Environmental threats to the Great Barrier Reef
Encyclopedia
The Great Barrier Reef
is the world's largest coral reef
system, composed of roughly 3,000 individual reefs and 900 islands that stretch for 2,600 kilometres (1,616 mi) and cover an area of approximately 344,400 km². The reef is located in the Coral Sea
, off the coast of Queensland
in northeast Australia. A large part of the reef is protected by the Great Barrier Reef Marine Park
.
The Great Barrier Reef's environmental pressures include lowered water quality from runoff including suspended sediment, excess nutrients, pesticides, and fluctuations in salinity. The effects of climate change, including increased temperatures, storms and coral bleaching. Cyclic outbreaks of the crown-of-thorns starfish
, overfishing which disrupts food chains, and shipping routes which can result in oil spills or improper ballast discharge also damage to the reef.
Thirty "major rivers" and hundreds of small streams comprise the Great Barrier Reef catchment area
, which covers 423000 square kilometres (163,321.2 sq mi) of land. Queensland has several major urban centres on the coast including Cairns, Townsville, Mackay
, Rockhampton
and the industrial city of Gladstone
. Dredging in the Port of Gladstone
is raising concern after dead and diseased fish where found in the harbour. Cairns and Townsville are the largest of the coastal cities, with populations of approximately 150,000 each.
There are many major water quality variables affecting coral reef health including water temperature
, salinity
, nutrients, suspended sediment
concentrations, and pesticides. The species in the Great Barrier Reef area are adapted to tolerable variations in water quality however when critical thresholds are exceeded they may be adversely impacted. River discharges are the single biggest source of nutrients, providing significant pollution of the Reef during tropical flood events with over 90% of this pollution being sourced from farms.
Due to the range of human uses made of the water catchment area adjacent to the Great Barrier Reef, some 700 of the 3000 reefs are within a risk zone where water quality
has declined owing to the naturally acidic sediment and chemical runoff
from farming, and to coastal development and the loss of coastal wetland
s which are a natural filter. Industries in the water catchment area are cotton growing, comprising approximately 262 km²; 340 dairy farms with an average area of 2 km² each, 158 km² cattle grazing, 288 km² horticulture including banana growing, sugarcane farming, and cropping of approximately 8,000 km² wheat, 1,200 km² barley, and 6,000 to 7000 km² sorghum and maize. Fertiliser use in the cotton, dairy, beef, horticulture and sugar industries is essential to ensure productivity and profitability. However, fertiliser and byproducts from sugar cane harvesting methods form a component of surface runoff into the Great Barrier Reef lagoon. Principal agricultural activity is sugar cane farming in the wet tropics and cattle grazing in the dry tropics regions. Both are considered significant factors affecting water quality. Copper
, a common industrial pollutant in the waters of the Great Barrier Reef, has been shown to interfere with the development of coral polyps. Flood plumes are flooding events associated with higher levels of nitrogen and phosphorus. In February 2007, due to a monsoonal climate system
, plumes of sediment runoff have been observed reaching to the outmost regions of the reef.
Runoff is especially concerning in the region south of Cairns, as it receives over 3000 mm of rain per year and the reefs are less than 30 kilometres (18.6 mi) away from the coastline. Farm run off is polluted as a result of overgrazing and excessive fertiliser and pesticide use. Mud pollution has increased by 800% and inorganic nitrogen pollution
by 3,000% since the introduction of European farming practices on the Australian landscape. This pollution has been linked to a range of very significant risks to the reef system, including intensified outbreaks of the coral-eating Crown of Thorns Starfish which contributed to a loss of 66% of live coral cover on sampled reefs in 2000.
It is thought that the mechanism behind excess nutrients affecting the reefs is due to increased light and oxygen competition
from algae
, but unless herbivory is unusually low, this will not create a phase shift from the Great Barrier Reef being primarily made up of coral to being primarily made up of algae.
It has been suggested that poor water quality due to excess nutrients encourages the spread of infectious disease
s among corals. In general, the Great Barrier Reef is considered to have low incidences of coral diseases. Skeletal Eroding Band
, a disease of bony corals caused by the protozoan Halofolliculina corallasia
, affects 31 species of corals from six families on the reef. The long-term monitoring program has found an increase in incidences of coral disease in the period 1999-2002, although they dispute the claim that on the Great Barrier Reef, coral diseases are caused by anthropogenic pollution.
Elevated nutrient concentrations result in a range of impacts on coral communities and under extreme conditions can result in a collapse. It also affects coral by promoting phytoplankton growth which increases the number of filter feeding
organisms that compete for space. Excessive inputs of sediment from land to coral can lead to reef destruction through burial, disruption of recruitment success or deleterious community shifts. Sediments affect coral by smothering them when particles settle out, reducing light availability and potentially reducing photosynthesis and growth. Coral reefs exist in seawater salinities from 25 to 42%. Salinity impacts to corals are increased by other flood-related stresses.
