Increase in water temperatures are causing stress to the coral reefs. When this happens, corals expel the zooxanthella algae and turn white or "bleached." If the algae doesn’t return the coral dies. Coral bleaching is being caused by elevated sea surface temperatures due to global climate change. One degree above the summer max is enough to bleach the corals. During the past 30 years, annual sea surface temperatures in the tropical region of the Atlantic increased nearly 2 degrees Fahrenheit.

Warmer ocean temperatures provide a double hit when it comes to disease—they stress the corals and make them more susceptible to disease, and they also boost the growth of the disease-causing organisms. There is a huge array of diseases that are causing mortality in corals. Most of them are named from the look they give the diseased coral: black band, white band, white spot, purple blotch, etc.

As more carbon dioxide is released into the atmosphere it will also have an adverse effect on the oceans. Rising levels of CO2 will cause the oceans to acidify as some of the excess carbon dioxide dissolves in the ocean water. The pH of the ocean is 0.1 units lower than it used to be—the most acidic in 400,000 years. These acid conditions prevent the corals from forming their calcium carbonate shells and prevent the growth of new coral.

Reasons For Hope

Recent research done by scientist have concluded that more heat resistant algae can be transplanted to the coral reefs and raise their resistance to warmer waters and prevent bleaching in some cases. Also much research has gone into reef rebuilding. In Japan they are developing technology that will allow them to hopefully “replant” coral reefs much like you would replant a tree.

In some areas that were affected by mass bleaching events in the late 90’s they have found much higher rates of coral growth than normal and many nations in the “coral triangle” (an area of corals in the Indonesia, Philippines, and Papa New Guinea) have realized the impact of global warming on their economies and biodiversity and are taking steps to mitigate the effects.

We can also help give coral reefs a fighting chance by halting pollutants and reducing over-fishing—two major factors that are allowing algae to take over coral reefs.