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A diver with tropical-reef fish in Indonesia
Georgette Douwma/getty images

Anyone who has spent time snorkeling in and around healthy coral reefs — which are formed by the accumulated­ calcium carbonate skeletons of corals, which are very small marine animals — knows why they have earned the nickname “rain forests of the sea.” ­Although they make up only around one-tenth of one percent of the marine environment — in areas from Australia to Indonesia to Tanzania, wherever waters are warm, clear and relatively shallow — coral reefs are home to an amazing 25 percent of all marine species, including about 4,000 kinds of fish. This dynamic is what makes an underwater journey by divers seem so otherworldly, like a visit to an impossibly well-stocked aquarium.

But visual attractiveness for visitors to tropical waters is perhaps one of the less-remarkable benefits that coral reefs offer to people and the natural world alike. Compounds created by reef-dwelling creatures have proven to be important building blocks for the development of drugs to fight diseases like HIV and malaria. Some researchers have already used a compound found in Caribbean sea squirts to develop a treatment for ovarian and other cancers.

In a more immediate sense, coral reefs also protect human health by providing a line of defense for coastal communities against the damage of powerful storms. In more than 100 countries and territories around the globe, the physical structure of reefs provides protection to communities along 94,000 miles of coastline by tamping down the energy of incoming waves during storms that might otherwise be destructive. On a day-to-day basis, reefs also protect buildings and roads along the shoreline by reducing erosion.

In many ways, the most important benefit reefs provide to people can actually be measured in dollars and cents. According to the “Reefs at Risk Revisited” report, the annual net benefits from reef-related goods and services total $11.5 billion from tourism, $6.8 billion from fishing and another $10.7 billion as a result of shoreline protection.