What Is Killing The Corals?

What Is Killing The Corals?

One of the reasons that reef-build corals are so successful is the symbiotic relationship that it forms with algae. However, extreme changes in the environment can disrupt this association harming, or even killing, the coral.

Corals provide shelter to microscopic algae in exchange for food these algae produce by photosynthesis. If the algae don't produce food, the coral finds itself giving away shelter for free. Corals can evict their symbiotic algae if the algae don't produce food. If this happens on a large scale, the coral turns white and it is called "coral bleaching". Sometimes the coral find new algae to feed them, and recover. But if they don't, the reef can die.

coral bleaching

Under normal conditions, the algae have no reason to stop supplying food. However, if something changes and the algae are stressed to the point where they can't produce enough food to feed themselves and supply the corals, coral bleaching can occur. One cause of this is when the water temperature gets too high.

Water temperature fluctuates with seasons, sun exposure, and with other environmental factors. In general, local water temperatures tend to stay within a relatively narrow range, to which the corals and algae have adapted. However, global warming creates greater swings in temperature, causing coral bleaching to become a widespread problem. Now that water temperatures have greater variability than they used to, coral bleaching has become more common, and it has become harder for corals to recover.

How Do We Know That?
Globalwarming.org
Marine Biology.org