Coral bleaching is sadly becoming a common headline in today’s ocean news, with massive events happening in once reef thriving waters around the world.  For the first time a team of scientists in Australia has captured the horrible event on a time-lapse video. “Mass coral bleaching events are a concern for scientists globally with recent events on the Great Barrier Reef highlighting the threat of elevated water temperatures to the health of reef ecosystems,” says Luke Nothdurft from Queensland University of Technology in Brisbane, Australia. Nothdurft and his team collected this footage from a recent study they were working on. Watch for yourself below as this coral specimen undergoes a coral bleaching event and violently loses one of the most critical components needed for its survival.



The Coral Study

Nothdurft and his team of fellow scientists in Australia put various plate corals (Heliofungia actiniformis) in aquariums in their lab. Here they were able to change water quality parameters and observe the change these sample corals exhibited. Under stress, coral organisms will puff up or inflate as well as contract violently releasing valuable algae from their bodies. Stress for a coral can be something as small as a single degree change in water temperature, thus making them highly susceptible to stress in changing environments.

In the case of this video, the water temperature was raised over a twelve hour period from 79 to 90 degrees Fahrenheit. Now, 11 degrees is a big change in water temperature, especially for coral organisms, which like I said previously, tend to have very specific limitations in terms of water quality. Within just a few hours, the team noticed the corals begin to inflate their bodies and suddenly expel or purge themselves of Symbiodinium. Nothdurft stated of the coral experiment, “Suddenly and violently contracting and ejecting Symbiodinium through their oral openings over four-to-eight day duration of the experiments.”

This mas exodus of Symbiodidium can be a major problem for the coral as Symbiodinium or commonly called zooxanthellae is a critical component of the coral’s survival. If the coral goes without it for a long period of time, the coral will die. To read the published study by Nothdruft and his team click here.



What is coral bleaching?

Like I’ve mentioned a few times already, coral has a very important relationship with symbiodinium  or zooxanthellae. Zooxanthellae are dinoflagellates that are present in the cytoplasm of many marine invertebrates like coral. They are photosynthetic algae that live in the tissues of coral organisms and many times give coral their vibrant hues. 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. Zooxanthellae also provide coral with essential products of photosynthesis like amino acids, glucose, and glycerol which is critical for the coral in order to make essential molecules such as fats, proteins, and carbohydrates. They also use the products zooxanthellae provide to produce calcium carbonate used to build their hard exterior. The relationship between zooxanthellae and coral reefs is so important that it drives the growth and productivity of coral reefs or the vast groupings of hard coral outgrowth.  This relationship is responsible for a tightly knit web of recycling nutrients in the often nutrient poor tropical ocean waters coral is most commonly found in. It is so prominent and important is the ocean, that 90% of organic matter that is photosynthetically produced in seawater is produced by zooxanthellae and is transferred to a host coral tissue.

Besides the critical productivity and recycling of nutrients, zooxanthellae are also the component of coral that give stony or hard coral species their beautiful, vibrant colors.  Zooxanthellae is not a true part of coral; that is in stressful or less than optimal conditions it leaves or expels from the coral tissue. These conditions could include any range of water quality or a taxi the zooxanthellae is exposed too.  This could include but is not limited temperature, pH, dissolved oxygen, salinity, light, and water movement.  When an exodus of zooxanthellae occurs from a coral, the coral becomes a white or bleached color. This of course gave rise to the nickname “coral bleaching” which sadly is very prevalent in ocean news today. Coral decline is often associated with coral bleaching or coral appearing bleached or less bright. 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. 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 leaves the coral very vulnerable and at high risk.

Coral bleaching events are occurring in massive occasions all around the globe due to rising ocean temperatures from global warming and El Nino events.  In the most 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.

Sadly as we know from the video, coral cannot survive very long without their zooxanthellae.  Zooxanthellae provide coral organisms with so many vital components that without them, the coral will eventually die. This relationship is one of the most intimate and conversely dependent mutualistic relationship seen among organisms in the ocean.  This closeness causes an animal (reef building coral) to respond to stimuli in their environment like a plant would.  Zooxanthellae need light for photosynthesis thus healthy coral organisms are found in clear water that sunlight can easily penetrate.  These waters tend to be areas of low turbidity (calm water) and also low productivity. These facts are what create the coral reef paradox that is part of what makes coral reefs such important ecosystems: they require clear, calm, nutrient-poor water but are one of the most productive and diverse ecosystems on the planet.


Help protect coral

It is easy to pretend like problems you read about but don’t see face to face aren’t reality. While this video intentionally puts a  living organism under stress, possibly such great stress that it could die, it is very important to better understanding how we can fight coral bleaching in the ever changing environment around us. Hopefully by watching this video clip, you feel a little more connected to the ocean and the major struggle and decline it is going through today and want to do your part to help. If not, I fear we will lose so much of the natural beauty and resources our oceans have to offer.




References and photos courtesy of