How do Corals Beat the Heat?
By Rachael A. Bay     Awards: Myers

Coral reefs are diverse ecosystems, providing homes for thousands of species and food for millions of people. Corals themselves are tiny animals that form vast colonies, and build the structure of this habitat. Corals, however, are sensitive to changes in their environment, and increasing ocean temperatures threaten coral reefs worldwide.

When stressed, corals expel algae that live in their cells, a condition known as bleaching. These algae normally provide nutrients to the coral animals. When corals bleach, they lose this nutrient source, which can lead to death. But some corals are tougher than others. These corals can withstand more stress before bleaching – they are more heat tolerant. The focus of my research is to determine why some corals thrive when others would bleach.

Two general mechanisms may be responsible for coral heat tolerance: adaptation and acclimation. Adaptation could occur if heat tolerance is inherited, meaning tough coral parents make tough coral offspring. Then, through the process of natural selection, whole populations could become heat tolerant. Acclimation, on the other hand, is based on the previous experience of an individual. Corals that are used to hotter temperatures are prepared for heat stress – in a way they have been trained to deal with it.

To test whether corals acclimate to increasing temperatures, I set up a series of experimental tanks with different water temperature regimes, in a sense a gym for corals. After a few weeks I subject corals to a fitness test: a tank of water that gets even hotter. Preliminary results indicate that the corals trained in warmer temperatures could survive the intense heat while other corals bleached. With this experiment, I will be able to learn how different temperature regimes increase a corals heat tolerance.

I am also investigating whether or not corals can adapt to rising temperatures. In this case, there would be genes that help some corals tolerate extreme heat. I am looking for these genes on Ofu Island in American Samoa. On the Ofu reef, water reaches temperatures that are much higher than most corals can tolerate, but corals still thrive. By comparing the DNA from heat tolerant corals to their more heat sensitive neighbors, I will be able to figure out what makes these heat tolerant coral unique and what genetic traits might increase heat tolerance.

Understanding how corals can increase their heat tolerance is particularly relevant when considering the projected increase in ocean temperature. Once we know more about the processes that increase heat tolerance and why some corals are tougher than others, we can make better plans to protect the species that form one of the most diverse ecosystems on the planet.