Insights into coral bleaching

Corals are animals that live in tropical oceans and for 100's of millions of years, corals have learned to work with small algae of microbial size and bacteria to better survive in these clear waters. This collaboration called a symbiosis works because the coral provides a home for the algae and the algae pay rent in the form of sugar. This is easy for the algae, it captures sunlight and converts solar energy into sugar (the same photosynthesis that goes on in terrestrial plants). The sugar is a critical source of carbon for the coral and provides a large percentage of corals energy. Food for shelter has been a successful partnership for millions of years.

 

This is a photo of an individual coral. The brown dots in the tentacles and at the base of the polyp are the symbiotic algae. A healthy coral with lots of algae looks brown.

 

But when the environment turns stressful a coral evicts its algae, making the coral tissue pale white as in this photo.

 

If there are no algae then what do the corals get to eat? The breakdown of this symbiosis does not kill the coral immediately, but the coral does go hungry. If bleaching lasts for a few days to a few weeks, most corals can survive and regain their algae. But if environmental stresses persist for a long time corals will die.

 

Our laboratory is actively researching patterns of coral bleaching in Hawaii. Some species of corals bleach some don't. Within the same species sometimes every coral on a reef bleaches and other times two individuals of the same species that are right next to each other are bleached and unbleached.

 

This pattern of paired bleached and healthy corals is really exciting. It means that some coral individuals exposed to the same environmental stress are resistant. Why? We don't know, but if you fund our project we will be able to test whether the symbiotic microbes in corals contribute to their resistance to bleaching. This research has global implications because reefs all over the world are bleaching more frequently, and if we discover what makes corals resistant to bleaching we may be able to assist corals survive a changing climate.