1. Running head: DREDGING GBR IMPACT CORAL 1
(Doubilet, 2011)
Casey Epperson
Dredging on the Great Barrier Reef:
An Overview of Impact with Special Focus on Coral
October 29, 2015

2. DREDGING GBR IMPACT CORAL 2
Introduction
Stretching over two thousand kilometers off the coast of Queensland, Australia is the Great
Barrier Reef, the world’s largest coastal reef ecosystem, and a United Nations Educational,
Scientific and Cultural Organization (UNESCO) World Heritage site since 1981. Within the Great
Barrier Reef’s diverse ecosystem of coral reefs and sea grass beds are thousands of species reliant
on the reef; including around 400 types of corals, at least 1,500 fish species, green sea turtles, and
many other species that utilize the reef as a key element in their survival (Great Barrier Reef, n.d.;
Brodie, 2014). The establishment of the Great Barrier Reef Marine Park and acceptance as a
UNESCO’s World Heritage sites was critical in the protection of the reef from ecologically
destructive processes then known to cause degradation, such as coral mining and fracking for oil
reserves (Kearney & Farebrother, 2014, p. 254). Although the reef is a World Heritage site and
one of the most prominent landmarks of Australia, it is slowly being degraded through the process
of dredging. The dredging occurring off the coast of Queensland is a result of port development to
increase access. The Great Barrier Reef serves as an obstacle along the coast that prevents ships
from reaching the shore in an efficient and timely matter.
The accessibility of ports in Queensland politically and economically outweighs the need
for conservation from degradation of the Great Barrier Reef, but only in the interim, as the full
long-term effects of dredging have not been thoroughly explored for all dredging sites or the
majority of coral species (Erftemeijer, Riegl, Hoeksema, & Todd, 2012). However, it is an
established fact that dredging causes an increase in turbidity and sedimentation that can potentially
negatively affect biota, such as the live coral and their reproductive processes. There is also
concern regarding habitat destruction of the Great Barrier Reef caused by the creation of access
lanes in the reef for ports and the resulting increased turbidity from fractured coral (Erftemeijer et

3. DREDGING GBR IMPACT CORAL 3
al., 2012). There is also evidence that dredged material, spoil, has a great possibility of leaking
heavy metals out into the open waters. Since the spoil from the Great Barrier Reef is being dumped
within the UNESCO World Heritage site borders, it can only be assumed that there is a potential
for heavy metals leakage. This issue is not fully explored within the literature on the reef, but the
notion of heavy metal leakage is dismissed by the Australian government and port management
companies, so it will only be touched upon in this paper.
Analysis
Dredging is an engineering practice associated with navigable waters and conducted
primarily by government entities. This worldwide activity is an engineering solution to economic
concerns related to port and marina access by cargo ships. The act of dredging, excavation of the
bottom sediments of a navigable water body, increases turbidity and sedimentation with negative
impacts to habitats. The more diverse a habitat, the greater the impact of dredging and this is
particularly relevant to the complex nature a reef habitat such as the Great Barrier Reef of
Australia, the largest known coral reef system in the world. Currently, the Queensland coast has
ports in Cairns, Townsville, Abbot Point, Hay Point, and Gladstone that are underway for dredging
expansions, beginning with Gladstone (Brodie, 2014). The increased amount of dredging in the
Gladstone, Hay Point and Abbot Point ports are desired for the expansion of the coal industry’s
exports.
Turbidity refers to the visual clarity of water, a high turbidity indicates muddy water, while
a low turbidity describes clear water (International Association of Dredging Companies, 2015).
The total suspended solids is related to turbidity through a measurable indication of how much
sediment is in the water, as opposed to turbidity which is determined by the size, color, and shape

4. DREDGING GBR IMPACT CORAL 4
of the particles. Sedimentation is the deposit of sediment materials, such as rock and soil particles.
The Great Barrier Reef has two varieties of reefs, nearshore fringing and barrier reef areas. Both
of these are affected by dredging through drastic increases in turbidity and sedimentation, the two
most commonly documented threats to coral reefs, with sedimentation affecting nearshore fringing
reefs more frequently (Jones, Ricardo, & Nergi, 2015). Turbidity and sedimentation have been
documented to negatively affect every stage of coral development from reproduction to coral
maturity, including leading to the mortality of corals.
Some species of hard corals are broadcast spawning species with the gametes being
fertilized externally in the open waters of the reef (Jones et al., 2015). Spawning is adversely
effected when water quality is threatened by increases in turbidity caused by suspended-sediment
concentrations. This is especially the case when there is a high concentration of silt-sized particles,
which are approximately the size of coral sperm. These suspended silt inhibit breeding by their
ability to bind into egg-sperm bundles to or entirely block the gametes from rising, a crucial
component in coral breeding. Although this interference in breeding is consistent with higher
levels of turbidity, a slight increase in suspended sediment concentrations has shown to protect the
new formed larvae at the surface from damaging ultraviolet rays. Jones et al. has demonstrated
that there are positive indicators for increased turbidity in that the cloudiness offers protection of
larvae from predators which is attributable to a lack of visibility (2015). However, a lower amount
of light is has also been shown to encumber coral larvae’s development suggesting a need to
understand the balance between acceptable levels of turbidity and potential negative impacts
(Brodie, 2014).
Mature coral can also be negatively affected by turbidity from dredging plumes resulting
in a high suspended-sediment concentration (McMahon, Lavery, & Mulligan, 2011). Suspended

