This report is compiled by the Great Barrier Reef Marine Park Authority as part of the BleachWatch program. The BleachWatch team monitors Reef conditions daily throughout summer and provides regular updates on conditions in the Great Barrier Reef Marine Park. This is the final report for the 2008/2009 bleaching season.

Reef wide summary

The summer of 2008/2009 was characterised by a series of extreme events affecting the Great Barrier Reef (the Reef). The Great Barrier Reef Marine Park Authority (GBRMPA) has developed a series of Early Warning System tools under the Coral Bleaching Response Plan to assess the risk of climate change impacts affecting the Reef each summer. The forecasts for summer 2008/2009 predicted extreme sea surface temperatures and still conditions, raising the risk of widespread coral bleaching to high. Extreme sea surface temperatures did occur during November and December 2008, fortunately the  prolonged monsoonal conditions from January 2009 reduced temperature stress across most of the Reef, keeping water temperatures below coral bleaching thresholds (figure1). As a result mass coral bleaching did not occur, and only localised, minor temperature-induced bleaching was observed on reefs in the northern half of the Marine Park.

Figure 1. The above plot shows accumulated temperature stress, measured in degree heating days (DHD) for the Great Barrier Reef as at 28 January 2009. DHDs – a cumulative measure of daily temperatures above the long term average – accrued rapidly in December and January. During previous bleaching events, significant bleaching has occurred after the accumulation of 60 – 100 DHDs. The red circled areas show areas that reached the coral bleaching threshold.

Other climatic events have caused significant stress to sections of the Reef this summer. Record rainfall (Ingham experienced 600mm of rain above the three month average) caused extensive flooding to the Cairns-Whitsunday region. Subsequent flood plumes lowered the salinity and were associated with severe stress and localised coral death on shallow, inshore reefs between Cairns and Townsville. While these impacts are serious for individual affected reefs, damage from floodwaters was relatively minor on a Reef-wide scale (figure 2).

Figure 2. Satellite image of the flood plume from the Burdekin River – courtesy of CSIRO

Tropical Cyclone (TC) Hamish, a category five system, tracked down the Reef between the 5^th and 11^th of March 2009 (figure 3.) TC Hamish resulted in highly destructive winds over extensive offshore areas in the southern Great Barrier Reef.  Although damage was reported Reef-wide, the most severe damage occurred south of the Whitsunday group of islands. Preliminary data from the Australian Institute of Marine Science indicates that affected reefs sustained the most damage on exposed windward faces, with leeward sides sustaining much less damage.

Figure 3. Tropical Cyclone Hamish track map -  courtesy of the Bureau of Meteorology

On their own, these extreme events are not unique. However the cumulative impact of these events could have significant consequences for Reef resilience. "Resilience is the ability of a system to absorb shocks, resist phase shifts, regenerate and reorganise… so as to maintain key functions and processes" (the resilience alliance). Under predicted climate change scenarios these events and cumulative impacts are likely to occur more frequently in the future.  

Mortality and recovery monitoring at affected sites is currently being conducted in partnership with research organisations to determine the cumulative impact of these extreme events.  This multi-agency monitoring response has been implemented under the GBRMPA's new Climate Change Incident Response Framework.  

Reports received from stakeholder groups and the community continue to provide essential information to the GBRMPA about trends in Reef health and climate impacts.  We would particularly like to acknowledge the contributions made this season from BleachWatch participants, the Eye on the Reef program, the tourism industry and staff from the Queensland Department of Environment and Resource Management.  This year GBRMPA will present Certificates of Appreciation to a number of participants for their outstanding participation and contribution to the BleachWatch program.

Regional summaries

The Great barrier Reef World Heritage Area covers an area of approximately 348 000 square kilometres, therefore the extent of the impacts of different climatic events will naturally vary throughout the entire reef region.

Reports containing the above general information as well as more detailed regional summaries of BleachWatch reports, events and conditions for the 2008/2009 bleaching season in the Great Barrier Reef are available for the Far Northern region, the Cairns/Cooktown region, the Townsville/Whitsunday region and the Mackay/Capricorn region.