The Australian and Queensland Governments have committed to act to protect the reef, and water quality monitoring programmes are in place. However, the World Wildlife Fund has criticised that progress against these commitments has been slow, saying that as many as 700 reefs are at risk from sediment runoff.
Most people believe that the most significant threat to the status of the Great Barrier Reef and of the planet's other tropical reef ecosystem
s is climate change
, consisting chiefly of global warming
and the El Niño effect
. Many of the corals of the Great Barrier Reef are currently living at the upper edge of their temperature tolerance, as demonstrated in the mass coral bleaching
events of the summers of 1998, 2002 and 2006. In February 2007, the current threat of mass coral bleaching was assessed as being "low" due to a monsoon
al climate system, although sites displaying some coral bleaching were monitored.
As demonstrated in 1998, 2002 and 2006, corals expel their photosynthesis
ing zooxanthella
e (which provide up to 90% of the coral’s energy requirements) and turn colourless, revealing their white calcium carbonate
skeletons, under the stress of waters that remain too warm for too long. At this stage the coral is still alive, and if the water cools, the coral can regain its zooxanthellae. If the water does not cool within about a month, the coral will die of starvation. Australia experienced its warmest year on record in 2005. Abnormally high sea temperatures during the summer of 2005-2006 have caused massive coral bleaching in the Keppel Island
group.
Most scientists studying the issue believe that climate change poses a massive threat to the future of the Great Barrier Reef. A draft report by the UN
Intergovernmental Panel on Climate Change
, the world's preeminent gathering of climate scientists, states that the Great Barrier Reef is at grave risk and will be "functionally extinct" by 2030, warning that coral bleaching will likely become an annual occurrence.
However, a few scientists hold that coral bleaching may in some cases be less of a problem than the mainstream believes. Professor Ridd, from James Cook University in Townsville was quoted in The Australian (a conservative newspaper) as saying; “They are saying bleaching is the end of the world, but when you look into it, that is a highly dubious proposition”. Research by scientist Ray Berkelmans “... has documented astonishing levels of recovery on the Keppel outcrops devastated by bleaching in 2006.” A related article in The Australian newspaper goes on to explain that; “Those that expel their zooxanthellae have a narrow opening to recolonise with new, temperature-resistant algae before succumbing. In the Keppels in 2006, Berkelmans and his team noticed that the dominant strain of zooxanthellae changed from light and heat-sensitive type C2, to more robust types D and C1.”
Nevertheless, most coral reef researchers anticipate severely negative effects from climate change already occurring, and potentially disastrous effects as climate change worsens. The future of the Reef may well depend on how much the planet's climate changes, and thus, on how high atmospheric greenhouse gas concentration levels are allowed to rise. On 2 September 2009, a report by the Australian Great Barrier Reef Marine Park Authority revealed that if carbon dioxide levels reached 450 parts per million corals and reef habitats will be highly vulnerable. If carbon dioxide levels are managed at or below 380 parts per million they will be only moderately vulnerable and the reefs will remain coral-dominated.
Global warming may have triggered the collapse of reef ecosystems throughout the tropics. Increased global temperatures are thought by some to bring more violent tropical storms, but reef systems are naturally resilient and recover from storm battering. Most people agree that an upward trend in temperature will cause much more coral bleaching; others suggest that while reefs may die in certain areas, other areas will become habitable for corals, and new reefs will form. However, the rate at which the mass bleaching events occur is estimated to be much faster than reefs can recover from, or adjust to.
However, Kleypas et al. in their 2006 report suggest that the trend towards ocean acidification
indicates that as the sea's pH
decreases, corals will become less able to secrete calcium carbonate. In 2009, a study showed that Porites corals, the most robust on the Great Barrier Reef, have slowed down their growth by 14.2% since 1990. It suggested that the cause was heat stress and a lower availability of dissolved calcium to the corals.
Climate change
and global warming
are one of the greatest threats to the reef. A temperature rise of between two and three degrees Celsius would result in 97% of the Great Barrier Reef being bleached every year. Reef scientist Terry Done has predicted that a one-degree rise in global temperature would result in 82% of the reef bleached, two degrees resulting in 97% and three degrees resulting in "total devastation". A predictive model based on the 1998 and 2002 bleaching events has concurred that a temperature rise of three degrees would result in total coral mortality.
Climate change has implications for other forms of life on the Great Barrier Reef as well - some fish's preferred temperature range
lead them to seek new areas to live, thus causing chick mortality in seabirds that prey on the fish. Also, in sea turtles, higher temperatures mean that the sex ratio of their populations will change, as the sex of sea turtles is determined by temperature. The habitat of sea turtles will also shrink.
