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Aug

5

2009
 
 

A Bleached Future?



Local stress makes corals more vulnerable to heat

White paintWarming alone may not be enough to explain recent bleaching of corals, according to a study in Global Change Biology. Rather, stress caused by nearby human activity appears to reduce corals’ tolerance for heat, making them more likely to bleach even when warming isn’t that severe.

Coral bleaching has become more widespread, and high ocean temperatures are thought to be a primary cause. But scientists have wondered whether other, human-induced factors – such as nutrient run-off – might help determine whether a reef bleaches or not.

A team used tree-ring techniques to study coral reef growth in Belize and Honduras over the last several decades. Ninety-five percent of the coral samples had a distinctive “stress band” indicative of bleaching around 1998, in agreement with previous reports. But no such pattern appeared for the years 1937 and 1958, which were even warmer.

Temperature-related declines in coral growth became more pronounced as the population of Honduras rose, they found, suggesting that human factors were lowering corals’ heat threshold. Reducing local stress could reverse the trend and help corals weather the next warming period, the authors say. – Roberta Kwok

Source: Carilli, J.E. et al. 2009. Century-scale records of coral growth rates indicate that local stressors reduce coral thermal tolerance threshold. Global Change Biology Accepted Article DOI: 10.1111/j.l365-2486.2009.02043.x

Image © flyfloor, iStockPhoto.com

Filed Under Climate change, Marine, Restoration | 

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