You may recognize us from the colorful reefs we form in tropical waters around the world, but did you know we are actually made of tiny organisms called polyps? Our polyps are soft-bodied, but secrete limestone skeletons for support. Our iconic reefs are formed when many, many polyps come together and build on one another. The result is a colony of polyps that actually act as one organism!
We get our colorful hues from algae called zooxanthellae (polyps are actually see-through!). Polyps and zooxanthellae have a symbiotic relationship, where we get food from the algae in exchange for housing and protection in our hard structure. When we get stressed out by things like pollution or high temperatures, we kick the zooxanthellae out. This is called coral bleaching, and can actually kill us if it goes on for too long!
Did You Know?
Our hard calcium carbonate skeletons contain bands, like tree rings, that record environmental changes in temperature, water chemistry and water clarity. These records help scientists reconstruct what past ages were like before humans kept records!
You may have heard us called “the rainforests of the sea.” Not to brag, but it’s for good reason! We coral reefs only take up about 1% of the ocean floor, but host about 25% of all ocean species! We provide complex, three-dimensional habitat for a huge variety of plants and animals (large and small!), and protect many young fish species as they grow.
We are also kind of like the “speed bumps of the ocean.” Our structure helps slow down and shrink waves as they hurtle towards shore, which helps protect coastlines from hurricanes, cyclones and tsunamis. We protect shorelines in 81 countries around the world, sheltering the 200 million people living along those coasts. On top of all that, we provide services for countless coastal-dwelling humans by providing food, recreation, tourism, jobs and more!
Unfortunately, it’s not an easy time to be part of a coral reef. Stressors such as climate change, ocean acidification, diseases, overfishing, sedimentation and pollution have degraded reefs around the world. Some of us fared worse than others: elkhorn (Acropora palmata) and staghorn (Acropora cervicornis), two species of reef-building corals, have declined between 92-97% since the 1970s! On top of it all, the ocean is acidifying due to increased carbon dioxide, making it harder and harder for us to build the physical structure of the reef. Thankfully, people are hard at work trying to replenish our numbers with coral reef nurseries to make sure we can stay intact for generations to come!
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