Coral Bleaching of the Great Barrier Reef

By Delaney Reynolds, SRC intern

Coral reefs are some of planet earth’s most spectacular, diverse and important ecosystems. Our planet’s coral reefs provide important shelter, habitats, and a source of food for many different species of marine organisms. They also act as a critical food source to humans, as well a natural barrier to help protect our coastlines from hurricanes and associated storm surges. Sadly, coral reefs face growing risks including the possibility of extinction from a variety of stresses that leads to coral bleaching.

Figure 1: Coral from which the zooxanthellae has been expelled, causing it to turn white (Image Source:

Coral bleaching is the process in which zooxanthellae, algae living symbiotically within the coral, are expelled from coral colonies due to a number of factors including an increase in temperature, decrease in pH, exposure to UV radiation, reduced salinity, and bacterial infections. Zooxanthellae provide the coral 30% of its nitrogen and 91% of its carbon needs to the coral host in exchange for a shelter, as well as waste produced by the coral from nitrogen, phosphorus, and carbon dioxide that is required for the algae’s growth (Baird, 2002).

When corals bleach, it effects entire marine communities due to their immense diversity. Fish populations that reside around coral reefs “are the most species dense vertebrate communities on earth, contributing critical ecosystem functions and providing crucial ecosystem services to human societies in tropical countries” (Graham, 2008). Researchers have found that when an ecosystem endures physical coral loss, fish species richness is extremely likely to decline due to their heavy reliance on the coral colony itself (Graham, 2008).

Perhaps the most famous current example of coral bleaching is Australia’s Great Barrier Reef. Scientists have determined that the main cause of Great Barrier Reef coral bleaching is induced thermal stress and that about 90% of the reef has been bleached since 1998 (Baird, 2002). As the corals bleach and temperatures increase, researchers have determined that shark and ray species that live in the area may be vulnerable to these climactic changes.

Figure 2: Exposure of Ecological Groups of GBR Sharks and Rays to Climate Change Factors. This figure displays the vulnerability different elasmobranch species face due to climate change, as well as the specific effects of climate change that they are vulnerable to, in the specific zones of the Great Barrier Reef. (Image Source: Chin et al. 2010)

Most of the Great Barrier Reef is located on the mid-shelf of the ocean floor, the approximate mid-point between the shallower coast of Australia and the continental shelf where the ocean bottom significantly drops in depth. Researchers found that the mid-shelf is the area where most of the shark species studied reside, while most rays dwell in coastal waters or closer to the continental shelf. It was also found that both areas are the susceptible to rising temperature, increased storm frequency and intensity, increasing acidity, current alterations, and freshwater runoff, all being caused by climate change (Chin, 2010). Based on these findings, researchers have concluded that the areas these elasmobranchs live in should be protected and preserved. Species in these highly vulnerable areas should also be monitored and considered for future conservation actions, as many of the shark species are already experiencing the effects of climate change from some of the aforementioned factors.

Typically, sharks are considered some of the strongest animals on earth, and while they have lived on earth for at least 420 million years, they are slow to adapt. This slowness has impeded their ability to survive in our rapidly changing climate. In the near future it will be common to see some species of marine organisms demonstrate plasticity, the ability to adapt to their changing environment, but other species, such as elasmobranchs, are expected to simply distribute to other habitats in search of cooler waters. Even though sharks are a highly vulnerable species to climate change, they sit at the top of the trophic level in many different niches and, thus, wherever they migrate to, it will be easier for them to find food than it would be for other species such as fish or rays. However, this is most likely only the case for adult sharks as embryos and juvenile sharks may be more vulnerable to increased temperatures. For instance, researchers found that the survival of bamboo shark embryos decreased from 100% at current temperatures to 80% under future ocean temperature scenarios and that the embryonic period was also shortened, not allowing the embryo enough time to develop fully (Rosa, 2014).

To decrease the effects of climate change on coral bleaching, corrective and mitigation measures can be taken. By utilizing green energy sources such as implementing solar power or wind power, walking or biking, and driving electric cars, we can reduce our use of fossil fuels and carbon footprint, thus decreasing the amount of carbon dioxide polluting and warming our atmosphere and oceans. While underwater and not always visible, coral reefs are truly a vital part of our ecosystem and need to be cherished and protected for generations to come.


