Satellite data warns of danger to coral reefs
Rising sea temperatures are a risk to corals, because they lose the algae that produce food and change colour in a process known as coral bleaching. The corals are not necessarily dead when they lose their colour, but need to reabsorb the algae quickly to get nutrients, and avoid diseases.
Bleaching can also occur with other environmental changes such as sudden drops in sea temperature, or changes in light or nutrients available.
Corals become stressed when the temperature exceeds the normal summertime highs by one degree, and the problem increases with increasing heat and the amount of time the temperatures remain above this threshold. Once the measurement exceeds four degree heating weeks, some coral bleaching is likely, with some species being more susceptible than others. After eight degree heating weeks, significant bleaching and coral death is likely.
The NOAA Coral Reef Conservation Program examines the risks to coral from ocean acidification as well as from rising sea temperatures.
The Coral Reef Alliance is among the organisations working to try to protect coral from damage by natural processes and human activities.
You can see the NOAA product on Coral Degree Heating Weeks going back to 2001 on the NOAAView Data Visualisation Tool.