Decline of Great Barrier Reef From Coral Bleaching, by Skye Thomas

The Great Barrier Reef is home to around 10% of the worlds fish species along with countless non-fish marine species such as mollusks, invertebrates, and marine mammals. It stretches for 2,300 kilometers off the northern coast of Queensland, Australia and covers an area of 344,400 square-kilometers. Coral is the result of a symbiotic relationship with a type of microorganism called a zooxanthellae. This dinoflagellate lives within the coral and provides oxygen and calcium, while the coral provides food and protection for it. But if this relationship  gets stressed in any way, through increased ocean temperatures, pollution, and ocean acidification, the algae will leave the coral which causes it to become more susceptible to disease (Heron 2016). This can be an issue for the hundreds of thousands of fish that call the Great Barrier Reef their home. The decline in coral along the Great Barrier reef has caused an equally, if not more intense decline in native fish species as they lose their habitat, food sources, and nesting grounds.

Aerial view of Hardy Reef, to the heart reef, in the Great Barrier Reef CC BY-NC-ND 2.0

As more and more carbon dioxide is pumped into the atmosphere, the chemical makeup of the ocean changes along with the global temperature increasing. The oceans are absorbing this atmospheric carbon, causing the oceans pH to lower. This has decreased coral calcification by as much as 14.2% since 1990 (De'ath 2013) and will continue to decrease unless atmospheric carbon is decreased in some way. Coral can also be damaged by increased water temperatures. The symbiotic algae can only take so much heat for so long, so when the waters get too hot, they tend to either die off or abandon the coral to find a safer place, leaving the coral to starve (James 2018). As global temperatures warm, the El Nino events get warmer as well, causing an increase in coral bleaching events (Hughes et al. 2018). Hughes (2018) stated that “Since 1980, 58% of severe bleaching events have been recorded during four strong El Niño periods (1982–1983, 1997–1998, 2009–2010, and 2015–2016)” with the rest occurring in other ENSO phases. But this is changing as the global temperature increases, and soon coral bleaching will occur with or without those phases. Other types of pollution can affect coral reefs too, especially plastic and other non-biodegradable trash. Millions of tons of plastic enter the ocean each year, but it often does ever leave the ocean. It can end up in coral reef systems where it smothers out the coral by clinging to branching tendrils and blocking out sunlight. By being in contact with plastic, corals likelihood of disease increases from 4% to 89% (Lamb 2018). All these causes are preventable, and unless something is done coral reefs will die, leaving many marine species without important space for their survival.

Butterfly fishes on Great Barrier Reef. (Hunter 2014)

Many fish use reefs as an area of refuge, so a decrease in coral will cause a similar decrease in species present. This is a common reaction and can be seen in areas like kelp forests after large storms or diseases wipe out the kelp. While the skeletons of the coral may still provide refuge, living coral is an integral part of a coral reef ecosystem, and without it many fish will no longer be able to survive (Wilson 2006). Coral is also a common food of corallivorous fish such as the chevron butterflyfish (Chaetodon trifascialis) and the bumphead parrotfish (Bolbometopon muricatum) (Pratchet 2005). These fish are often part of the backbone of the food web and are the prey of many important predators. Coral reefs can also provide an easy and central space for many species of fish to spawn. It isn’t uncommon to see hundreds of the same fish all grouped together for spawning along with many other fish hanging around for an easy meal. If the reefs disappear, this whole delicate ecosystem will collapse, having lasting repercussions on marine and human life.

Trends in bleaching stress along the Great Barrier Reef  (Spalding et al. 2017)

The death of the Great Barrier reef will affect humans greatly as well, especially considering how many people rely on money from fish caught there and tourism from people who want to see it. The reef directly supports 64,000 jobs in Australia and has been valued at A$56 billion with a contribution of A$6.4 billion each year to the Australian economy (O'Mahoney, 2017). These reefs also act as important guards against storms and waves, acting as break waters to mitigate raging seas. Without the healthy reefs the waves can simply break through the dead, calcified coral and make it to land unhindered (Guannel 2016). As stated by Guannel, live corals “moderate the impact of waves and storms, thereby further reducing the vulnerability of coastal regions”. Without the money from tourism a good amount of people will lose their livelihoods in Queensland and the surrounding areas, with the same happening to many fishermen and charter boats. Even fisheries that exist off the Great Barrier reef could be impacted due to fish loosing spawning grounds and refuges for certain parts of the year

