Coral bleaching on the doorstep of Lizard Island
The Australian Museum has operated a research station at Lizard Island, in the far northern sector of the Great Barrier Reef, since 1973. The AM’s Lizard Island Research Station annually supports more than 100 research projects by 350 researchers and their assistants.
Recently, much of this research has focused on the impacts of climate change. In particular, how increasing sea temperatures and ocean acidification will affect coral communities and other marine life.
Many species of corals rely on tiny, symbiotic algae (zooxanthellae) for much of their nutritional requirements. This tiny algae also plays a part in the corals colouration. Stress can come in many forms but it is often thermal stress that causes corals to expel their zooxanthellae. Corals generally go from a dark to pale to white colour as the density of their zooxanthellae is reduced. However, some corals become even more colourful when stressed due to fluorescing pigments in their tissue before turning white. Corals can tolerate some bleaching and in fact corals can bounce back from a bleaching event if the stress isn’t too severe or doesn’t last too long. However, a severe, prolonged bleaching event often causes the coral to die.
The Bureau of Meteorology, the National Oceanic and Atmospheric Administration and other organisations have been forecasting a strong El Nino event for the western Pacific for some time. Typically, these events bring elevated sea temperatures plus hot and dry conditions on land. At Lizard Island, sea temperatures were normal through 2015 but they started to climb markedly early in 2016. In addition, during much of February, the area experienced mostly hot days, calms seas and clear skies. The combination of these conditions has resulted in the ‘perfect storm’ for coral bleaching, at least in the vicinity of Lizard Island, but probably also to varying levels elsewhere on the Great Barrier Reef.
At Lizard Island, some corals at shallow lagoonal sites started appearing light pale in early February due to sea temperatures being 1-2 degrees C above the normal summertime temperatures. By the beginning of March, many corals at these shallow sites had advanced to at least mild bleaching. However, some colonies of acroporid corals are now totally white and a few are dead.
Without doubt, this is the worst coral bleaching event in the Lizard Island lagoon since 2002. Lizard Island has experienced some mild summer bleaching events since 2002 but nothing comparable in severity to the current one.
At the moment, we can only monitor the impacts of bleaching and keep our fingers crossed for favourable weather conditions (heavy cloud cover, rain and some wind). This obviously is not a very satisfactory way of looking after one of Australia’s greatest natural assets. There is no doubt that these recurring bleaching events are due to climate change. The only way to save corals on the GBR from heat stress is to dramatically and quickly reduce our carbon footprint.