Magazine article UNESCO Courier

Corals under Siege

Magazine article UNESCO Courier

Corals under Siege

Article excerpt

Threatened by pollution, overfishing and global warming, coral reefs -- a lifeline for millions of people -- are dying off at an alarming rate

The vibrantly coloured rainforests of the sea received a disturbing bill of health during a recent gathering of marine biologists in Bali: in the past few decades, more than one quarter of the world's coral reefs have been destroyed by human activity. At the present rate, at least 57 percent will be lost within our lifetime.

This destruction threatens not only coral reefs, but also the lives of some 500 million or so people in southeast and southern Asia, eastern Africa and the Caribbean. For many of these coastal communities, corals are the largest source of protein: a healthy reef can provide more than 15 tonnes of fish and seafood per square kilometre each year, enough food for 2,500 people. And often they are the only source of income, employment and foreign exchange.

Coastal communities depend on their reefs to attract tourists, develop the capacity for commercial fishing, and protect shorelines from erosion and storm damage. In the British Virgin Islands, for example, 45 percent of revenue comes from tourism, which provides more than half of the territory's employment. A loss of reefs would probably cause the water to cloud with algae and the beaches to erode under the pressure of waves, leading to an estimated $130 million loss in income.

Created by more than 50 million years of evolution, coral reefs are one of the most complex and fragile webs of biodiversity on earth. Naturalists have catalogued more than 800 species of reef-building coral and 4,000 species of reef-dwelling fish. In total, coral reefs may shelter as many as one quarter of all marine species, and are especially important as nurseries for young fish.

So why are these lifelines disappearing faster than ever? On a local level, overfishing has decimated many individual reefs, notably in Malaysia, Vietnam, Indonesia and the Philippines. The removal of too many plant-eating fish allows algae to overgrow and kill the coral, beginning a chain reaction of local extinctions that quickly grows beyond the reef's natural ability to recover. Several fishing techniques are particularly lethal.

Blast fishing, when fishers explode homemade devices over reefs to kill fish, has severely damaged corals in eastern Africa. Fishing with sodium cyanide is no better: exposure to this chemical makes tropical fish slow and clumsy, and therefore much easier to catch, while at the same time killing off corals and many other reef animals.

Cyanide-fished reefs are often stripped of their marine life and overgrown by algae. Despite efforts to halt cyanide fishing, its frequency has increased in the past few years, driven by the high prices paid for live fish at tropical fish restaurants in Asia and aquariums in North America. Since this form of fishing began in the 1960s, the amount of cyanide dumped on coral reefs in the Philippines alone has exceeded one million kilograms.

But fishing is just one chapter of the story. Reefs are also being killed by industrial pollution, sediments running down rivers from deforested land and run-off from agricultural fertilizers. Activities such as coral mining, dredging, ship-grounding and construction break apart large coral strips and shatter delicate branches. Since reef-building corals only grow at a rate of 1.3 to 10.2 centimetres per year, each blast-fishing explosion and dragged object can destroy a century of reef development. …

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