ECOSYSTEMS

Let’s Learn About Coral Reefs

These colorful and diverse habitats are under threat.

Coral reefs are brilliantly colorful ecosystems, filled with diverse kinds of life. But they are under threat as climate change heats the oceans and fills them with extra carbon dioxide.

By Bethany Brookshire

Coral reefs provide spots of brilliant color under the waves. These ecosystems are wildly diverse — home to everything from crabs to sea turtles. It’s all based on coral — small marine animals that build themselves stony skeletons, often on top of older corals.

But these busy underwater rainforests are in danger. Coral gets their gorgeous color from zooxanthellae — single-celled, brightly colored algae that live with the coral. But when the water around coral reefs gets too warm, corals get stressed. This makes them kick out their algal roommates. With the colorful algae gone, the corals appear ghostly white. That’s why these events are called coral bleaching. If the coral can’t attract another algae roommate in time, the coral itself will die. A bleached reef can spell trouble for the many species that call it home.

Coral bleaching is happening more often and in more places lately. That’s because of climate change. As the Earth’s temperature rises, the oceans have taken in a lot of the heat. Warmer oceans results in more bleaching events. The oceans are also storing much of the carbon dioxide that people produce by burning fossil fuels. The extra carbon dioxide results in oceans that are more acidic, makes it harder for corals to build their rocky homes. More than half of the world’s coral reefs are in danger of disappearing.

Scientists are working to figure out how to help bleached corals and plant new coral reefs. They’ve found that some corals bleach not white, but neon. The neon colors might lure algae back. They’ve also found that playing a soundtrack from a healthy reef can lure fish back to a sick one — making it easier for the sick reef to recover. They’re also planting tiny bits of coral in new places, trying to help new reefs get a good start.

Going bright may help corals recover from bleaching: Coral pigments act as sunscreen and may make a friendlier home for returning algae.

Healthy coral reef sounds attract fish searching for a home: Underwater speakers may prove useful in efforts to restore some reefs.

Bird poop helps keep coral reefs healthy, but rats are interfering: Nitrogen from bird guano makes for more productive reef ecosystems, but snacking rats means fewer birds.