Coral Reefs: The Rainforests of the Ocean

Coral reefs are the most biodiverse ecosystems in the ocean — and one of the most threatened on Earth. Covering less than 1% of the ocean floor, they support an estimated 25% of all marine species. Losing coral reefs wouldn't just be an environmental tragedy — it would be a catastrophe for the entire ocean food web.

What Is Coral?

Coral reefs are built by coral polyps — tiny, soft-bodied animals related to jellyfish. Each polyp secretes a hard calcium carbonate skeleton and lives in a colony with millions of others. Most coral gets its color and nutrition from zooxanthellae — tiny algae that live symbiotically inside coral tissue and provide up to 90% of the coral's energy through photosynthesis.

Why Are Coral Reefs Called the Rainforests of the Ocean?

Like tropical rainforests, coral reefs pack an extraordinary amount of biodiversity into a small area. The Great Barrier Reef alone contains 1,500 fish species, 4,000 mollusk species, 240 bird species, 30 whale and dolphin species, and 6 sea turtle species. This density of life rivals any ecosystem on the planet.

Why Are Coral Reefs Dying?

The main threat is coral bleaching — caused by rising ocean temperatures. When water is too warm, corals expel their zooxanthellae, turning white and starving. Without the algae, coral dies. The Great Barrier Reef has experienced 5 mass bleaching events since 1998. Pollution, runoff, ocean acidification, and destructive fishing also kill reefs.

How Fast Are Reefs Disappearing?

Scientists estimate that 50% of the world's coral reefs have been lost since the 1950s. If current trends continue, virtually all reefs could be severely damaged by 2050. Protecting reefs is one of the most urgent conservation challenges on Earth.

Amazing Coral Reef Facts

• The Great Barrier Reef is the world's largest living structure — visible from space.
• Coral reefs protect 500 million people from storm damage by buffering coastlines.
• Coral grows incredibly slowly — about 1 inch per year for massive coral.
• Many coral species spawn simultaneously once a year in a spectacular mass event called the "coral spawning."
• Some reef fish are cleaner fish that set up "cleaning stations" where larger fish line up to have parasites removed.