As climate change results in warmer, more acidic waters, all marine life is affected. As with any environmental change, some creatures will benefit, while others will perish. An increasing number of scientific studies indicate that coral will fall, unfortunately, into the latter group.
There are several thousand species of corals, with the majority living in shallow, warm and well-lit areas. These tropical corals build coral reefs that are essential for the survival of millions of animals, plants and microbes. Thousands of coastal communities depend on coral reefs as a source of food and protection from storms, while many countries use coral reefs to drive tourism generating much-needed money and jobs.
Each coral is a community of thousands of individual polyps that secrete calcium carbonate to form a hard skeleton. Although polyps have tentacles that catch prey like shrimps, most energy is sourced from photosynthetic micro-algae called zooxanthellae that live in the tissue of the polyp. Unfortunately, zooxanthellae are very sensitive to changes in temperature, and will die or be expelled from the coral if waters warm too much. This process is called “coral bleaching”.
A study by Alvarez-Filip and colleagues found that abnormally warm water in the late 1990’s caused wide-spread coral bleaching throughout the Caribbean. This caused many corals to die, which greatly reduced the architectural complexity of coral reefs, resulting in loss of shelter and refuge for many commercially important species like lobsters and fish. Because many corals and their symbiotic zooxanthellae are already at their thermal limit, warmer waters resulting from climate change will cause more widespread bleaching and fewer coral reefs.
Corals are also under attack from “ocean acidification”. Caused by high levels of anthropogenic CO2 that’s absorbed by our oceans making them more acidic (=lower pH), ocean acidification can prevent coral polyps from secreting their calcium carbonate skeleton. A recent study by Silverman and colleagues determined that corals reefs may actually start dissolving when atmospheric CO2 doubles.
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