Third-ever global mass coral bleaching event underway

By: Ashley Gustafson



Picture 1. Bleached Coral

To the majority, it comes as no surprise that the planet earth is in a pivotal state. That is, as human beings, we must either change the way we treat our planet or simply deal with the consequences of our contribution to pollution and the degradation of our planet’s once substantial ecosystems. As an active participant in modern society, you would have to be living in utter denial to not have heard of global warming and the effects it is having on the world’s oceans (which In case you missed it, that is 71% of the earth’s surface). In recent news, the National oceanic and atmospheric administration (NOAA) has released a new prediction on the fate of coral reef systems around the globe. They suspect that within the next two years that 6% of coral reefs will be destroyed due to bleaching events. While 6% may seem insignificant at first glances that could lead to more than a third of coral disappearing forever.


Figure 1. Coral Bleaching Sketch

Coral bleaching is a term used so frequently today that it is easy to read about it and not understand what is actually happening to coral reefs that suffer such a loss. Fundamentally, coral bleaching occurs when living coral becomes stressed due to changes in the water it lives. These changes most commonly include changes in temperature, light, or nutrients. When this happens, the coral is forced to reject and expel their symbiotic photosynthetic algae, zooxanthellae, which live in the coral’s tissue. Zooxanthellae and coral have a mutualistic symbiotic relationship, thus they benefit each other by a cooperative existence. Coral gives the zooxanthellae a safe environment and compounds they need for photosynthetic events while zooxanthellae produces oxygen and helps the coral remove waste. Since zooxanthellae is what gives coral their characteristic vibrant hue, when the zooxanthellae is expelled it causes the coral to become white or appear bleached. While coral bleaching brings the coral closer to mortality, it does not kill the coral instantaneously. In other words, the coral survives the bleaching events but it is like the equivalent of taking away an NFL player’s football pads and telling him to go have a great game; it leaves the coral very vulnerable and at high risk.


Coral decline due to bleaching events is a devastation we have seen in the past and will continue to see in the future. Last year, NOAA reported 12% of the world’s reefs showed symptoms of coral bleaching. That is roughly an area of 24,000 sq. km of coral and of this about 12,000 sq. km (half) may be lost permanently. In 2016, they suspect that the waters of the Caribbean will be next and combined with the previous events could lead to 15,000 sq. km or 6% of the world’s coral reefs destroyed. If NOAA is correct, and the bleaching hits the Caribbean next, that means the every tropical ocean basin on Earth will have suffered since June 2014.

Due to the nature of these events, it very difficult to predict how long they will last. While in the midst of the third largest bleaching event, Dr. Mark Eakin, coordinator of NOAA’s Coral Reef Watch programme, reflects back to the first major bleaching events in 1998, “It probably won’t be as big as 1998, so we’re probably talking hopefully no more than 10%. Even if we’re talking one to 10% of the coral reefs around the world that’s a huge amount of coral reef area.” A valid and important point to remember when looking at these events since only a mere 2% of the world’s ocean is covered with coral reefs.

The past major bleaching events occurred in 1998 and 2010 This is a frightening sequence because according to Professor Ove Hoegh-Guldberg, director of the Global Change Institute at the University of Queensland, before 1998 large bleaching events such as these only happened every “hundreds, if not thousands, of years”. The progression from the first in 1998 to the second in 2010 (12 years) has now been cut in half (just5-6 years) by this predicted third mass event. The big question is why?

I’m sure as soon as I suggested a “why” global warming popped into your head which is good. Rising ocean temperatures are the number one cause in these mass bleaching events. Not only do they cause higher temperatures but they change water composition in terms of pH and nutrient levels which the corals simply can’t cope with. While it is absolutely correct to point a figurative finger at global warming, scientists have found another trend with these massive bleaching events and that is El Niño. El Niño is a seasonal tropical storm that causes and upwelling of warm water in the Pacific Ocean. For those of you who have been paying attention, this makes perfect sense. In 1998, there was a massive El Niño that caused the beginning of warming events in oceans all over the world that destroyed up to 19% of the world’s existing coral reefs at the time. With that being said, we are currently experiencing this year’s El Niño, which is no coincidence. While there is no doubt that global warming is the mastermind behind mass coral bleaching, it is El Niño who gives the extra push to make the event even more detrimental.

Climate change has created splashes of hot water within the world’s oceans. A rather large patch referred to as “the blob” began in the reefs of the Hawaiian and Marshall Islands in the June last year and has been making its way across the northern Pacific. While they have no nicknames, other hot patches of water have made their way through the South Sea Islands in the southern Pacific as well as through reefs in the Indian Ocean. These massive changes in ocean temperatures are not good news to coral. In nature, coral are a rather specific animal that is they only can tolerate a very narrow range of conditions to survive. To illustrate this, even a 1 degree Celsius change can cause them to bleach. If the temperature change is small or temporary, the coral may be able to regain their zooxanthellae and their color. Sadly, this is often not the case with the mass increase in ocean temperatures worldwide. As we have seen, when exposed to major temperature changes over and over again corals bleach and do not recover causing them to die.

If it is even possible to mend this damage, it will take not years but decades to rebuild. By looking at the past, we can develop an expected loss for now and future bleaching events. In 1998 40% of reefs in the Seychelles were lost to bleaching and now they have been replaced by weed plants and algae. According to researchers, when this change happens it is unlikely for corals to be able to return.

While there is little we can do now to prevent current bleaching, there is some hope to help the currently stressed coral recover but it will not be easy. Global warming not only causes these mass bleaching events but it also can hinder coral recovery. Coral that go through bleaching need to be exposed to more ideal or simply less stressful conditions to recover. It is hard to say we will be able to provide that after this predicted mass bleaching event. While awareness for global warming is higher than ever, it is also true that oceans are still getting warmer. Currently, there has been 0.8 Celsius change which is mild compared to the potential 2, 3 or 4 Celsius change if nothing changes.

As worldwide coral bleaching events become closer together and more sequential, it is much more difficult for previously bleached surviving corals to rebuild. While these periods of higher water temperatures are currently temporary, the question remains how high will the ocean temperature rise? Will the once high temperatures become the new norm? Will corals be able to cope? These are all questions researchers are trying to answer by studying coral closely not only in times of great decline but in times of recovery as well. It is important to remember that your daily actions and choices make a difference for coral reefs. There is no doubt that if we do not make major changes in how we treat the planet and our beloved oceans, that as early as mid this century we will lose coral reefs and the likely the life that they support forever. We can’t continue to take our planet for granted and we must make eco-friendly choices to start healing the damage that has been done so that future generations will be able to enjoy the magical world of coral reefs.


Picture 2. Healthy, vibrant coral reef