Each summer, we keep an eye on the Great Barrier Reef to see how it’s faring, as this period brings an increased risk to the Reef from coral bleaching, extreme weather and flooding. Stressful conditions can lead to coral disease outbreaks, and poor water quality may also lead to an increase in the abundance of coral eating crown-of-thorns starfish.

Environmental conditions

2012/2013 summer wrap up

As of the end of April 2013, conditions on the Great Barrier Reef remain neutral according to information from the Bureau of Meteorology:

• All indicators of El Niño-Southern Oscillation (ENSO) are within the neutral range.  This state is set to continue throughout autumn into early winter.
• Sea surface temperatures in the tropical Pacific Ocean have been persistently warm since December 2012.
• There was a greater than 50 per cent chance that the Great Barrier Reef region would experience a below average number (less than four) of tropical cyclones this season. A tropical low pressure system associated with ex-tropical cyclone Oswald crossed Cape York Peninsula on 21 January 2013 and moved down the Queensland coast, bringing strong to gale force winds, heavy rain, damaging waves and floods. At the start of May 2013, another tropical low pressure system associated with ex-tropical cyclone Zane crossed into the Marine Park from the Coral Sea and moved over Cape York Pennisula, affecting areas from Cape Grenville to Cooktown. Other than ex-tropical cyclone Oswald and ex-tropical cyclone Zane, no tropical cyclones or other weather systems of similar magnitude affected the Great Barrier Reef this summer.
• Queensland experienced below average rainfall levels throughout summer 2012-2013, apart from south east Queensland and parts of the Central Coast that received above average levels.  In these areas, rainfall levels in January 2013 increased to 50–400mm higher than the monthly average due to the influence of ex-Tropical Cyclone Oswald.  
• The heavy rainfall associated with ex-tropical cyclone Oswald resulted in flooding of many of the major river systems that flow into the Great Barrier Reef or bays in southern Queensland.  Minor to major flooding occurred in all major river systems south of Mackay to the Queensland–New South Wales border. Flood plumes have been documented for several of these major river systems.

Our table of observations and forecasts provides more detailed information. Reef health monitoring is ramped up over this time to keep an eye on the marine environment.

Coral reef health reports

GBRMPA, the Queensland Parks and Wildlife Service (QPWS) and the Eye on the Reef monitoring network have conducted 693 reef health and impact surveys across 78 reefs on the Great Barrier Reef since 1 December 2012.  The majority (73 per cent) of these surveys were completed in the Cairns/Cooktown sector of the Marine Park.

Of all the surveys throughout the Marine Park, 31 per cent recorded healthy coral reefs with no impacts, 34 per cent recorded the presence of one type of impact per survey and another 35 per cent recorded a combination of impact types. The results confirm existing knowledge of the increasing presence of crown-of-thorns starfish in the Cairns/Cooktown region. Crown-of-thorns starfish were observed in 37 per cent of surveys, while Drupella snails were recorded in only 4 per cent of surveys.  Of all the surveys, 20 to 30 per cent indicated some signs of coral stress, such as low level coral bleaching, disease and partial mortality.

Approximately 27 per cent of surveys reported signs of coral damage.  This damage was generally low level (tips and edges of corals).  About 12 per cent of the reported damage was considered moderately severe (parts/branches). Anecdotal reports indicate some of this damage was caused by ex-Tropical Cyclone Oswald.

Following ex-Tropical Cyclone Oswald, there were reports of moderate to major levels of damage on reefs from Cairns to the Capricorn Bunker Group.  The high winds and heavy rainfall associated with this event have potentially affected individual coral reefs and sea grass beds, particularly in southern areas.  These effects include physical damage from waves, as well as the effects of low salinity, sediments and turbidity from the flood plumes.