Coral can tell us a lot about the Earth. In his first scientific book, The Structure and Distribution of Coral Reefs, published in 1842, Charles Darwin sets out the notion that change is the natural state of our planet, an inspiration he was to pursue and refine for the next 17 years, culminating in The Origin of Species.
For Steve Jones, author of Coral: A Pessimist in Paradise, “With every breath and every death we take part in a series of transactions in which the currency of life moves through the reserves held in the soil, the skies and – most of all – the seas. Its slow revolutions made the modern world, but… it may soon break down, with disastrous consequences for the corals and for ourselves”.
In the OECD Insights Fisheries: While Stocks Last? we describe the overexploitation of coral reefs. The million tons of fish taken from them each year is three times beyond the sustainability limit. Deep-water reefs support fish populations, but they snag nets until bottom trawlers come along and pulverise them. And when nets and traps no longer find anything, fishermen, imitating the aquarium trade, use explosives or cyanide to stun the fish and make them easy to catch.
Urbanisation and the growth of coastal populations are taking their toll as well. Wastes flushed into the sea clog the organisms and provoke coral diseases. Some of these are of human origin. White pox is caused by a bacterium usually found in the human gut and seems to survive in sewage. Herpes viruses are the main cause of coral disease, and the human herpes virus has been found in corals off Panama.
Only a third of the world’s coral reefs are healthy and a fifth have already been destroyed completely, but even without overfishing and sewage, the remainder would probably be doomed anyway. Strong sunlight plus warm water causes coral bleaching, a stress-induced reaction when the coral polyps expulse algae because the algae are photosynthesising too fast and producing too much oxygen. So as the oceans heat up, the stress will intensify, and become more permanent.
The effects of ocean acidification are worse still. The rate of calcification (building shells) is projected to be cut by half by 2100 if carbon emission trends continue unchanged, in a process that one expert has likened to osteoporosis in humans. This makes the coral reefs much more vulnerable to erosion, and they could simply wither away.
Atmospheric CO2 concentration is expected to exceed 500 parts per million and global temperatures to rise by at least 2°C by 2050-2100. This is much higher than the values under which most of today’s marine organisms evolved. The result will be less diverse reef communities and collapse of reef structures.
The World Resources institute has just published Reefs at Risk Revisited, a study on coral reefs, part of a project involving the UN World Conservation Monitoring Centre, the Global Coral Reef Monitoring Network and numerous other agencies including the International Institute for Reef Studies and NOAA.
The new report confirms the Insights description. According to the report, over 60% of the world’s reefs are under immediate and direct threat from one or more local sources such as those mentioned above.
Overfishing — including destructive fishing — is the most pervasive immediate local threat, affecting more than 55% of the world’s reefs. Coastal development and watershed-based pollution each threaten about 25% of reefs. Marine-based pollution and damage from ships is widespread, threatening about 10% of reefs.
Approximately 75% of the world’s coral reefs are rated as threatened when local threats are combined with thermal stress, which reflects the recent impacts of rising ocean temperatures, linked to the widespread weakening and mortality of corals due to mass coral bleaching.
There is some hope though. Reefs have shown a capacity to rebound from even extreme damage, while active management is protecting reefs and aiding recovery in some areas.