The nearing demise of the Great Barrier Reef

Just another harbinger of Holocene Extinction that can be ignored?

by Enakshi Sivasudhan

At a Glance:
Coral reefs around the world are facing unprecedented damage due to global warming. The Great Barrier Reef of Australia, a world heritage-listed natural inspiration has recently captured the attention of the media with its gradual depletion over the past few decades due to anthropogenic activities. In this article, the causes of this reef ecosystem destruction are explored. Loss of marine species could be an indication of a potential mass extinction in the near future.

A controversial obituary hit the media a few months ago, causing uproar not only among the scientific community but also the rest of the world population. This somewhat tongue-in-cheek obituary simply stated that the 25 million-year-old Great Barrier Reef had passed away in 2016 after a long illness [1]. Although the news was later dismissed as deliberately hyperbolic and inaccurate, such heartbreaking news prompts an urgency to take immediate steps towards conserving what’s left of the Great Barrier Reef [2].

Australia’s Great Barrier Reef is the largest coral reef system on earth, sprawling over a jaw-dropping 344,000km2, and is the only living thing visible from space. This magnificent ecosystem was declared a World Heritage site in 1981 and later added to the National Heritage List in 2007. Composing of nearly 3,000 individual reef systems and 600 tropical islands, this complex labyrinth of habitats comprises of an astounding variety of marine flora and fauna – from primeval sea turtles to variegated coral structures that attract tourists all around the year [3]. However, in recent years, this glorious marine ecosystem has started to degrade due to recent climate changes mainly triggered by anthropogenic activities. It is also facing a growing number of threats such as coral bleaching, ocean acidification, fishing, farm pollution and industrialisation [4].

A major contributing factor to coral bleaching is rising seawater temperature caused by global warming. Several species of corals maintain a symbiotic relationship with algae known as zooxanthellae, which give corals their vibrant colours. These autotrophic photosynthesisers, which live inside the corals, are efficient food producers that provide up to 90% of the energy essential for corals to grow and reproduce. When the ocean heats up, corals are stressed and expel zooxanthellae algae, causing the corals to become transparent and to reveal their white skeleton underneath. Without the energy provided by these algae, the corals eventually die and get coated by an invasive layer of seaweed [5].

Figure 1: Coral bleaching at Lizard Island, Great Barrier Reef (image credit: WWF Australia / XL Catlin Seaview Survey)

Rising ocean acidity, which is likely the most significant impact of global warming, can lead to an irreversible depletion of the reef ecosystem. Since the Industrial Revolution, there has been a significant increase in the atmospheric CO2 due to anthropogenic activities such as burning fuels and deforestation. With the aim of establishing concentration equilibrium between the atmosphere and the ocean, a certain amount of CO2 dissolves in the ocean, altering the seawater chemistry. This absorbed CO2 reacts with water molecules (H2O) and produces a weak carbonic acid, H2CO3.  This acid then dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3). An increase in the H+ ions causes a drop in pH, and thus acidifying the ocean. This series of reactions reduce the amount of carbonate  (CO32-) ion, which is a crucial inorganic carbon found in marine animals such as crustaceans, corals and mollusks. These organisms rely on the intake of carbonate ions to produce their calcareous shells and skeletons through a process known as calcification. When the amount of carbonate ion decreases, in order to maintain the concentration equilibrium of such ions in the ocean, the calcified coral and skeletal structures start to dissolve. It is predicted that, if the current trend of atmospheric CO2 augmentation remains unaltered, the ocean’s pH may drop from 8.2 to 7.8 by 2100, endangering the lives of millions of marine organisms [6].

Besides coral bleaching and ocean acidification, degradation of coral reef ecosystem by terrestrially derived pollution is a widespread issue and the topic of intense management activity. Changes in terrestrial fluxes of sediments, nutrients and harmful pollutants such as pesticides and heavy metals as a result of land clearing, agricultural and industrial development, reservoir construction and removal of ecosystem’s filtering capacity can have devastating effects on the marine life especially coral reefs. For example, nitrogen run-off from farms in the mainland can lead to algal proliferation, which starfish larvae feed on, and further promote population explosions [7].

Furthermore, poor and frivolous management of fishing is imposing threats to many of Great Barrier Reef’s endangered species such as turtles, dugongs and inshore dolphins. Port expansion, another unfavourable scope of industrialisation, can lead to dredging of the ocean floor, which further increases the shipping traffic and inflicts other negative impacts on the delicate coral reef environment [8]. Tourism too can have a negative impact on the coral reefs. Reef walking can damage coral species, fuel leaks and anchor dropping by boats carrying tourists and even the run-off of sweat and suntan lotions from divers and underwater explorers could have a detrimental effect on these delicate living structures [9].

Loss of the Great Barrier Reef and other coral reefs around the world can severely affect the fishing and tourism industry, eventually paving the way to a worldwide economic disaster. Besides, countries like Maldives depend on coral reefs as a natural barrier that protects the island against incoming stormy waves and rising sea levels. According to the International Union for the Conservation of Nature (IUCN) nearly 500 million people rely on coral reefs for their livelihood, so one can imagine the catastrophic consequences of coral reef extinction [10].

