Witnessing a Murder: Snorkeling the Great Barrier Reef

Adriane here-

A view of Queensland and its coastline in northeastern Australia (inset image). The Great Barrier Reef is the long feature, highlighted by the white lines, that stretches along the coast. Images from Google Earth (2017).

Last summer, I was lucky enough to be chosen as one of the scientists to sail on the International Ocean Discovery Program Expedition 371 to the Tasman Sea (read more about my adventure here). The ship we sailed on, the JOIDES Resolution, left from the port of Townsville, Australia. Because I was already flying to the Southern Hemisphere, my husband and I decided it was the perfect opportunity to take our delayed honeymoon (we had been married two years at that point, but better late than never!). We stayed on Magnetic Island, located right offshore from the city of Townsville for a week, sight seeing, koala-petting (Queensland is one of the few places in the world that allows you to pet wild koalas), and snorkeling.

A rare sight: An on-the-move koala family on Magnetic Island.

Being a naturalist and animal-lover, I have quite a lengthy bucket list. One of the items on that list was to snorkel the Great Barrier Reef. Lucky for me, the reef was just a 2 hour boat ride from Magnetic Island! My husband and I signed up months in advance for a snorkeling adventure on the reef, and we were both extremely excited about it! I prepared for the snorkeling adventure by doing extensive research on the reef, learning species of corals, fish, and sharks that are common on the reef, and also what human-made products (such as sunscreen) were harmful to the reef so we could avoid using them the day of our snorkel. But I also had to prepare myself mentally for what I knew was unavoidable: witnessing a reef community in peril.

Lodestone Reef, a small reef part of the Great Barrier Reef that we snorkeled.

Before I explain, allow me to dazzle you with reef facts. Reefs all over the world are amazing places (OK, this is probably more of an opinion, but I’m not wrong, right?). They are home to a huge number of animal species, all who interact with each other. Reefs themselves are defined by the community of corals, fish, crabs, etc. that live together. Reefs are located in warm, shallow, clear waters, and that is why they are found in tropical waters. Reefs occur all across the world, but the biggest and most impressive reef, by far, is the Great Barrier Reef. Check out this Google Street View of Heron Island, Great Barrier Reef to see some of the wildlife and coral species that live on the reef.

A colony of healthy table coral with striped damselfish swimming about.

The Great Barrier Reef (I’ll refer to it as the GBR from here) stretches 2,300 kilometers (1,430 miles) along the Queensland (northeastern Australia) coastline. It covers about 344,400 square kilometers (132,974 square miles) of area, which is approximately the size of 70 million football fields, or the size of Italy. Because of its size, the GBR is visible from space, and is listed as one of the 7 wonders of the world. Together, the GBR is made up of 2,900 individual reefs, and contains 600 continental islands. It also includes about 300 coral cays (cays, or keys, are small sandy areas located near a coral reef) and ~150 mangrove islands (mangroves are an important plant that live along coastlines; their roots offer protection for small fish and animals and help stabilize the soil in which they grow).

The reef itself is home to over 1,625 fish species, which accounts for ~10% of the world’s fish species! The fish rely on over 600 species of corals for protection and shelter. Over 133 species of sharks and rays also inhabit the reef, feeding off fish. Sea snakes slither their way across the reef, with about 14 different species found in the GBR. 30 species of whales and dolphins also visit the warm, clear waters of the reef to raise their young every year. Of the 7 species of marine turtles alive today, 6 can be found in the GBR. Thus, the GBR is a true natural treasure, with its beautiful marine life, vibrantly colored corals, and abundance of geographic features.

A solitary (one animal that lived by itself rather than in a colony) horn coral, one of the earliest species of corals from the Ordovician. Image from the Digital Atlas of Ordovician Life.

Corals first appeared in the rock record ~548 million years ago during the Cambrian Period. True reefs didn’t make an appearance until about 100 million years later, during the Ordovician Period. These reefs were very different from our reefs today, but the point is, they have survived all 5 major mass extinctions  in Earth’s history, and have become extremely successful. But all of that is changing today with global climate change. Reefs all over the world are in dying because of us, humans. It is estimated that from 1985-2012, about 50% of the GBR corals have died (De’ath et al., 2012).

