Coral Reefs
Coral reefs represent some of the most biologically diverse ecosystems on Earth, providing critical habitat to approximately 25 percent of marine species. In addition, these ecosystems provide economic benefits through tourism and fisheries. One recent estimate valued the annual net economic benefits of the world’s coral reefs at $30 billion. However, human activities including development in coastal areas, over-fishing, and pollution have contributed to a global loss of over 10 percent of these valuable ecosystems. An additional 15 percent have been lost due to warming of the surface ocean, and climate change will further contribute to coral reef degradation in the decades ahead.
Turning White
Most corals have a narrow temperature tolerance. Coral bleaching occurs when corals become stressed, most often when ocean water gets too warm. Corals will “eject” the symbiotic algae (called zooxanthellae) that live inside them. When corals lose their algae, they not only lose their color (turning white) but also their built-in food source. Scientists have declared three global coral bleaching events: 1998, 2010 and 2014-2017. This most recent event was the longest and most widespread bleaching event ever recorded, killing as much as two-thirds of the corals in the northern part of Australia’s Great Barrier Reef. Although corals can survive a bleaching event, they will eventually die if they are under repeated stress. Outbreaks of coral disease typically follow bleaching events since stressed corals are more susceptible to infection. A recent special report from the Intergovernmental Panel on Climate Change (IPCC) states that with an additional half-degree of warming above today’s levels, tropical coral reefs will face “very frequent mass mortalities,” although coral adaptation is possible. If temperatures rise an additional degree to 2 degrees above pre-industrial levels, coral reefs are in danger of vanishing entirely.
