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Great Barrier Reef Marine Park Authority :: Final Bleaching Summary Report 2005/2006

Final Bleaching Summary Report 2005/2006

This report is compiled by the Climate Change Response Programme of the Great Barrier Reef Marine Park Authority. The Climate Change Response Programme provides regular reports on conditions in the Great Barrier Reef Marine Park throughout summer and publishes early warnings of increased stress levels or widespread coral bleaching. This is the sixth and final report for the summer of 2005/06.
 

May 2006

Summary

On the basis of seasonal temperature trends, the threat of widespread coral bleaching for the Great Barrier Reef Marine Park has now passed for this year. Sea temperatures have cooled and are expected to remain below temperatures known to cause stress to corals, at least until the onset of next summer.

The hot water anomaly that persisted over the southern area of the Great Barrier Reef Marine Park, and developed briefly over the central and northern region, has now dissipated.
Regional sea temperatures have returned to below the long-term summer maxima. This regional cooling brought relief to many sites that previously had been at, or were approaching, temperatures known to cause stress to corals.

Generally, bleaching severity was low in the Lizard Island (far northern), Cairns (northern), Townsville (central) and the Whitsunday Islands (southern) regions. However, severe bleaching was recorded in the far southern region, in particular at the Keppel Islands.

According to Great Barrier Reef Marine Park Authority surveys and BleachWatch reports, bleaching in the remainder of the Marine Park is either no longer evident or corals have shown signs of recovery, with only minor bleaching remaining in the central and northern Great Barrier Reef Marine Park. Severe coral bleaching is still evident in the southern area, and the Great Barrier Reef Marine Park Authority will continue to monitor these reefs for recovery and mortality.

 

Weather and Sea Temperatures

At the start of summer, a hot water anomaly developed early and persisted over much of the southern area of the Great Barrier Reef Marine Park. In January, monsoonal conditions developed in north Queensland bringing cloud cover to the central and northern Great Barrier Reef Marine Park, cooling water temperatures in this region. However, waters in the southern region continued to warm (Figure 1a).

The whole region experienced a hot period through February and early March. During this time there was little cloud cover, minimal or no wind and as a result sea temperatures increased throughout the Great Barrier Reef Marine Park (Figure 1b). Tropical Cyclone Larry and Tropical Cyclone Wati contributed to a general cooling the water in all regions towards the end of March (Figure 1c), and sea temperatures have remained below the long-term summer maxima since.

2006_05_final_report

2006_05_final_report_02Satellite monitoring of sea surface temperatures by the National Oceanic and Atmospheric Administration show temperatures in the Great Barrier Reef Marine Park are no longer above the expected summer maximum. This is consistent with the observed temperatures at weather stations (Reef Futures) and normal seasonal trends.

Current weather conditions can be found on the Bureau of Meteorology web site.

Summary of coral bleaching surveys for 2005/2006

At the height of summer, sea temperatures were either at or above levels known to cause thermal stress to corals in all regions of the Great Barrier Reef Marine Park, particularly in the far southern area. Great Barrier Reef Marine Park Authority scientists surveyed 34 reefs within the Great Barrier Reef Marine Park in collaboration with Pelican Expeditions and the Department of the Environment and Heritage. 

The aim was to assess the spatial extent and severity of coral bleaching throughout the Great Barrier Reef Marine Park. The surveys were timed to coincide with the peak of the bleaching event, and to document the spatial and taxonomic patterns of bleaching. This information is necessary to report on the extent and severity of bleaching, and to interpret the causes and significance of changes in reef condition.

Each survey assessed the condition and composition of the benthic community at reefs in five cross-shelf regions. These were located at latitudes centred on Lizard Island, Cairns, Townsville, Whitsunday Islands and the Capricorn Bunker Group. Surveyed reefs were those regularly visited as part of the Australian Institute of Marine Science Long-Term Monitoring Programme.

Low level bleaching (< 10 per cent) recorded in the Lizard Island, Cairns, Townsville and Whitsunday survey regions was confined to bleaching sensitive corals such as Acropora (staghorn and plate corals) and Pocillopora (needle and bushy corals), as well as soft corals in some locations.

Severe bleaching (>75 per cent) was recorded in the far southern region. The proportion of corals bleached at each site ranged from 1.5 per cent (lower slope of Wreck Island) to 100 per cent (upper slope of Halfway Island), with an overall average of 46 per cent for the region. Mortality from bleaching was generally very low at the time of the survey (2 to 6 per cent), and confined to the inshore sites around the Keppel Islands.

The inshore reefs were the worst affected, with an average of 84 per cent of corals affected by bleaching in this region. Acropora (staghorn and plate corals), Pocillopora (needle and bushy corals), as well as some soft corals, were most commonly affected although bleaching was also recorded for massive corals such as Faviids and Porites in the worst affected areas.

The Great Barrier Reef Marine Park Authority will continue to monitor the fate of bleached corals, particularly in the Keppel Islands, to determine the extent of recovery and mortality at reef sites that have experienced severe bleaching.

Results from the Great Barrier Reef Marine Park Authority surveys reflect the patterns of bleaching reported by BleachWatch participants. Over 130 reports from 95 participants were received during summer, providing an essential early warning system of coral bleaching. BleachWatch participants were the first to report severe bleaching in the Keppel Island region. Regular reports from participants in the central and northern areas helped track the onset of minor bleaching and document the recovery soon after temperatures cooled.

The Great Barrier Reef Marine Park Authority is grateful for the support of BleachWatch participants, the Australian Institute of Marine Science, the National Oceanic and Atmospheric Administration, Marine Studies Centre of University of Queensland, and Pelican Expeditions for helping monitor bleaching in the Great Barrier Reef Marine Park throughout the summer.

If you are interested in participating in BleachWatch for the summer of 2006/2007 please contact the BleachWatch Coordinator.

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