Global climate change caused by humans expelling carbon dioxide (CO2), a greenhouse gas, at an accelerated rate is the leading cause of coral reef decline. As our atmosphere warms, our oceans are also warming. The oceans absorb about 93% of atmospheric heat. Although corals thrive in warm waters, they have a very narrow temperature tolerance (most can live in waters no less than 64 degrees Fahrenheit, and no more than 84 degrees Fahrenheit). When waters become too warm for the corals, they become extremely stressed. Prolonged stress leads to coral bleaching events. This occurs when corals expel the algae, called zooxanthellae, that live in their tissue. The zooxanthellae are what give corals their colors, so after expulsion, the coral turns white. Corals can survive without their zooxanthellae for a short period of time, but if they don’t return, the coral then dies. Check out this page and graphic by NOAA to understand more about coral bleaching.

My husband swimming next to a healthy community of various coral species. Some of the corals at Lodestone Reef are enormous, which indicates the coral is probably decades old.

Coral skeletons are made of calcium carbonate, or calcite (CaCO3). This mineral is also what bivalves and gastropods make their shells out of, so it is commonly found in reef environments. As humans pump more CO2 into the atmosphere, the oceans not only absorb heat, they also absorb this CO2 (about 30% of the CO2 released by humans has been absorbed by our oceans).  When CO2 is dissolved in seawater, it creates biocarbonate ions, carbonate ions, free hydrogen ions, and carbonic acid (read more about this process on our ‘Ocean Chemistry & Acidification‘ page). The amount of free hydrogen ions, H+, are what causes ocean waters to become more acidic or basic. An increase in H+ ions leads to the ocean becoming acidic, whereas a decrease in H+ ions leads to more basic waters. So as the oceans absorb more CO2, they become more acidic. Calcium carbonate, what corals make their skeletons out of, dissolve in the presence of acid. So not only are the corals stressed from increased water temperatures, it is also harder for them to grow and build colonies because they are dissolving in increasingly acidic waters.

Elkhorn corals in various stages of bleaching at Lodestone Reef. The fleshy-colored coral at the top of the image is healthy, the white coral directly under it is bleached, and the dark coral with bacteria feeding off the dead animal is at the bottom of the image.

I was well aware of the effects of global climate change on reef communities before I snorkeled the GBR (at this time, one of the worse coral bleaching events was taking place), but I had never seen the effects of human life on the reefs up close and personal. When we jumped off the boat (which was aptly named ‘Adrenaline’) at Lodestone Reef, I was instantly blown away by the wildlife swimming all around me. Sea cucumbers, starfish, and fish were everywhere, as were several species of coral! Elkhorn coral, brain coral, and species of table coral were abundant all around us. I was in total and absolute awe.

But it didn’t take long to find stressed, dying, and dead corals. Healthy corals are vibrantly colored, while some are flesh-colored. Stressed corals experiencing bleaching events are white, and those that are dead appear black. Dead corals will also have wispy bacteria hanging off the skeletons, as they are feeding off the decaying flesh of the animal. My heart sank faster than an anchor thrown overboard when I first witnessed the stressed, dying, and dead corals. Here I was, in the midst of the world’s largest, most wondrous reef, and it was being decimated. Suddenly, I was overcome with guilt: Guilt at not living a more earth-friendly lifestyle, guilt at not talking about the effects of climate change and its effects on reefs more to my students and the public, guilt that humans are carelessly destroying our Earth’s most precious resources. I was, in fact, witness to one of the largest, most extensive mass murders taking place in my lifetime: the death of our coral reefs.

But I’m not one to end on a sad note; rather, I’m hopeful that we can help our reefs (and all marine life) rebound from the damages we have incurred. There are several organizations that are committed to protecting the Great Barrier Reef and reefs all around the world. Some countries have created fishing restrictions and regulations for their reefs to protect the fish and marine communities that inhabit them. The Paris Agreement, a coalition of over 195 countries, was created in 2015 to  curb global CO2 emissions (as of writing this post, the U.S. is still a member of the agreement, but has plans to withdraw by November 2020). Scientists are gathering data on our reefs to quantify how fast they are responding to climate change, and are also working with aquariums to regrow species of corals for release back into the wild. As an individual, you can contribute to protecting our reefs in quite a few ways. First, you can actively vote for government officials that have a track record in supporting science and curbing CO2 emissions. Second, recycle. Most of our trash ends up in the oceans, and that leads to another set of problems for marine life. Third, you can reduce the amount of plastics you use in your daily life by refusing straws at restaurants, using reusable bags, baggies, and containers. Fourth, reduce the amount of time you spend driving a car. Instead, take public transportation, ride a bike, walk, or carpool with friends and family. All of these activities reduce your carbon footprint. Lastly, you can donate to foundations and organizations that work to protect our reefs. 

Here’s a list of foundations and organizations that are committed to protecting our reefs, and places where you can find additional information about reefs:




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