All over the world coral reefs are dying out. Marine pollutants, agricultural run-off and, above all, global warming, are taking a toll on these fragile marvels of nature. The Great Barrier Reef, the world’s largest living organism, has already suffered coral die-off in almost one third of its 133,000 square miles. Many corals are so tightly coupled to local conditions they cannot survive if average sea temperature rises by more than a single degree, a figure we are approaching in some parts of the world. Politicians may be able to deny global warming, corals, sadly, don’t have that option.
Since the nineteenth century the Great Barrier Reef (GBR) has warmed an average of 0.4 degrees, but scientists at the Australian Institute of Marine Science (AIMS) say this already enough to cause serious damage. Corals live near the upper limit of their temperature tolerance so any sustained rise may push them over the edge. In 1998, 2002 and again in 2006 water temperature in the region rose 1-2 degrees above the seasonal average and the GBR experienced large scale-bleaching events. “The pace of warming is of major concern,” says AIMS coral expert Ray Berkelmans, “it gives organisms little time to respond or adapt.” By the end of this century, current projections suggest that the GBR could be 1-3 degrees warmer, making bleaching an annual event and causing devastation on a wide scale.
Ocean warming is not the only danger that results from our output of greenhouse gasses. Of all the carbon dioxide spewing into the atmosphere, around 30% will ultimately be absorbed by the oceans. This excess CO2 increases ocean acidity, with dire consequences for corals. “More acidic waters make it difficult for corals and other calcifying organisms, such as animals with shells, to form their skeletons, which are ultimately responsible for building the physical structure of the reef,” says AIMS research scientist, Dr Janice Lough. There is now general scientific consensus that the acidity of the world’s oceans is increasing, posing a threat to many marine ecosystems and potentially leading to weakening of coral reef structures.
As if rising temperatures and acidity were not enough to contend with, coral reefs also face stresses from increased cyclone intensity – another consequence of escalating greenhouse gas emissions. Agricultural and other land run-off, including poorly treated sewerage add further pressures. In April 2007, a report by the Intergovernmental Panel on Climate Change (IPCC) will be released with a chapter devoted to the effects of global warming on the Australian landscape and the Great Barrier Reef.