In Hot Water - the Great Barrier Reef

In Australia and around the world we are looking at the final chapter for coral reefs. In March of this year, I spent time on the northern Great Barrier Reef around Lizard Island and am still recovering from what was the most miserable week of my life. To describe what my students and I saw as apocalyptic sounds like an exaggeration, but in truth this is an understatement as we could not see the whole 1000km of reef North of Lizard that was also undergoing a similar transformation. Even when we got to the ‘outer reef’ to the edge of the Great Barrier where surely, bathed in oceanic water the coral was safe, we found massive coral bleaching and already, widespread coral death. 

Predictions from several very carefully considered sources state that we may lose all remaining coral reefs within 20-40 years and with current trajectories in climatic change, those predictions looks more and more probable. Exploring a coral reef is one of the most enlightening experiences available to man. For some the ocean is alien territory. Everything around you is faster, more colourful, perhaps has teeth or spines but overwhelmingly, it is the explosion of life before your eyes that always leaves a lasting impression. So, why are we killing it? Humanity has found a beautiful animal and is slowly, deliberately pulling its legs and wings off.

I remember my first reef snorkel as a six-year-old on Key Biscayne in Florida. Clinging to my Father’s back, I was terrified, partly because of the explosion of fishes going on beneath my mask and also because my Dad was not a great swimmer. He was however an expert ichthyologist, Her Majesties’ Curator of Fish at The British Museum of Natural History in London. I was fortunate to grow up in a world of marine biology, and learned to love the reef from an early age. After getting over the terror of my first frantic fish experience, I wanted to dedicate my life to the study of what goes on in the their world.

I moved to Australia two decades ago and I have been researching coral reefs for the last 30 years. I began with the incredible mantis shrimp, an animal that I still study and wonder at today. Every field trip back to the reef is unforgettable and inspirational; the more I learn about this ecosystem, the more amazing it becomes. But now, I am faced with an unexpected moment of terror. I have a field trip coming up in July, and I do not want to return to the reef. I do not want to put my mask in the water for fear of what I might see.

With a few exceptions, reefs worldwide are not in good shape right now. We are at the pointy-end of the third and worst global coral bleaching event. The first in 1998 saw the demise of 16% of the world’s reefs, and this one is likely to be more destructive. Why are our coral reefs disappearing so fast? Without pointing specific fingers, this is because of our inability to act and look after a beautiful and necessary part of our planet. Reef decline, glacier and polar ice-cap melt and other rapid environmental changes currently occurring are the result of man-induced climate change. The cyclical El Niño weather currently underway is often blamed for coral reef decline in the press. It is however merely an additive effect to global climate change and one that our world has successfully dealt with for thousands of years.

Do not blindly believe what you read in the media especially some Australian newspapers or the words of our current government who have swept this disaster under the carpet in a bid to get re-elected. Mass coral bleaching started only 20 years ago. Along with the alarming acidification of the ocean, it is due to our addiction to fossil fuels and dirty energy that consistently pump billions of tonnes of carbon dioxide into the atmosphere.

Sir David Attenborough, one of the greatest natural history communicators, summarises this far better than I can: “Do we really care so little about the earth on which we live that we don’t want to protect one of its greatest wonders from the consequences of our behaviour?”

He was referring to the Great Barrier Reef in a documentary series on which I was the chief scientist. I had the honour of riding in a submersible with him and showing him around the reefs of Lizard Island and Northern Queensland. It will remain a pinnacle in my scientific career. Sadly, many of the reefs we saw together are now history, not natural history, and the unfortunate answer to his somewhat rhetorical question is currently, “Yes.”

If we truly value coral reefs and our wellbeing on this planet, we need to take immediate action. An accelerated renewable energy agenda is the only thing that will give our reefs a chance. We must work together to do everything we can, both locally and globally, to reduce our carbon emissions.  If we do not do this now, we will be handing our children a future of environmental devastation and uncertainty.

