Threats to the Great Barrier Reef

Threats from human activity

• Shipping accidents• Oil Spills• Tourist visits

Natural Threats

• Coral bleaching• Crown of Thorns Starfish• El Nino/El Nina and Climate Change

Shipping Accidents• The Great Barrier Reef sees a huge amount of ocean

traffic pass through its waters every day of the year for tourism and commercial purposes (like coal transports).

• Debris and other foreign objects from ships enter the water and remain there for a long period of time.

• Shipwrecks (including ships running aground) can damage the reef.

• Many larger vessels passing through the oceans of the reef can release a substance known as Tributyltin (or “TBT”) which is used as to preserve the condition of ship hulls that is toxic to sea water and which can damage marine organisms where it is released.

Oil Spills• Oil drilling is banned on the reef but spills caused by passing oil

container ships have still continued to occur, • The most recent oil spill occurred in 2010 when the Chinese bulk

coal carrier Shen Neng 1 – travelling 10 kilometres outside the regulation shipping lane – struck the reef, scraping along its surface for a substantial length and creating a massive grounding scar over 3 kilometres in length (the longest in recorded history).

• As a result, some of the damaged areas have become uninhabitable for marine life.

• Experts believe the reef may take up to 10 to 20 years to recover from the incident.

• To date, 283 total oil spills have occurred over the waters of the Great Barrier Reef since 1987.

Over-fishing

• The fishing industry earns over $1 billion per year to Australia.

• Fishing on the reef occurs for commercial and leisure/sport.

• The majority of the reef is off-limits for fishing with an emphasis on reef sustainability.

• Trawling inevitably leads to other species getting caught in the nets as a side effect.

• The nets themselves can also damage the ocean floor and its inhabitants as a result of its “drag effect”.

• Fishing also adds additional pollution from the boats.

Impact of Advances in Fishing Technology

Tourism

• Millions of tourists visit the Great Barrier Reef every year.

• Pollution from boats, walking on the reef, runoff from sunscreens and many other activities all have a negative impact on the reef.

• This is also not taking into account intentionally or neglectfully destructive practices such as littering and various other forms of man-made pollution.

Coral Bleaching• Corals are given their vibrant colours as a result of the algae who

inhabit them.• When the water temperature rises, the warmer waters kill off the

algae which then leads to the coral losing its colouration and results in the “bleach” effect.

• The death of algae in turn results in the death of creatures that use them as their primary source of food, which once again has a ripple effect up the chain and renders the affected section of reef a veritable underwater ghost town.

• Scientists and researchers largely attribute the relatively sudden changes in water temperature to such natural phenomenon as the El Nino effect.

• In 2002, 60% of the Great Barrier Reef experienced bleaching. • The reef can recover from bleaching if the water temperature

returns to normal quickly.

Crown of Thorns Starfish

• The Crown of Thorns starfish feeds on the polyps of coral, releasing neurotoxins to absorb the tissue of the coral and quite literally “sucking the life” out of the reef’s backbone.

• If there are few predators (such as the Giant Triton) around, the Crown of Thorns can destroy parts of the reef.

• Many researchers believe that the current abundance of Crown of Thorns starfish could be a result of agricultural runoff which increases the amount of algae which serve as food for the starfish.

El Nino and Climate Change• The El Nino effect can cause an increase in water

temperatures. • This can cause coral bleaching. • Climate Change is also leading to higher ocean

temperatures. • Some scientists believe that the reef will become

practically extinct by the year 2030. • A temperature rise of 2-3 degrees C is believed to

put 97% of the reef in the danger zone of bleaching every year.

Now to you…

• In your opinion, what is the greatest threat to the Great Barrier Reef?