When the coral reefs turn white

"El Niño" has now become a household word. It is associated with a dry, hot climate. Farmers fear it because it means drought and disaster for water-demanding crops such as rice. Even housewives know the El Niño. They blame it for water shortages and power interruptions. (Paradoxically, even while this is happening to our country, some other parts of the world, like the United States, may be experiencing unusual torrential rains!) The El Niño is a climatic, nearly global phenomenon that occurs regularly. Unfortunately for us, its frequency of occurrence has been increasing (why and how should be the subject of an article on climate change).

What very few people in this country know is that the effects of El Niño can also be profound and dramatic in the ocean, that is, beneath the surface of the water where we do not see them. I am one of a team of professors who teach an undergraduate course at UP Diliman called "Introduction to the Marine Sciences." What really astounded me is the fact that not a single one of my students had heard of the catastrophic El Niño of 1998, when many coral reefs in all oceans of the world bleached, meaning, they turned white. But then again, why would I expect them to have heard of it? I try hard to recall the media coverage of the event at that time. Now that I think hard about it, there seemed to be almost none at all. On the other hand, we marine scientists were running around frantically, sending teams out to the field, and communicating with our colleagues abroad because of the sheer magnitude and seriousness of the event. After all, the Philippines has very extensive and rich coral reefs (this, at least, should be public knowledge by now). Coral reefs are extremely important natural resources in the country, generating much of the fish we eat. In 1998, they were under severe threat. Perhaps it is partly our fault that we failed to properly inform the public about this through the media, maybe because the alarm bells were ringing so loudly in our ears that we could not think of anything else but the scientific tasks immediately on hand. But we were on top of the event, if you could call it that. Our oceanographers were continuously monitoring a mass of heated water that was slowly moving southward from the northwestern part of the Philippines, in the South China Sea. This was made possible because of close collaboration with scientists abroad who had real-time access to satellite images of the ocean. As the hot water mass progressed southward, the reefs along the way were bleaching almost in a systematic fashion.

But let me move back in time a bit, to the beginnings of the 1998 El Niño episode. Since the El Niño, as already mentioned, is a global climatic event, it takes time to evolve and develop. With present day knowledge and technology, it is now possible for scientists to predict, with accuracy, whether an El Niño will occur the following year. This exercise is usually a form of cooperation between scientists studying the atmosphere and those involved with the ocean. A year before an El Niño event occurs, the central part of the Pacific Ocean starts warming up. This process is accompanied by unusually large swings in atmospheric pressure over parts of the central and southern Pacific Ocean. (This is why the more complete and correct term is "El Niño-Southern Oscillation" or ENSO). These features are the readily detectable and measurable ones, but are directly related to more distant phenomena such as the strength of the trade winds.

In the autumn of 1997, climate and ocean scientists noticed that the central Pacific was getting really warm. In other words, not only was there a coming El Niño, but this one was going to be a whopper. Much later, after the event had passed, scientists reported that the positive temperature anomaly (to use scientific jargon) was an incredible five degrees Centigrade. For the surface of the ocean, in this case, the vast Pacific, to warm up that much must really take a huge, huge amount of heat. It is for this reason that the 1998 El Niño is known to be the biggest ever in living human memory and documented history.

It so happened that in December of 1997, I took my parents for a visit to the Bolinao Marine Laboratory, our field station. One of the highlights of that trip was an excursion to the ocean nursery of the giant clam project run by Professor Ed Gomez. My parents remarked how big and beautiful the clams were, so clearly visible in the shallow water. But more importantly, they said, how peaceful their world was. For my part, on the other hand, my thoughts started racing: clear water, shallow… my God, if and when the El Niño does strike, these poor creatures would suffer incredibly.

Why? After a roundabout route, I come to the heart of the bleaching story. Giant clams, like the hard corals that build our reefs, have a special relationship with tiny plant-like creatures called dinoflagellates (this is what we refer to, in technical terms, as a symbiosis). Hard corals, like the clams, are animals, even if some of them look like they harbor flowers, forming fantastic, colorful gardens underwater. The dinoflagellates, which are one-celled algae, live inside the cells of clams and corals. They contribute to the vivid colors that many coral and clam species are known for. More importantly, they are an in-house source of food for the host animals. Through a process known as photosynthesis, they are able to convert raw materials such as water and carbon dioxide, with the help of energy from the sun, into simple sugars, fats and proteins.

When conditions in the surrounding environment, particularly levels of temperature and light, rise above normal, the animals become stressed, and tend to expel their resident, symbiotic algae into the surrounding water! The obvious results are: the animals (the corals and clams) lose their color and become white, and they proceed to starve because they lose an important food source.

The first real alarm that sounded the fact that the El Niño had finally arrived in the Philippines was a report by a graduate student that dead coral reef fish were seen floating on the surface of waters of a reef a few kilometers from the marine station. This was around June of 1998. Measurements were immediately taken of the temperature of the water in the area, along with the dissolved oxygen (DO) content of the water. Sure enough, temperature was higher than normal, and DO was low to actually be stressful for animals that need to breathe oxygen. In the following days, more and more dead fish started to float up to the surface, even the ones that normally would be hiding among the rocks and crevices of coral reefs. They had died from either heat stress, or suffocation, or both.

But the most dramatic scenes were yet to come. With warning of a coming El Niño, station staff had started an evacuation effort for the giant clams, to relocate as many of these wonderful creatures as possible to deeper waters. But each mature clam can weigh more than a hundred kilos! Hence, the process was slow. I swam out with a team once during this rescue effort, and beheld a sight I had never seen before. The remaining clams in shallow water had turned a stark WHITE. A visiting scientist from the US called them "boiled clams," but they were still alive.

During that summer I snorkeled and dived around the familiar coral reef flats and slopes in a daze of disbelief. Whole colonies, entire expanses of reef, had turned white. Corals on the reef flat measuring a meter or more in diameter looked like white-washed tombs, so that the whole area appeared like a cemetery. The deeper slopes covered with bleached coral resembled white, snow covered Alpine slopes.

After a terrific environmental stress like that, marine creatures are hardly expected to recover. Sure enough, a lot of the clams and corals died afterwards. After a year, the sublime underwater landscapes that used to be sculptured by coral were covered by an amorphous mass of algae. The algae had used the dead coral as substrate on which to gain a foothold and grow. The colorful fish that used to shelter and feed around the coral were replaced by those that eat algae, the herbivores. This scene was repeated in many parts of the world, in the Pacific, Indian and Atlantic oceans. Many years later, the recovery of affected reefs by means of recruitment of new coral is patchy.

One of the questions a layman would surely pose is: As a scientist, if you know that an El Niño is coming, what should you do? What a difficult question! How does one prepare for a natural event, the effects of which cover an entire country (and many parts of the world)? How does one minimize the negative impacts? These considerations are now part of ongoing research programs undertaken by the international scientific community. But one lesson is clear: reefs that are already abused because of other reasons, such as pollution or overfishing, are more vulnerable to an additional stress such as warming, than are healthy reefs.

Perhaps the best form of action the scientists, hand in hand with the public, can undertake is to protect our remaining reefs from environmental abuse, and keep them as healthy as possible. This should be the subject of another article.

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Helen T. Yap obtained her Doctor rerum naturalium from the University of Rostock, Germany. She is a professor at the UP Marine Science Institute, Diliman, Quezon City. Her research interests include benthic ecology and coral reefs as complex systems. She can be reached at [email protected].