Baird, A. H., & Marshall, P. A. (2002, July 18). Mortality, growth and reproduction in scleractinian corals following bleaching on the Great Barrier Reef. Retrieved from

Chin, A., Kyne, P. M., Walker, T. I. and McAuley, R. B. (2010), An integrated risk assessment for climate change: analyzing the vulnerability of sharks and rays on Australia’s Great Barrier Reef. Global Change Biology, 16: 1936–1953. doi:10.1111/j.1365-2486.2009.02128.x

Graham, N. A., McClanahan, T. R., MacNeil, M. A., Wilson, S. K., Polunin, N. V., Jennings, S., . . . Sheppard, C. R. (2008, August 27). Climate Warming, Marine Protected Areas and the Ocean-Scale Integrity of Coral Reef Ecosystems. Retrieved from

Rosa, R., Baptista, M., Lopes, V. M., Pegado, M. R., Paula, J. R., Trubenbach, K., . . . Repolho, T. (2014, August 13). Early-life exposure to climate change impairs tropical shark survival. Retrieved November 2, 2017, from

Clean, Clear, and Under Environmental Control: The Coal Mining Industry’s Impact on the Great Barrier Reef

By Casey Dresbach, SRC Intern

Australia’s Great Barrier Reef is home to 348,000 km (approximately 216237.175 miles) of marine ecosystems, an expansive realm is almost equivalent to the size of Germany. However, its grand location is at mercy to shipping channels, rail transport networks, major ports, and most detrimental, several coal mines. In July 2015, the World Heritage Committee called attention to the consequences of these coal deposits. Climate change, poor water quality, and coastal development are jeopardized for industrial preference. This multi-billion dollar coal industry is great economically but scientifically, the cons outweigh the pros. They are not particularly fixing anything. They seem to touch upon the short-term effects and not the long term. Research has shown that the integration of both short and long term impacts could potentially serve a far more effective plan for change.

Aerial Shot of Reef JPEG aligned center (Caption: Photograph of The Great Barrier Reef shot from a helicopter ride over the Reef at the Witsunday Islands, Australia.).

Photograph of The Great Barrier Reef shot from a helicopter ride over the Reef at the Whitsunday Islands, Australia.).

Coal power plant emissions contain several toxic elements that suffocate the environment. Global warming comes hand in hand with the emissions as far too much C02 is released into the air. Not only do those emissions affect the air but also the ocean’s pH level.  Ocean acidification becomes the reality, which ultimately leads to bleaching of the corals. Environmental impact statements (EISs) are currently instated to assist Australian Governments and Queensland to consider the impact of new coal mining proposals when deciding whether to approve them and inform the development of appropriate conditions for environmental management. Their role is to describe the environment’s current state which is extremely beneficial but the problem here is that they only report direct local impacts of mining operations and do not consider the indirect impacts of the mines at a broader spatial or temporal scale. Australia’s Reef is massive and the EISs do not consider its vastness. It is so crucial to understand the incremental accumulation of impacts, which have led to its own decline.

Consequences of Coal Industry JPEG aligned in text to the left (Caption: Schematic condition of a mine fire configuration, with emissions of dust, fine particles, radon, mercury vapor, CO, CO2, NOx, SO2, etc… source pollution and gas contributing to the greenhouse effect.).

Schematic condition of a mine fire configuration, with emissions of dust, fine particles, radon, mercury vapor, CO, CO2, NOx, SO2, etc… source pollution and gas contributing to the greenhouse effect.).

A World Heritage Site is a place that is listed by the United Nations Educational, Scientific and Cultural Organization (UNESCO) as being of special physical significance. The Great Barrier Reef is categorized as such and the failure of the EISs to consider the progressive factors coal mining inundates has led to sharp decreases in World Heritage values.

An alternative assessment to the EISs is the Cumulative Impact Assessment (CIA) which systematically analyzes, evaluates, and predicts cumulative environmental change over time and across a grand spatial extent of a particular environment, focusing on pressures of interactions. For example, they would hone into the negatives of coal mining in combination with already polluted land from said mining. They might also combine such interaction with the present coastal development and its potential impact on climate change. CIAs are all encompassing and they focus on the broader, the potential, what could happen in time to come.

