Coral reproduction on the Great Barrier Reef falls 89% after repeated bleaching


Morgan Pratchett, James Cook University

The severe and repeated bleaching of the Great Barrier Reef has not only damaged corals, it has reduced the reef’s ability to recover.

Our research, published today in Nature, found far fewer baby corals are being produced than are needed to replace the large number of adult corals that have died. The rate at which baby corals are settling on the Great Barrier Reef has fallen by nearly 90% since 2016.

While coral does not always die after bleaching, repeated bleaching has killed large numbers of coral. This new research has negative implications for the Reef’s capacity to recover from high ocean temperatures.

How coral recovers

Most corals reproduce by “spawning”: releasing thousands of tight, buoyant bundles with remarkable synchronisation. The bundles burst when they hit the ocean surface, releasing eggs and/or sperm. Fertilised eggs develop into larvae as they are moved about by ocean currents. The larvae settle in new places, forming entirely new coral colonies. This coral “recruitment” is essential to reef recovery.




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The research team, led by my colleague Terry Hughes from the ARC Centre of Excellence for Coral Reef Studies, measured rates of coral recruitment by attaching small clay tiles to the reef just before the predicted mass spawning each year. These settlement panels represent a standardised habitat that allows for improved detection of the coral recruits, which are just 1-2mm in size.

Almost 1,000 tiles were deployed across 17 widely separated reefs after the recent mass bleaching, in late 2016 and 2017. After eight weeks they were collected and carefully inspected under a microscope to count the number of newly settled coral recruits. Resulting estimates of coral recruitment were compared to recruitment rates recorded over two decades prior to the recent bleaching.

Australian Academy of Science.

Rates of coral recruitment recorded in the aftermath of the recent coral bleaching were just 11% of levels recorded during the preceding decades. Whereas there were more than 40 coral recruits per tile before the bleaching, there was an average of just five coral recruits per tile in the past couple of years.




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Reef resilience

The Great Barrier Reef (GBR) is the world’s largest reef system. The large overall size and high number of distinct reefs provides a buffer against most major disturbances. Even if large tracts of the GBR are disturbed, there is a good chance at least some areas will have healthy stocks of adult corals, representing a source of new larvae to enable replenishment and recovery.

Larvae produced by spawning corals on one reef may settle on other nearby reefs to effectively replace corals lost to localised disturbances.

It is reassuring there is at least some new coral recruitment in the aftermath of severe bleaching and mass mortality of adult corals on the GBR. However, the substantial and widespread reduction of regrowth indicates the magnitude of the disturbance caused by recent heatwaves.

Declines in rates of coral recruitment were greatest in the northern parts of the GBR. This is where bleaching was most pronounced in 2016 and 2017, and there was the greatest loss of adult corals. There were much more moderate declines in coral recruitment in the southern GBR, reflecting generally higher abundance of adults corals in these areas. However, prevailing southerly currents (and the large distances involved) make it very unlikely coral larvae from southern parts of the Reef will drift naturally to the hardest-hit northern areas.

It is hard to say how long it will take for coral assemblages to recover from the recent mass bleaching. What is certain is low levels of coral recruitment will constrain coral recovery and greatly increase the recovery time. Any further large-scale developments with also greatly reduce coral cover and impede recovery.




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Reducing carbon emissions

This study further highlights the vulnerability of coral reefs to sustained and ongoing global warming. Not only do adult corals bleach and die when exposed to elevated temperatures, this prevents new coral recruitment and undermines ecosystem resilience.

The only way to effectively redress global warming is to immediately and substantially reduce global carbon emissions. This requires that all countries, including Australia, renew and strengthen their commitments to the Paris Agreement on climate change.

While further management is required to minimise more direct human pressure on coral reefs – such as sediment run-off and pollution – all these efforts will be futile if we do not address global climate change.The Conversation

Morgan Pratchett, Professor, ARC Centre of Excellence for Coral Reef Studies, James Cook University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Great Barrier Reef Foundation chief scientist: science will lie at the heart of our decisions


Peter J Mumby, The University of Queensland

Much has been made of the federal government’s decision to invest A$500m into management of the Great Barrier Reef (GBR), A$443.3m of it to be administered by the Great Barrier Reef Foundation, of which I am the chief scientist.