The Crown-of-Thorns Starfish
is a coral reef predator which preys on coral polyps by climbing onto them, extruding its stomach over them, and releasing digestive enzyme
s to absorb the liquified tissue. An individual adult of this species can eat up to six square metres of living reef in a single year. Geological evidence suggests that the Crown-of-Thorns Starfish has been part of the Great Barrier Reef's ecology for "at least several thousand years", but there is no geological evidence for Crown-of-Thorns outbreaks. Large outbreaks of these starfish can devastate reefs. In 2000, an outbreak contributed to a loss of 66% of live coral cover on sampled reefs in a study by the CRC Reefs Research Centre. Although large outbreaks of these starfish are believed to occur in natural cycles, human activity in and around the Great Barrier Reef can worsen the effects. Reduction of water quality associated with agriculture can cause the crown-of-thorns starfish larva
e to thrive. Overfishing of its natural predators, such as the Giant Triton
, is also considered to contribute to an increase in the number of crown-of-thorns starfish. The CRC Reef Research Centre defines an outbreak as when there are more than 30 adult starfish in an area of one hectare
.
of keystone species
, such as the Giant Triton
and sharks, can cause disruption to food chain
s vital to life on the reef. Fishing also impacts the reef through increased pollution from boats, by-catch
of unwanted species (such as dolphins and turtles) and reef habitat destruction
from trawling
, anchors and nets. Overfishing of herbivore populations can cause algal growths on reefs. The Batfish
Platax pinnatus
has been observed to significantly reduce algal growths in studies simulating overfishing. Sharks are fished for their meat, and when they are part of bycatch, it is common to kill the shark and throw it overboard, as there is a belief that they interfere with fishing. As of 1 July 2004, approximately one-third of the Great Barrier Reef Marine Park
is protected from species removal of any kind, including fishing, without written permission. However, illegal poaching is not unknown in these no-take zones.
. The leading cause of shipping accidents in the Great Barrier Reef is human error.
Although the route through the Great Barrier Reef is not easy, reef pilots consider it safer than outside the reef in the event of mechanical failure, since a ship can sit safely while being repaired. 75% of all ships that use the Great Barrier Reef as a route use the inner route. On the outside, wind and swell will push a ship towards the reef and the water is deep right up to the reef so anchoring is impossible. Captain Cook in the Endeavour
nearly came to grief that way, being utterly becalmed and pushed towards the reef by the swell. Right up to within 80 metres (262 ft) of the Great Barrier Reef, the water was so deep that no ground (to anchor against) could be felt with 220 metres (722 ft) of line. There have been over 1,600 known shipwrecks in the Great Barrier Reef region.
Waste and foreign species discharged in ballast water from ships (when purging procedures are not followed) are a biological hazard
to the Great Barrier Reef. Tributyltin
(TBT) compounds found in some antifouling paint
on ship hulls leaches into seawater and is toxic to marine organisms and humans; efforts are underway to restrict its use.
In April 2010, the bulk coal carrier Shen Neng 1 ran aground on the Great Barrier Reef
causing the largest grounding scar to date and creating a oil slick of heavy fuel oil 2 nmi (3.7 km; 2.3 mi) long.
, after a 1923 paper suggested that it had the right rock formation to support "oilfields of great magnitude". After the Commonwealth Petroleum Search Subsidies Act of 1957, exploration activities increased in Queensland, including a well drilled at Wreck Island
in the southern Great Barrier Reef in 1959. In the 1960s, drilling for oil and gas was investigated throughout the Great Barrier Reef, by seismic and magnetic methods in the Torres Strait
, along "the eastern seaboard of Cape York
to Princess Charlotte Bay
" and along the coast from Cooktown to Fraser Island. In the late 1960s, more exploratory wells were drilled near Wreck Island in the Capricorn Channel, and near Darnley Island in the Torres Strait, but "all results were dry".
In 1970, responding to concern about oil spill
s such as the Torrey Canyon
, two Royal Commission
s were ordered "into exploratory and production drilling for petroleum in the area of the Great Barrier Reef". After the Royal Commissions, the federal and state governments ceased allowing petroleum drilling on the Great Barrier Reef. A study in 1990 concluded that the reef is too young to contain oil reserves
. Oil drilling remains prohibited on the Great Barrier Reef, yet oil spills due to shipping routes are still a threat to the reef system, with a total of 282 oil spills between 1987-2002.
Tropical cyclones are a cause of ecological disturbance to the Great Barrier Reef. The types of damage caused by tropical cyclones to the Great Barrier Reef is varied, including fragmentation, sediment plumes, and decreasing salinity following heavy rains (Tropical Cyclone Joy). The patterns of reef damage are similarly 'patchy'. From 1910–1999, 170 cyclones' paths came near or through the Great Barrier Reef. Most cyclones pass through the Great Barrier Reef within a day. In general, compact corals such as Porites fare better than branching corals under cyclone conditions. The major damage caused by Tropical Cyclone Larry
was to underlying reef structures, and breakage and displacement of corals, which is overall consistent with previous tropical cyclone events.
Severe tropical cyclones hit the Queensland coast every 200 to 300 years; however, during the period 1969–1999 most cyclones in the region were very weak – category one or two on the Australian Bureau of Meteorology scale.
On February 2, 2011, Severe Tropical Cyclone Yasi struck northern Queensland and caused severe damage to a stretch of hundreds of kilometres within the Great Barrier Reef. The corals could take a decade to recover fully. Cyclone Yasi had wind speeds of 290 kilometers per hour.
