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Seven Surprising Facts about Coral

When imagining the ocean, you might visualize the magnificent colors and shapes of a coral reef teeming with aquatic life. Though stunningly beautiful on its own, there is much more to coral than meets the eye. Learn about what makes coral special and a vital asset to protect — for our oceans and our planet.

A closeup of toadstool coral reveals that every upward facing surface is covered in fine, hair-like fleshy polyps that move with the movement of the water.

1: Corals Are Animals

Corals are sometimes mistaken for plants with their branchlike features, or rocks for the hard calcium carbonate skeletons some create around their soft bodies, but they are animals!

“Coral is an animal, with plant-like cells living inside of it,” said Shedd Research Biologist Dr. Ross Cunning.

Small coral polyps, each with a mouth and a stomach, grow and divide to form large colonies that are the building blocks of coral reefs. As slow-growing organisms, a new coral will start as one polyp and can grow and divide over hundreds or thousands of years to form colonies as big as a car or a house!

Reef-building corals are cousins of animals like jellyfish and sea anemones, classified together as “Cnidarians.” Coral reefs are some of the world’s largest living structures, and can be seen from outer space.

Bright orange corals grow on craggy rocks.
Many branching arms of coral, orange with pink tips.

2: Corals Can Be Fluorescent

“Some corals can naturally produce fluorescent pigments that can appear as a wide array of colors,” Cunning said. “It’s thought that the fluorescent molecules may have a protective function to shield coral from ultraviolet and high light.”

Corals are indicator species, meaning they are very sensitive to environmental changes in their ecosystem. In great environmental conditions, coral colonies have been documented to live for hundreds or thousands of years. In perfect conditions, researchers think they could live forever!

Corals look like plants with their repeating "branches", but are in fact made up of many smaller animals living symbiotically.

3: Corals Eat Plankton/Small Fish

Each coral polyp has stinging cells in its tentacles that are used like harpoons to spear floating plants and animals, called plankton. Like their jellyfish cousins, corals have stinging cells to help them catch, debilitate and eat their plankton and fish prey.

Coral cells also have a symbiotic, or mutually beneficial, relationship with algae. As another source of energy, the tiny algae live inside the coral’s cells and harness sunlight to produce food for the coral. Yum!

Coral polyps are visible on rigid red stalks of scarlet sea whip coral.
Green star polyps are tiny, each with eight narrow "fingers" comprising each star.

4: There Are Hundreds of Coral Species of All Colors, Shapes and Sizes

Corals are so diverse in their shapes, sizes and colors. Mound and boulder corals grow to look like their name as enormous, round mounds on the sea floor. Brain corals look like a human brain, with maze-like patterns weaving across their shape.

Branching corals can grow up and out like tree branches or create a flat top like a table. Sea fans, a type of soft corals that doesn’t create a hard exoskeleton, have giant flat fans that wave gently back and forth with the water’s current. Sea pens or sea whips look like trees, forming what can truly look like an underwater forest. Pillar corals grow in tall columns that, in colonies, can look like a city skyline.

Tropical fish swim near the bottom with various corals.

5: Corals Can Move

Though adult corals are attached to the ocean floor, corals in the larval, or baby, life stage can swim!

When corals reproduce, they release sperm and eggs into the water. When the eggs and sperm come together and fertilize, they form tiny baby swimming coral larvae. The babies can ride ocean currents and when they find a new suitable place to live, they will swim down and attach themselves to the bottom and grow into a new coral colony.

Coral polyps are viewed close up.
Hammer corals grow in round clusters.

6: Corals Support 25 Percent of Ocean Life

Coral are often referred to as a foundational or architect species, or ecosystem engineers, for constructing the physical spaces where animals live.

“Think of a coral reef like an underwater forest, a three-dimensional structure growing up from the sea floor,” Cunning said. “There would be no forest without the trees. That framework, the nooks and crannies of a coral reef, provides a habitat and a home for a huge, biodiverse community of ocean life.”

In addition to supporting marine life, coral provide food and income for hundreds of millions of people. Corals produce our sandy white beaches and protect our shores from up to 90 percent of potentially damaging waves and flooding. The benefits that coral reefs provide us is estimated to be worth $10 trillion per year.

Lumpy, plant-like and cup-like coral formations in the blue waters of the Bahamas.

7: Climate Change Is the Biggest Threat to Corals

Warming waters due to climate change are putting immense stress on our vulnerable coral populations.

“Coral bleaching is a stress response that corals have when the water is too warm,” Cunning said. “Rising ocean temperatures are causing corals to ‘bleach’ by expelling their symbiotic algae, leaving them bone-white and vulnerable to starvation and disease. Bleached corals are essentially starving and likely to die if the water temperature doesn’t go back down.”

Coral bleaching is happening more frequently and severely as our oceans are warming due to climate change. If we do not take action to reduce our greenhouse gas emissions, climate change threatens to wipe out most coral reefs over the next few decades, Cunning said.

Everyone can play a part to reduce the impact of climate change, like encouraging immediate and dramatic action for climate change policy from state and national representatives, and raising awareness and communicating the importance of climate change advocacy.

If we do that, we have a chance of saving coral reefs and many ecosystems that are in danger.

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