If my conversations with colleagues in the reef research field are any guide, there is still a lot of confusion over the intended use of these funds, the disbursement process, and whether big business will interfere with how the reef is managed.

Filling funding gaps

Over the past five years, the foundation has funded or managed multiple research projects that aim to support long-term management of the reef. Many of these projects would be considered either too risky or not “pure science” enough to be funded by the Australian Research Council (the exception being the ARC Linkage program).

I mean “risky” not in the sense of posing a risk to the GBR, but rather to describe research plans that are at the cutting edge, where the potential rewards are high but so is the risk of failure.

In this way, the GBR Foundation has filled a critical gap in funding researchers who are working at the interface of science, climate change, and reef management. This has included teams from multiple universities, the Australian Institute of Marine Science (AIMS), and CSIRO.

Decisions over funding allocations are made through a conventional procedure involving external and internal review and two scientific advisory committees with representatives from each of the major research organisations (the University of Queensland, James Cook University, AIMS and CSIRO), the Great Barrier Reef Marine Park Authority, and an independent chair.




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As a professor of coral reef ecology at the University of Queensland, I participated in the foundation’s technical advisory group for several years and collaborated on several of the funded projects. As my own research focus includes how management can improve coral reef resilience, I was invited some months ago to serve as the GBR Foundation’s chief scientist, a part-time role alongside my main job as a University of Queensland professor.

I accepted this position for several reasons. First, scientists and practitioners have been calling for a major government investment in the GBR and I am keen to help steer the process in the most cost-effective way possible. I can help by ensuring that the right people are engaged in the process and that projects are subject to intense scientific scrutiny.

Second, having been involved with the GBR Foundation for some time, I know that its approach is both inclusive and merit-based, soliciting the best minds irrespective of which insitution they work for. This is important if we are to deliver the best value for taxpayers’ money.

Third, the foundation’s decision-making process is science-led, and I have never seen any interference from the board. Although some people have expressed concerns over the board’s links to the fossil fuel industry, climate change has been the focus of the foundation’s funded research for as long as I can remember.

Funding focus

The government’s decision to entrust environmental management and research to a private foundation is not unprecedented internationally. The US National Fish and Wildlife Foundation, for example, receives funds from both government agencies and private donations, which it uses to fund a range of conservation programs.

The A$443.3m provided to the GBR Foundation is intended to pursue a range of aims:

  • improving the quality of freshwater reaching the reef (A$201m)

  • reducing the impact of crown-of-thorns starfish (A$58m)

  • engaging traditional owners and the broader community in reef conservation (A$22.3m)

  • improving monitoring of reef health (A$40m)

  • supporting scientific research into reef restoration, with a specific focus on tackling challenges created by climate change (A$100m).

The latter is particularly significant because this program aims to expand the toolbox of interventions available to reef managers as climate change continues to intensify.

Of course, reef researchers and managers can’t fix climate change on their own. Other funding and incentives will also be needed to help our wider society reduce greenhouse emissions.

But here’s the important point: dealing with climate change will necessitate a wide range of responses, both to address the root cause of the problem and to adapt to its effects. The A$443.3m will help Australia do the latter for the GBR.

Clarifying misconceptions

I’d like to clarify some of the misconceptions I have heard around the funding awarded to the GBR Foundation.

The funds do indeed consider the impacts of climate change, specifically in helping coral reefs – and the associated management practices – adapt to the coming changes.

Science will lie at the heart of the decisions over how best to parcel out the funds, and although the foundation’s board will sign off on the approvals, it will have no say in what is proposed for funding.

Those research and management projects that do receive funding will be carried out by the most appropriate agencies available, whether that be universities, small or large businesses, other charities, AIMS, CSIRO, Natural Resource Management organisations, and so on. All of these agencies are well used to applying for funding under schemes like this.




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Finally, I have heard concerns about the involvement of major corporations on the Foundation’s board. Everyone is, of course, entitled to their view on the appropriateness of this. But for what it’s worth, my own is that progress on climate change will be strengthened, not weakened, by a close dialogue between those responsible for managing the impacts of climate change and those in a position to exert significant change in our society.

Many of world’s greatest innovations occur in major industry, and I hope this will also apply to the Great Barrier Reef.The Conversation

Peter J Mumby, Chair professor, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.