Great Barrier Reef
The Great Barrier Reef is the world'slargest reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometres over an area of approximately...
is the world's largest coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
system, composed of roughly 3,000 individual reefs and 900 islands that stretch for 2,600 kilometres (1,616 mi) and cover an area of approximately 344,400 km². The reef is located in the Coral Sea
Coral Sea
The Coral Sea is a marginal sea off the northeast coast of Australia. It is bounded in the west by the east coast of Queensland, thereby including the Great Barrier Reef, in the east by Vanuatu and by New Caledonia, and in the north approximately by the southern extremity of the Solomon Islands...
, off the coast of Queensland
Queensland
Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...
in northeast Australia. A large part of the reef is protected by the Great Barrier Reef Marine Park
Great Barrier Reef Marine Park
The Great Barrier Reef Marine Park protects a large part of Australia's Great Barrier Reef from damaging activities. Fishing and the removal of artefacts or...
.
The Great Barrier Reef's environmental pressures include lowered water quality from runoff including suspended sediment, excess nutrients, pesticides, and fluctuations in salinity. The effects of climate change, including increased temperatures, storms and coral bleaching. Cyclic outbreaks of the crown-of-thorns starfish
Crown-of-thorns starfish
The crown-of-thorns starfish is a large nocturnal sea star that preys upon coral polyps. The crown-of-thorns receives its name from venomous thorn-like spines that cover its body. It is endemic to tropical coral reefs in the Red Sea, the Indian Ocean, and the Pacific Ocean...
, overfishing which disrupts food chains, and shipping routes which can result in oil spills or improper ballast discharge also damage to the reef.
Water quality
Water quality was first identified as a threat to the Great Barrier Reef in 1989.Thirty "major rivers" and hundreds of small streams comprise the Great Barrier Reef catchment area
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
, which covers 423000 square kilometres (163,321.2 sq mi) of land. Queensland has several major urban centres on the coast including Cairns, Townsville, Mackay
Mackay, Queensland
Mackay is a city on the eastern coast of Queensland, Australia, about north of Brisbane, on the Pioneer River. Mackay is nicknamed the sugar capital of Australia because its region produces more than a third of Australia's cane sugar....
, Rockhampton
Rockhampton
Rockhampton can refer to:* Rockhampton, Queensland is a city in Queensland, Australia* Rockhampton City, Queensland, a suburb of Rockhampton, Queensland* Electoral district of Rockhampton, Queensland, Australia...
and the industrial city of Gladstone
Gladstone, Queensland
- Education :Gladstone has several primary schools, three high schools, and one university campus, Central Queensland University. It is also home to CQIT Gladstone Campus.- Recreation :...
. Dredging in the Port of Gladstone
Port of Gladstone
The Port of Gladstone is Queensland's largest multi-commodity port and the fifth largest multi-commodity port in Australia. It is the world's fourth largest coal exporting terminal. It forms and integral part of the City of Gladstone in Central Queensland and is located about 525 km north of...
is raising concern after dead and diseased fish where found in the harbour. Cairns and Townsville are the largest of the coastal cities, with populations of approximately 150,000 each.
There are many major water quality variables affecting coral reef health including water temperature
Sea surface temperature
Sea surface temperature is the water temperature close to the oceans surface. The exact meaning of surface varies according to the measurement method used, but it is between and below the sea surface. Air masses in the Earth's atmosphere are highly modified by sea surface temperatures within a...
, salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
, nutrients, suspended sediment
Sediment transport
Sediment transport is the movement of solid particles , typically due to a combination of the force of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained...
concentrations, and pesticides. The species in the Great Barrier Reef area are adapted to tolerable variations in water quality however when critical thresholds are exceeded they may be adversely impacted. River discharges are the single biggest source of nutrients, providing significant pollution of the Reef during tropical flood events with over 90% of this pollution being sourced from farms.
Due to the range of human uses made of the water catchment area adjacent to the Great Barrier Reef, some 700 of the 3000 reefs are within a risk zone where water quality
Water pollution
Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....
has declined owing to the naturally acidic sediment and chemical runoff
Surface runoff
Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...
from farming, and to coastal development and the loss of coastal wetland
Wetland
A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....
s which are a natural filter. Industries in the water catchment area are cotton growing, comprising approximately 262 km²; 340 dairy farms with an average area of 2 km² each, 158 km² cattle grazing, 288 km² horticulture including banana growing, sugarcane farming, and cropping of approximately 8,000 km² wheat, 1,200 km² barley, and 6,000 to 7000 km² sorghum and maize. Fertiliser use in the cotton, dairy, beef, horticulture and sugar industries is essential to ensure productivity and profitability. However, fertiliser and byproducts from sugar cane harvesting methods form a component of surface runoff into the Great Barrier Reef lagoon. Principal agricultural activity is sugar cane farming in the wet tropics and cattle grazing in the dry tropics regions. Both are considered significant factors affecting water quality. Copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, a common industrial pollutant in the waters of the Great Barrier Reef, has been shown to interfere with the development of coral polyps. Flood plumes are flooding events associated with higher levels of nitrogen and phosphorus. In February 2007, due to a monsoonal climate system
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
, plumes of sediment runoff have been observed reaching to the outmost regions of the reef.
