Freezing winter temperatures in North America have had a devastating effect on Floridas coral reefs.

Water temperatures need to be just right for coral to survive, but last winter was lethal, with temperatures dropping six degrees lower than average.

Some coral areas were fortunate enough to be protected by the Florida Current - a warm water mass that blocks extreme temperature variations but much of the reef fell victim to the sharp drop in temperature.

Al Jazeeras Cath Turner has this report.