When coral dies, tiny invertebrates boom. This could dramatically change the food web on the Great Barrier Reef


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Kate Fraser, University of TasmaniaThis week, international ambassadors will take a snorkelling trip to the Great Barrier Reef as part of the Australian government’s efforts to stop the reef getting on the world heritage “in danger” list.

The World Heritage Centre of UNESCO is set to make its final decision on whether to officially brand the reef as “in danger” later this month.

To many coral reef researchers like myself, who have witnessed firsthand the increasing coral bleaching and cyclone-driven destruction of this global icon, an in-danger listing comes as no surprise.

But the implications of mass coral death are complex — just because coral is dying doesn’t mean marine life there will end. Instead, it will change.

In recent research, my colleagues and I discovered dead coral hosted 100 times more microscopic invertebrates than healthy coral. This means up to 100 times more fish food is available on reefs dominated by dead coral compared with live, healthy coral.

This is a near-invisible consequence of coral death, with dramatic implications for reef food webs.

When coral dies

Tiny, mobile invertebrates — between 0.125 and 4 millimetres in size — are ubiquitous inhabitants of the surfaces of all reef structures and are the main food source for approximately 70% of fish species on the Great Barrier Reef.

These invertebrates, most visible only under a microscope, are commonly known as “epifauna” and include species of crustaceans, molluscs, and polychaete worms.




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When corals die, their skeletons are quickly overgrown by fine, thread-like “turfing algae”. Turf-covered coral skeletons then break down into beds of rubble.

We wanted to find out how the tiny epifaunal invertebrates — upon which many fish depend – might respond to the widespread replacement of live healthy coral with dead, turf-covered coral.

A sample of epifauna under the microscope.
Kate Fraser

I took my SCUBA gear and a box of lab equipment, and dived into a series of reefs across eastern Australia, from the Solitary Islands in New South Wales to Lizard Island on the northern Great Barrier Reef.

Underwater, I carefully gathered into sandwich bags the tiny invertebrates living on various species of live coral and those living on dead, turf-covered coral.

But things really got interesting back in the laboratory under the microscope. I sorted each sandwich bag sample of epifauna into sizes, identified them as best I could (many, if not most, species remain unknown to science), and counted them.

I quickly noticed samples taken from live coral took just minutes to count, whereas samples from dead coral could take hours. There were exponentially more animals in the dead coral samples.

The Great Barrier Reef may soon be listed as ‘in danger’
Rick Stuart-Smith

Why do they prefer dead coral?

Counting individual invertebrates is only so useful when considering their contribution to the food web. So we instead used the much more useful metric of “productivity”, which looks at how much weight (biomass) of organisms is produced daily for a given area of reef.

We found epifaunal productivity was far greater on dead, turf-covered coral. The main contributors were the tiniest epifauna — thousands of harpacticoid copepods (a type of crustacean) an eighth of a millimetre in size.

In contrast, coral crabs and glass shrimp contributed the most productivity to epifaunal communities on live coral. At one millimetre and larger, these animals are relative giants in the epifaunal world, with fewer than ten individuals in most live coral samples.

Dead coral rubble overgrown with turfing algae.
Rick Stuart-Smith

These striking differences may be explained by two things.

First: shelter. Live coral may look complex to the naked eye, but if you zoom in you’ll find turfing algae has more structural complexity that tiny epifauna can hide in, protecting them from predators.

A coral head is actually a community of individual coral polyps, each with a tiny mouth and fine tentacles to trap prey. To smaller epifauna, such as harpacticoid copepods, the surface of live coral is a wall of mouths and a very undesirable habitat.




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Second: food. Many epifauna, regardless of size, are herbivores (plant-eaters) or detritivores (organic waste-eaters). Turfing algae is a brilliant trap for fine detritus and an excellent substrate for growing films of even smaller microscopic algae.

This means dead coral overgrown by turfing algae represents a smorgasbord of food options for the tiniest epifauna through to the largest.

Meanwhile, many larger epifauna like coral crabs have evolved to live exclusively on live coral, eating the mucus that covers the polyps or particles trapped by the polyps themselves.

Harpacticoid copepod are just an eighth of a millimetre in size.
Naukhan/Wikimedia, CC BY

What this means for life on the reef?

As corals reefs continue to decline, we can expect increased productivity at the base level of reef food webs, with a shift from larger crabs and shrimp to small harpacticoid copepods.

This will affect the flow of food and energy throughout reef food webs, markedly changing the structure of fish and other animal communities. The abundance of animals that eat invertebrates will likely boom with increased coral death.

We might expect higher numbers of fish such as wrasses, cardinalfish, triggerfish, and dragonets, with species preferring the smallest epifauna most likely to flourish.

The dragonet species, mandarinfish, feeds on the smallest harpacticoid copepod prey.
Rick Stuart-Smith

Invertebrate-eating animals are food for a diversity of carnivores on a coral reef, and most fish Australians want to eat are carnivores, such as coral trout, snapper, and Spanish mackerel.