Many of the people reading this magazine already know and may agree with what I am suggesting but please, do not simply huddle, talk and blame the politicians. Vote for politicians that offer the best future for our coral reefs and our natural world. Take steps to reduce carbon emissions in your own life. Educate your children. Look them in the eyes and say, “I am going to give you a future. I am going to give you a cleaner world with coral reefs, penguins and polar bears.” I am determined to try to make a positive difference through a citizen-science organisation, CoralWatch ( that promotes reef guardianship and forward-looking behaviour. If you are interested, please get in touch.

Recent facts and figures on the reef are as follows:

1.      From November 2015 to May 2016, the Great Barrier Reef (GBR) has suffered its worst ever mass coral bleaching event.

2.      Based on extensive surveys by the Centre of Excellence for Coral Reef Studies, ( we know that only 7% of the GBR avoided bleaching.

3.      The severity of this bleach is on average greater and longer than previous mass coral bleaching and splits the GBR into three regions:

a)      The top (1,000 kilometres) section is the most severely affected, with many of the reefs there 90% bleached.

b)      The middle area (Port Douglas to Makay), with reefs averaging around 50% bleached.

c)      The southern section has been lucky and 25% of the reefs are not bleached at all (GBR coral bleach map – from

d)      Some areas are now recovering as the water cools over the whole reef and there are still many areas of the GBR that are stunningly beautiful.

e)      Best estimates for the severely bleached Northern section, however, suggest that only 50% or less of the coral there will recover in the short term.

When coral is heat-stressed for too long—and this may only constitute a 1-2oC temperature increase for a few weeks—its vital symbiotic relationship breaks down. This symbiosis, or mutually beneficial living arrangement, is between the coral polyp animal and unicellular symbiotic algae called zooxanthellae. In fact, the green or kaki-brown of many corals is the result of a curtain of these algal cells in the coral tissue. The algae photosynthesise and produce carbohydrates and sugars, some of which are shared with the polyp. The polyps also feed on zooplankton at night and the algae benefits from this, as well as the shelter it receives within the coral. For reasons still not completely understood, too much heat and light causes the algae cells to be expelled resulting in bleaching of the coral. (For more details refer to, ).

Some of the photographs in this essay are recently bleached corals. Some may seem beautiful, showing the brilliant white of the coral skeleton or the fluorescent pink, blue, purple, green or yellow colours of the coral polyp underneath. However these are deeply-stressed animals, the healthy green/brown curtain of the symbiotic algae has vanished. While coral may recover in the short term by regaining or regrowing its symbiotic housemate, this requires a drop in temperature and removal of other possible stressors. After the 1998 coral bleach, many of our corals on the GBR recovered. However, we must remember that bleaching is a deeply physiologically challenging event for coral and their reproductive success and vitality is compromised.  Weeks of starvation do little good for any animal.

In the event that the coral colony loses the fight and the polyps die, this is not obvious until the macro-algae (seaweed or turf-algae) take over the space. Just like in a forest where some trees grow taller or broader to catch the light and overshadow neighbours, macro-algae and coral fight for space. Some of the photographs here show this succession and as Figure X shows, it can be easy to mistake coral regaining its colour for recovery, as both the macro-algae and the microscopic symbiotic algae are green/brown in colour.

A quick calculation based on reef area (not coral cover) suggests that an area of the GBR the same size as Scotland currently has corals within it that are dying. When most or all of the coral on a reef bleaches and subsequently dies, what is left can still be called a ‘reef’, but its ecological complexity and vibrant beauty are lost. Other animals including fish, some of which underpin our own food fisheries, can disappear as well. We are only beginning to come to terms with this unfortunate reality now on the GBR. The fish that rely on coral for food or shelter from predators have nowhere to go when their coral home and food source dies. One quarter of all marine life lives on or passes through a coral reef, and their loss will definitely affect the Australian economy and peoples’ livelihoods. 

Full recovery can occur over a number of spawning seasons but just like re-growing trees in a forest, it takes time and the right conditions. This is where local factors such as good water quality and low nutrient load are important. They can be achieved through sustainable farming practises with an emphasis on responsible fertiliser use and minimizing sedimentation by controlling dredge dumping. Fertiliser encourages the growth of macro-algae and can also be directly linked to Crown-of-Thorns starfish outbreaks on reef systems; high nutrients stimulate plankton growth, providing larval starfish with food triggering a population surge. Both macro-algae and these coral-eating starfish are bad for coral recovery.