We should make the CIA the primary choice of assessment even though there are barriers to cumulative impact assessments. The Reef 2050 Plan is the framework set for protecting and managing the Great Barrier Reef from 2015 to 2050. The issue is that it hasn’t managed to establish accuracy in long-term research models. They focus on qualitative studies rather than the broader interactive research to better understand potential problems in the future. The continuing of such failure will send us back to EISs, which are far from influential leading to more piecemeal decisions that ignore the lengthy and extensive accumulation of impacts responsible for the Reef’s decline.

Moving forward, independent CIA commissions should be instated to se the terms of reference, review the assessment’s outputs by deeming them continuous or not, and initiating public input by ensuring well established time frames and focusing on the long term issues. The Great Barrier Reef should most definitely have precedence over the coal industry because coal isn’t the hottest commodity today. Given its predicted to slow anyway, Australia Bank is no longer planning to fund mining projects. Neither are Deutsche Bank, HSBC, Morgan Stanley, Citigroup and other lenders because they’re nervous of jeopardizing their reputations. The consequences the coal industry allocates to the environment are no secret yet the trade still seems to continue its operation year after year. All potential funders are aware of the negatives and don’t want their names paired with such negativity. We need to standardize and focus on the long term issues of coal mining and less so on the business or monetary gains from the industry.



Ackerman, S. (2009, December 27). Amazing Great Barrier Reef 1. Retrieved January 11, 2015, from Wikimedia Commons:

Bretwood Higman, G. T. (n.d.). Coal Seam Fire. Retrieved from Ground Truth Trekking:

Grech, A., R. L. Pressey, and J. C. Day. “Coal, Cumulative Impacts, and the Great Barrier Reef.” Conservation Letters (2015).


Patterns of serial exploitation of sea cucumbers in the Great Barrier Reef Marine Park

By Jake Jerome, RJD Graduate Student and Intern

There is no doubt that overfishing is a major threat to ocean ecosystems. When most people think of overfishing, they think of the over harvesting of fish species that many in the world rely on. However, there are species besides fish that face the threat of exploitation. Eriksson and Byrne found in 2013 that the tropical sea cucumber fishery in Australia’s Great Barrier Reef Marine Park (GBRMP) is following patterns of overexploitation.

To reach this conclusion, the authors performed a meta-analysis of catches in the fishery from 1991 to 2011 by reviewing data published in peer reviewed literature and fisheries reports.  From their analysis they found that the sea cucumber fishery initially focused only on harvesting high-valued species but shifted towards lower-valued species over time. The initial target was black teatfish (Holothuria whitmaei) until 1999, when a 70% decline in the catch of black teatfish was noted, and subsequent effort then shifted towards the white teatfish (H. fuscogilva). The fishery was subsequently diversified after the collapse of the black teatfish to include other species of medium and low-value. Despite the addition of these new species into fishery efforts in 1999, most of them no longer appeared on catch lists as of 2005. Two new key target species prompted an increase in the harvest during the 2004 to 2011 period, though they were species of lower value than the teatfish.


Catch records from the Queensland East Coast bêche-de-mer fishery (ECBDMF). The three areas indicated in the figure are conceptual periods in the fishery based on the composition of catch. (Eriksson and Byrne 2013)

A major problem with the sea cucumber fishery in the GBRMP is the lack of information about the original population sizes of the species targeted. Without a baseline of knowledge, predicting the critical threshold beyond which a species can no longer recovery is extremely difficult. Because of this, many of these species may have been fished past their critical threshold and may not be able to avoid extinction.

With Australia being a developed high-income country, it is expected that management of fisheries is better resourced then it would be in low developed countries. This study showed that serial expansion and the quick replacement of high-valued species with lesser valued individuals is not limited to fishing practices in low-income developing countries and is a common trend in the overexploited global sea cucumber fishery. This is important to the fishery because it points out gaps in the management of sea cucumbers. Although Australia tried to manage this particular fishery with a rotational zoning scheme (RZS) in 2004, it proved to be either too late or ineffective. In addition, this study illustrates that providing relatively few fishermen access to a large fishing area through licensing, does not necessarily transfer to sustainable sea cucumber harvest.


White teat sea cucumber (Holothuria fuscogilva). (Stacy Jupiter/Marine Photobank)

In the end, it is clear that more studies need to be done on population sizes of tropical sea cucumbers to accurately assess their vulnerability. Without being able to monitor populations as they are harvested, effectively managing the many now threatened or endangered sea cucumbers will continue to be a problem.


