Coral reefs are small on a world map, but they matter on a global scale. They hold a remarkable share of the ocean’s biodiversity, they underpin the food supply and economies of many tropical nations, and they physically protect coastlines that hundreds of millions of people live on. Understanding why reefs are important is also the key to understanding why their decline is such a concern. Below are the main reasons, from the ecological to the economic and cultural.

Biodiversity: the rainforests of the sea

Reefs are among the most biologically diverse ecosystems on Earth. For their size, they support more species than almost any other habitat in the ocean.

The intricate structure built by corals provides homes, hiding places, hunting grounds and nurseries for thousands of fish species and a far larger number of invertebrates — molluscs, crustaceans, echinoderms, sponges, worms and many more. Roughly a quarter of known marine species are thought to use reefs at some stage of their lives, and scientists continue to discover new reef species every year. That diversity is valuable in itself, and it also makes the ecosystem more resilient, with many species sharing important jobs such as grazing algae and recycling nutrients.

The ecological importance of reefs extends beyond their own borders: they act as nurseries for fish that later move to other habitats, they are linked to seagrass beds and mangroves, and they export food and larvae to the open sea. That side of the story is covered in why coral reefs are important in a marine ecosystem.

Coastal protection

Coral reefs are natural breakwaters. By forcing waves to break offshore, they protect beaches, homes and infrastructure from erosion, flooding and storm damage.

A healthy reef crest can dissipate most of the energy of incoming waves — estimates of up to about 97% are widely cited. That protection is especially important for low-lying islands and atolls, where the reef may be the only barrier between the ocean and the land, and for coastal cities and towns in storm-prone regions. Reefs also shelter the calm lagoons where seagrass and mangroves grow, which in turn stabilise the shore.

Studies that compare the cost of artificial sea walls with the protection reefs provide for free consistently find that reefs are extremely valuable infrastructure. When reefs degrade and flatten, more wave energy reaches the coast, increasing erosion and flood risk at precisely the time sea levels are rising.

Food and livelihoods

For many coastal and island communities in the tropics, reefs are the main source of protein and a major source of income.

Reef fisheries supply fish, octopus, lobster, crab, conch, clams and sea cucumbers. Much of this catch comes from small-scale fishers who feed their families and sell to local markets. In many small island nations, there is little room for farming, so reef seafood is central to diets and food security. Reefs also support commercial fisheries indirectly by acting as nurseries for species caught elsewhere.

Altogether, hundreds of millions of people are estimated to depend on reefs for food, income or coastal protection, many of them in developing countries where alternatives are limited. That is why reef decline is not only an environmental issue but also a question of food security and poverty. Well-managed reefs can provide food indefinitely; overfished or degraded reefs cannot. See why coral reefs are overexploited.

Tourism and recreation

Reefs are one of the world’s great natural attractions. Diving, snorkelling and beach tourism bring income and jobs to reef nations.

Millions of people travel each year to see reefs in places such as the Caribbean, the Red Sea, Southeast Asia, the Maldives and Australia’s Great Barrier Reef. That tourism supports hotels, dive operators, boat crews, restaurants, guides and many other businesses. In some island economies, reef-related tourism is among the largest sources of foreign income. Crucially, much of this value depends on reef health: visitors come for colourful corals and abundant fish, so a degraded reef is worth far less to the tourism economy than a thriving one.

Medicine and science

Reef organisms produce a remarkable variety of chemicals, and some of them have become the basis for medicines.

Living in a crowded environment where they cannot run from predators or competitors, many reef animals — sponges, soft corals, sea squirts, cone snails — defend themselves chemically. Researchers have screened thousands of these compounds for activity against pain, cancer, infections and inflammation. A painkiller derived from cone snail venom has been approved for treating severe chronic pain, and several compounds originally discovered in marine organisms have been developed into cancer treatments. Coral skeletons have even been used as bone-graft material because of their porous structure.

Reefs are also natural archives. Long-lived corals lay down annual growth bands, and their chemistry records past sea temperatures and ocean conditions, helping scientists reconstruct climate history.

Sand, islands and cultural heritage

Reefs build land as well as living space. Many tropical beaches and islands are made from reef material.

As corals, calcareous algae and shells break down — helped by parrotfish that grind coral into fine sand — reefs produce the carbonate sand that forms white tropical beaches. Over long periods, sand and rubble pile up into reef islands and cays, and several nations, including the Maldives, Kiribati, Tuvalu and the Marshall Islands, are built largely on atolls. For these countries, the health of the reef is a matter of national survival.

Reefs also have deep cultural importance. Many Indigenous and coastal communities have fished and navigated reefs for countless generations, and reefs feature in traditional knowledge, stories, customary management systems and spiritual life. See what coral reefs do for more on these roles.

Putting a value on coral reefs

Economists have tried to estimate what reefs are worth. The figures vary widely, but they all point to the same conclusion: reefs are far more valuable alive than degraded.

Valuation studies add up the money reefs generate through fisheries and tourism and the costs they avoid by protecting coasts from storm damage. Global estimates run into very large sums each year, and individual reefs near popular tourist areas or vulnerable coastlines can be worth a great deal per hectare. These numbers are imperfect — it is hard to price biodiversity, cultural value or future medical discoveries — but they have helped governments and insurers recognise reefs as natural infrastructure worth investing in. In a few places, reefs have even been insured, with payouts used to repair them after hurricanes.

Everyone can help protect that value. Cutting carbon emissions addresses the biggest threat; supporting marine protected areas and sustainable fisheries tackles local ones. When visiting reefs, choose operators that use mooring buoys, never touch or stand on corals, avoid buying coral or shell souvenirs and keep plastic out of the sea.

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• What Are Coral Reefs Made Of?
• Why Are Coral Reefs In Tropical Waters?
• What Do Coral Reefs Eat?
• How Have Coral Reefs Changed Over Time?
• In What Environment Do Coral Reefs Form?
• What Happens When Coral Reefs Die?
• What Animals And Plants Live In Coral Reefs?
• A Coral Reef Is a Community
• Why Are Coral Reefs Dying Off?
• Coral Reef Reproduction
• How Much Of The Ocean Is A Coral Reef?