Like the rest of us, coral reefs have good reason to be stressed regarding climate change. Warmer water temperatures, higher water acidity and stronger storms take their toll on corals and the marine life that depend on them.

Just how stressed are reefs in the western Indian Ocean? WCS marine scientists have made it their job to find out. They have developed a test that measures how well, or poorly, the reefs are handling their changing water conditions. This enables researchers to map out which reefs have the best shot at survival over the next 50 years or so, and therefore where to best direct conservation efforts.

"The future is going to be more stressful for marine ecosystems, and coral and their dependent species top the list of animals that are going to feel the heat of climate warming," said WCS’s Tim McClanahan, the study’s lead author. "The study provides us with hope and a map to identify conservation and management priorities where it is possible to buy some time for these important ecosystems until the carbon emissions problems have been solved."

The model integrates historical data, satellite imagery, and field observations as a way of assessing the health of coral communities, their diversity, and their vulnerability to bleaching. Such evaluations are important at a time when climate change is beginning to affect ecosystems worldwide and resources to address them are limited.

The western Indian Ocean exhibits a significant portion of the Earth’s overall biodiversity within tropical reef systems. Unfortunately, the swath of sea between the Maldives and South Africa has already been the scene of coral death and severe coral bleaching incidents—when higher water temperatures cause corals to expel the colorful algae living within their tissues. For instance, during a very warm spell in 1998, an estimated 45 percent of living coral died. When corals perish, the reef’s communities of plants, anemone, crabs, fish, turtles and other marine species often follow or migrate elsewhere.

Now, it’s time for the good news—relatively.

Which reefs showed the highest biological diversity and the lowest environmental stress? The results shine most optimistically on the coastal regions stretching from southern Kenya to northern Mozambique and to northeastern Madagascar. Reefs off the Mascarene Islands and the coastal border of Mozambique and South Africa also hold promise for holding strong against climate change.

"Reducing human impacts to minimize the multiple stressors on these globally important reefs will give corals a fighting chance in the age of global climate change," said Caleb McClennen, director of WCS-Marine. "These results reveal a window of opportunity for the future conservation of the ocean’s most biodiverse ecosystem."