Feb 16, 2023 by John Lockton
Coral Reef Bleeching

Healthy coral reefs are the most spectacular, diverse, and economically valuable marine ecosystem on the planet. Complex and productive, coral reefs are central to biodiversity in the oceans, providing a home to 30,000 to 60,000 species of plants and animals, a nursery for many commercially important fish, and a protective coastal barrier against storm waves. Hundreds of billions of dollars in food, jobs, and tourist spending depend upon the continued existence of healthy coral reefs.

You may have heard that coral reefs are on an extinction path, the result of global warming around the world. It doesn't take much looking to find an article saying all coral reefs will be dead in twenty, or at least fifty years. Your own experience can confirm this devastation. On a dive or snorkeling adventure a few years ago in the Caribbean, Hawaii, or Mexico you came out of the water almost in tears. Your beloved brightly colored coral was bleached white in large areas. Is what you saw the precursor to the end? Are your diving and snorkeling days over because ten or twenty years from now all you’ll see is bleached rock, a tragedy so great you won’t even want to get in the water? As with many issues involving global warming it's a very complex story.


Coral is an animal. ”A coral” is made up of thousands of tiny animals called polyps, "a coral” being tens of thousands of polyps living side by side. Different corals create different coral shapes as a result of the varying patterns in which they extrude the calcium carbonate (i.e. limestone) that builds the reefs. There are thousands of shapes as there are over two thousand species of cora—brain coral, stag horn coral, finger coral, mushroom coral, table coral, and so on. 

The polyps don’t eat in the normal sense. Instead they depend for food on a symbiotic relationship with a minuscule plant, zooxanthellae. (I will call them “Zs”.) Zs live within the tissue of the polyps in mutual dependency. The photosynthesis of the Zs provides the polyps with glucose, glycerol, and animo acids that the polyps use to make proteins, fats, and carbohydrates, and also provide the material to recycle to make calcium carbonate, the stone of the reef. Polyps in turn provide the Zs with a protected environment and compounds they need for photosynthesis. The symbiotic, food producing and food sharing relationship between Zs and polys is what allows the polyps to live in clear, tropical waters virtually devoid of nutrients.

Z’S AND BLEACHING--- So why talk about Zs? It’s because they that have the color that you see in coral. The polyps are colorless without their Z inhabitants. Bleaching is the result of the polyps stressing and expelling the Zs. This can occur because of heat (global warming), pollution, pesticide and other contaminants discharged from land, and changes in acidity of the water. Once expelled by a polyp, if the Zs don't come back to the polyp, the polyp will eventually die, starved to death.

In 1998, 2002, and 2016 there were mass bleaching events across the globe. 2016 was the hottest year on record. Since then global warming has stabilized and even declined slightly, a gift that will assuredly be taken back. The good news is that after each mass bleaching event, the coral color has returned. If you visit the sites at which you saw bleached coral a few years ago, you’ll see new color with the exception of sites where man’s pollution and other intrusion was the cause of bleaching. One marvelous example of the reversal of bleaching is the Great Barrier Reef where there was major bleaching in the 2016 mass bleaching event and colors are starting to come back.


Palmyra Atoll, a remote island in the Pacific, is a principal site for the study of coral. The island is uninhabited and its waters pristine. Long term research on Palmyra reefs show corals can renew themselves after a bleaching event. Some kinds of Z seem to be more resistant to heat and these repopulate the coral. The stressed coral expels its Z and eventually the stronger type of Z, or perhaps a Z mutation, replaces the expelled Zs. Viola. Color. This does not mean we won’t have bleaching in the future. Other mass bleaching events like those in 1998, 2002, 2916 will undoubtedly occur. However, nature loves its coral as we do. We now know life strives to bring Zs back to bleached coral.


Man is also taking a hand in the renewal of bleached reefs. I belong to a club in Antiqua, British West Indies, that is working to renew its reefs by growing finger coral in a controlled environment. When grown, the coral is attached to damaged reefs. Larger projects include the Plant a Million Corals Foundation in Summerland, Key, Florida. They are employing a technique involving slicing polyp tissue into small fragments and depositing the fragments on dead coral. Growth rate is twenty times higher than for naturally growing coral. The most massive effort is on the Great Barrier Reef in Australia. $4.4 Billion has been allocated for a many-phased project that involves enhancing water quality, protecting reefs from human intrusion, elimination of crown-of-thorns starfish (which eat polys), and many other things, with the most interesting being polyp hatcheries. Polyps spawn once a year. Researchers are gathering millions of eggs from the Great Barrier Reef, growing them in a protected environment, and then reintroducing them to the reef. The project started in 2016 and already some of the coral is dinner plate size.


Coral reef death is not all about bleaching and loss of Zs. In coastal waters, and sometimes offshore, there can be nutrients/farmland discharge that causes a blossoming of Zs and other algae. This can suffocate the reef. The nature provided remedy is the parrot fish. It feasts on the algae and keeps the reef clean and healthy. Unfortunately in many parts of the world the parrot fish are being fished out to virtual non-existence. And in some places cyanide poison is being used to kill and harvest fish on the reef. Worse is using dynamite to stun the reef fish and then pick them up with scoop nets. Dynamite fishing is now prohibited in about every part of the world. However, when you see a recently lost finger on the hand of a fisherman on an outlying Philippine island you know it continues.

There is reason for hope as gradually fishermen are being persuaded that they can do better financially from the tourist dollars of those snorkeling and diving a local reef than they can from fishing the reef. An example is Cabo Pulmo, Mexico, an area in the Gulf of California near La Paz. By the 1990s the Cabo Pulmo reef, sixty two miles long, one of the largest in Mexico, had been fished out by local fishermen. The government stepped in and persuaded the fishing villages that they would earn far more in tourist dollars from preserved reefs than they could ever earn from reef fishing. A marine reserve area was instituted in 1995. The experiment worked. Biodiversity on the reef increased five hundred percent in ten years with the reef achieving one the highest fish populations per square mile in all of Mexico. And tourist money has flowed into local villages.

To complete the story of bleaching there is one other contribution by man, the spread of coral diseases. Discharges from ocean vessels are spreading coral diseases around the globe, and a severe infestation can cause bleaching. As I write this the U.S. Environmental Protection Agency is being sued for not instituting regulation on ship discharges in a timely fashion.


Of course there are many coral rescue organizations to which one can contribute. Think of it as animal rescue/shelter support for a very small animal. Also, the way you dive or snorkel can help greatly. Despite repeated admonitions “not to touch,” the public often ignores this mandate. How many times have I seen snorkelers adjusting their masks while stepping on the reef? How many times have I seen a diver making a sharp turn between coral heads and a flipper striking some coral? Coral is so fragile and slow growing it will take ten years for the polyps to grow back. You have killed a host of small animals and that should haunt you just as if you killed some small, defenseless, land based animals.

So in summary all is not lost. Nature has its way of bringing back coral after a bleaching event. But repeated bleaching events weaken the coral and make it more susceptible to human pollution, over use, and other human interference with the course of nature. We may try and blame all coral death on global warming, as we blame many things. Ultimately, though, it comes down to the action of humans.

ODYSSEY’S CHILD--- My new book, "Odyssey’s Child", explores the coral reefs of the Caribbean, brings readers into the way of life on the reef surrounded Caribbean islands islands, introduces you to remarkable people, surrounds you with terrors on sea and land as in the original “Odyssey," and ultimately uplifts you through the survival of a boy in a great sea adventure reminiscent to "Life of Pi.” "Odyssey’s Child" is available on Amazon and more of my blogs are to be found here on my website,