Runoff is especially concerning in the region south of Cairns, as it receives over 3000 mm of rain per year and the reefs are less than 30 kilometres (18.6 mi) away from the coastline. Farm run off is polluted as a result of overgrazing and excessive fertiliser and pesticide use. Mud pollution has increased by 800% and inorganic nitrogen pollution
Eutrophication
Eutrophication or more precisely hypertrophication, is the movement of a body of water′s trophic status in the direction of increasing plant biomass, by the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system...
by 3,000% since the introduction of European farming practices on the Australian landscape. This pollution has been linked to a range of very significant risks to the reef system, including intensified outbreaks of the coral-eating Crown of Thorns Starfish which contributed to a loss of 66% of live coral cover on sampled reefs in 2000.
It is thought that the mechanism behind excess nutrients affecting the reefs is due to increased light and oxygen competition
Competition (biology)
Competition is an interaction between organisms or species, in which the fitness of one is lowered by the presence of another. Limited supply of at least one resource used by both is required. Competition both within and between species is an important topic in ecology, especially community ecology...
from algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
, but unless herbivory is unusually low, this will not create a phase shift from the Great Barrier Reef being primarily made up of coral to being primarily made up of algae.
It has been suggested that poor water quality due to excess nutrients encourages the spread of infectious disease
Infectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...
s among corals. In general, the Great Barrier Reef is considered to have low incidences of coral diseases. Skeletal Eroding Band
Skeletal Eroding Band
Skeletal eroding band is a disease of corals that appears a black or dark gray band that slowly advances over corals, leaving a spotted region of dead coral in its wake...
, a disease of bony corals caused by the protozoan Halofolliculina corallasia
Halofolliculina corallasia
Halofolliculina corallasia is a heterotrich ciliate identified as a cause of the syndrome called Skeletal Eroding Band . It is the first coral disease pathogen that is a protozoan as well as the first known to be an eucaryote; all others identified are bacteria...
, affects 31 species of corals from six families on the reef. The long-term monitoring program has found an increase in incidences of coral disease in the period 1999-2002, although they dispute the claim that on the Great Barrier Reef, coral diseases are caused by anthropogenic pollution.
Elevated nutrient concentrations result in a range of impacts on coral communities and under extreme conditions can result in a collapse. It also affects coral by promoting phytoplankton growth which increases the number of filter feeding
Filter feeder
Filter feeders are animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...
organisms that compete for space. Excessive inputs of sediment from land to coral can lead to reef destruction through burial, disruption of recruitment success or deleterious community shifts. Sediments affect coral by smothering them when particles settle out, reducing light availability and potentially reducing photosynthesis and growth. Coral reefs exist in seawater salinities from 25 to 42%. Salinity impacts to corals are increased by other flood-related stresses.
The Australian and Queensland Governments have committed to act to protect the reef, and water quality monitoring programmes are in place. However, the World Wildlife Fund has criticised that progress against these commitments has been slow, saying that as many as 700 reefs are at risk from sediment runoff.
Climate change
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
s is climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
, consisting chiefly of global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
and the El Niño effect
El Niño-Southern Oscillation
El Niño/La Niña-Southern Oscillation, or ENSO, is a quasiperiodic climate pattern that occurs across the tropical Pacific Ocean roughly every five years...
. Many of the corals of the Great Barrier Reef are currently living at the upper edge of their temperature tolerance, as demonstrated in the mass coral bleaching
Coral bleaching
Coral bleaching is the loss of intracellular endosymbionts through either expulsion or loss of algal pigmentation.The corals that form the structure of the great reef ecosystems of tropical seas depend upon a symbiotic relationship with unicellular flagellate protozoa, called zooxanthellae, that...
events of the summers of 1998, 2002 and 2006. In February 2007, the current threat of mass coral bleaching was assessed as being "low" due to a monsoon
Monsoon
Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea...
al climate system, although sites displaying some coral bleaching were monitored.
As demonstrated in 1998, 2002 and 2006, corals expel their photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
ing zooxanthella
Zooxanthella
Zooxanthellae are flagellate protozoa that are golden-brown intracellular endosymbionts of various marine animals and protozoa, especially anthozoans such as the scleractinian corals and the tropical sea anemone, Aiptasia....
e (which provide up to 90% of the coral’s energy requirements) and turn colourless, revealing their white calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
skeletons, under the stress of waters that remain too warm for too long. At this stage the coral is still alive, and if the water cools, the coral can regain its zooxanthellae. If the water does not cool within about a month, the coral will die of starvation. Australia experienced its warmest year on record in 2005. Abnormally high sea temperatures during the summer of 2005-2006 have caused massive coral bleaching in the Keppel Island
Great Keppel Island
Great Keppel Island lies 15 kilometres from the coast off Yeppoon, Central Queensland, Australia. The island is the largest of the eighteen islands in the Keppel Group, and covers an area of more than 14.5 square kilometres...
group.
