Threats to the Great Barrier Reef
Climate change is the biggest threat to the reef’s future. The Great Barrier Reef Marine Park Authority’s Outlook Report for the Great Barrier Reef in 2009 stated: “the threats of increasing sea temperature, ocean acidification and rising sea level are assessed as very high risk to the ecosystem... . Their impact will be compounded by each other and by other existing regional and local threats.”
The reef has already experienced two mass coral bleaching events – in 1998 and 2002. Bleaching was more severe in 2002, when aerial surveys showed that almost 60% of reefs experienced bleaching of some degree.
Sediment, nutrient and pesticide pollution from catchment run-off is also affecting the health and resilience of the reef ecosystem.
The amount of sediment flowing into the marine park has quadrupled over the past 150 years. This increase can largely be attributed to grazing and cropping expansion in the catchment, which has also resulted in the loss of native vegetation and wetlands.
Nutrient loads have also increased, encouraging algal blooms, which, in turn, provide food for larvae of the devastating crown-of-thorns starfish. In addition, nearly one-third of the reef is now exposed to pesticides.
Not only is the reef subject to high levels of fishing pressure. Fishing practices, such as trawling for prawns, are permitted in over one-third of the marine park, resulting in untargeted fish capture (bycatch), and damage to the seafloor and its resident plants and animals.