The Federal government of Australia and Queensland State governments are beginning to address this issue at local levels (; however, it is at the global climate change level that Australia currently falls flat on its back. In the months after returning from the 2015 Paris climate summit COP21, the federal and state government of Queensland signed off on allowing one of the world’s largest coal mines to open in Queensland, right next the GBR. This screams a blatant lack of sound judgement. 

The way forward is obvious. We must work harder to reduce carbon dioxide emission, otherwise mass reef bleaching will continue to occur more frequently. Estimates suggest we will have no major reef ecosystems left within the next 20 to 40 years. Notably, Earth is about to surpass 400 parts per million (ppm) of carbon dioxide in the atmosphere. Like the continued loss of the GBR, the shrinking ice caps and loss of wildlife at the poles is another indication of our inability to act appropriately. Some have said we are already too late, that we are past the tipping point. However, biology often has surprises and coral reefs are incredibly resilient. I refuse to give up. Surely, it is better to fight to keep the boat afloat than to give up and wait for it to sink.

Perhaps what is most significant is the fact that this is a global catastrophe and other reefs around the world are bleaching as well not just the GBR. Well over 500 million people around the world rely on their reef systems for sustenance and their livelihoods are now under threat. As we collectively continue to burn fossil fuels for energy, we are killing the reefs of all countries, even those that have made a more positive commitment to using cleaner, renewable energy sources. Our inaction is destroying the life of many island nations such as the Maldives, Solomons and Kiribati. 

At a local level, I certainly refuse to leave my children to face the consequences of past and current generations’ inability to act. Already, the reefs we used to go to as a family are now covered with algae and seaweed. We are fortunate that the GBR is so big that we can pick reefs in the southern third region that are still brilliant to visit. But with global temperature on the rise, how long will these reefs be around? 

CoralWatch, the citizen science group I already mentioned, aims to get as many people to a reef as possible and help them understand reef issues through classroom events and gatherings. This band of helpers also collects publicly available coral health data, adding to the other layers of information necessary to keep an eye and a close focus on our reefs. We have team members in 70 countries and interact with schools, tourism operators and even politicians in Australia. The leaps in understanding that I see from the power of participation in a problem give me hope. Even the politicians are beginning to understand.

I know we can “save the reef” and that this will come through people power. The key to reef survival anywhere is to ensure we look after it at both local (water quality) and global (climate change mitigation) levels. One cannot proceed effectively without the other.

Think hard about what you throw away, where you throw it, and what goes down the creeks and rivers. If you are fortunate enough to visit any coral reef, cherish every moment, show your children, and share the wonder. Do everything in your power to reduce your carbon footprint. Encourage whoever you can at the political level, with a tick in the best box and with ongoing community conversation. We all need to run full pelt at renewable energy options. Fossil fuels are for fossils.

Read More Articles - Sign-up for More Full Articles (free)

by Professor Justin Marshall  ( OG 37)

About the Author

Prof. Justin Marshall was awarded a D.Phil 25 years ago from The University of Sussex, UK. Previously an Australian Research Council (ARC) Discovery Outstanding Research Awardee (DORA), he was awarded Australia’s most prestigious (ARC) Laureate Fellowship in 2014. His research focusses on the ecology and sensory ecology of coral reefs. This includes finding out how animals use colour for communication and camouflage and takes a comparative approach to finding answers. He is a Research Professor in The Queensland Brain Institute (QBI) In 2004 he started CoralWatch (, a citizen science organisation now available across 70 countries and translated into 12 languages. He has participated in the making over 30 science documentaries including two with Sir David Attenborough – most recently the new Great Barrier Reef three-part documentary.  In 2014, he published “Visual Ecology” (Princeton University Press), which won the American Publishers prize for best prose in science. 

Blog & Review Categories

Blog & Review Archive

© 2016 Ocean Geographic Society. All Rights Reserved.