Stressed Out Corals
 

Summary

On Ofu Island in American Samoa live some of the strongest corals we have ever tested. These corals, found in the back reef pools continuously washed by warm water at low tide, are highly resistant to stress! We set up an experiment using Coral Stress Tanks to test just how much stress these corals can stand.

What are Coral Stress Tanks?

Coral Stress Tanks are compact and can be used anywhere, including remote locations.  They are made with:

• a cooler
• chillers to cool water off
• an aquarium heater to heat the water up
• a small pump to move water around
• floodlights to provide light for the corals to photosynthesize
• a laptop computer is used to control the temperature in the tanks

When we fill the stress tanks with fresh seawater, it creates an environment that mimics the reef when it heats up. We can then observe whether the coral responds negatively to the heat bleaching (that is getting rid of symbionts that feed the coral and color its tissues), or whether the particular coral in the tank is strong and resilient to that specific heat event.

The Experiment

The stress tanks contain corals collected that morning from two places on the reef. The tanks slowly heat up to 34° C (about 5 degrees less than human body temperature). By the afternoon, the coral from one reef zone is alive, but the coral from the other zone is dead. The corals are the same species and have been in the same tanks. The only difference is that the corals that are still alive come from a part of the reef that is naturally warmer. The corals that died came from a part of the reef that is cooler.

Conclusion

We can't protect every reef from every stress. But the Coral Stress Tanks let us know which corals are resistant to the really hot water that happens during a bleaching event. By knowing where on a reef those corals are located, we can decide which part of the reef to protect.