Coral Bleaching in the Philippines in 2024

Coral reefs are among the natural wonders that rightfully inspire pride in Filipinos and draw thousands of visitors to the island nation every year. There are indeed fantastic coral reefs to be seen in the archipelago.

Small coral gobies living on a healthy staghorn coral. The small fishes absolutely rely on the protection by the hard corals

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But this year, marine experts have noticed that the corals in an increasing number of areas in the country have started to bleach. Reefs which at health showed a mix of brownish, red, blue and orange colors turned, at least partially, eerily white. This is not a fashion statement by the corals, but a sign that they are in serious trouble.

What is coral bleaching?

Coral bleaching is a failure of the coral-algae collaboration, caused by rising ocean temperatures.

The pink color of this coral is an early sign of bleaching

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To understand the nature of this trouble, we have to understand that a coral isn’t just an animal, but an “animal-plus.” The corals themselves are invertebrate animals (not possessing a spinal cord like humans, dogs, fishes, lizards and birds) related to sea anemones. But what makes corals special is that they play hosts to countless single-celled algae. The algae find protection in the hard skeletons of the corals, and in turn supply the corals with nutrients. This mutually beneficial relationship is called a symbiosis. Corals are animals plus algae in their bodies: A powerful combination which has allowed them to flourish in the tropical oceans of the world.

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The hard corals, or the ones which build the impressive coral reefs of the Philippines, heavily rely on this symbiosis with the algae. When the algae turn sunlight into biological energy (or what is known as photosynthesis), they produce oxygen as a by-product. This is a good thing, in principle, since all animal life on Planet Earth depends on oxygen. But too much of a good thing can be very harmful; in the case of the algae embedded in the corals: excessive oxygen destroys the tissues of the corals.

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The same species of small coral goby, but this time in a completely bleached coral. As long as the structure of the corals is intact, even the bleached corals provide cover for the small, vulnerable fishes. But sadly the bleached coral will soon die and disintegrate, and provide no more protection for the gobies

PHOTO: Klaus Stiefel

Such excessive oxygen production can happen when the temperature of the ocean rises too high. Only a few degrees above the typical ocean summer temperatures are necessary to create this unpleasant situation. Then, the coral, in a “panic reaction” expels the algae to prevent more damage to its tissues by the excessive oxygen. The colorful algae drift off into the ocean, and the corals turn bleached white.

Algae often overgrow corals after they bleach and die

This is a dramatic situation which the corals can only survive for a few weeks. It’s akin to a person who is malnourished and lacking vitamins; such a state doesn’t lead to immediate death, but will eventually kill a human. Similarly, bleached corals can eventually take up a new set of algae which feed them. Alternatively, if the water temperature remains too high for too long, they will die. The bleached corals then turn drab brown when filamentous algae (very different from the algae which live within the corals) grow on them. Eventually, the skeletons of the dead corals fall apart.

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The blue color of this coral is due to the strain of symbiotic algae resident in its tissues

This year in the Philippines, bleaching was observed in places such as Punta Baja, Palawan, Zambales, and Negros Occidental. Fortunately, other places were spared, such as the area around Dumaguete and Dauin in Negros Oriental. Likely, colder currents coming from the east have spared the corals in this location from too much heat stress. Local factors can make a big difference when it comes to coral bleaching.

What can be done to stop coral bleaching? And what can the average citizen do?

How you can help with the coral bleaching issue in the Philippines

The main push will have to be to wean the world economy off fossil fuels. This is, of course, a massive challenge, both politically as well as technologically. But only if this succeeds will the atmosphere cease to warm much further, and only then can coral bleaching be stopped from becoming globally catastrophic.

Corals in Apo Island, Negros Oriental province, with a healthy, non-bleached color

PHOTO: Klaus Stiefel

It’s also important to work on keeping one’s coral reefs healthy on a local level. Reefs which are kept intact in marine protected areas are protected from overfishing by reasonable local fishing policies, and are safe from run-off and ill-advised land reclamation projects. These reefs will also be able to cope with coral bleaching much better. These measures all don’t directly affect coral bleaching, but they will allow healthy coral reefs to thrive, which will make it more capable of returning back to health. Healthy reefs recover faster, just as a well-rested human who drinks a lot of calamansi juice will bounce back faster from a cold. Supporting local conservation measures which keep the marine environment in overall good shape is probably the best contribution a citizen can make to not exactly prevent, but somewhat buffer the detrimental effects of coral bleaching.

The start of coral bleaching

There are also efforts to “garden” corals, where scattered, broken-off pieces of coral are affixed to grids or nets, and grow to a size where they then can be re-planted into damaged reefs, hence regenerating a reef devastated by bleaching. This can, in principle work, but it requires expertise and a very thorough assessment of the situation. In no case will it significantly dent the problem of coral reef decay as a whole.

The Philippines possess about 27,000 square kilometers of coral reefs, and even the most successful coral gardening project will only regenerate a small fraction of a square kilometer. It’s also worth noting that a permit by the Bureau of Fisheries and Aquatic resources is necessary in the Philippines before attempting coral gardening.

The newly grown tip of a staghorn coral. This is not necessarily a sign of bleaching; The symbiotic algae might not have completely colonized the coral

Equally, the breeding of heat-resistant “super corals,” while scientifically very interesting, is still in its infancy and will most likely not solve this global environmental problem.

What is important is to understand the problem of coral bleaching as well as possible. Even with very ambitious efforts, the nation’s marine scientists will only be able to monitor a small fraction of the Philippines’ coral reefs. This is where citizen scientists can come in—educated amateurs who share their observations with professional scholars. Such a citizen science report, supplemented by a few underwater photographs, can give scientists an idea how the coral reefs in a region are responding to elevated ocean temperatures.

This table coral shows a healthy part, a bleached part, and a part which has already died and is overgrown by algae and tunicates, in the front

A worthwhile effort in this direction is Philippine coral bleaching watch, you can see their summaries of the problem in the archipelago here, submit your own report here, and find them on Facebook here. Please contribute your observations if you can!

More Areas in the Philippines are Starting to Experience Coral Bleaching

What is coral bleaching?

How you can help with the coral bleaching issue in the Philippines