Published: Dec 10, 2011 12:12 AM EST

ALTAMONTE SPRINGS, Fla. (AP) - Bleaching of Florida's coral reefs has reached a new high.
    
The Nature Conservancy said on Friday that the most extensive bleaching since monitoring began in 2005 occurred this summer.
    
Coral that's under stress expels the colorful algae that live in its tissues, exposing its stark white skeleton.
    
Bleaching makes the coral susceptible to disease and is a major contributor to the decline of reefs.
    
The Nature Conservancy's Florida coastal and marine resilience director, Chris Bergh, said the findings were not surprising. That's because 2011 is tied for the 10th hottest year on record.
    
Bleaching and paling at rates of up to 50 percent were found through most of the Florida Reef Tract that extends from the Florida Keys to Martin County.

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