Interim report on 2016 coral bleaching event on the Great Barrier Reef

30 Sep 2016

This report includes the preliminary results of in-water reef health and impact surveys conducted by GBRMPA and the Queensland Parks and Wildlife Service. The surveys provided a rapid assessment of the spatial extent and severity of the 2016 mass coral bleaching event in the Great Barrier Reef Marine Park. Similar information was provided to the public through regular updates on GBRMPA’s website and associated communication tools. The agency and the Queensland Parks and Wildlife Service are also preparing to undertake further Reef-wide surveys in October and November 2016 to assess recovery rates and survivorship.

In-water survey data has documented widespread but patchy bleaching of varying levels of severity throughout the Marine Park as a result of prolonged heat stress. The most severe bleaching occurred between the tip of Cape York and just north of Port Douglas (that is, in the remote northern third of the Marine Park). This area experienced the greatest heat stress, with abnormally high sea surface temperatures persisting for a long period of time and as a result, a substantial amount of severely bleached coral died. The Torres Strait also had severe bleaching, but is not covered in this report.

Die-off of corals (coral mortality) south of Port Douglas was highly variable by location, and many reefs escaped with little or no mortality. Bleaching-related mortality of corals was highest on inshore and mid-shelf reefs in the far north around Cape Grenville and Princess Charlotte Bay. Severe bleaching also occurred at all shelf locations in the Lizard Island region, with substantial coral die-off now reported. Variability in bleaching severity was highest among reefs in the Cairns–Port Douglas and Townsville areas. Most reefs south of of Cairns escaped major impacts. The strong latitudinal gradient and high variability of bleaching severity among reefs has left many reefs relatively unaffected and still in relatively good condition. Despite the bleaching event, the Great Barrier Reef remains in a much better state than many other coral reef ecosystems around the world.

Surveys detailed in this report were supplemented by additional surveys by science partners, and information from a network of tourism industry operators and the public. In particular, the Australian Institute of Marine Science conducted in-water surveys and the ARC Centre of Excellence for Coral Reef Studies conducted aerial and in-water surveys. Science partners are also conducting further assessments throughout 2016. All information on the event is being used to build a comprehensive picture of reef health and condition, and the impacts of bleaching. Full analyses are ongoing and will be reported on in future joint publications. Analyses show the Great Barrier Reef has typically been robust in response to disturbances and is likely to fare better than most reef regions around the world. However this severe bleaching will have lasting impacts on the health and resilience of affected reefs, primarily via reductions in the amount of coral, shifts in coral community structure, and flow-on effects for reef fish and invertebrate communities. Such impacts then have the potential to affect the social and/or economic value of reef sites important to Reef-based industries. The severity of this bleaching event reinforces the need for a concerted international effort to rapidly mitigate global climate change, as well as national and local actions to build the Reef’s resilience by reducing direct and indirect impacts. These efforts are our best insurance for protecting this precious natural icon.

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