Coral Bleaching and Reef Degradation

The warmer air and ocean surface temperatures brought on by climate change impact corals and alter coral reef communities by prompting coral bleaching events and altering ocean chemistry. These impacts affect corals and the many organisms that use coral reefs as habitat. Reef degradation also reduces the ability of these systems to respond to change and mitigate storm surge events – a valuable ecosystem service.

How are Coral Bleaching and Reef Degradation Occurring?

Warmer water temperatures and higher ocean acidity can result in coral bleaching. When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white. This is called coral bleaching. When a coral bleaches, it is not dead. Corals can survive a bleaching event, but they are under more stress and are subject to mortality. As the climate changes, coral bleaching is predicted to become more frequent and severe.


NOAA reports that in 2005, the U.S. lost half of its coral reefs in the Caribbean in one year due to a massive bleaching event. Comparison of satellite data from the previous 20 years confirmed that thermal stress from the 2005 event was greater than the previous 20 years combined.  Additionally, it appears not all bleaching events are due to warm water. In January 2010, cold water temperatures in the Florida Keys caused a coral bleaching event that resulted in some coral death, leading researchers to believe that extreme changes in ocean temperature increases and coral stress from other impacts may increase corals’ vulnerability to bleaching.

Additionally, as carbon dioxide in the ocean increases, ocean pH decreases or becomes more acidic, a process called ocean acidification. With ocean acidification, corals cannot absorb the calcium carbonate they need to maintain their skeletons and the stony skeletons that support corals and reefs can dissolve. Already, ocean acidification has lowered the pH of the ocean by about 0.11 units (SCOR 2009). As the NSF relates, moving the ocean’s pH from 8.179 to a current pH of 8.069, which means the ocean is about 30% more acidic now than it was in 1751. If nothing is done to reduce carbon dioxide emissions into the atmosphere, ocean acidification will continue to increase and more and more corals will be damaged or destroyed.

Implications for Land Trusts

The consequences of coral bleaching and reef degradation include negative impacts to species composition and marine system health. Ecological impacts of coral bleaching events include:

  • Bleached corals are likely to experience reduced growth rates, decreased reproductive capacity, increased susceptibility to diseases and elevated mortality rates.
  • Changes in coral community composition can occur when more susceptible species are killed by bleaching events.
  • Changes in coral communities also affect the species that depend on them, such as the fish and invertebrates that rely on live coral for food, shelter, or recruitment habitat. Change in the abundance and composition of reef fish assemblages may occur when corals die as a result of coral bleaching.

Reef degradation and coral die-off are also associated with greater impacts to terrestrial systems – as USGS summarizes, recent research indicates reef systems provide substantial protection against natural hazards by reducing wave energy by an average of 97 percent. Countless fish species rely on healthy intact reef systems for survival. In addition to ecological impacts, the collapse of reef systems can have direct impacts to tourism, aquaculture, and pharmaceutical industries (reefs are a valuable source of pharmaceutical compounds) as well as reduce the overall resilience of coastal communities

Tips for Planning: What Land Trusts Are Doing

Cooperatively Working Towards Conservation Goals.

Land trusts are responding to coral bleaching and reef degradation in various ways. Some groups are launching coral restoration projects in order to support the biodiversity and long-term resilience of these fragile and essential marine systems. In addition to employing strategic conservation planning to reduce risks and enhance resilience, some land trusts are also supporting efforts to mitigate greenhouse gas emissions to reduce the extent of future climate change. Many conservation organizations assert that conservation and restoration alone will not be enough to protect vulnerable reef systems, and advocate global policy action to limit temperature change to less than 2°C by the end of the 21rst century.

Land trusts must determine the right planning approach for their organization, however, more and more, conservation organizations are working with their communities to identify opportunities to reduce vulnerabilities and prepare for changing temperatures. Agencies are making similar strides to implement projects that reduce risks and plan for resilience by incorporating adaptation, mitigation, and engagement into their strategic goals and objectives. For example, the U.S. Fish and Wildlife Service’s Strategic Plan for Responding to Accelerating Climate Change identifies seven planning and development goals to support sustainable landscapes. Conservation groups are increasingly partnering with agencies as well as other nonprofits and for-profit organizations to respond to this global challenge at local levels.

Building resilience for multiple management objectives.

Resilience describes the ability of a system to persist through extreme change. By working to identify and reduce potential threats land managers can build resilience and achieve multiple management objectives. Assessing vulnerabilities is a critical step in the strategic conservation planning process that helps land trusts identify key threats to resources. Adaptive management planning enables conservation practitioners to implement interventions to reduce vulnerabilities and to monitor and revise strategies as new information becomes available. There is no one-size-fits-all solution to addressing management challenges associated with warming average temperatures, however, planning that acknowledges vulnerabilities can help land trusts better achieve their conservation objectives.

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