Environmental threats to the Great Barrier Reef

Md. Arafat Rahman

Great Barrier Reef is the world’s largest reef systems, stretching along the East coast of Australia from the northern tip down to the town of Bundaberg. It is composed of roughly 2,900 individual reefs and 940 islands and cays. 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.

Climate change is the most significant environmental threat to the Great Barrier Reef, while the other major environmental pressures are listed as decreased water quality from land-based runoff, impacts from coastal development and some persistent impacts from fishing activities. The reef is also threatened by storms, coral bleaching and ocean acidification. While numerous marine life species have recovered after previous declines, the strength of the dugong population is continuing to decline.
The Great Barrier Reef is neither a singular reef nor a physical barrier that prevents exchange between reefs; it is a mixture of thousands of productive reefs and shallow areas lying on a continental shelf with complex oceanic circulation. The Great Barrier Reef is important for world life. It is considered that climate change, poor water quality, coastal development, and some impacts from fishing to be the area’s major threats, but reef scientists stated that the cumulative effects of many combined impacts is the real issue.
Water quality was first identified as a threat to the Great Barrier Reef in 1989. There are many major water quality variables affecting coral reef health including water temperature, salinity, nutrients, suspended sediment concentrations, and pesticides. 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 due to the naturally acidic sediment and chemical runoff from farming.
The most significant threat to the status of the Great Barrier Reef is climate change, due to the consequential rise of sea temperatures, gradual ocean acidification and an increase in the number of intense weather events. Furthermore, a temperature rise of between two and three degrees Celsius would result in 97% of the Great Barrier Reef being bleached every year. One-degree rise in global temperature would result in 82% of the reef bleached; two degrees would result in 97%, while three degrees would result in total devastation.
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. 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. An upward trend in temperature will cause much more coral bleaching. 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.

Climate change has implications for other forms of life on the Great Barrier Reef. 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.
Scientists expressed alarm that the impact of climate change could cause massive damage to the ecosystem. The Great Barrier Reef ‘glue’ is at risk from ocean acidification. In the present-day context of rapid global climate change, changes in dissolved carbon dioxide, pH and temperature, could lead to reduced microbial crust formation, thereby weakening reef frameworks in the future. Sampling of the Great Barrier Reef fossil record has shown that the calcified scaffolds that help stabilize and bind its structure become thin and weaker as pH levels fall.

The unsustainable overfishing of keystone species, such as the Giant Triton and sharks, can cause disruption to food chains vital to life on the reef. Fishing also impacts the reef through increased pollution from boats, by-catch of unwanted species and reef habitat destruction from trawling, anchors and nets. 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.
Shipping accidents continue to be perceived as a threat, as several commercial shipping routes pass through the Great Barrier Reef. Waste and foreign species discharged from ships in ballast water are a biological hazard to the Great Barrier Reef. Tributyltin (TBT) compounds found in some antifouling paint on ship hulls leaches into seawater and are toxic to marine organisms and humans.

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 are varied, including fragmentation, sediment plumes, and decreasing salinity following heavy rains. The patterns of reef damage are similarly patchy. Most cyclones pass through the Great Barrier Reef within a day. In general, compact corals fare better than branching corals under cyclone conditions.
In 1967, efforts began to conserve the Great Barrier Reef. It was proposed to mine lime from Ellison Reef, but surveys showed that the reef supported a diverse community of corals and fish. The Australian and Queensland Governments committed to act in partnership to protect the reef, and water quality monitoring programs were implemented. However, the World Wildlife Fund raising a concern that as many as 700 reefs continued to be at risk from sediment runoff. UNESCO recommended that thorough assessments should be made before any new developments that could affect the reef are approved.

Md. Arafat Rahman, Columnist & Asst. Officer,

Career & Professional Development Services Department, Southeast University