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staghorn coral

A coral reef may look like a colorful underwater garden, but these living structures are made by thousands of tiny animals called coral polyps. Coral polyps begin life floating in the water, but then settle and live anchored to the sea floor. Most corals live in groups called colonies. Together, they share nutrients and form the familiar branching or mound-like shapes of the reef.

Stats

Story

Night on the Reef
Adult coral polyps have no brains, no eyes, and can't move in search of mates. So how do they reproduce?

Most corals spawn in unison, releasing billions of eggs and sperm on the same night. For their offspring to survive, timing is everything—and it's all based on moonlight.

Even without eyes, corals can sense the full Moon using cryptochromes, chemicals that respond to light. By measuring moonlight, temperature, and length of day, corals can spawn at the same time. The male and female cells unite and become larvae. The larvae settle and grow into polyps, forming a new colony.

Stumper

The rocky limestone structure of a coral reef is made of:

shells left by other reef animals

seafloor rocks washed up by waves

skeletons of living and dead corals

Correct!

Some coral species produce hard skeletons around their bodies. The skeletons protect the corals and give new polyps a place to attach. Over time, layers of skeleton build up in a variety of shapes. Coral shapes usually depend on the species that built it.

Stumper

How do coral polyps get food?

they catch prey with tiny stinging tentacles

they get nutrients from algae that live on them

both of these

Correct!

Coral polyps usually feed at night, extending their tentacles to catch tiny animals floating by. They also depend on plant-like algae that live with them. These algae give corals their bright colors. Algae thrive in warm, clear water—so corals do too!

Stumper

Corals are most closely related to:

sea anemone

seaweed

starfish

Correct!

Like the sea anemone, the coral polyp attaches itself to a hard surface, and has a mouth surrounded by tentacles.

Fact or Fiction

Most coral polyps can clone themselves.

Fact

Fiction

Fact

Polyps release male and female cells, but they also reproduce by cloning. A young polyp can divide or produce a "bud" growing out of its side. Many polyps that bud from each other form a colony.

Fact or Fiction

Image credits: main image, via Wikimedia Commons (CC BY-SA 3.0).

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Correct!

Correct!

Correct!

Fact

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