Corals in Crisis Coral Reefs—Home To More Than 4,000 Species of Fish—May Not Be Long for This Earth

From Australia to Panama to the Caribbean, coral reefs are dying. Water temperatures have increased, and acidification continues as the ocean absorbs excess carbon dioxide. These changes in ocean chemistry are thought to be the main cause of coral bleaching.

corals in crisis, credit: eutrophication&hypoxia, flickrccCoral reefs are some of the most biodiverse ecosystems on Earth and home to more than 4,000 species of fish, though they cover less than 1% of the planet’s surface. Resources from the reefs are estimated to be worth over $300 billion annually. Reefs are the foundation of most major fishing industries and estimated to be worth $100 million in commercial value. In developing countries, reefs contribute to almost one-quarter of fish catches, providing food to millions of people. Reefs also buffer shorelines from major waves and erosion and act as barriers protecting wetlands, harbors and ports.

National Oceanic and Atmospheric Administration researchers warn that “Bleaching and infectious disease outbreaks are likely to be more frequent and severe as temperatures rise, increasing coral mortality.” Coral polyps, the tiny organisms that make up a coral reef, contain the photosynthetic algae zooxanthellae. The coral and algae have a mutualistic relationship: The coral provides the algae with material to carry out photosynthesis, while the algae produce oxygen and provide nutrients to the coral. Zooxanthellae are also responsible for corals’ beautiful colors. When water temperatures rise, coral become stressed and the polyps lose their algal companions. Eventually, the coral starves to death.