While we didn’t investigate exactly which species are likely to increase following widespread coral death, it’s safe to say populations of fish targeted by recreational and commercial fisheries on Australia’s coral reefs are likely to change as live coral is lost, some for better and some for worse.




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The Great Barrier Reef is undoubtedly in danger, and it’s important that we make every effort to protect and conserve the remaining live, healthy coral. However, if corals continue to die, there will remain an abundance of life in their absence, albeit very different life from that to which we are accustomed.

As long as there is hard structure for algae to grow on, there will be epifauna. And where there is epifauna, there is food for fish, although perhaps not for all the fish we want to eat.The Conversation

Kate Fraser, Marine Ecologist, University of Tasmania

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

Almost 60 coral species around Lizard Island are ‘missing’ – and a Great Barrier Reef extinction crisis could be next


Michael Emslie

Zoe Richards, Curtin UniversityThe federal government has opposed a recommendation by a United Nations body that the Great Barrier Reef be listed as “in danger”. But there’s no doubt the natural wonder is in dire trouble. In new research, my colleagues and I provide fresh insight into the plight of many coral species.

Worsening climate change, and subsequent marine heatwaves, have led to mass coral deaths on tropical reefs. However, there are few estimates of how reduced overall coral cover is linked to declines in particular coral species.

Our research examined 44 years of coral distribution records around Lizard Island, at the northern end of the Great Barrier Reef. We found 16% of coral species have not been seen for many years and are at risk of either local extinction, or disappearing from parts of their local range.

This is alarming, because local extinctions often signal wider regional – and ultimately global – species extinction events.

Healthy coral near Lizard Island in 2011, top, then six years later after two bleaching events, bottom.
Healthy coral near Lizard Island in 2011, top, then six years later after two bleaching events, bottom.
Zoe Richards

Sobering findings

The Lizard Island reef system is 270 kilometres north of Cairns. It has suffered major disturbances over the past four decades: repeated outbreaks of crown-of-thorns seastars, category 4 cyclones in 2014 and 2015, and coral bleaching events in 2016, 2017 and 2020.

Our research focused on “hermatypic” corals around Lizard Island. These corals deposit calcium carbonate and form the hard framework of the reef.

We undertook hard coral biodiversity surveys four times between 2011 and 2020, across 14 sites. We combined the results with published and photographic species records from 1976 to 2020.

red fleshy coral with blue spots
Micromussa lordhowensis is popular in the aquarium trade.
Zoe Richards

Of 368 hard coral species recorded around Lizard Island, 28 (7.6%) have not been reliably recorded since before 2011 and may be at risk of local extinction. A further 31 species (8.4%) have not been recorded since 2015 and may be at risk of range reduction (disappearance from parts of its local range).

The “missing” coral species include:

  • Acropora abrotanoides, a robust branching shallow water coral that lives on the reef crest and reef flat has not been since since 2009
  • Micromussa lordhowensis, a low-growing coral with colourful fleshy polyps. Popular in the aquarium trade, it often grows on reef slopes but has not been seen since 2005
  • Acropora aspera, a branching coral which prefers very shallow water and has been recorded just once, at a single site, since 2011.

The finding that 59 coral species are at risk of local extinction or range reduction is significant. Local range reductions are often precursors to local species extinctions. And local species extinctions are often precursors to regional, and ultimately global, extinction events.

Each coral species on the reef has numerous vital functions. It might provide habitat or food to other reef species, or biochemicals which may benefit human health. One thing is clear: every coral species matters.




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reddish coral underwater
Acropa abrotanoides, one of the corals ‘missing’ from around Lizard Island.
Zoe Richards

A broader extinction crisis?

As human impacts and climate threats mount, there is growing concern about the resilience of coral biodiversity. Our research suggests such concerns are well-founded at Lizard Island.

Coral reef communities are dynamic, and so detecting species loss can be difficult. Our research found around Lizard Island, the diversity of coral species fluctuated over the past decade. Significant declines were recorded from 2011 to 2017, but diversity recovered somewhat in the three following years.

Local extinctions often happen incrementally and can therefore be “invisible”. To detect them, and to account for natural variability in coral communities, long-term biodiversity monitoring across multiple locations and time frames is needed.

Green coral
Acropora aspera has been recorded just once, at a single location, since 2011.
Anne Hoggett

In most locations however, data on the distribution and abundance of all coral species in a community is lacking. This means it can be hard to assess changes, and to understand the damage that climate change and other human-caused stressors are having on each species.

Only with this extra information can scientists conclusively say if the level of local extinction risk at Lizard Island indicates a risk that coral species may become extinct elsewhere – across the Great Barrier Reef and beyond.




