The impact of the worst mass global bleaching event on record has been revealed, with high level results revealing a stark contrast between the northern and southern regions of the Great Barrier Reef.
The Great Barrier Reef Marine Park Authority (GBRMPA) and Australian Institute of Marine Science (AIMS) together with other research organisations carried out extensive post-bleaching surveys throughout October and November, with the Foundation providing direct funding support.
The preliminary survey results show the northern third of the Reef is the worst hit region, as expected. North of Port Douglas, more than half of the bleached corals died on average. In this area around two thirds of the shallow water corals have not survived.
This contrasts with the bottom two-thirds of the Reef which suffered minimal or no coral mortality.
AIMS Research Program Leader Dr Britta Schaffelke points out that mortality due to the bleaching varies widely between regions, between reefs within a region, and even on individual reefs where the deeper corals were less affected.
“While there was a clear north-to-south gradient in overall impact, bleaching severity and subsequent mortality varied significantly between regions and individual reefs,” said AIMS Research Program Leader Dr Britta Schaffelke. “The reasons are most likely a combination of exposure to heat stress and the specific tolerance of the local coral communities.”
With this variability, there are plenty of bright spots within the 2,300 km long Reef.
GBRMPA Director of Reef Recovery Dr David Wachenfeld said the Reef remained one of the best protected marine ecosystems in the world and was "very, very far from dead".
“The surveys show there are still many reefs throughout the Marine Park with abundant living coral, particularly in popular tourism locations in the central and southern regions, such as the Whitsundays and Cairns,” Dr Wachenfeld said.
“The far north offshore area, which includes outer-shelf reefs in the northernmost part of the Marine Park, also escaped the most severe bleaching and mortality, compared to elsewhere in the north.”
The Marine Park Authority says it will take several months to complete analyses and reporting. Detailed findings from these latest surveys will be available in early 2017, including updated estimates of bleaching-related impacts and information on the early stages of coral recovery.
GBRMPA Chair and Chief Executive Dr Russell Reichelt said that ensuring Reef resilience is his core priority and his team is doing everything possible to support its recovery.
“The Reef is a very large and resilient ecosystem. While the bleaching this year was very serious, recent studies have shown that in the three years prior to the bleaching coral cover increased by 19 per cent across the Marine Park,” Dr Reichelt said.
“The Great Barrier Reef still remains in a much better state than many other coral reefs around the world; however, the severity of the global mass bleaching event reinforces the need for a concerted international effort on climate change as well as national and local actions to reduce all other pressures on the Reef.”
AIMS CEO John Gunn said that looking towards the future and learning from this event is critical.
“The AIMS Long-term Monitoring Program has been surveying the health of the reef for 30 years, through many disturbance and recovery cycles,” Mr Gunn said.
“To learn as much as possible from this bleaching event, AIMS will conduct studies to assess the ongoing impact of heat stress and will investigate recovery processes, in detail, to identify and understand patterns of chronic stress or recovery between regions. This work will provide important insights for research, currently being conducted in the National Sea Simulator at AIMS, into coral adaptation, reef restoration and assisted evolution.”