French-Australian research and innovation to the rescue of the coral reef #ST9 [fr]

In early 2020 an episode of massive bleaching, the third in only five years, affected for the first time the three regions (north, central, and south) of the Great Barrier Reef. This followed the study of 1,036 reefs by air in March 2020 by the ARC Centre of Excellence for Coral Reef Studies at James Cook University, after the surface water temperature reached its highest value for a single February since measurements began in 1900, according to the Australian Bureau of Meteorology.

The data suggest that this event may be the most severe of the five massive bleaching events after the 2016 event. To confirm this, a key factor in describing severity is the rate of coral mortality, rather than the amount of bleaching. However, due to operational constraints due to COVID-19, less data on coral mortality/recovery rates have been collected until now.

Bleaching and its impact on the reef ecosystem

The first recorded massive bleaching along the Great Barrier Reef occurred in 1998, when abnormally high temperatures were observed on a large scale, causing the death of 16% of the world’s reefs. Further massive bleaching of the site has since occurred in 2002, 2006, 2016, 2017 and now in 2020, also caused by unusually high sea surface temperatures during the summer season (thermal bleaching). Rarer, two smaller bleaching events (in 2008 and 2011) were caused by an influx of freshwater following extremely high rainfall in Queensland (freshwater bleaching). The gap between bleaching episodes is narrowing, preventing full reef recovery, particularly during consecutive bleaching events - the first example in the summers of 2016 and 2017.

This bleaching originates from the breakdown of the symbiosis between the coral (host) and a type of unicellular algae, commonly known as zooxanthellae. These algae normally live inside the coral cells and help the coral to live, providing up to 90% of the energy needed for its metabolism by converting light energy into chemical energy through photosynthesis. This balance is fragile and depends on many parameters. Among them, the boundary between the beneficial and harmful effects of temperature is narrow, and above a certain value (which varies according to coral species) it alters the chemical activity of the algae, causing damage to the host cells. When this stress is too great, the corals expel the zooxanthellae massively. The zooxanthellae, and on a larger scale, the reef, then loses its coloration and becomes transparent, making its calcareous skeleton visible. Corals have the capacity to survive there, but are very weakened: slower growth, reduced reproduction and predisposition to disease.

The death of the reefs leads to a long-term collapse of the existing ecosystem, reducing the area available, in terms of shelter and food, for fish communities and other associated organisms. In addition to the high ecological cost, this threat also has a socio-economic cost on several human industries, such as fishing and tourism. It should be noted that the sheer size of the Great Barrier Reef has always been one of its main assets in terms of resilience, but as the area of bleaching expands, as events intensify and are repeated, with delays between bleaching episodes becoming shorter, there is concern that the natural resilience of the reef may be compromised.

A story under surveillance

For 30 years the Australian Institute of Marine Sciences (AIMS) has funded a long-term monitoring programme of the Great Barrier Reef, monitoring 47 mid and deep-sea reefs. This work represents the longest continuous record of reef community health over such a large geographical area. Successive dives along the same sections of reef study fish populations by visual census and record the condition of corals and other organisms. A separate component is monitoring the effects of the 2004 re-zoning plan (classification of land and marine areas according to the protection to be provided).

Two other programmes have also been studying coastal reefs (which can be reached from the shore by a small boat, 32 study points), which are more vulnerable to threats than those further from shore, since 2005, as well as Scott Reef (north-western Australia, since 1994), due to its isolation from other reefs.

These data document the effects of disturbances, such as outbreaks of spiny crown starfish, coral disease, cyclones and bleaching events. The results of this monitoring are regularly reported, allowing them to be used for in-depth analyses in numerous scientific publications. Biannual newsletters are available in English on the Government’s Great Barrier Reef Marine Park Authority (GBRMPA) website.

Chronology of recent events

As episodes occur, the number of reefs that have escaped severe bleaching continues to decline. These reefs are located offshore, in the far north and in remote areas in the south.

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The north was the most affected region in 2016 (more than 50% of corals on this section died, and 22% of corals along the entire site), followed by the central region in 2017. In 2020, the cumulative bleaching footprint expanded further to include the south.

In parallel with these observations, a report published in the journal Nature on 3 April 2019 noted that new coral births fell by 89% in 2018, a direct consequence of the successive bleaching events of 2016 and 2017. The reef ecosystem will be reorganized in the long term if the trend continues, as researchers also found that the mix of species that make up the new generation of corals has changed dramatically: Acropora, the branched corals that are the dominant species and make up the structure of the reef, for example, have decreased by 93%. Some species are expected to take up to two decades to recover their reproductive capacity.

If the reef structure becomes less three-dimensional and complex, habitat and food sources are reduced, and this has repercussions on the food chain. As a result, the diversity of fish and other marine life is likely to decline as the transition proceeds, more rapidly than expected.

Government Response and Action by Research Institutes

In 2015, the federal government presented a long-term sustainability plan to protect the Great Barrier Reef. Scaled over 35 years, the Reef 2050 Plan, for an amount of 2.7 billion dollars in collaboration with the Queensland Government, combines an investment strategy (R&D) with legislative progress. Within this framework, the R&D phase of the Reef Restoration and Adaptation Program (RRAP), responsible for implementing the Reef 2050 Plan, was launched on 16 April 2020 for an initial amount of 150 million dollars.

Australia’s research and education sector is fully engaged in this strategy and is working closely with the Great Barrier Reef Marine Park Authority, particularly institutions such as AIMS (Australian Institute of Marine Science, which owns the National Sea Simulator), CSIRO, University of Queensland, Queensland University of Technology, James Cook University, Southern Cross University, Great Barrier Reef Foundation, etc.

Among the actions underway, CSIRO is currently developing the eReefs research project:

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The eReefs research project is a collaboration between the Great Barrier Reef Foundation, CSIRO, Australian Institute of Marine Science, Bureau of Meteorology, and Queensland Government. It aims to develop a platform that will provide a picture of what is currently happening on the reef and what will likely happen in the future.

The system spans the catchments, estuaries, reef lagoon and the open ocean. It will provide information on physical processes, sediment transport, biogeochemistry and ocean colour. The project addresses enhanced monitoring, data standards, data architecture, operational modelling, reporting and data visualisation. The dedicated eReefs website provides access to data and many of the tools that have been developed as a result of this research.

Mathieu Mongin, a French researcher at the CSIRO in Hobart and head of AFRAN network in Tasmania, tells us more in this interview:

In an upcoming Science Thursday, the French Embassy in Australia will present the CORAL REEF PARK project: eReefs-QHub Operational Demonstrator, a promising collaboration between the CSIRO and BlueCham, an innovative New Caledonian company in the field of Earth observation from the IRD.

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Dernière modification : 08/07/2020

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