Coral Coral and Coral

So I turned in my paper on coral. I wrote it to be a simple intro to what coral is, what coral bleaching is, the causes, and the fixes. So here it is! (I posted other stuff but wordpress apparently deleted them or never uploaded them…)

Life without Coral

When coral reef comes to mind many people think of the Great Barrier Reef, a beautiful tourist location and the largest reef in the world (located near Australia). Coral reefs, such as the Great Barrier Reef, make up almost 2% of the ocean’s ecosystem yet over 25% of marine life depends on them to survive. Even financially, the reefs are important. Fisheries, tourism, and recreation net over $15 billion per year in the US alone. Worldwide many cultures depend on reefs as a way of life.

The importance of this topic is coral is in danger. Perhaps while hearing about the Great Barrier Reef you’ve heard of coral bleaching or when Netflix began promoting “Chasing Coral” this past summer 2017 or read a review about it. Taking a crash course in coral will help create a deeper understanding of coral bleaching, what causes it, and how scientists are working to fix this problem.

Coral is a fascinating yet delicate animal that has a symbiotic relationship with microscopic plants. Base coral (coral that makes up the bed for all other coral) grows very slowly at 0.2 – 1 inch per year. Coral that branches out can grow as quickly as 8 inches a year but is dependent on base coral. The Great Barrier Reef is around 500,000 years old but was mostly destroyed by the ice age. Currently most of the coral and foundation of this reef are around 8,000 years old.

In the long run – well, for a reef to be as grand as The Great Barrier Reef, it needs thousands of years to grow. So obviously, if something bad happens to the reef, it is not a problem that can be fixed overnight. Unfortunately, that is precisely what is happening. Coral is dying and being destroyed at a far faster rate than it can recuperate. This destruction has had such a negative impact on coral that scientists estimate wild coral will go extinct by the year 2050. In fact, in the last 30 years we have lost an estimated 40%-50% of the world’s coral.

So now you know what coral is and why it’s important. Now, it’s time to learn about what is destroying it. Well, there are a few things that contribute to this destruction. Specifically, tourism, as much money as it brings in also brings in people. People can be destructive despite no touch policies enforced on reefs. Storms can also be destructive to reefs, causing rough seas which will break some coral. Usually storms do not destroy coral at a rate in which cannot restore itself. There are also invasive species which devour the coral quickly and harm marine life that help support coral reef ecosystems. Disease can also spread through coral. Combined, all these issues are serious and are killing coral, but none of them come close to the event of coral bleaching.

Remember that coral is an animal that has a partnership with microscopic plants. These plants, also called “photosymbionts”, are a type of algae called zooxanthellae. Coral colors come from these plants and they are part of a process called photosymbiosis, which is when two living organisms bind together to benefit one another. The “photo” part of the definition refers to the plants which utilize light to create energy. This energy is then fed to the coral. Coral receives most of its energy from this relationship, nearly 75% in fact. This makes the pairing between coral and plant extremely important. The algae require a very specific environment to thrive in: shallow waters so it can receive sunlight, clear water so the algae aren’t shaded from the sun, specific salt water concentrations, and specific temperatures (warm, but not too warm). Without these conditions, algae cannot thrive, nor can the coral that depend on them.

So, what do photosymbionts have to do with coral bleaching? Well, remember two things: coral receives nearly 75% of its energy from them as well as its colors. Coral bleaching occurs when the algae die or get “evicted” from coral. This is caused by multiple factors. Time to investigate the major causes of coral bleaching. One issue can be disease that kills off algae leaving coral behind. Another is human interaction, primarily over fishing. Many species of marine animals are “gardeners” of reef ecosystems. They devour algae that live outside coral as well as remove decomposing matter to keep the water area relatively clean. Due to over fishing, these gardeners are removed. In turn the algae they feed on keeps growing eventually blocking the light the photosymbionts require to produce energy. Lastly, the biggest issue is when the algae’s living conditions are not being met because something (temperature, salt, or sunlight) are too high or too low. This in turn either kills the algae or stresses the coral into booting the algae out. Without the algae, coral turns white and loses its primary source of energy. The term “Coral Bleaching” begins to make more sense at this point. Now it’s time to explore why ocean temperature is rising.

Global Warming – a dreaded term – is the main cause behind rising temperatures. While many argue global warming is a hoax or that the Earth’s temperature has always varied, it is a very real and dangerous thing. Greenhouse gases produced by humans creates a layer that traps heat on the planet (known as the “Greenhouse Effect”). Weather and temperature worldwide has been unstable but these factors haven’t been too extreme just yet. This is because the ocean is one giant heat sink. The ocean absorbs heat which in turn keeps the rest of the world from overheating too quickly.