5. DREDGING GBR IMPACT CORAL 5
sediments have the potential of decreasing the amount of obtainable light reaching habitats beyond
the shallow waters likely due to absorption by the darker suspended sediment. Without a suitable
quantity of light for photosynthesis, the zooxanthellae algae, a symbiotic partner of many coral
species, cannot complete the food production process. Since zooxanthellae live inside coral
species’ gastrodermis tissues, the inability to nourish themselves and subsequently support the
coral coupled with the lack of mobility for coral results in mortality for both (Erftemeijer et al.,
2012).
The polyps of the coral are the breeding grounds for corals that exhibit internal fertilization.
These polyps are critical to the larvae’s development, but sedimentation and temporary smothering
from dredging causes the polyps obstructed by sediment thus preventing or delaying the larvae
from forming. The structure of the coral reef has an increased sensitivity to sedimentation and
through sediment rejection can actively defend against particles through inflation and mucus
production (Erftemeijer et al., 2012). If there is a strong current turbulence, such as in with the
inshore fringing reefs of the Great Barrier Reef, smaller amounts of sedimentation can be passively
detached by continuous waves. If there is complete smothering of corals, active cleaning occurs as
polyps defend against particles through increase polyp inflation and mucus production (Erftemeijer
et al., 2012). The factors playing into the coral’s use of active sediment rejection or passive
cleaning depend on the species of the corals, the physical characteristics and amount of sediment,
and the turbulence of the area.
Although corals have been able to remove sedimentation, the processes of sedimentation
and removing sediment hinder the larvae from settling into the polyps and affect the mature coral.
Overtly large amounts of sediment can lead to burial of corals and necrosis, especially of the coral
reefs of the Great Barrier Reef that have weaker water currents than inshore fringing reefs, which

6. DREDGING GBR IMPACT CORAL 6
have greater turbulence due to wave activity (Erftemeijer et al., 2012). Yet, when chronic dredging
and spoil dumping is not assessed, that increase in mucus production to reject sediment can cause
a population boom of bacteria. This can not only harm the coral, but the other marine species
dependent on the reef, which have been shown to decline as chronic turbidity increases.
A supplementary concern to consider when dredging through the Great Barrier Reef to
create shipping lanes is the physical structure of the coral material in the spoil that is being
transported (Erftemeijer et al., 2012). When reefs are dredged the destruction caused by crushing
the coral is intensified as the coral breaks down further into particles that become the size of fine
silt. Although this can be mistaken as simply an additional increase in suspended sediment, the
silt-sized sediments are more harmful than larger particles. Because their chemical properties
permit them to colloidally bind nutrients, these silt-sized particles remain buoyant for sustained
periods of time and are able to cross large bodies of water resulting in adverse effects of nutrient
depletion across a greater portion of surface water than the defined site of dredge and fill. Sub-
lethal effects of dredging such as nutrient deficiency are reducing the growth of coral, which was
previously in jeopardy by the higher temperatures from climate change causing massive coral
mortality.
Heavy metal leakage and other toxic materials is a major concern about the spoil from
dredging, but the dredging, shipping, and port management, companies suggest that this is not a
concern with dredging in the Great Barrier Reef (Ports Australia, 2014). As the Ports Australia
stated in their Dredging and Australian Ports: Subtropical And Tropical Ports report, dredged
sediment undergoes a chemical analysis to test for toxic materials, including polychlorinated
biphenyl (PCB). Any spoil with identifiable toxins is then dumped inland instead of the ocean,
which raises more questions than this paper can answer. The notion of the dredging companies

