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Weekly Great Barrier Reef health update for March 2020

by GBRMPA 16 Mar 22:42 UTC
Weekly reef health update for March 2020 © GBRMPA

Heat stress accumulated rapidly in February 2020, the warmest sea surface on record for the Great Barrier Reef for any month since 1900 — at 1.25 degreesC above average. February 2016 was the second warmest on record at 1.11 degreesC above average.

This is an important part of the explanation of why heat stress on the Reef accumulated so rapidly during February.

This difference between 2016 and 2020 will likely have consequences for the extent and severity of coral bleaching. We will closely monitor Reef health in the coming month to track these consequences.

Much of the Great Barrier Reef has been covered by cloud since Sunday 8 March.

With stronger winds, cloud cover and rain over the Reef, we are starting to observe sea surface temperatures reducing across the Reef.

Water temperatures at all the Australian Institute of Marine Science weather stations within the Reef have reduced over the last two days, but these will be monitored to determine whether this is a long-term trend.

Coral health reports

The Great Barrier Reef Marine Park Authority continues to receive reports of coral health across the Reef.

Where we've received reports of bleaching, it matches where the Bureau's ReefTemp tool shows the greatest thermal stress accumulation over summer — that is, on Far Northern inshore and mid-shelf reefs and the inshore Central and Southern reefs.

Observations during aerial patrols conducted between Townsville and Mackay and the Capricorn-Bunkers over 6 to 8 March in the areas where there is the greatest thermal stress accumulation.

The most severe bleaching was observed on inshore reefs. In the Capricorn-Bunker group, there was a bleaching gradient observed, with more severe bleaching in the northern reefs. There was less in the southern reefs of this group, however, there was indications of thermal stress at all reefs visited.

There are further observations of minor and patchy bleaching throughout many other areas of the Reef. To date, offshore reefs (those closest to the edge of the continental shelf) show little to no signs of bleaching.

Local weather conditions over the next few weeks will play a key role in determining overall outcomes for the Reef this summer.

We continue to work with our science partners including the Australian Institute of Marine Science, Bureau of Meteorology, James Cook University, University of Queensland and National Oceanic and Atmospheric Association.

Next week's outlook

Forecast tools from both the Bureau and the US National Oceanic and Atmospheric Association (NOAA) agree that thermal stress, although still currently high, is likely to start to decrease in the Marine Park throughout the rest of March and into April.

The tropical low pressure system currently situated off the east coast of Australia will create unsettled weather across the Reef, which is currently resulting in cooling of Reef waters.

Aerial surveys

The Marine Park Authority is working with our partners to best understand the health of the Reef this summer.

On 17 March 2020, aerial surveys to assess the extent and severity of coral bleaching are scheduled to commence across the Great Barrier Reef.

These surveys will be conducted by the ARC Centre of Excellence for Coral Reef Studies at James Cook University and the Authority will be an observer as part of these aerial surveys.

Experience has shown this is the best and most effective way to understand where coral bleaching has, and has not, occurred and the severity of coral bleaching across the expanse of the Reef.

The flights are timed to coincide with the anticipated peak of coral bleaching across the Reef, when corals are white or fluorescing and most visible from the air. This will ensure we have an accurate understanding of the patterns of bleaching that are present.

The surveys will follow the past flight paths of 2016 and 2017 surveys. The flights will also cover the Torres Strait where the actual Great Barrier Reef extends. The flights will take about nine days over about a two week period, dependent on weather.

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