Coral Bleaching and Reef Health
Photo credit: Underwater Earth / XL Catlin Seaview Survey / Christophe Bailhache
#Reef health update - 15 February 2021
Like last week, cloud cover continues to restrict the ability of satellites to accurately measure sea surface temperatures over much of the Reef and modelled data showing warmer areas should be interpreted with caution.
Where observations were possible in recent days, sea surface temperature looks close to the long-term monthly average in the south and central parts of the Reef and above average in the far northern section.
We will get a better understanding of current conditions when cloud cover dissipates.
The Australian Institute of Marine Science in-water temperature loggers at a subset of reefs across the Reef indicate temperatures currently remain below bleaching thresholds.
The Bureau of Meteorology is forecasting warmer and wetter than average conditions, and above average sea surface temperatures across the Marine Park catchment between February and April.
As usual, local and regional weather conditions over the next few weeks will play a key role in determining overall outcomes for the Reef this summer.
Most of the central Great Barrier Reef coast and catchment received significant rainfall over the past week, with multiple flood warnings currently still in effect near Tully.
Models indicate a monsoon trough may develop across northern Australia in about a week, with widespread rainfall and tropical cyclone development becoming more likely.
Monitoring providers continue to be on flood watch with more rains expected, and teams are sampling the routine wet season Tully sites this week.
We’ve received reports of localised coral bleaching from locations in the far north of the Reef this past week.
Surveys by the Australian Institute of Marine Science’s Long-Term Monitoring Program are currently underway at reefs in the Cairns and Innisfail Sectors, with updates available shortly.
The Reef Joint Field Management Program commence scheduled trips next week to reefs between Cairns and Raine Island, with reports on observations of coral bleaching to follow.
#Our involvement and response
The Foundation is working to support the work of GBRMPA in their management response to this emerging bleaching situation, with our focus on supporting 3 key areas:
recovery assistance; and
Immediate Response projects and support for our partners includes:
Supporting GBRMPA and partners in priority monitoring out on the Reef, from the air and in-water, to quickly and accurately assess the emerging bleaching and impacts. This includes supporting rangers in the field as well as mobilising and empowering community members to actively contribute to monitoring on their own and tourist vessels, eg through Eye on the Reef
eReefs – Using and enhancing the functionality of the eReefs Reef-wide monitoring tool pioneered by the Foundation. This includes the Bureau of Meteorology-hosted ReefTemp which tracks ‘degree heating days’ and sea surface temperatures to help pinpoint where direct action is needed.
Recovery support (medium-term) includes:
Protect the surviving reefs in critical areas by removing or reducing other stressors to give them the best chance of staying healthy. This includes controlling crown-of-thorns starfish outbreaks and community education.
Continue to engage and inform communities to ensure support and up-take of temporary protection measures
Resilience (longer term) includes:
Accelerate natural recovery through innovations such as coral IVF (larval reseeding) and stabilising loose corals.
Actively restore reefs through techniques like coral outplanting.
Protect and actively restore critical reef sites and potential refuges for marine life, eg our Reef Islands Initiative including Lady Elliot Island
Developing an innovative toolkit of reef restoration and adaptation science solutions to help build the Reef’s ability to bounce back and recover from the growing combination of manmade and natural threats
Our pioneering projects are already helping scientists and managers fill critical knowledge gaps and prepare for the next stage of development in tackling the long-term impacts, and future events:
‘Stress test’ for corals – Developing an early warning system to detect coral reefs under stress before any physical signs are visible using metabolomics.
Searching for super corals – Identifying the genetic markers for corals more tolerant to heat stress.
Sun shield for the Reef – Developing the technology to scale up deployment of micro-thin, biodegradable surface films that block up to 30% of light to help combat coral bleaching at a local scale.
Reef in 3D – Investigating the impact of bleaching on the 3-dimensional structure of the reef and understanding how this links to changes in other reef communities such as fish.
Automated detection – Using computer image recognition software and remote sensing to accurately detect bleaching.
#What is coral bleaching?
The first visible sign that a coral is under stress is a change in colour from its original hue to a brilliant white. Stress causes the living coral animal to expel the tiny marine algae that live inside its tissue. These algae provide the coral with much of its food and colour. Without these algae (called zooxanthellae), the coral tissue appears transparent, revealing the coral’s bright white skeleton.
#What causes coral bleaching?
Bleaching occurs when corals are under stress. A primary cause of coral bleaching on the Great Barrier Reef during summer is heat stress resulting from high sea temperatures and increased UV radiation. A temperature increase of just one degree Celsius for only four weeks can trigger bleaching. Deprived of their food source, corals begin to starve once they bleach. If these increased temperatures persist for longer periods (eight weeks or more) corals begin to die. High water temperatures can affect reefs at regional and global scale.
Other stressors that can also cause bleaching include colder temperatures, freshwater inundation (low salinity), and poor water quality from sediment or pollutant run-off.
#Can corals recover from bleaching?
A bleached coral is not dead.
Corals can recover from bleaching if heat stress lessens, temperatures reduce, and conditions return to normal. Following previous mass bleaching events recorded on the Great Barrier Reef prior to 2016 and 2017, the vast majority of corals survived. In 1998, 50% of the reefs on the Great Barrier Reef suffered bleaching and in 2002 60% were affected, yet only around 5% of the coral reefs experienced coral mortality on both occasions. Not surprisingly, different corals recover at different rates, eg the fast growing branching corals are usually the first to bounce back.
Since 2017, there have been promising signs of recovery on reefs locally, however it is widely accepted that the Reef still needs more time to recover from the unprecedented back to back mass bleaching events in 2016 and 2017.