Most scientists studying the issue believe that climate change poses a massive threat to the future of the Great Barrier Reef. A draft report by the UN
United Nations
The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...
Intergovernmental Panel on Climate Change
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...
, the world's preeminent gathering of climate scientists, states that the Great Barrier Reef is at grave risk and will be "functionally extinct" by 2030, warning that coral bleaching will likely become an annual occurrence.
However, a few scientists hold that coral bleaching may in some cases be less of a problem than the mainstream believes. Professor Ridd, from James Cook University in Townsville was quoted in The Australian (a conservative newspaper) as saying; “They are saying bleaching is the end of the world, but when you look into it, that is a highly dubious proposition”. Research by scientist Ray Berkelmans “... has documented astonishing levels of recovery on the Keppel outcrops devastated by bleaching in 2006.” A related article in The Australian newspaper goes on to explain that; “Those that expel their zooxanthellae have a narrow opening to recolonise with new, temperature-resistant algae before succumbing. In the Keppels in 2006, Berkelmans and his team noticed that the dominant strain of zooxanthellae changed from light and heat-sensitive type C2, to more robust types D and C1.”
Nevertheless, most coral reef researchers anticipate severely negative effects from climate change already occurring, and potentially disastrous effects as climate change worsens. The future of the Reef may well depend on how much the planet's climate changes, and thus, on how high atmospheric greenhouse gas concentration levels are allowed to rise. On 2 September 2009, a report by the Australian Great Barrier Reef Marine Park Authority revealed that if carbon dioxide levels reached 450 parts per million corals and reef habitats will be highly vulnerable. If carbon dioxide levels are managed at or below 380 parts per million they will be only moderately vulnerable and the reefs will remain coral-dominated.
Global warming may have triggered the collapse of reef ecosystems throughout the tropics. Increased global temperatures are thought by some to bring more violent tropical storms, but reef systems are naturally resilient and recover from storm battering. Most people agree that an upward trend in temperature will cause much more coral bleaching; others suggest that while reefs may die in certain areas, other areas will become habitable for corals, and new reefs will form. However, the rate at which the mass bleaching events occur is estimated to be much faster than reefs can recover from, or adjust to.
However, Kleypas et al. in their 2006 report suggest that the trend towards ocean acidification
Ocean acidification
Ocean acidification is the name given to the ongoing decrease in the pH and increase in acidity of the Earth's oceans, caused by the uptake of anthropogenic carbon dioxide from the atmosphere....
indicates that as the sea's pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
decreases, corals will become less able to secrete calcium carbonate. In 2009, a study showed that Porites corals, the most robust on the Great Barrier Reef, have slowed down their growth by 14.2% since 1990. It suggested that the cause was heat stress and a lower availability of dissolved calcium to the corals.
Climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...
and global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
are one of the greatest threats to the reef. A temperature rise of between two and three degrees Celsius would result in 97% of the Great Barrier Reef being bleached every year. Reef scientist Terry Done has predicted that a one-degree rise in global temperature would result in 82% of the reef bleached, two degrees resulting in 97% and three degrees resulting in "total devastation". A predictive model based on the 1998 and 2002 bleaching events has concurred that a temperature rise of three degrees would result in total coral mortality.
Climate change has implications for other forms of life on the Great Barrier Reef as well - some fish's preferred temperature range
Temperature range
Atmospheric temperature range is the numerical difference between the minimum and maximum values of temperature observed in a given location....
lead them to seek new areas to live, thus causing chick mortality in seabirds that prey on the fish. Also, in sea turtles, higher temperatures mean that the sex ratio of their populations will change, as the sex of sea turtles is determined by temperature. The habitat of sea turtles will also shrink.
Crown-of-thorns starfish
Crown-of-thorns starfish
The crown-of-thorns starfish is a large nocturnal sea star that preys upon coral polyps. The crown-of-thorns receives its name from venomous thorn-like spines that cover its body. It is endemic to tropical coral reefs in the Red Sea, the Indian Ocean, and the Pacific Ocean...
is a coral reef predator which preys on coral polyps by climbing onto them, extruding its stomach over them, and releasing digestive enzyme
Digestive enzyme
'Digestive enzymes' are enzymes that break down polymeric macromolecules into their smaller building blocks, in order to facilitate their absorption by the body. Digestive enzymes are found in the digestive tract of animals where they aid in the digestion of food as well as inside the cells,...
s to absorb the liquified tissue. An individual adult of this species can eat up to six square metres of living reef in a single year. Geological evidence suggests that the Crown-of-Thorns Starfish has been part of the Great Barrier Reef's ecology for "at least several thousand years", but there is no geological evidence for Crown-of-Thorns outbreaks. Large outbreaks of these starfish can devastate reefs. In 2000, an outbreak contributed to a loss of 66% of live coral cover on sampled reefs in a study by the CRC Reefs Research Centre. Although large outbreaks of these starfish are believed to occur in natural cycles, human activity in and around the Great Barrier Reef can worsen the effects. Reduction of water quality associated with agriculture can cause the crown-of-thorns starfish larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e to thrive. Overfishing of its natural predators, such as the Giant Triton
Triton (mollusk)
Triton is the common name given to a number of very large sea snails, predatory marine gastropods in the genus Charonia. The name "triton" is also often applied as part of the common name, to other, much smaller sea snails of other genera within the same family, Ranellidae.Tritons are named after...
