PracticeAssessing

Assessing Coral Bleaching

Inquiry Activity
A learning activity by Tom J. McConnell, Ball State University.

Scientists who study corals and coral reefs often need to evaluate the health of the corals by assessing the level of bleaching. Coral bleaching is the loss of the color seen in corals that is caused by symbiotic zooxanthella, a type of algae that lives inside the tissue of healthy corals.

Learn more about the symbiotic relationship between coral and zooxanthellae

When corals are stressed, they eject the algae from their tissues. This makes it hard for coral to survive because they depend on the food created by the zooxanthellae through photosynthesis.

Learn more about coral bleaching and its causes

So coral researchers and those who help protect or restore reefs use the Coral Health Chart seen here to assess the amount of bleaching. The lighter the color of the coral, the more severe the threat to the survival of the coral.

There are several kinds of zooxanthellae, and the type living a coral's tissue determines their color. On the chart, you see four different colors indicate by letters (B, C, D, or E). The darker colors are shown by higher numbers (1 through 6). The higher the number, the healthier the coral.

IN this activity, you will practice using the Coral Health Chart to "score" some images of corals using the same tools and processes as coral researchers around the world!

Download the Coral Health Chart in printable PDF format.

Let's Try Using the Coral Health Chart

For a first step, let's try out the chart! The images below are photos of healthy and bleached corals taken at Mote Marine Laboratory's International Coral Reef Restoration and Research Center in Sommerland Key, FL. The bleached samples are used as a comparison, and the healthy corals show some color!

Us the Coral Health Card above to compare the colors of the corals, and give them a "score." Beneath each picture, we have added our own score to help you learn how we use the card.

Brain coral plug being grown in lab.
Our Rating: E5. (Curry © 2023)

Elkhorn coral (dead).
Our Rating E1. (Ackerman © 2023)

These are pretty easy! Let's try some other samples on the next page that include some images of corals in the wild.

Try Another Set of Samples!!