Published Sep. 12, 2008
Coral reefs harbour the highest concentration of marine biodiversity in the world, form the basis of ecosystems and food webs that sustain communities and provide coastal protection. However, according to recent research, climate change and human impacts are placing one-third of reefs at serious risk of extinction. Areas at risk include the Caribbean and the Coral Triangle in the western Pacific. Humans can have negative impacts on coral reefs through a number of means, including increased coastal development, sedimentation due to poor land-use and watershed management, sewage discharge, pollution from agrochemicals, coral mining and over-fishing.
These impacts reduce the resilience of corals to withstand global threats from a rise in sea surface temperatures and increased ocean acidification arising from climate change. Higher temperatures lead to heat stress, which causes the coral to expel the zooxanthellate algae that live in their tissues in a protective, symbiotic relationship. This increases the risk of mass coral bleaching and mortality from diseases, some of which can kill 500 year old colonies within months. Additionally, ocean acidification is reducing ocean carbonate ion concentrations which in turn limits the ability of corals to build skeletons and reef structures.
Categories and criteria from the International Union for Conservation of Nature (IUCN) Red List were used to identify corals that are ‘Vulnerable’, ‘Endangered’ or ‘Critically Endangered’. The results emphasise the widespread plight of coral reefs and the urgent need for conservation measures. The majority of the species were found to be vulnerable. Of 704 species studied that could be assigned conservation status, 32.8 per cent were in categories with an elevated risk of extinction.
Among the researchers’ other findings were:
- The proportion of corals threatened with extinction has increased dramatically over the last 2 decades
- Corals are at greater risk of extinction than any group of land-based animals apart from amphibians
- 40 per cent of coral species only inhabit shallow-waters and are therefore more vulnerable to human impacts
- 303 species are highly susceptible to bleaching, and of these, only 102 species can easily recover within a few
- Each year, 1-2 per cent of coral is lost in the Indo-Malay-Philippine Archipelago
The Caribbean has been devastated by population declines of two key species, the staghorn and elkhorn corals, which were recently listed under the US Endangered Species Act. This area has the largest number of corals that are listed as Critically Endangered or Endangered categories, while the Coral Triangle of the western Pacific has the highest proportion of threatened species overall.
The authors draw attention to the high aesthetic, resource and recreational value of coral reefs. By identifying the areas and species most at risk, it is hoped that the research can help policy makers set priorities for biodiversity conservation.