7. DREDGING GBR IMPACT CORAL 7
analyzing spoil has been met with justifiable skepticism by dredging opponents and activists. In
2011, the seas off the Queensland coast experienced a major loss of marine species due to disease
(Brodie, 2014). Although the Official Queensland and Australian Government reports suggested
floods from agricultural areas, the effects of dredging and a potential heavy metal leakage was
only briefly considered only once news from the inaccurately monitoring of the water quality
monitoring programs established by the dredging companies began making headlines in the news.
It has been suggested that the bundles once containing the spoil had leaked the toxins and that an
independent group analyze the reports and have their own monitoring of water and spoil bundle
quality, but this has yet to be resolved.
Management of the processes in dredging and further research into its affects should be
used into order to protect marine ecosystems, such as the Great Barrier Reef. The Australian
government and port companies have economic motives behind dredging waterways for cargo
ships exporting their goods. In order to have a just report on the effects of dredging, there should
also be at least one independent group analyzing the water quality from dredging and dumping soil
with a baseline water quality that shows the changes between the processes. There needs to be
special measures to insure that spoils containing heavy metals are properly disposed of, possibly
creating a more safe dumping system for those that are, and what steps are being taken to assure
that turbidity and sedimentation effects are being reduced. One of the methods to protect coral that
has been implemented since 1993 is that dredging activities must cease during the coral’s
spawning. This window is from five days before gametes are released to 7 days afterwards, and
has been shown to lessen the destructive effects on coral breeding. Another factor that should be
taken into account is the capacity for turbidity and sedimentation in areas. Along the inshore
fringing reef of the Great Barrier Reef have a strong water current from wave activity, while the

8. DREDGING GBR IMPACT CORAL 8
waters near the barrier reefs out shore have a low turbulence. A closer monitoring of the barrier
reef is needed as dredging is cutting through the reef in order for cargo ships to gain access to the
Queensland ports. This process is creating a more silt-sized turbidity that is greatly affecting the
survival of coral.
Conclusion
The Great Barrier Reef’s diverse ecosystem containing thousands of species that utilize the
reef are in jeopardy as the ports off the Queensland coast are expanding their cargo shipping lanes
for greater access. The Great Barrier Reef serves as an obstacle along the coast for these cargo
ships that seemingly hinder productively to circumvent the reef. Dredging the bed of the reef to
create deeper waterways is causing ecological damage to the reef. Turbidity and sedimentation the
most common threats to coral in the Great Barrier Reef. Turbidity effects the reproductive cycles
of coral by hindering external reproduction through silt-sized, and thus sperm-sized, particles
attaching to the gametes. Turbidity also inflames coral polyps and increases mucus production
hindering breeding and cause bacteria to flourish in the environment. High amounts of
sedimentation completely bury coral reefs, but at lower amounts of chronic sedimentation can
cause mortality as well. Overall, dredging negatively affects the marine ecosystem of the Great
Barrier Reef for the sake of easy commercial profits. Water quality monitoring programs and cut
off periods during coral breeding could reduce the harm caused by dredging, as this practice likely
will not discontinue.

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References Cited
(Formatted for the American Psychological Association)
Brodie, J. (2014). Dredging the Great Barrier Reef: Use and misuse of science. Estuarine, Coastal
and Shelf Science, 142, 1-3. doi:10.1016/j.ecss.2014.01.010
Doubilet, David. (2011) Diver among the corals [Online Image]. From
http://ngm.nationalgeographic.com/2011/05/great-barrier-reef/holland-text
Erftemeijer, Paul L.A., Riegl, Bernhard, Hoeksema, Bert W., & Todd, Peter A. (2012).
Environmental impacts of dredging and other sediment disturbances on corals: A review.
Marine Pollution Bulletin, 64(9), 1737-1765. doi:10.1016/j.marpolbul.2012.05.008
Great Barrier Reef. (n.d.). Retrieved September 30, 2015, from http://whc.unesco.org/en/list/154
International Association of Dredging Companies. (2015). Facts About Turbidity & Dredging: An
Information Update from the IADC.
Jones, R., Ricardo, G., & Negri, A. (2015). Effects of sediments on the reproductive cycle of corals.
Marine Pollution Bulletin. doi:10.1016/j.marpolbul.2015.08.021
Kearney, Bob, & Graham Farebrother. (2014). Chapter Seven: Inadequate Evaluation and
Management of Threats in Australia's Marine Parks, Including the Great Barrier Reef,
Misdirect Marine Conservation. In: Magnus L. Johnson and Jane Sandell, (eds), Advances
in Marine Biology (Vol. 69, p. 253–288). Elsevier Ltd.
McMahon, Kathryn, Lavery, Paul S., & Mulligan, Michael. (2011). Recovery from the impact of
light reduction on the seagrass Amphibolis griffithii, insights for dredging management.
Marine Pollution Bulletin, 62(2), 270–283. doi:10.1016/j.marpolbul.2010.11.001
Ports Australia. (2014). Dredging And Australian Ports: Subtropical And Tropical Ports. Sydney,
New South Wales, Australia: RMC Pty Ltd.

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Casey Epperson
Global Conservation
September 17, 2015
Paper Topic
I want to examine the impact of fracking on the Great Barrier Reef with a focus on the
legislature influencing the amount and placement of fracking and how the biota (coral, fish,
turtles, etc.) is impacted.