A school of bumphead parrotfish (Bolbometopon muricatum)   (LTMP, AIMS)

The Great Barrier reef is the source of habitat and food for hundreds of thousands of fish species and is an ecological hub of activity. The bleaching of this reef system would spell disaster for the food web of the area and could have lasting impacts around Australia and beyond. This not only will affect the fish that live and feed there, but also the humans that make their livelihoods off activities based around the reef. The reef also protects the coast of Queensland from intense waves and storms, acting as a natural sea wall. Without this the people living along the coast would be in more danger from storms than before. What is happening to the Great Barrier Reef is not unusual, and many other reefs around the world are facing the same issues. As Hughes (2018) said, “we are already approaching a scenario in which every hot summer, with or without an El Niño event, has the potential to cause bleaching and mortality at a regional scale”. The time between these bleaching events is getting smaller and smaller, not allowing the coral populations to recover between the events (Hughes et al. 2018). In order to protect the reef and other areas sensitive to climate change, global emissions must drop to 55% by 2030 (IPCC, 2018) to prevent the atmosphere from warming another 1.5 degrees Celsius. This means a decrease from 53.5 gigatons of equivalent carbon dioxide to 29 gigatons, a difference of about 24.5 gigatons. Unless something is done, the reef will die and with it many of the fish that rely on it for their survival.

Values from Great Barrier Reef ecosystem (O'Mahoney 2017).

References

Hughes, T. et al. 2018. Spatial and temporal patterns of mass bleaching of corals in the Anthropocene. Science, 80-83.

De'ath G, L. J. 2013. Declining coral calcification on the Great Barrier Reef. Science, 342(6158):559.

Greg Guannel, K. A. 2016. The Power of Three: Coral Reefs, Seagrasses and Mangroves Protect Coastal Regions and Increase Their Resilience. PLOS One.

Hunter, J.  2014. Great Barrier Reef Gets A Little Good News. Smithsonian Magazine. Retrieved from www.smithsonianmag.com: https://www.smithsonianmag.com/science-nature/great-barrier-reef-warming-good-news-180951762/

IPCC. (2018). SPECIAL REPORT: GLOBAL WARMING OF 1.5 ºC. Geneva: World Meteorological Organization.

James, L. E. (2018). Half of the Great Barrier Reef Is Dead. National Geographic.

O'Mahoney, R. S. (2017). At what price? The economic, social and icon value of the Great Barrier Reef. Brisbane: Deloitte. Retrieved from www2.deloitte.com/au.

Lamb, J. B.  (2018). Plastic waste associated with disease on coral reefs. Science, 460-462.

LTMP, AIMS. (n.d.). A school of bumpheaded parrotfish (Bolbometapon muricatum). Retrieved from eatlas.org.au: https://eatlas.org.au/media/240

NOAA. (2018. Coral Bleaching During & Since the 2014-2017 Global Coral Bleaching Event Status and an Appeal for Observations. Retrieved from coralreefwatch.noaa.gov: https://coralreefwatch.noaa.gov/satellite/analyses_guidance/global_coral_bleaching_2014-17_status.php

Pratchet, M. 2005. Dietary overlap among coral-feeding butterflyfishes (Chaetodontidae) at Lizard Island, northern Great Barrier Reef. Marine Biology, 373-382.

Scott F. Heron, J. A. 2016. Warming Trends and Bleaching Stress of the World’s Coral Reefs 1985–2012. Scientific Reports.

Spalding, M., L. Burke, S.A. Wood, J. Ashpole, J. Hutchison, P. z. Ermgassen. 2017. Mapping the global value and distribution of coral reef tourism. Marine Policy 82:104-113. 

Wilson, S. 2006. Multiple disturbances and the global degradation of coral reefs: are reef fishes at risk or resilient? Global Change Biology, 2220-2234.