• Brooke Collier

What is Coral Bleaching & Why is Coral Dying?


Coral reefs are the most diverse marine ecosystems on earth. Reefs offer shelter to thousands of animal species. Millions of people also rely on coral reefs for fisheries, tourism and coastal protection. In an unfortunate contradiction to their outstanding abilities, coral reefs are dying at an alarming rate all around the globe.


Without corals, reefs begin their journey to extinction. Coral reefs are currently facing various stresses including pollution, overfishing, and climate change. In consequence, over 50 percent of the world’s coral reefs have died in the last 30 years, and up to 90 percent may die within the next century. Currently, there are very few pristine reefs still in existence.


Despite existing for over 400 million years, coral is unable to adapt to the speed of human induced trauma. As for most species, sexual reproduction is of vital importance for coral existence. Reproduction maintains genetic diversity, and allows coral and other species to adapt to a naturally dynamic environment. Under immense stresses, corals are likely to stop sexual reproduction.

American Samoa (2014/2015)

Image credit : The Ocean Agency


Coral degradation is caused by a number of factors including; illegal fishing techniques, pollution, careless tourism, other natural phenomena such as earthquakes and hurricanes, and of course, climate change.


The most current and devastating culprit of coral death is coral bleaching. Coral bleaching takes place when coral loses their visual vibrancy and in turn become bleached white. How? Coral are noticeably colored because of a microscopic algae called zooxanthellae. Coral and zooxanthellae share a mutually beneficial relationship for survival. When ocean temperatures rise, from instances such as increasing atmospheric greenhouse gas levels, the coral stresses and expels the algae. If temperatures remain high, the coral and algae will no longer maintain symbiosis, causing the coral to lose all color and eventually die.


Stages of Coral Bleaching

Image credit : Counting Coral


In addition to ocean temperatures, conditions such as light, nutrients, and water pollution also causes the coral to expel the symbiotic algae living in their tissues. Corals can survive a bleaching event, however the extreme stress that it causes heightens the chance of mortality. If the source of coral strain does not resolve, the bleaching will lead to extinction.


Maui, Hawaii (Aug. 2015/Nov. 2015)

Image Credit : The Ocean Agency


Another tragic cause of coral death is the use of cyanide and other poisons to fish for coral reef dwellers. This poison is used to scare fish from their homes, making them an easier target to catch. In the process, the cyanide gets inside the gaps of the reef often causing the coral to die in the cloud of poison.


Oil, fertilizer, and human or animal waste are dumped in areas where coral reefs struggle to survive due to the change in chemical makeup of the water. The waste can also block sunlight, a necessity for reefs to survive. Floating trash can also damage young coral polyps and affect their ability to get the nutrients that they need to grow into a thriving reef


Once these corals die, reefs rarely resurge. With few corals surviving, their inability to reproduce stresses entire ecosystems in which both wildlife and people depend on.

As stated by the National Oceanic and Atmospheric Association, between 2014 and 2017 around 75% of the world’s tropical coral reefs experienced heat-stress severe enough to trigger bleaching. For 30% of the world’s reefs, that heat-stress was enough to kill coral.


Predominantly in developing countries, fisheries and tourism provide important livelihoods that directly depend on healthy coral reefs. In areas frequently impacted by hurricanes and storms, coral reefs offer natural coastal protection. In addition, the great biodiversity of coral reefs serves as an important source for new medicinal remedies. A world without corals leads to a less diverse and beautiful ocean, as well as an economic disaster.





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Counting Coral is an ocean non-profit organization seeking to save the coral reefs through direct, innovative action.