thorns starfish eats coral polyps. It reportedly is
poisonous if stepped on.
Photo courtesy of NOAA/Department of Commerce and Dr. James P. MCVey. Anthrosphere | Atmosphere | Biosphere | Hydrosphere | Lithosphere Glossary ..|.. Related Links ..|.. References |..PBL Model Home ..|.. Teacher Pages ..|.. Modules & Activities |
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