Shading reduces bleaching risk, but to be effective it must be reliable. Heavy cloud cover during a bleaching event may protect corals from bleaching, but clouds are not a reliable factor. On the other hand, topographical and bathymetric features are reliable year-round.

Shading is important in certain locations such as Palau, the Philippines, and anywhere there are steep-sided limestone or volcanic islands that offer protection:

• Islands of high relief that are oriented along a north-south axis provide reefs with shade for half of each day.

• Steep-sided reefs with a north-south axis may also provide shade for half of each day, but this has yet to be demonstrated.

• Aspect relative to the sun for steep-sided reefs in high latitudes may provide for greater shading of slopes facing away from the equator.

• Limestone islands or coastlines undercut by erosion at the waterline may provide shade for reefs growing on shelves around their perimeter.

• Trees on steep islands further enhance their shading effect.

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"Dr. James Oliver of Worldfish has devoted his career to coral reef conservation biology" Rodney Salm, is Director of Transforming Coral Reef Conservation, The Nature Conservancy. Rod has launched a global program to build resilience in the face of change into marine protected areas and has developed the Reef Resilience toolkit concept.