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Explore the Underwater World

The Rainforests
of the Sea

Coral reefs are among the most biodiverse and threatened ecosystems on Earth. Dive in to discover their beauty, mystery, and why they need our help.

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800+
Coral Species
25%
Marine Life
70M+
Years Old
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About Reefs

What Are
Coral Reefs?

Coral reefs are large underwater structures composed of the skeletons of colonial marine invertebrates called coral. The coral species that build reefs are known as hermatypic, or "hard," corals because they extract calcium carbonate from seawater to create a hard, durable exoskeleton that protects their soft, sac-like bodies.

These incredible ecosystems are found in shallow, warm-water tropical oceans, typically between 30°N and 30°S latitude. They cover less than 1% of the ocean floor but support an estimated 25% of all marine species.

Tropical Oceans Biodiversity Hotspots Living Structures Calcium Carbonate
Coral reef underwater
1M+
Species Depend on Reefs
Did You Know?

5 Amazing Facts
About Corals

Prepare to be amazed by these underwater architects.

FACT 01

Coral Reefs Are the Largest Living Structures on Earth

The Great Barrier Reef in Australia stretches over 2,300 kilometers and is so massive that it can be seen from outer space. It consists of nearly 3,000 individual reef systems and hundreds of islands — all built by tiny coral polyps no bigger than a fingernail.

FACT 02

Corals Are Animals, Not Plants or Rocks

Despite their rocky appearance, corals are living animals related to jellyfish and sea anemones. Each coral "head" is a colony of thousands of tiny polyps with tentacles that catch plankton at night.

FACT 03

They Have a Solar Power Partnership

Corals share a symbiotic relationship with zooxanthellae — microscopic algae that live inside their tissues. These algae provide up to 90% of the coral's energy through photosynthesis, which is why reefs need clear, sunlit waters to survive.

FACT 04

Corals Are Medical Goldmines

Coral reef organisms have produced compounds used to treat cancer, arthritis, Alzheimer's, and heart disease. The HIV drug AZT was inspired by compounds found in a Caribbean reef sponge. Scientists have only examined a fraction of reef species for medical potential.

FACT 05

Some Corals Can Live for Over 4,000 Years

Deep-sea black corals (Leiopathes) have been found that are over 4,000 years old — making them some of the oldest living organisms on the planet. Even shallow-water reef corals like the Porites species can live for several centuries, silently recording centuries of ocean climate data in their skeletons.

Under Threat

Why Reefs
Need Us

Rising Temperatures

Ocean warming causes coral bleaching — when corals expel their algae partners, turning white and becoming vulnerable to disease and death.

Ocean Acidification

As oceans absorb more CO₂, the water becomes more acidic, making it harder for corals to build their calcium carbonate skeletons.

Pollution & Overfishing

Plastic waste, agricultural runoff, and destructive fishing practices devastate reef health and disrupt the delicate balance of marine ecosystems.

Every Action
Makes a Wave

Reduce your carbon footprint, choose reef-safe sunscreen, support marine conservation organizations, and spread awareness. Together, we can give coral reefs a fighting chance.

Support Coral Restoration Learn More at NOAA