Anthropogenic impact is the environmental effect of human activity. Fishing, agriculture, irrigation, energy production, mining, and manufacturing all bring about changes in the environment, and those changes are frequently harmful. Humans have annihilated many species in recent history and it is also theorized that humans caused for the disappearance of prehistoric megafauna such as woolly mammoths and giant sloths.
Anthropogenic extinction continues apace, and one species that is particularly at risk is coral. The U.S. Coral Reef Task Force describes coral reefs, which are one of the world’s most complex ecosystems, as the rainforests of the sea. The Task Force warns that 10% of the world’s reefs have been destroyed by human activity, and estimates that another 60% is in danger of meeting the same fate.
A coral reef is a delicately balanced ecosystem which is home to many species of fish, and which may be adversely impacted by many aspects of human activity. The basis of the coral reef are reef-building corals, small marine animals that live together in colonies. Each individual coral produces a hard shell of calcium carbonate, and as the colony grows it gradually lays down a base of carbon carbonate that slowly grows into a reef. The corals have a symbiotic relationship with photosynthetic algae which supply them with nutrients. In order for the algae to be able to carry out photosynthesis, the corals require clear water that will allow sunlight to penetrate.
One of the most significant threats to coral is pollution. Corals can be suffocated by plastic bags caught on a reef, or poisoned by land-based pollution such as runoff from industry, sewage treatment plants, and agriculture. Other pollutants go directly into the ocean: marine fuel, bilge discharge from boats, dumped aviation fuel, and oil pipeline leaks to name but a few.
Another major threat is sedimentation, an increase in the cloudiness of water, which prevents sunlight from penetrating and prevents the coral’s symbiotic algae from producing energy through photosynthesis. Sedimentation may be caused directly by shoreline construction and dredging. It also increases when inland erosion causes more sediment to be washed into rivers and ultimately into the ocean. Human activities which increase inland erosion include logging, construction, mining, and farming along riverbanks. In addition, mangroves, which protect the shoreline from erosion and filter a great deal of sediment, are being cut down for firewood, to create beaches, or to be replaced by fish farms.
Many fishing practices are also responsible for harming coral reefs. Careless fishermen collecting tropical fish for the aquarium trade are only a minor part of the problem. Cyanide fishing is a problem in over 15 countries, while blast fishing is an issue in over 40 countries. Deep water trawling, muro-ami netting, and discarded fishing nets also endanger the reefs.
In addition, coral reefs are destroyed by mining. While some coral is collected to make souvenirs or jewelry, even more is used for bricks or to make cement for new construction.
As if all this was not enough, coral is also threatened by changes in the ocean itself which are also caused by human activity.
Coral is extremely sensitive and may be stressed by changes in ultra violet radiation and water temperature. Depletion of the ozone layer, caused by emissions of man-made halocarbons such as freon and CFCs, means that ultra violet radiation levels have increased. In addition, human use of fossil fuels has increased the amount of carbon dioxide in the atmosphere, and resulted in warming of both the atmosphere and the ocean. Stressed corals expel their photosynthetic algae, become white or bleached, and frequently die as a consequence.
Much of the carbon dioxide produced by human activity is ultimately absorbed by the ocean, where it forms carbonic acid. As carbon dioxide levels in the atmosphere have increased, so has ocean acidification, which causes the weakening of coral skeletons.
Increasing population pressure and economic development have resulted in increased coastal development. The coral reefs which were once found in the waters off of Honolulu, for example, have been destroyed by construction activities, dredging, pollution, and sedimentation. Coral reefs are threatened by so many factors that their future seems as bleak as a piece of bleached coral. However, awareness of the issue is increasing due to the work of the International Coral Reef Initiative, and the international community is working to protect the world’s irreplaceable coral reefs.