Figure 2: Carol bleaching (image source: http://oceanservice.noaa.gov/facts/coralbleaching-large.jpg)

I began this article by posing the question, whether the definitive proof that the Great Barrier Reef heralding the predicted Sixth mass extinction[1] (also known as the Holocene extinction), is something that can be neglected. The Holocene extinction is the ongoing extinction event of species happening in the present Holocene epoch that began 11,700 ago [11]. Since 1900, 69 mammal species and 400 types of vertebrates have gone extinct [12]. In a recent study published by Science Advances, biologists have found that our planet is losing several species of flora and fauna at a rate of 20-100 fold higher than the past millennia event based on recent statistical data that show 19% of the planet’s coral reefs are dead and that if current trend of extinction rate continues, the remaining reefs might disappear in the next 40 years [13].

Nevertheless, in an interview with The Huffington Post, chief of the Coral Reef Ecosystem Program at NOAA’s Pacific Islands Fisheries Science Center, Russel Brainard said “We’re very far from an obituary”, when questioned about the current state of the Great Barrier Reef. Immediate initiatives should be carried out to protect the reefs [2]. Steps should be taken towards the gradual reduction of farm pollution, governments should fund improved farm management, and laws and regulations should be put in place for industrialisation projects pertaining to port development. Illegal fishing should be stopped at all costs to prevent turtles and dugongs being trapped in fishing nets. By committing to 100% renewable electricity, the use of fossil fuels can eventually be ceased, thus rapidly reducing global warming [14].

Human activities could harshly affect the world around us, our future and the lives of the forthcoming generations to come. The Great Barrier Reef is a masterpiece of millions and millions of years of evolution. It has been shaped by Mother Nature and should be preserved at all costs. It is never too late to start working on conserving this planet we call home.

Figure 3: 10 ways to protect carol reefs (image source: http://oceanservice.noaa.gov/facts/coralinfographic-large.jpg )

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[1] Throughout history, despite various rates of extinction, five major events have qualified for the ‘mass extinction’ status: near the end of the Ordovician, Devonian, Permian, Triassic and Cretaceous Periods. Given the current accelerating levels of extinction, scientists predict the 6th mass extinction is not very far away from happening, most likely to occur within the present Holocene epoch

About the author

Enakshi Sivasudhan is a Sri Lankan who graduated from The University of Nottingham with a Bachelor in Biotechnology with Honours. She previously worked as a Research Trainee at Applied Agricultural Resources in Malaysia and is currently working in Sri Lanka. Her research interests include Bioinformatics and Synthetic Biology and she hopes to pursue a career as a Research Scientist. She loves to indulge herself in studying the ethical consideration of scientific research. Her favourite things about Malaysia are Nasi Lemak and Pasar Malam. Find out more about Enakshi by visiting her Scientific Malaysian profile: http://www.scientificmalaysian.com/members/enakshilklk/

References

[1] Rowan Jacobsen (2016) Obituary: Great Barrier Reef (25 Million BC-2016): http://www.outsideonline.com/2112086/obituary-great-barrier-reef-25-million-bc-2016

[2] Chris D’Angelo (2016) Great Barrier Reef Obituary Goes Viral, To The Horror Of Scientists

http://www.huffingtonpost.com/entry/scientists-take-on-great-barrier-reef-obituary_us_57fff8f1e4b0162c043b068f

[3] J.E. Brodie, F.J. Kroon, B. Schaffelke (2012) Terrestrial pollutant runoff to the Great Barrier Reef: An update of issues,

priorities and management responses, Marine Pollution Bulletin; vol.65:81-100.

[4] Glenn De’atha, Katharina E. Fabriciusa, Hugh Sweatmana (2012) The 27–year decline of coral cover on the Great Barrier Reef and its causes, PNAS, vol.109 no.14:17995–17999.

[5] Michael P. Lesser (2007) Coral reef bleaching and global climate change: Can corals survive the next century?, PNAS, vol.104 no.13, pp. 5259–5260.

[6] Scott C. Doney, Victoria J. Fabry, Richard A. Feely (2009) Ocean Acidification: The Other CO2 Problem, Annu. Rev. Mar. Sci. 2009. Vol.1:169–92.

[7] Frederieke J Kroon, Petra M. Kuhnert, Brent L. Henderson (2012) River loads of suspended solids, nitrogen, phosphorus and herbicides delivered to the Great Barrier Reef lagoon, Marine Pollution Bulletin, vol.65:167–181.

[8] WWE: The Great Barrier Reef http://www.wwf.org.au/what-we-do/oceans/great-barrier-reef

[9] Australian Government Department of the Environment News Bulletin: http://www.australia.gov.au/about-australia/australian-story/great-barrier-reef

[10] International Union for the Conservation of Nature (IUCN) Coral Reefs https://www.iucn.org/theme/marine-and-polar/get-involved/coral-reefs

[11] Anthony D. Barnosky, Nicholas Matzke, Susumu Tomiya (2011) Has the Earth’s sixth mass extinction already arrived?, Nature, vol.471:51-57.

[12] Gerardo Ceballos, Paul R. Ehrlich, Anthony D. Barnosky (2015) Accelerated modern human–induced species losses: Entering the sixth mass extinction, Science Advances, vol.01,no 05: e1400253.

[13]United Nations Environment Programme (2008) Migratory Species Get Conservation Boost at International Wildlife Conference: http://www.unep.org/Documents.Multilingual/Default.asp?DocumentID=553&ArticleID=6014&l=en

[14] Fight for the Reef organization http://fightforthereef.org.au/