Summer 2011/12 in review

Summer brings increased risks for the Great Barrier Reef. Unusually high water temperatures can lead to coral bleaching, cyclones can cause damaging waves and monsoonal conditions send stressful floodwaters into the Great Barrier Reef. Stressful conditions can lead to coral disease outbreaks and poor water quality may also lead to an increase in the abundance of predatory crown-of-thorns-starfish.

Environmental Conditions

According to the Bureau of Meteorology (BoM), Summer 2011/2012 was influenced by moderate La Niña conditions, which began weakening to a neutral phase in March 2012.  Environmental conditions on the Great Barrier Reef remained relatively mild throughout most of January, until a period of still, calm conditions in late February, when sea temperatures rose above monthly averages across most of the Reef.  This was followed by a period of monsoonal rains and high cloud cover which limited a further increase in sea temperature.  However, conditions across the northern and central Great Barrier Reef from Port Douglas to Mackay sustained sea temperatures at levels known to be mildly stressful to corals.  Sea surface temperatures remained above average monthly levels into April.  The Great Barrier Reef Marine Park Authority (GBRMPA) and the Queensland Parks and Wildlife Service (QPWS) continued to monitor reef health throughout this period.

Although La Niña conditions normally bring cyclones, no cyclone activity affected the Great Barrier Reef in the recent summer. The summer monsoon did produce localised flooding from the Fitzroy and Burdekin rivers. However, these flood plumes were not on the same scale as the large flood plumes during the 2010/2011 summer, and only extended as far as some inshore reefs.

For more detailed information, view our table of observed and forecast environmental conditions.

Coral health reports

Participants in our early warning system have reported incidences of low to moderate level coral bleaching predominantly in some reefs in the central region, as well as isolated incidences in the northern and southern regions. Most of the coral bleaching observed was on temperature sensitive species such as the needle coral (Seriatopora hystrix) and some branching Acropora species.

Increased numbers of juvenile and adult crown-of-thorns starfish were reported from some reefs in the northern region. Low levels of coral disease, and isolated incidents of coral damage associated with anchoring and a vessel grounding were also observed.  

The legacy of damage from Tropical Cyclone Yasi (February 2011) remains evident, with low cover of fragile branching and plate corals at affected reefs. There are signs of early recovery in the form of young corals beginning to establish on reef areas cleared by the cyclone. However, full recovery from this event is expected to take a decade or more.

Summary of results:

The Great Barrier Reef Marine Park Authority, Queensland Parks and Wildlife Service, researchers and industry partners completed 374 reef health surveys covering 54 reefs between 1 Dec 2011 and 30 April 2012.

Overall, survey results indicate a low level of coral stress on the Great Barrier Reef during summer 2011/12 and autumn 2012. Half of all surveys (52 per cent) recorded no impacts to reef health.  Of the remainder, 31 per cent of surveys reported one type of reef health impact, and 17 per cent of surveys recorded more than one type of impact.  Of the surveys that found impacts, physical damage was the most common type found (35 per cent), closely followed by coral bleaching (31 per cent). Coral disease was noted in 17 per cent of surveys, and less than 10 per cent of surveys recorded signs of predation from crown-of-thorns-starfish or Drupella snails. Whilst impacts were recorded on 48 per cent of surveys in the majority of cases these impacts were mild in severity and unlikely to result in serious or lasting damage.

The Great Barrier Reef Marine Park Authority will continue to work with partner industries, organisations and the community to keep a close eye on the health of the Reef throughout the year.

More information

Understanding the impacts of extreme weather events can help us to better comprehend the implications of climate change for the Great Barrier Reef.

These updates on current conditions are provided as part of the Great Barrier Reef Marine Park Authority's Reef Health Incident Response System. Our summer response is a key part of the Great Barrier Reef Climate Change Action Plan.

For more information on monitoring environmental conditions on the Great Barrier Reef, as well as reef health monitoring please email the Great Barrier Reef Marine Park Authority.