Just like college students, coral reefs can get stressed out too. When coral gets stressed out, it loses its color, a process called coral bleaching.
Healthy coral has a symbiotic relationship with single-celled, microscopic algae called zooxanthellae that live in the coral’s tissue. The algae are their primary source of food and are what give coral its color. If coral get stressed due to environmental factors, the algae leave the coral’s tissue. Without its major source of food, the coral turns white or very pale and is susceptible to disease.
Several environmental factors can be a source of stress for coral including: agricultural runoff and pollution, overexposure to sunlight due to rising global temperatures, and exposure to the air during extremely low tides. However, the leading cause of coral bleaching is changing ocean temperatures due to climate change.
Coral bleaching does not mean the coral is dead. Corals can recover if the bleaching is not severe and can survive if water temperatures return to normal quickly, but if the algae loss is prolonged and the stress continues, the coral will eventually die.
“In 2005, the United States 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” (National Oceanic and Atmospheric Administration).
Coral bleaching not only has negative effects on the coral itself, but also on the coral reef ecosystems and the organisms that depend on the coral, including humans. Both fish and invertebrates rely on alive and healthy coral for food and shelter. In cases where coral bleaching leads to coral mortality, there can be large shifts in fish populations as a result. These shifts can translate into reduced catches for fishermen going after reef fish species, which in turn leads to impacts on food supply and economic activity in fishing communities who rely on the fish to support their livelihood. Damaged reefs without their vibrant colors and bustling fish schools underpin the reef’s aesthetic appeal necessary for the tourism industry. The resulting loss of revenue from reduced tourist activity can threaten the livelihoods of local communities dependent on the tourism industry. Finally, coral reefs are a valuable source of pharmaceutical compounds. Degraded and dead reefs are less likely to serve as a source for important medicinal resources such as drugs to treat heart disease, cancer, and other illnesses.
Coral bleaching is a serious side effect of climate change that has multiple adverse effects on larger communities. From the Time article linked below, “If you think of corals as canaries [in a coal mine], they’re chirping really loudly right now…the ones that are still alive, that is.”