Coral bleaching and climate change

A Pacific coral reef with many corals

A Pacific coral reef with many corals

The activities are as follows:

Corals are animals that build coral reefs. Coral reefs are home to many species of animals – fish, sharks, sea turtles, and anemones all use corals for habitat! Corals are white, but they look brown and green because certain types of small plants, called algae, live inside them. The algae produce food for the corals so they can grow big, and the corals provide the algae a safe home. The algae and corals form a mutualism, or a relationship between two species where both partners benefit each other and do better together than they would alone.

When the water gets too warm, algae can no longer live inside corals. The corals turn from green to white, called coral bleaching, because they do not have algae living in them. Climate change has been causing the Earth’s air and oceans to get warmer. With warmer oceans, coral bleaching is happening more often. If the water stays too warm, bleached corals will die without their algae mutualists.

Scientist Carly working on a coral reef

Scientist Carly working on a coral reef

Carly is a scientist who wanted to study coral bleaching so she could help protect corals and coral reefs. One day, Carly observed an interesting pattern. Corals on one part of a reef were bleaching while corals on another part of the reef stayed healthy. She wondered, why? Why can some corals and their algae still work together when the water is warm while others cannot?

Ocean water that is closer to the shore (inshore) gets warmer than water further away (offshore). Perhaps corals and algae from inshore reefs are used to warm water. She wondered whether inshore corals were better able to work with their algae in warm water because they are used to these temperatures. If so, inshore corals and algae may bleach less often than offshore corals and algae. Carly designed an experiment to test this. She collected 15 corals from inshore and 15 from offshore reefs in the Florida Keys. She brought them into an aquarium lab for research. She cut each coral in half and put half of each coral into tanks with normal water and the other half into tanks with heaters. The normal water temperature was 27°C and is a temperature that both inshore and offshore corals experience during the year. The warm water tanks were 31°C and are a temperature that inshore corals experience, but offshore corals never experienced in the past but may experience with climate change in the future. After six weeks she recorded the number of corals that bleached in each tank.

 Featured scientist: Carly Kenkel from The University of Texas at Austin

Flesch–Kincaid Reading Grade Level = 7.9

There are two scientific papers associated with the data in this Data Nugget. The citations and PDFs of the papers are below. The lab webpage can be found here.

If your students are looking for more data on coral bleaching, check out HHMI BioInteractive’s classroom activity in which students use authentic data to assess the threat of coral bleaching around the world. Also, check out the two videos below!

  • Another BioInteractive video, appropriate for upper level high school classrooms. Visualizes the process of coral bleaching at different scales. Video includes lots of complex vocabulary about cells and the process of photosynthesis.





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