, is also considered to contribute to an increase in the number of crown-of-thorns starfish. The CRC Reef Research Centre defines an outbreak as when there are more than 30 adult starfish in an area of one hectare
Hectare
The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...
.
Overfishing
The unsustainable overfishingOverfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
of keystone species
Keystone species
A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. Such species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and...
, such as the Giant Triton
Triton (mollusk)
Triton is the common name given to a number of very large sea snails, predatory marine gastropods in the genus Charonia. The name "triton" is also often applied as part of the common name, to other, much smaller sea snails of other genera within the same family, Ranellidae.Tritons are named after...
and sharks, can cause disruption to food chain
Food chain
A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...
s vital to life on the reef. Fishing also impacts the reef through increased pollution from boats, by-catch
By-catch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
of unwanted species (such as dolphins and turtles) and reef habitat destruction
Habitat destruction
Habitat destruction is the process in which natural habitat is rendered functionally unable to support the species present. In this process, the organisms that previously used the site are displaced or destroyed, reducing biodiversity. Habitat destruction by human activity mainly for the purpose of...
from trawling
Trawling
Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net that is used for trawling is called a trawl....
, anchors and nets. Overfishing of herbivore populations can cause algal growths on reefs. The Batfish
Ephippidae
Ephippidae is the fish family containing the spadefishes. There are about eight genera, with a total of 20 species, mostly marine. The most well-known species are probably those in the reef-dwelling genus Platax, the batfishes, which are kept as aquarium fish. They are spade-shaped, laterally...
Platax pinnatus
Platax pinnatus
Platax pinnatus, also known as dusky batfish or red-faced batfish is a fish from the western Pacific that occasionally is kept in marine aquariums.-Anatomy and morphology:...
has been observed to significantly reduce algal growths in studies simulating overfishing. Sharks are fished for their meat, and when they are part of bycatch, it is common to kill the shark and throw it overboard, as there is a belief that they interfere with fishing. As of 1 July 2004, approximately one-third of the Great Barrier Reef Marine Park
Great Barrier Reef Marine Park
The Great Barrier Reef Marine Park protects a large part of Australia's Great Barrier Reef from damaging activities. Fishing and the removal of artefacts or...
is protected from species removal of any kind, including fishing, without written permission. However, illegal poaching is not unknown in these no-take zones.
Shipping
Shipping accidents are also a pressing concern, as several commercial shipping routes pass through the Great Barrier Reef. The GBRMPA estimates that about 6000 vessels greater than 50 metres (164 ft) in length use the Great Barrier Reef as a route. From 1985-2001, there were 11 collisions and 20 groundings on the inner Great Barrier Reef shipping routeShipping route
A shipping route is a trade route used by merchant ships.Early routes usually were coastal in nature as navigators had to rely on the coastal landmarks...
. The leading cause of shipping accidents in the Great Barrier Reef is human error.
Although the route through the Great Barrier Reef is not easy, reef pilots consider it safer than outside the reef in the event of mechanical failure, since a ship can sit safely while being repaired. 75% of all ships that use the Great Barrier Reef as a route use the inner route. On the outside, wind and swell will push a ship towards the reef and the water is deep right up to the reef so anchoring is impossible. Captain Cook in the Endeavour
HM Bark Endeavour
HMS Endeavour, also known as HM Bark Endeavour, was a British Royal Navy research vessel commanded by Lieutenant James Cook on his first voyage of discovery, to Australia and New Zealand from 1769 to 1771....
nearly came to grief that way, being utterly becalmed and pushed towards the reef by the swell. Right up to within 80 metres (262 ft) of the Great Barrier Reef, the water was so deep that no ground (to anchor against) could be felt with 220 metres (722 ft) of line. There have been over 1,600 known shipwrecks in the Great Barrier Reef region.
Waste and foreign species discharged in ballast water from ships (when purging procedures are not followed) are a biological hazard
Biological hazard
Biological hazards, refer to biological substances that pose a threat to the health of living organisms, primarily that of humans. This can include medical waste or samples of a microorganism, virus or toxin that can impact human health. It can also include substances harmful to animals...
to the Great Barrier Reef. Tributyltin
Tributyltin
Tributyltin compounds are a group of compounds containing the 3Sn moiety, such as tributyltin hydride or tributyltin oxide. They are the main active ingredients in certain biocides used to control a broad spectrum of organisms...
