Why Coral Reefs Are Essential to Ocean Life
They cover a tiny fraction of the seafloor, shelter a huge share of marine species and protect coastlines from waves.
By Biosphere Editorial Team · 2026-09-15
Coral reefs are built by tiny animals. Each coral polyp lays down a skeleton of calcium carbonate, and over centuries colonies of polyps build structures large enough to be seen from space.
A partnership that powers the reef
Most reef-building corals host microscopic algae, called zooxanthellae, inside their tissues. The algae photosynthesize and share sugars with the coral; the coral gives them shelter and nutrients. The algae also give corals much of their colour.
What bleaching means
When water stays too warm for too long, corals expel their algae and turn white — this is bleaching. Bleached corals are not dead yet, but if the heat stress lasts they can starve. In 2024 NOAA confirmed the fourth global coral bleaching event on record.
Reefs protect people too
Reefs act as natural breakwaters. A global review published in 2014 found that coral reefs reduce wave energy reaching the shore by an average of 97%.
Reef residents range from the clownfish, which lives among the stinging tentacles of sea anemones, to the green sea turtle, which grazes the seagrass beds that often surround reefs.
What helps reefs
- Reducing greenhouse gas emissions, the main driver of marine heatwaves
- Improving water quality near coasts
- Well-managed marine protected areas
- Coral restoration, as a complement to the above rather than a replacement