A UNESCO World Heritage Site, Australia’s Great Barrier Reef is home to more than 1,500 species of fish, and one-third of the world’s corals. It generates an annual income of $3.9 billion per year, and provides employment for nearly 70,000 people. Unfortunately, and as many divers will know, a recent study shows that this incredible natural wonder is in the middle of an unprecedented disaster. According to a series of surveys undertaken by the Australian Research Council Centre of Excellence for Coral Reef Studies (ARC Centre), 93 percent of the reef’s corals have been damaged by large-scale bleaching. Australia and many other Pacific countries are currently in the grip of an unusually long El Niño, a climate phenomenon that causes water temperatures throughout the region to rise significantly; this year’s El Niño is is particularly severe in part due to greenhouse gases and subsequent global warming.
Led by Professor Terry Hughes, the team from the ARC Centre led aerial and underwater surveys of 900 of the Great Barrier Reef’s individual reefs, which together form a continuous structure around 1,400 miles long. The results showed just 7 percent of the reef system to be entirely free from coral bleaching, with the worst damage focused on the northernmost section of the GBR. In this region, which stretches from Port Douglas to the northern Torres Strait Islands, 80 percent of the reefs surveyed were classified as severely bleached.
Coral bleaching occurs as a result of abnormally high water temperatures, which cause corals to expel the zooxanthellae living within their tissues. As well as giving coral its color, the zooxanthellae provide nutrients for their hosts via photosynthesis — without them, the coral will eventually die. Bleaching can be reversed only if water conditions return to normal and the zooxanthellae are allowed to repopulate the coral within a certain amount of time. Devastatingly, it is already too late for 50 percent of corals in the northern sector of the reef.
Experts working with the ARC Centre expect that this mortality rate could increase to more than 90 percent if the causes of the bleaching are not reversed soon. When speaking of the devastation in the northern sector, Hughes says that the damage caused looks as though “ten cyclones have come ashore all at once.” Fortunately, bleaching in the middle and southern sections of the reef is slightly less severe, with only 1 percent of reefs in the southernmost region classified as severely bleached.
Although only one quarter of reefs in these areas are untouched by bleaching, scientists hope that it is not too late for the majority of the reefs to recover. The healthier condition of the southern reefs can be attributed to greater cloud cover and rainfall in these regions of the GBR in recent months.
The Great Barrier Reef has suffered two other large-scale bleaching events in recent years, once in 1998 and once in 2002, both of which were also during El Niño. However, the current disaster eclipses both of these events, the worst of which saw 54 percent of the GBR affected by bleaching. Climate change is undoubtedly a contributing factor behind the unprecedented damage wreaked by this year’s El Niño, as the effects of the phenomenon are exacerbated by already elevated sea temperatures.
Tragically, the extent of the recent devastation is so extreme that scientists are predicting it will take decades — at best — for the reef to recover, if at all. Many of the corals that have already died were long-lived, slow-growing species that take centuries to form. Consequently, the reefs of the future are likely to be dominated by other, faster-growing species, which will affect the balance of marine life throughout the ecosystem. According to Hughes, the northern Great Barrier Reef may never return to what it once was. To our mind, it’s nothing less than tragedy on a global scale.