(TBT) compounds found in some antifouling paint
Biofouling
Biofouling or biological fouling is the undesirable accumulation of microorganisms, plants, algae, or animals on wetted structures.-Impact:...
on ship hulls leaches into seawater and is toxic to marine organisms and humans; efforts are underway to restrict its use.
In April 2010, the bulk coal carrier Shen Neng 1 ran aground on the Great Barrier Reef
2010 Great Barrier Reef oil spill
The 2010 Great Barrier Reef oil spill occurred on 3 April 2010, when the Chinese bulk coal carrier, ran aground east of Rockhampton in Central Queensland, Australia. The vessel is owned by Shenzhen Energy Transport Co. Ltd....
causing the largest grounding scar to date and creating a oil slick of heavy fuel oil 2 nmi (3.7 km; 2.3 mi) long.
Oil
It was suspected that the Great Barrier Reef is the cap to an oil trapOil reservoir
A petroleum reservoir, or oil and gas reservoir, is a subsurface pool of hydrocarbons contained in porous or fractured rock formations. The naturally occurring hydrocarbons, such as crude oil or natural gas, are trapped by overlying rock formations with lower permeability...
, after a 1923 paper suggested that it had the right rock formation to support "oilfields of great magnitude". After the Commonwealth Petroleum Search Subsidies Act of 1957, exploration activities increased in Queensland, including a well drilled at Wreck Island
Wreck Island (Queensland)
Wreck Island is a small coral cay. It is located near the Tropic of Capricorn in the southern Great Barrier Reef, 93 km due northe east of Gladstone, Queensland, Australia, and 460 km north of the state capital Brisbane....
in the southern Great Barrier Reef in 1959. In the 1960s, drilling for oil and gas was investigated throughout the Great Barrier Reef, by seismic and magnetic methods in the Torres Strait
Torres Strait
The Torres Strait is a body of water which lies between Australia and the Melanesian island of New Guinea. It is approximately wide at its narrowest extent. To the south is Cape York Peninsula, the northernmost continental extremity of the Australian state of Queensland...
, along "the eastern seaboard of Cape York
Cape York Peninsula
Cape York Peninsula is a large remote peninsula located in Far North Queensland at the tip of the state of Queensland, Australia, the largest unspoilt wilderness in northern Australia and one of the last remaining wilderness areas on Earth...
to Princess Charlotte Bay
Princess Charlotte Bay
Princess Charlotte Bay is a large bay on the east coast of Far North Queensland at the base of Cape York Peninsula, 350 km north northwest of Cairns. Princess Charlotte Bay is a part of the Great Barrier Reef Marine Park and it is a habitat for the dugong....
" and along the coast from Cooktown to Fraser Island. In the late 1960s, more exploratory wells were drilled near Wreck Island in the Capricorn Channel, and near Darnley Island in the Torres Strait, but "all results were dry".
In 1970, responding to concern about oil spill
Oil spill
An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially marine areas, due to human activity, and is a form of pollution. The term is mostly used to describe marine oil spills, where oil is released into the ocean or coastal waters...
s such as the Torrey Canyon
Torrey Canyon
The Torrey Canyon was a supertanker capable of carrying a cargo of 120,000 tons of crude oil, which was shipwrecked off the western coast of Cornwall, England in March 1967 causing an environmental disaster...
, two Royal Commission
Royal Commission
In Commonwealth realms and other monarchies a Royal Commission is a major ad-hoc formal public inquiry into a defined issue. They have been held in various countries such as the United Kingdom, Australia, Canada, New Zealand, and Saudi Arabia...
s were ordered "into exploratory and production drilling for petroleum in the area of the Great Barrier Reef". After the Royal Commissions, the federal and state governments ceased allowing petroleum drilling on the Great Barrier Reef. A study in 1990 concluded that the reef is too young to contain oil reserves
Oil reserves
The total estimated amount of oil in an oil reservoir, including both producible and non-producible oil, is called oil in place. However, because of reservoir characteristics and limitations in petroleum extraction technologies, only a fraction of this oil can be brought to the surface, and it is...
. Oil drilling remains prohibited on the Great Barrier Reef, yet oil spills due to shipping routes are still a threat to the reef system, with a total of 282 oil spills between 1987-2002.
Tropical cyclones
Cyclone Larry
Severe Tropical Cyclone Larry was a tropical cyclone that made landfall in Australia during the 2005-06 Southern Hemisphere tropical cyclone season. Larry originated as a low pressure system over the eastern Coral Sea on 16 March and was monitored by the Australian Bureau of Meteorology in...
was to underlying reef structures, and breakage and displacement of corals, which is overall consistent with previous tropical cyclone events.
Severe tropical cyclones hit the Queensland coast every 200 to 300 years; however, during the period 1969–1999 most cyclones in the region were very weak – category one or two on the Australian Bureau of Meteorology scale.
On February 2, 2011, Severe Tropical Cyclone Yasi struck northern Queensland and caused severe damage to a stretch of hundreds of kilometres within the Great Barrier Reef. The corals could take a decade to recover fully. Cyclone Yasi had wind speeds of 290 kilometers per hour.