Unfortunately, this leads to various ocean issues such as melting glaciers, creating massive storms, and killing temperature-sensitive marine life, such as symbionts and coral. When the ocean is no longer able to absorb heat, we begin to see damage to land. Terrestrial life is already seeing the beginning effects of global warming.

Climate, temperature, and weather have always varied, there is no argument there. We see evidence of this in old trees, rocks, fossils, etc. But in 650,000 years it has not varied as much as it has over the past 100 years. Due to this quick change in temperature, living organisms that have temperature sensitivity are not able to adapt, and what does not adapt, dies. In turn, photosymbionts die and coral is left to fend for itself.

A couple things to know and remember: Bleached Coral is stressed but it is still alive. Coral can actually “hunt” using tiny tentacle-like structures called polyps. They grasp tiny organisms called plankton (a mixture of small animals and plants) to feed itself. Primarily, this feeding occurs at night but barely covers a quarter of the energy and food a coral requires to survive. Additionally, another issue that arises in these situations is Ocean Acidification. CO2 is absorbed by the ocean and causes a decrease to pH. The ocean, normally saturated with calcium, begins to lose that saturation due to the pH drop. Coral requires calcium to grow and develop polyps. A lack of calcium means reduced growth and restoration of coral. If coral cannot develop its polyps, it cannot capture prey to feed itself. Regardless, the polyps still require assistance from the photosymbionts. In rare circumstances, bleached coral can acquire new algae and recover from its bleaching. Unfortunately, as stated, this is a rare occurrence. Once Coral Bleaching has occurred, death is usually not far behind. After death a series of changes begin to occur in the coral.

While coral is in its bleached state many marine animals that call the reef their home will remain behind in what looks like a graveyard of bones. But as stated, the coral will die and the animals will relocate. With the animals gone, there will be less gardeners. With less gardeners, algae and seaweed will begin to take over the coral skeletons. They will strangle and destroy whatever remains thus destroying any chance the coral had at regaining new photosymbionts. Not all hope is lost however.

A few things have helped with coral recruitment (recruitment in nature is when an organism shows signs of regrowth or repopulation). In Japan, for example, it’s been noted that typhoons bring in colder sea water to the warmer shallows which bring the overall temperature down. Thanks to this, coral has a nicer temperature range with which to propagate. But relying on typhoons isn’t the best solution. They have the potential to destroy coral just as easily as they do to help coral recruitment.

Humans have put many preventatives in place to help slow and stop coral destruction as well. The fight against Global Warming in general is a boon to nature around the world. But none benefit as much as the ocean and its inhabitants. Reducing the creation of Carbon Dioxide is the number one step being taken. Basic steps like investing in renewable resources and decreasing energy use at home can be accomplished by individuals. In the long term, this reduces emission which lowering the Earth’s heating. When heating is reduced the ocean doesn’t have to absorb and compensate for temperature. If the ocean cools down or returns to normal temperatures, coral can begin to restore itself.

Although all this sounds good for coral, the unfortunate fact is that it’s not enough and Global Warming has done a great deal of damage and is still far from being defeated. On top of that, governments (such as that of the US) have removed or changed many laws that protect the environment. Whether this is for profit or to save money, the reasons vary. As previously stated, coral has a high risk of becoming entirely extinct by 2050. This could potentially lead to the extinction of a great deal of marine life that is dependent on coral reefs. A domino effect would happen: animals (including humans) that are dependent on ocean life will have to adapt to alternate sources or perish. New sources would become stressed and possibly cave under the pressure of supporting more life. This could lead to damage and death of terrestrial plants and animals and continue up the chain.

Solutions for these problems are needed, and luckily, we have some. If we can’t fight Global Warming, we can potentially give plants and animals the tools to adapt and survive against it. For coral, the idea is simple: adapt the photosymbionts to the current changes in temperature. Scientists have managed (on a small scale) to do just that. The Great Barrier Reef (GBR) was the first test subject for this adaptation procedure. The primary focus is the slow growing base coral that makes up the structure of many reefs worldwide. The next portion is to focus on the photosymbionts.

Due to drastically long lifespans that include long reproductive cycles, coral does not easily adapt by itself. However, symbionts do have the potential to adapt quickly to thermal changes if given the chance. And scientists are working on giving photosymbionts that chance. Using a procedure called “heat stress” scientists can kill weaker symbionts and find the survivors. Using the survivors of heat stress, they can then grow more of them. Heat stress is applied to generation after generation of symbionts thus picking out the strongest for survival.

Scientists looked for specimens that showed various genetic capabilities, not just the ability to survive warmer temperatures. The ability to speed up the growth rate of photosymbionts is an important one. The faster they grow the more generations scientists could adapt through heat stress. With more generations going through heat stress and surviving scientists could have a very large and stable group of photosymbionts. It’s not the only genetic trait they were looking for, there were still other issues to resolve.

