Why Coral Reefs Matter: Rainforests of the Sea Explained
Coral reefs cover less than 1% of the ocean floor yet support a quarter of marine species. How reefs work, why they are dying, and why their loss affects everyone.
Global Animal Guide · June 23, 2026
Quick answer
Coral reefs are underwater ecosystems built by tiny animals called coral polyps that secrete limestone skeletons. Though they cover less than 1% of the seafloor, reefs shelter roughly 25% of known marine species, protect coastlines from storms, and support fisheries and tourism worth billions. They are threatened mainly by warming seas (coral bleaching), pollution, overfishing, and acidification.
What is a coral reef?
A coral reef is a living structure built over centuries by billions of tiny coral polyps — soft-bodied animals related to sea anemones. Each polyp sits in a cup of calcium carbonate (limestone) it secretes. Over generations, these skeletons fuse into massive formations: fringing reefs, barrier reefs, and atolls ringing sunken volcanoes.
Inside many reef-building corals live zooxanthellae — microscopic algae that photosynthesise and share sugars with the coral. This partnership is why clear, sunlit tropical waters suit reefs best.
Why reefs are ecologically vital
Reefs punch far above their weight:
Biodiversity hotspots — An estimated quarter of all marine species depend on reefs at some life stage, from parrotfish and clownfish to sharks, sea turtles, and countless invertebrates.
Nurseries for fisheries — Many commercially caught fish spawn or grow up around reef structure.
Coastal protection — Reef crests absorb wave energy, reducing erosion and storm damage for hundreds of millions of people living near coasts.
Medicine and science — Reef organisms produce compounds studied for pain relief, antivirals, and cancer treatments.
Threats reefs face today
Ocean warming — Even 1–2°C above normal can trigger mass bleaching. Without their algae, corals starve. The 2016 and 2017 global bleaching events damaged large sections of Australia’s Great Barrier Reef and reefs worldwide.
Ocean acidification — Absorbed CO₂ lowers pH, making it harder for corals and shellfish to build skeletons.
Pollution and runoff — Sediment, fertiliser, and sewage cloud water and fuel algal blooms that smother corals.
Overfishing and destructive practices — Removing herbivorous fish lets algae overrun corals; blast fishing and anchor damage destroy structure instantly.
Disease — Stony coral tissue loss disease and others spread faster in stressed systems.
Why reef loss matters on land
When reefs decline, coastal communities lose fish protein, tourism income, and natural storm buffers. Global fisheries and carbon cycles feel ripple effects. Reef collapse is not a distant ocean problem — it reaches economies and food security far inland.
Hope and action
Marine protected areas, sustainable fishing, wastewater treatment, and reducing carbon emissions all help. Scientists cultivate coral fragments in nurseries and replant them on damaged reefs. Local restoration works best when combined with cutting the root causes — especially greenhouse gas emissions.
Related reading: What makes an animal endangered? · Why habitats disappear · Sea turtle guide
Frequently asked questions
Are corals plants or animals?
Corals are animals — colonial cnidarians related to jellyfish. Many reef-building corals also host algae that photosynthesise and feed the colony.
What is coral bleaching?
When water gets too warm, corals expel their symbiotic algae and turn white. Prolonged bleaching kills the coral.
How fast do coral reefs grow?
Most reef frameworks grow a few millimetres to centimetres per year — recovery after damage can take decades.
Can coral reefs recover?
Some reefs recover if stress eases quickly and fish populations remain healthy, but repeated bleaching events outpace natural repair.