Eriksson, H. and Byrne, M. (2013), The sea cucumber fishery in Australia’s Great Barrier Reef Marine       Park follows global patterns of serial exploitation. Fish and Fisheries. doi: 10.1111/faf.12059

The Great Barrier Reef

By Amanda Wood, RJD Intern

The Great Barrier Reef is undoubtedly one of the most famous coral reef systems in the world. The Marine Protected Area is an important source of revenue for Australia, especially in the Queensland region. In the year 2012 alone, the reef attracted over 1.5 million visitors from across the globe with its captivating beauty and astonishing diversity.

Despite its high visitation numbers, the reef has seen better days. Located just off the northeastern coast of Queensland, the reef is in close proximity to the main agricultural region of Australia. As rivers in the catchment area flow towards the reef, it is exposed to terrestrial runoff throughout the year.

When agriculture consisted of small, local farms, runoff was not a major cause for concern. However, the introduction of chemical pesticides coupled with an increased use of fertilizers shifted traditional farming to large-scale, industrialized agriculture (van Dam et al. 2011). As a result, terrestrial runoff containing sediments, pesticides, and inorganic nutrients are transported to the Great Barrier Reef. Each of these pollutants poses a distinct threat to the reef system, and there is evidence that increasing ocean temperatures could exacerbate their effects(Waterhouse et al. 2012).

Sedimentation occurs when rivers pick up soil particles from the land (e.g. agricultural regions) and carry them to large bodies of water, in this case the Pacific Ocean. The particles are then deposited along the coast, and remain suspended in the water column until conditions allow them to settle. In the Great Barrier Reef, sediments tend to be distributed within 50km of the coastline (Devlin and Brodie 2005). While the particles are floating freely, they cause the water to become cloudy. This cloudiness, known as turbidity, makes it difficult for aquatic plants to absorb enough sunlight to conduct photosynthesis. Seagrasses, algae, and phytoplankton experience a reduced photosynthetic output as a result. As primary producers of the marine food web, these organisms are vital to the survival of a marine ecosystem. Their reduced photosynthetic abilities place stress on the many organisms that rely on them for energy and shelter.



The Great Barrier Reef is exposed to terrestrial runoff, as pictured above. Photo by NASA Goddard Space Flight Center, via Wikimedia Commons

Corals experience another risk as many of the corals in the Great Barrier Reef have a symbiotic relationship with tiny algae organisms called zooxanthellae. These symbionts, of the genus Symbiodinium, are housed within the tissues of corals, and give the animals their iconic colors. Through their photosynthetic processes, the algae provide corals with supplemental energy in the form of carbon, which many of the corals seem to use for reproduction and thickening of tissues.  When exposed to high levels of turbidity, the zooxanthellae cannot produce as much photosynthetic carbon, and corals suffer. Some studies have shown that corals subjected to high sedimentation rates reabsorb their eggs in order to compensate for energy deficiencies(Cantin et al. 2007).  When the corals do not reproduce, the future of the reef is at stake.

Chemical fertilizers also present a threat to marine photosynthetic organisms. Though Australia has over 200 chemical pesticides authorized for use, PS-II herbicides may be the greatest cause for concern.  These herbicides inhibit a specific electron receptor protein within chloroplasts, effectively preventing plants from synthesizing carbon. They are heavily used in the sugarcane industry of Australia to abolish weeds. Unfortunately they are also carried to the coast by terrestrial runoff, and have the undesired effect of harming photosynthetic organisms in the marine environment. These marine phototrophs, such as Symbiodinium spp., use the same PS-II protein found in land plants. Some research has shown that when corals are exposed to PS-II herbicides, the zooxanthellae fail to produce enough carbon to maintain a stable symbiotic relationship. The corals then expel the symbionts, a phenomenon known as coral bleaching (van Dam et al. 2011).



Above, a brain coral experiences bleaching. Photo by Smckenna, via Wikimedia Commons

The final major class of marine pollutants is inorganic nutrients. The nutrients of primary concern are dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorous (DIP). Nitrogen and phosphorous are naturally occurring, and can be introduced to an ecosystem through upwelling and fixation by marine organisms. However, the use of agricultural fertilizers introduces more nutrients to the natural environment. Fertilizers that are applied to agricultural fields are carried by rivers to the coast, and remain dissolved in the water for extended periods of time. Some research suggests that DIP and DIN can remain present until they reach salinities of at least 25 ppt. This means that the dissolved nutrients can be retained in the marine water column as far as 200 km away from the river that deposited them. As a result, nutrients can be transported great distances, and impact countless ecosystems (Devlin and Brodie 2005).

