Coral reefs Environmental Issues

Collection of coral for construction and use in the curio trade

Coral has a multitude of uses as a construction tool. It can be utilised for the production of lime kilns, house foundations and embankment of streets, canals and fish ponds. Huge businesses also thrive on collecting coral and selling it as souvenirs or exporting it for sale in the aquarium trade.

Chemical Pollution

Agriculture and industry release a variety of chemicals into coastal waters. Pesticides and fertilisers used in agricultural development projects are carried in run off to sea and have been known to take part in coral reef destruction. Pesticides can destroy or damage zooplankton or reef communities. They cause further damage by accumulating in animal tissue and may affect physiological processes. Herbicides may interfere with the basic food chain by destroying or damaging zooxanthallae in coral, free living phytoplankton, algal or sea grass communities.

Exposure to chemicals (namely hydrocarbons) released by spillage from oil tankers, harbours and pipelines has been known to affect reproduction, growth rate and feeding, defensive responses and cell structure in corals. Industrial practices such as mining, dredging and refining all release heavy metals into coastal waters. Some coral species are sensitive to these, although the extent is not yet known.

Nutrients Loading/Sewage

The discharge of fertilisers, waste feed and other materials from aquaculture and agriculture into coastal waters can result in nutrient loading. The introduction of organic compounds results in eutrophication and subsequent oxygen depletion. Europhication is where the nutrient load gets to an extent that the community becomes dominated by algal/seaweed, exceeding the capacity to control by grazing organisms. This leads to oxygen and light reduction and perhaps death of the communities living there.

Coral reef ecosystems have been described as oases in the oceanic desert due to the lack of nutrients present in their environment. When faced with large quantities of nutrients, they are easily overcome by algae and severely damaged, if not killed. Sewage from coastal developments and local communities can supply these nutrients providing food for algae, which go on to overgrow the coral.

Overfishing

Over exploitation affects the vast majority of the world’s reefs. This leads to an average decrease in the size of the fish and a reduction in predatory target fish. Removal of key herbivores and predator species may result in large scale ecosystem change. If grazers are removed from reefs, algae are quick to take over and dominate, especially if the area is also suffering from organic pollution.

Destructive fishing and boating practices

Fishing methods in the tropics can be particularly destructive especially those of dynamite ‘blast’ fishing, cyanide or poison (duva) fishing and fish hunting with gum boots. Other adverse fishing practices include disintegration of the reef structure in order to weight traps and remove hiding places and beating coral surfaces to herd fish into nets. Anchor damage and accidental grounding of boats can be a serious threat to reefs. For example, one cruise ship destroyed 3150km2 anchoring on one occasion. These practices lead to habitat destruction and disintegration of the reef ecosystem.

For example: here are photos of the broken coral heads left behind when Tiger IV hit the reef next to Malolo Island in 2006.

Construction and Sedimentation

Sedimentation (losing soil from upland areas) is an extremely important cause of coral reef destruction. Coastal construction and shoreline development often result in heavy sediment loading. Further effects are caused by inadequate land management and deforestation where soil run off from farms and settlements delivers sediments to the reefs. Watersheds cleared of their forests and other vegetation cover is vulnerable to erosion and flooding, resulting in increased levels of sediments reaching the reefs. Chemicals applied to upland agriculture also make their way down to the reefs via run off from land and rivers.

Dredging has many very serious implications for reefs. The most dramatic effects are caused by suspension of silt, sedimentation, turbidity, oxygen reduction and the release of bacteria and toxic matter. A large quantity of either coarse or fine particles will bury the corals, which are unable to withstand cover for more than one or two days.