What Coral Reefs Are and Why They Matter
What Coral Reefs Are and Why They Matter
By Clarisa Strohmeyer | May 29, 2026 | 6 min read
Coral reefs cover less than one percent of the ocean floor. That single statistic understates everything. These ecosystems support a quarter of all known marine species, provide food and income for more than one billion people worldwide, protect coastlines from erosion and storm surge, and generate an estimated $30 billion annually in tourism, fisheries, and coastal protection services. They are not a beautiful curiosity. They are one of the most critical systems on the planet.
Coral reefs are underwater ecosystems built by tiny animals called coral polyps, which secrete calcium carbonate skeletons over thousands of years to form the complex structures we call reefs. They cover roughly 284,300 square kilometers of ocean floor, mostly in shallow tropical waters. Despite covering less than 1% of the ocean, they are home to at least 25% of all marine species and provide food, income, and coastal protection for over one billion people.
What Corals Actually Are
Most people think coral is a plant or a rock. It is neither. Coral is an animal, closely related to jellyfish and sea anemones. Each coral colony is made up of thousands of tiny individual animals called polyps, each barely a few millimeters in diameter. These polyps build hard calcium carbonate skeletons around their soft bodies, and over hundreds and thousands of years, these skeletons accumulate into the vast reef structures we can see from space.
Living inside the coral tissue are microscopic algae called zooxanthellae. These algae photosynthesize sunlight and share the resulting nutrients with their coral hosts, providing up to 90% of the coral’s energy needs. This relationship is what makes coral reefs so productive in the nutrient-poor tropical waters they occupy. It is also what makes them so vulnerable. When water temperatures rise, the coral expels its zooxanthellae in a stress response. Without the algae, the coral loses its color, turns white, and begins to starve. This is coral bleaching.
Why Coral Reefs Matter: The Full Picture
Biodiversity
The Coral Triangle, which encompasses the Philippines, Indonesia, Malaysia, Papua New Guinea, the Solomon Islands, and Timor-Leste, contains 76% of all known coral species and 37% of all reef fish species. Scientists call it the Amazon of the seas. No other marine ecosystem comes close to this level of biodiversity per unit of area.
Food Security
Reef fisheries provide the primary source of protein for millions of people across Southeast Asia, the Pacific Islands, and the Caribbean. In the Philippines alone, reef fisheries support an estimated 1.5 million fisherfolk and their families. When reefs degrade, catches decline, food security erodes, and coastal communities face rising poverty and displacement.
Coastal Protection
Healthy coral reefs act as natural breakwaters, absorbing up to 97% of incoming wave energy before it reaches the shore. They protect coastlines from erosion, reduce flooding during storms and typhoons, and prevent loss of life and property damage in communities that have no other coastal defense. The U.S. alone receives $1.8 billion annually in flood protection benefits from its coral reefs.
Medicine
Coral reef organisms are a source of some of the most promising compounds in modern medicine, including treatments for cancer, HIV, cardiovascular disease, and pain management. Many of the compounds currently being researched come from organisms that live only in reef ecosystems. If the reefs disappear, so do these potential treatments.
Coral Reefs in the Philippines
The Philippines hosts approximately 27,000 square kilometers of coral reef, making it one of the most reef-rich nations on earth. Cebu Province alone is surrounded by some of the most species-rich reef systems in the Coral Triangle. Sites like Moalboal, Malapascua, and Olango Island have been celebrated by divers and marine scientists for decades as among the most biodiverse dive destinations in the world.
Reef Without Borders begins in Cebu because this is where our founder has dived for 25 years, where our Director of Dive Operations has lived and worked his entire career, and where the need for reef restoration is urgent, documented, and actionable.
How long does it take a coral reef to form?
Large reef structures take thousands of years to form. Individual coral colonies grow between 1 and 10 centimeters per year depending on the species and water conditions. A reef that takes 10,000 years to build can be destroyed in a single bleaching event.
How deep are most coral reefs?
Most reef-building coral species thrive in shallow water between 1 and 30 meters deep, where sunlight can reach the zooxanthellae algae that live inside them. Some deep-water coral species exist at much greater depths but do not form the complex reef structures associated with tropical reefs.
Are coral reefs only found in warm water?
Most reef-building corals require water temperatures between 23 and 29 degrees Celsius. They are found primarily in a band between the tropics of Cancer and Capricorn. The Philippines, Indonesia, and Australia’s Great Barrier Reef are among the most significant reef regions on earth.
The reefs of the Philippines are not gone yet. Reef Without Borders funds and documents restoration dives in Cebu so that future generations can still find what we found when we first went underwater.
Clarisa Strohmeyer is the Founder and Executive Director of Reef Without Borders, a Houston-based nonprofit dedicated to coral reef restoration in the Philippines and across the Indo-Pacific. Learn more at reefwithoutborders.org/
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