The impacts of dissolved nutrients can be devastating. When reefs are exposed to DIP and DIN, they often experience macroalgae blooms. As macroalgae compete with corals for resources, nutrients, and substrate, a macroalgae bloom can effectively dominate corals and shift the ecological balance of the reef. The corals themselves are threatened by macroalgae, but the multitudes of animals that live among the corals also suffer from the change (Fabricius 2005).  With this in mind, the growing concentration of fertilizer use in the GBR catchment area is of grave concern to scientists.

In light of the many reports of pollution in the Great Barrier Reef system, the Australian and Queensland governments are makings strides to reduce agricultural runoff. In 2003 Australia released its Reef Quality Protection Plan with the intention of reducing the pollutant load in the GBR catchment area. The plan was revised in 2009 with more concrete goals: reduce concentrations of nitrogen, phosphorous, and pesticides 50% by the year 2013. Also, the plan aimed to reduce the load of suspended sediments 20% by 2020 (Brodie et al. 2012).

Queensland released its own “Reef Protection Package” in 2009. This package created distinct water quality guidelines for the GBR area, and made PS-II herbicides a high priority for management. A new class of environmentally relevant activity was determined for sugarcane and beef grazing, and introduced a requirement for industries to keep records of any application of chemicals and fertilizers. Also, certain high-risk operators must have an accredited environmental risk management plan (ERMP) in order to decrease their negative impact on the GBR system (King et al. 2013).

Though it is still unclear whether or not the new regulation schemes of Australia and Queensland will be effective, there is hope for the Great Barrier Reef. The reef system is not only an integral part of the economic stability of Australia, but also an exquisite example of marine diversity. As such, it has been the focus of scientific research by marine biologists, ecologists, and coral reef scientists for decades. With so much information available about the functioning and health of the reef system, Australian policy makers have a unique opportunity to save their prized resource. With a deeper understanding of reef interactions, government officials can make more informed, and ultimately more effective, decisions in regards to reef management (King et al. 2013).




  1. Brodie JE, Kroon FJ, Schaffelke B, Wolanski EC, Lewis SE, Devlin MJ, Bohnet IC, Bainbridge ZT, Waterhouse J, Davis AM (2012) Terrestrial pollutant runoff to the Great Barrier Reef: An update of issues, priorities and management responses. Mar Pollut Bull 65: 81-100
  2. King J, Alexander G, Brodie J (2013) Regulation of pesticides in Australia: The Great Barrier Reef as a case study for evaluating effectiveness. Agriculture, Ecosyst, and Environ 180: 54–67
  1. Cantin NE, Negri AP, Willis BL (2007) Photoinhibition from chronic herbicide exposure reduces reproductive output of reef-building corals. Mar Ecology Press Series 344: 81–93
  2. Devlin MJ, Brodie J (2005) Terrestrial discharge into the Great Barrier Reef Lagoon: nutrient behavior in coastal waters. Mar Pollut Bull 51: 9-22
  3. Fabricius KE (2005) Effects of terrestrial runoff on the ecology of corals and coral reefs: review and synthesis. Mar Pollut Bull 50:125-146
  1. Van Dam JW, Negri AP, Uthicke S, Mueller JF (2011) Ecological Impacts of Toxic Chemicals. In: Sánchez-Bayo F, van den Brink PJ, Mann RM (eds) Ecological impacts of toxic chemicals. Bentham Books, pp 187-211
  2. Waterhouse J, Brodie J, Lewis S, Mitchell A (2012) Quantifying the sources of pollutants in the Great Barrier Reef catchments and the relative risk to reef ecosystems. Mar Pollut Bull 65: 394-406




Photo attributions:

  1. Sedimentation of GBR: By NASA Goddard Space Flight Center (Flickr: Heavy Sediment along the Queensland Coast) [CC-BY-2.0 (], via Wikimedia Commons
  1. Brain coral:  By Smckenna (Own work) [CC-BY-SA-3.0 ( or GFDL (], via Wikimedia Commons