Current and Future Impacts on the Great Barrier Reef

 

The Great Barrier Reef Outlook Report 2009 identified climate change as one of the greatest threats to the long-term health of the Great Barrier Reef.

Climate change is already slightly affecting the Reef currently but will increasingly worsen in a number of ways in the future if climate change continues, including:

- frequency of severe weather events

- Ocean acidification

- Rising sea temperature

 

 

Sea temperature

- Rising sea temperatures over the past 30 years have meant corals on the Great Barrier Reef are now at their 'normal' state of thermal thresholds. This means when temperatures increase again, particularly during summer months, corals will exceed these thresholds and move to a state of thermal stress.

- Thermal stress is most visible when corals bleach. Too much heat means corals and zooxanthellae separate, the zooxanthellae taking the   colour (hence 'bleaching') and energy sources with them. Coral bleaching is not always fatal, but has been one of the main causes of coral death around the world in the last 20 years.

- Increased sea temperatures can also affect the growth and reproduction of corals. Experiments have shown a quicker embryo development, reduced egg and sperm production and an incomplete fertilisation cycle in corals due to warm water.

- Fish body temperature is moderated by water temperature. Increasing sea temperatures can affect important biological processes of fish including growth, reproduction, swimming ability and behaviour.

- Reproduction is only possible in a narrow temperature range, and therefore could be affected by the forecast temperature rises associated with climate change. Temperature also influences the sex of fish, which may have an effect on population dynamics.

 

Ocean acidification

- Ocean acidification is an additional threat to coral reef survival. It reduces the corals' ability to build their skeletons. This will result in weaker coral structures, thus reducing their ability to withstand physical disturbances from storms, they will have less energy to respond to stress and disease and there will be fewer protective habitats for other marine life.

- Lots of species of fish live in and around coral reefs, and most feed on the microbes in the water, which provide fish with their carbon requirements. In general, the overarching affects of ocean acidification on coral formation and the abundance of carbon in the food chain will impact fish species through habitat and food availability.

 

Increased frequency of severe weather events

- Predictions suggest an increase in the frequency of severe weather events which could lead to more serious physical damage, with less time between events to recover.

- The most immediate impact is coral breakage, dislocation and degradation from wind and waves. However, the effect doesn't stop there. Heavy rainfall events lead to flood plumes stretching across the Reef, exposing inshore coral reefs to freshwater inundations.

- Freshwater run-off reduces salinity levels, sometimes causing bleaching, and brings increased nutrients and sediments, which can lead to disease outbreaks, algae blooms and murky water reducing light reaching corals.

- The vulnerability of coral reefs to these impacts is dependent on the effect of other climate change impacts. For example, reefs that are weakened by ocean acidification or stressed from high sea surface temperatures will respond poorly to a major storm or flood event.

- Seabirds are one of the few Great Barrier Reef species in danger of immediate death during a cyclone or storm. Eggs and chicks are most likely to be harmed during a major storm, with the nest providing limited protection. Due to the loss of infants, species populations may take some time to re-establish following a cyclone, particularly when food availability is reduced and their habitats have been destroyed.

 

 

The Great Barrier Reef will be irreversibly damaged by climate change in just 16 years. The reef has already lost about half its coral coverage since the mid-1980s, with increased carbon dioxide concentrations contributing about 10 per cent alongside damage from other sources such as invasive species and farm nutrient run-off. Climate change, though, is fast taking over as the main threat to the world's reefs as warmer waters increase the frequency of coral bleaching, while acidifying oceans weaken or erode coral structures.Not only will shrinking coral reefs diminish the annual $6 billion reef tourism industry and the 63,000 jobs it supports, there will be other impacts.