Coral Reefs: A Reef Resilience Toolkit Module

Bleaching Impacts

Bleached coral reefs are weakened and unable to provide the ecosystem services of shoreline protection or buffering from wave energy. Photo © S. Summerhays

Coral bleaching not only has negative impacts on coral and fish communities, it also affects the human communities that depend on coral reefs for food and income, especially when bleaching leads to mortality. Some of the more obvious impacts of coral bleaching and related mortality include:

• Coral reefs that bleach are weakened, and therefore unable to provide the ecosystem services on which local communities depend. For example, weakened reefs cannot provide the benefits of shoreline protection or buffering from wave energy.
• Bleached corals can be less visually appealing. In contrast to the vibrancy of healthy reefs, stark bleached reefs may be less attractive to divers, and may turn them away from traditionally popular diving sites. Of course, nobody wants to see dead corals and this loss of revenue from decreased tourist activity can threaten the livelihoods of local communities.
• Bleached reefs dominated by susceptible species may change their coral composition to species with a higher resistance or a faster recovery rate, resulting in susceptible species that ultimately die as a result of bleaching.


After a bleaching event, the reef appears dead. With the corals absent, fish and invertebrates that rely on the coral for food and habitat leave. Photo © Stacey Kilarski, Thailand

• Changes in coral species also affect the species that depend on them. Immediately following the mortality event, the most obvious effect is on fish that rely on live coral for food, shelter, or recruitment habitat. In the long term, coral communities are negatively affected.
• Significant declines occur in coral genetic and species diversity when corals die as a result of bleaching.
• Change in the size structure of the reef fish populations and assemblages when corals die as a result of bleaching.
• Bioerosion and collapse of structural complexity of the reef will accelerate changes in reef communities, erosion of beaches, and loss of coral islands.