Warmer oceans are causing widespread damage to coral reefs. According to an article posted on sciencemag.org, in the Indian Ocean and throughout Southeast Asia pervasive coral bleaching is comparable to 1998 levels, when El Niño conditions in the South Pacific raised global sea surface temperatures, destroying 16% of the world’s coral reefs.
The National Oceanic and Atmospheric Administration’s Coral Reef Watch indicates that sea surface temperatures this year have been above average throughout the Caribbean and Tropical Atlantic. Temperatures in the Caribbean and Western Pacific are expected to rise until mid-October. This has prompted NOAA to issue an alert for the Western Pacific and the Caribbean.
Photosynthetic algae called zooxanthellae, living on corals and responsible for their color, produce nutrients and oxygen which drive reef growth. Long periods of above average water temperatures and intense sunlight cause corals to expel zooxanthellae, resulting in bleaching. If severe temperatures don’t endure the algae can reinhabit corals, but long-term bleaching leads to death.
“If you get too many repetitive lethal events the corals will not recover,” says Clive Wilkinson, a coral reef ecologist at Australia’s Reef and Rainforest Research Center, quoted in the sciencemag.org article.
El Niño has played a role in increasing ocean temperatures this year, but, according to NOAA coral reef ecologist C. Mark Eakin, also quoted in sciencemag.org, global warming is forcing baseline sea temperatures upward, upping the frequency of bleaching events.
“Unless there is concerted action to reduce greenhouse gases bleaching will become increasingly common and not just during extraordinary weather events,” he says.
*Image: taken by Bruno de Giusti, 8 July, 2006. ‘A part of Moofushi coral reef, strongly hit by 1998’s El Niño.’ Licensed under Creative Commons Attribution-Share Alike 2.5 Italy.