A third of the world’s coral species are threatened with extinction, according to an international study that revealed rapid and alarming deterioration in the state of coral reefs over the past 10 years.
Many will have disappeared by the end of the century unless global warming, pollution and over-fishing are curbed, warned scientists in the most damning and definitive assessment on tropical corals yet delivered.
Coral reefs, the only living structures that can be seen from space, are often compared with tropical rainforests for the diversity and wealth of wildlife and plants that live in and around them. Their loss could also threaten the 25 per cent of marine species that need them for survival, as well as endangering the livelihoods of the estimated 200 million people who rely on them either for food or as a source of income.
An international team of scientists found that 231 of the 704 reef-building corals the study was able to assess were in such a poor state that they had fallen into the three most-threatened categories of species as defined by the International Union for the Conservation of Nature (IUCN). Its Red List of species has seven categories. As of yesterday, the 231 coral species on the Red List have been formally classified as either “vulnerable”, “endangered” or “critically endangered”.
The 39 scientists from 14 countries also investigated the remaining 141 reef-building coral species but could not gather enough information on them to make an accurate assessment. But they believe many of these corals are also highly likely to be threatened with extinction.
What made the study even more urgent was scientists’ ability to calculate what state the corals were in before 1998, when a significant rise in sea-surface temperatures was linked with a worldwide outbreak of coral “bleaching”, when corals as far apart as the Caribbean and the Indian Ocean lost their colour because of heat stress.
The scientists found that only 13 species of reef-building corals before 1998 would have fallen into the three most-endangered categories. This means there has been an almost 20-fold increase in the threat to corals in a decade.
They cited rising sea temperatures, caused by global warming, pollution from such human activities as sewage and agricultural run-off, and over-fishing as the biggest threats. But they warn that all of these may be eclipsed by the threat of rising ocean acidity caused by increases in atmospheric carbon dioxide, which could eventually dissolve the calcium carbonate skeletons of reef-building corals.
Kent Carpenter of the Old Dominion University in Norfolk, Virginia, who directed the global coral assessment for the IUCN, said the threat to the corals is probably unprecedented in modern times. “The results of this study are very disconcerting,” Dr Carpenter said. “When corals die off, so do the other plants and animals that depend on coral reefs for food and shelter, and this can lead to the collapse of entire ecosystems. If you are interested in biodiversity I would say this is one of the most alarming findings in terms of marine life.”
The threat of the extinction of corals could match the mass extinction that wiped out almost half of the corals 65 million years ago, along with the dinosaurs, in a geological event known as the Cretaceous-Tertiary boundary, he said. “We know that conditions existed on Earth that allowed huge numbers of extinctions. These extinctions that existed in geological times could be mimicked by what is happening on Earth today.
“The sort of changes that we as humans are bringing about could essentially be the same sort of catastrophic event that caused the Cretaceous-Tertiary mass extinctions. That took a while. This is probably faster.”
The study is published in the journal Science and was released yesterday at the International Coral Reef Symposium in Fort Lauderdale, Florida. The scientists said corals are now rated second only to amphibians as the most threatened group of animals on Earth. “The proportion of corals threatened with extinction has increased dramatically in recent decades and exceeds most terrestrial groups,” they added. Roger McManus, vice president of marine programmes at Conservation International, said that if sea-surface temperatures continue to rise, causing more frequent episodes of coral bleaching, it will be increasingly difficult for corals to survive further environmental insults.
“These results show that as a group, reef-building corals are more at risk of extinction than all terrestrial groups, apart from amphibians, and are the most vulnerable to the effects of climate change,” Dr McManus added. “The loss of corals will have profound implications for millions of people who depend on coral reefs for their livelihoods.”
Julia Marton-Lefevre, director general of the IUCN, said: “We either reduce CO2 emissions now or many corals will be lost forever. Improving water quality, global education and the adequate funding of local conservation practices are also essential to protect the foundation of beautiful and valuable coral reef ecosystems.”