What happens when you ask two ocean enthusiasts to share their thoughts and images about coral reefs? One of our Pacific Specialists, along with a seven-time WT adventurer, combine their gifts to lend insight into the wonderful underwater world.

Coral, which is often mistaken for a rock or a plant, is actually an animal, or more precisely, hundreds to thousands of individual polyps. These tiny animals are related to jellyfish and sea anemones, and apart from a short stage where they are free-swimming creatures, they live their entire lives sheltered in one place. Every thriving reef needs one thing—healthy coral. Not only does coral provide food to support a diverse array of species, but it also offers protection and other tools for the ocean’s ecosystems. Here are the main things you should know about coral.

This photo of Komodo’s reef exemplifies the range of species that a thriving coral reef supports, from sponges to fish to crustose coralline algae.

How Does Coral Survive and Thrive?

Coral lives in symbiosis with zooxanthellae, the photosynthetic marine algae that live within the tissues of coral polyps. The coral animals can “hunt” by extending tentacles into the water to feed on tiny animals like zooplankton, but they cannot survive on this alone. They need the zooxanthellae to provide what can be thought of as the corals’ veggies. Because the zooxanthellae must photosynthesize to make food, they need to live in environments with a lot of light.

How Many Types of Coral Exist?

There are two main types of coral: hard coral and soft coral. Hard coral polyps secrete calcium carbonate, or aragonite, which has a similar chemical structure to limestone. This chalky material is what makes a reef a reef, as it is continually built up over time. The large structure created by corals is not only a beautiful place to snorkel or dive, but it also provides protection to coastlines during storms.

Hard corals exhibit various growth forms, from the fast-growing branching blue-tipped Acropora…

…to the massive, slow-growing Porites that resemble boulders.

These photos of hard coral below were taken in Solomon Islands.

Soft corals, on the other hand, do not secrete calcium carbonate so they have a less rigid structure than hard corals. They are still sessile, meaning that they can’t “swim,” but they can drift back and forth through the water with the currents and tides. This allows them to obtain more of their food from organisms in the water. Since they don’t rely on the zooxanthellae as much, they can live in shadier and darker environments. 

The vibrant pink organism in the photo below is a soft coral (Dendronephthya sp.), photographed in Raja Ampat. The orange coral is also a species of Dendronephytha, photographed in the Solomon Islands.

Best places to see healthy coral reefs

The region known as the Coral Triangle encompasses parts of Indonesia, the Philippines, Malaysia, the Solomon Islands, and various other Pacific islands. It is known to have the highest coral diversity in the world. Unfortunately, there are many perils affecting coral reefs, including bleaching (where heat stress causes the coral to expel their zooxanthellae, and thus die), ocean acidification (where increased CO2 in the atmosphere enters the oceans and increases the pH, and thus corals cannot secrete their calcium carbonate), direct damage from things such as ship anchors and people kicking coral with their fins, and various other stressors.

While many of the world’s coral reefs are in critical condition, it is still possible to see healthy reefs, particularly in areas where direct human impact is not a factor. Our Snorkeling Raja Ampat, Snorkeling Expedition to Cenderawasih Bay, Komodo Dragons and Coral Reefs of the Alor Archipelago, and Palau Snorkeling and Sea Kayaking trips all take place in areas of the world with little to no coral bleaching, and you will have ample opportunities to observe both hard and soft coral in thriving conditions!

—Text by WT staff Sydney Dillon, photos by 7-time WT adventurer Norm Vexler.

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