The photosymbionts could over-photosynthesize and stress the coral out (as we learned earlier as one of the issues causing coral bleaching). From there the coral evicts the symbionts and becomes bleached. So even if the photosymbionts are adapted to survive warmer temperatures it could encourage them to photosynthesize far worse than they were doing prior. Another trait scientists are breeding for is the ability for symbionts to stop over-photosynthesizing. Instead they would release the excess energy as heat instead of stressing the coral. Without the coral being stressed the symbionts will not get evicted.

Tests in which the photosymbionts are injected back into bleached coral have so far been positive in laboratory settings. Using lab-reared photosymbionts in the wild is still far from being field tested or field ready. It’s necessary to invest funding into important projects such as these. Adapting the photosymbionts and giving coral the chance to catch up on adaption by prolonging their lifespan is the best way to keep coral (and nearly a quarter of marine life) from going extinct within the next 50-100 years. Educating people about coral bleaching and ways to fix it is key to making projects like photosymbiont adaption a success and in turn save coral reefs.








Annotated Bibliography

Chasing Coral. Directed by Jeff Orlowski. Sundance Film Festival. Distributed by Netflix, July 14, 2017.

This is a documentary backed by Netflix concerning coral bleaching and coral death. It follows several coral reefs worldwide over the course of months and years (some locations were filmed longer than others). The use of underwater cameras that snap continuous pictures for months shows the devastation of live healthy coral undergoing bleaching. After some time with the coral unable to recover it dies and creates an eerie-like death bed of coral. This in turn displaces thousands of animals who were using the coral as their home.


Bernardo, L. P., C., Nadaoka, K., Nakamura, T., & Watanabe, A. (2017). Island-enhanced cooling mechanism in typhoon events revealed by field observations and numerical simulations for a coral reef area, sekisei lagoon, japan. Ocean Dynamics, 67(11), 1369-1384. doi:

While many types of storms can be bad for coral reefs research shows that typhoons are potentially beneficial. Bernardo and Nakamura investigate typhoons in Japan and their effects on the surrounding reefs. Shallow ocean water is easier to warm than deeper ocean water. Since most reefs are located in rather shallow water they are heavily affected by the rise in water temperature. Typhoons however drag deeper ocean water – colder ocean water into the shallows thus dropping the temperatures of shallow water.


Edmunds, P. J. (2017). Unusually high coral recruitment during the 2016 el niño in Mo’orea, french polynesia. PLoS One, 12(10) doi:

This article by Edmunds touches on the damage major storms do to coral. First severe storms are a part of global warming causing temperatures to rise leading to coral bleaching. Second, they also can drop the sea level leaving coral stranded out of water. While some coral can adapt to these conditions most end up perishing. Edmunds investigates unusually high coral recruitment (the regrowth of coral in early stages) after massive storms have passed through a reef (in this case El Nino in French Polynesia).


Mumby, P. J., Sanchirico, J. N., Broad, K., Beck, M. W., Tyedmers, P., Morikawa, M., . . . Lubchenco, J. (2017). Avoiding a crisis of motivation for ocean management under global environmental change. Global Change Biology, 23(11), 4483-4496. doi:

This article clarifies global warming, ocean acidification, and what the government is and is not doing to prevent or reduce the impacts on various ecosystems. Coral reef systems are mentioned as they are very important to marine life and fisheries. A discussion on funding and preventative measures is introduced but while this article has hope it’s clear that preventative measures are falling short on saving the environment.


Osborne, K., Thompson, A. A., Cheal, A. J., Emslie, M. J., Johns, K. A., Jonker, M. J., . . . Sweatman, H. P. A. (2017). Delayed coral recovery in a warming ocean. Global Change Biology, 23(9), 3869-3881. doi:

Coral cannot recover in current ocean temperatures and it’s only going to get worse. In prior years coral (a very slow growing animal) would grow and recover as older coral perished. Due to warmer ocean temperatures this recovery period is happening slower or not at all in various locations. This article helps emphasis Chakravarti’s article about the need to adapt photosymbionts to save coral.

Chakravarti LJ, Beltran VH, van Oppen MJH. Rapid thermal adaptation in photosymbionts of reef-building corals. Glob Change Biol. 2017;23:4675–4688.

Chakravarti’s piece on “Rapid Thermal Adaption in Photosymbionts of Reef-building Coral” is important in breaking down two things: Global warming is happening at a rate that Earth has not experienced in millions of years and certain vital species are unable to keep up with it. This article then gives way to artificially adapting photosymbionts to adapt to global warming temperature changes thus preventing mass extinction of coral. It covers the species and experiments used to adapt photosymbionts with encouraging results.

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