Reef health

Reef health summer 2018-19

The Great Barrier Reef remains a vibrant, beautiful ecosystem of immense value to Australians and the world and continues to attract millions of visitors each year. However, like other coral reefs globally, the Reef is under pressure from climate change and other threats.

Climate change impacts on coral reefs are predicted to worsen and critically affect the survival of coral reefs globally without the strongest possible climate change mitigation.

The Reef is already experiencing the consequences of climate change — most notably, two consecutive years of coral bleaching.

Global action on climate change is vital and urgent. Australia has ratified the Paris Agreement to reduce greenhouse gas emissions. Limiting global warming closer to the stricter 1.5°C position — not just the 2°C overarching target — reduces climate risks to coral reefs.

Now more than ever, it’s vital to address climate change at the global level and implement local actions to boost reef resilience.

Reef health over the last five years

There’s been multiple significant impacts on the Great Barrier Reef over the last five years, with some of the most significant of those impacts occurring since 2016. This includes unprecedented back-to-back years of coral bleaching, outbreaks of coral disease and crown-of-thorns starfish, and severe cyclones and subsequent flood plumes.

The Reef’s scale and natural resilience means it has the capacity to recover from impacts to an extent, given benign environmental conditions and adequate time free from disturbance. Under a changing climate, recovery capacity is already limited and will be further impaired by the predicted increase in the frequency of bleaching events.

Most impacts are concentrated in the northern two-thirds of the Marine Park. An estimated 29 per cent of shallow-water coral cover was lost during 2016 across the Marine Park. Over 75 per cent of this mortality occurred in the far north — the 600-kilometre stretch between the tip of Cape York and just north of Lizard Island.

As at mid-2018, coral cover in the Region’s north was less than half of what it was in 2013. This is unprecedented and due to mortality caused by two severe cyclones, severe coral bleaching in 2016 and 2017, and ongoing crown‐of‐thorns starfish outbreaks.

As of September 2018, survey results from our Eye on the Reef program indicate there are minor levels of coral disease and coral damage throughout the Marine Park, and isolated cases of very minor coral bleaching beginning to appear from Port Douglas in the north to the Capricorn-Bunker Group in the south.

The current crown-of-thorns starfish outbreak has progressed south to reefs in the Innisfail region and offshore from Townsville.

Current condition by region

The Australian Institute of Marine Science’s (AIMS) Long-term Monitoring Program provides an annual summary of coral reef condition. AIMS divides the Great Barrier Reef into three regions for reporting purposes: Northern (last surveyed in 2017), Central and Southern (last surveyed in 2018).

For the first time in the history of the monitoring program, trends in average hard coral cover on reefs in all three regions show a steep decline.

  • Northern region: as of early 2017, average coral cover declined to approximately 10 per cent (less than half of what it was in 2013) as a result of two severe tropical cyclones and the 2016 mass coral bleaching event. Survey results do not yet take into account the impacts of the 2017 bleaching event. These locations are scheduled for re-survey in 2018-19.
  • Central region: as of May 2018, average coral cover had declined from 22 per cent in 2016 to 14 per cent in 2018 as a result of mass coral bleaching and crown-of-thorns starfish outbreaks.
  • Southern region: as of May 2018, average coral cover had declined for the first time in seven years, dropping from 33 per cent in 2017 to 25 per cent in 2018 as a result of crown-of-thorns starfish outbreaks. AIMS Long-term Monitoring Program survey results do not yet take into account the impacts of cyclone Debbie in the Whitsundays. These locations are scheduled for re-survey in 2018-19.

Survey results from our Marine Monitoring Program show average coral cover on inshore coral reefs in the Whitsundays was high prior to cyclone Debbie, however declined by more than half following the impact.

As coral is the foundation of the reef ecosystem, when coral is effected there are flow-on effects to other animals and habitats.  While these impacts are significant, the Reef’s size means there are areas unaffected by any given event.

Those corals that survived on the Reef are “genetic gold” — they’ve proven resilient to tough conditions and will play an important role in reef recovery through spawning other corals.

Recovery is being seen on some parts of the Reef, which is promising, though it generally takes even the fastest growing corals up to 10 years to fully recover from impacts, provided there’s sufficient time between these events.

Risk over summer

Summer is the highest risk period for coral reef due to elevated temperature, with corals highly sensitive to even small variations in temperature.

Over this time, we assess the health of reefs in the Great Barrier Reef Marine Park, as this part of the year poses a greater risk of extreme weather, particularly heat waves, cyclones and flooding.

Stressful conditions can lead to coral disease outbreaks, while poor water quality may make coral more susceptible to bleaching and lead to greater numbers of coral-eating crown-of-thorns starfish.

From December 2018, we will provide updates on reef condition over summer via our website.

Monitoring reef health

We use the best available science contributed by a wide range of research institutions, government agencies, and universities to manage the Reef and ensure it remains healthy for future generations.

There’s a range of programs in place to look at Reef health, including our Reef Integrated Monitoring and Reporting Program and the Long-term Monitoring Program by the Australian Institute of Marine Science.

Any long-term flood or cyclone-related impacts on coral reefs will be determined by surveys from that program and also through the Reef 2050 Marine Monitoring Program.

Because it’s important we have accurate, real-time information on Reef conditions, any visitors to the Reef can also report observations of coral bleaching, disease, predation or damage through the Eye on the Reef program.

Published every five years, our Outlook Report also provides a holistic view of Reef health and management. The next report will be published in 2019.