Among the world’s greatest wonders are the ocean’s reefs. Blooming with vivid colors, thousands of people explore these underwater attractions each year. However, the reefs are being attacked by our dependence on products that emit pollutants and other harmful chemicals. These chemicals have created a hole in the ozone layer and heavily contribute to global warming. As the use of these chemicals increase, the coral slowly die. What once was a prosperous ecosystem is now a graveyard of coral skeletons.

What Causes Coral Bleaching?

Corals live in an endosymbiotic relationship with tiny algae called zooxanthellae. The algae live in the coral’s tissues and are responsible for the coral’s color. Together, they share resources that help them survive. The algae provides 90% of the coral’s energy and nutrients through photosynthesis. In return, the coral provides the algae with carbon dioxide and ammonium, which is needed to carry out photosynthesis. However, when the coral become stressed due to changes in their habitat conditions, the burden of providing for the algae becomes too much. To survive, the coral expels the algae. Without the algae to provide color, the coral turns white, which dubbed the name “bleaching.” Expelling the algae allows them to survive on a short-term basis, but the coral cannot provide enough energy to survive for a long time. Eventually, these bleach coral will starve. However, the coral can recover if the algae re-enter its tissues and restart the photosynthesis process.

Global Warming

Many things can cause the stressors that make the coral expel the algae. Some stressors include disease, pollution, changes in ocean salinity, and sedimentation.  However, the most common stressor is water temperature. Above-average ocean water temperatures due to global warming are the number one cause of coral bleaching. In 2016, the Great Barrier Reef lost a total of 67% of its shallow water corals. According to the United Nations Environment Programme, the longest bleaching event took place between 2014 and 2016. Utilizing satellite data from the past 20 years, scientists determined that the thermal stress peaked during these years.

While hot ocean waters are the leading cause of bleaching right now, cold waters can also affect the coral. In 2010, Florida Keys experienced water temperatures that were 12.06 degrees Fahrenheit lower than the average temperature. This caused a mass bleaching event that resulted in a lot of coral dying.

Why is Coral Bleaching Bad?

A cascade of negative effects occurs when coral bleaching ensues. When coral dies, they decay and leave behind their calcium carbonate skeletons. These skeletons are then recolonized by the algae, which blocks any sort of coral regrowth. After a while, the skeletons will erode away, which collapses the reef structure. Since reefs shelter 25% of marine species, the collapse of the reef could cause a mass extinction.

As the marine life die off, many human societies will be affected. Many industries depend on fish for food and business. At the current rate of coral bleaching, there has been a 44% decrease in fishing industries in the Florida Keys area and an 80% decrease in the Caribbean.

How are the Reefs Today?

Although the loss of the coral is sad, there is hope for the future. Scientists were able to successfully revive areas of coral from the Great Barrier Reef. They have seen coral regrowth in the central and southern regions, and they project that it will return to its previous state. This opens the door to the possibility that we can undo the damage we caused.

Furthermore, many coral species are acclimating to the stressors. Scientists at Penn State found that species of coral in the Andaman Sea were thriving despite the increased water temperature. These particular coral utilized a different species of algae that helped them tolerate the heat. Using this information, researchers are trying to condition algae to acclimate to the changing ocean, and the studies show promising results.


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