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The Conversation


Zoe Richards, Senior Research Fellow, Curtin University

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

Is Australia really doing enough for the Great Barrier Reef? Why criticisms of UNESCO’s ‘in danger’ recommendation don’t stack up


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Terry Hughes, James Cook University; Jon C. Day, James Cook University, and Ove Hoegh-Guldberg, The University of QueenslandIn case you missed it, last week the World Heritage Centre of UNESCO revealed its draft decision to list the Great Barrier Reef as “in danger” — a decision that appeared to shock the Australian government.

In an opinion piece published yesterday in The Australian newspaper, Environment Minister Sussan Ley acknowledged climate change is the biggest threat to the Great Barrier Reef, and that it “has been through a few rough years”.

She has also suggested, however, UNESCO’s draft in-danger decision is a surprise and was politically motivated. Neither of these claims is credible.

So let’s look at Australia’s reaction so far, and why criticisms of UNESCO’s draft decision don’t stack up.

The poster child for climate change

An in-danger listing of a World Heritage property recognises a decline in the “outstanding universal value” that makes the site internationally significant. It sets off alarm bells to identify the underlying causes of decline, and triggers stronger interventions to prevent further damage.

Ley foresees a negative effect of the proposed in-danger listing on reef tourism. However, there’s no evidence from the Galapagos Islands, the Belize Barrier Reef or the Everglades National Park — all World Heritage properties and tourism hotspots — that an in-danger listing led to any discernible impacts on tourist numbers.

Most tourists, international or domestic, are already well aware of the pressures facing the Great Barrier Reef, but they are still keen to see it. From 2015–2018, more than two million visitors each year used a tourism operator to visit the reef. During 2020, COVID led to significant decline in visitor numbers so this period has been particularly difficult for the tourism industry.

Ley also claimed Australia, and the reef, didn’t deserve to be the poster child for climate change perils. But why can’t they be? The Great Barrier Reef is one of the most obvious examples of the costs of inaction on anthropogenic climate change.

The Great Barrier Reef was inscribed as a World Heritage Area in 1981. And for the past two decades Australia has meticulously documented its ongoing deterioration.

According to Australia’s regular reporting to UNESCO, the major causes of the reef’s decline in outstanding universal value is pollution from agricultural runoff, which has now been eclipsed by heat stress from climate change.




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Extreme summer temperatures in 1998, 2002, 2016, 2017 and 2020 have reduced coral cover and changed the mix of species, altering the biodiversity and other World Heritage attributes of the reef for many decades to come.

Unless global warming is stabilised soon, the reef will become unrecognisable. Indeed, in 2019, Australia’s latest five-yearly Great Barrier Reef Outlook Report projected the future of the reef as “very poor”.

Is Australia doing enough?

Ley also suggests Australia is doing everything it can to protect the reef — but is it really?

UNESCO certainty doesn’t think so. The draft decision from UNESCO, which will be considered next month by the World Heritage Committee, noted that interventions to reduce inshore pollution over the past five years have been “largely deficient”.

Bleached coral
There has been slow progress in meeting reef water quality targets.
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There have been some positive achievements in reducing water pollution levels. But the slow progress in meeting many of the water quality targets is documented clearly in the 2017–2018 and 2019 reef Water Quality Report Cards, produced jointly by the federal and Queensland governments.

UNESCO cites Australia’s poor progress on reducing emissions as an additional area requiring considerable improvement, to meet the objectives of the Paris Agreement and Australia’s responsibilities under the World Heritage Convention.




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UNESCO has also asked Australia to work with it to develop corrective measures and to ensure the revised Reef 2050 Plan — the overarching framework for protecting the reef to 2050 — addresses the threats.

An in-danger listing is a call to arms to all countries to work together to save the reef from human-caused heating. So the ongoing collaboration between Australia and UNESCO could then enable the Great Barrier Reef’s removal from the in-danger list.

Is Australia suddenly being singled out?

Ley wrote that the Great Barrier Reef was suddenly and unexpectedly “singled out” for an in-danger listing, which she interpreted as a suggestion that “Australia can single-handedly change the emissions trajectory of the whole world”.

However, the dialogue between UNESCO and Australia on the Great Barrier Reef’s protection has a long history. And in making its in-danger recommendation, UNESCO acknowledged Australia “on its own cannot address the threats of climate change”. But UNESCO does appear to have concerns about Australia’s record on emissions reduction.

For example, in 2011 the World Heritage Committee expressed “extreme concern” over the approval for liquefied natural gas facilities on Curtis Island within the boundary of the Great Barrier Reef World Heritage area. A year later, it asked Australia to ensure coastal development isn’t permitted if it effects the outstanding universal value of the property.

In 2012, 2013 and 2014, prior to the annual meetings of the World Heritage Committee, UNESCO raised the possible inscription of the Great Barrier Reef on the in-danger list.

Significantly, in 2017, the World Heritage Committee emphasised the importance of state parties (countries adhering to the world heritage convention, such as Australia) undertaking the most ambitious implementation of the Paris Agreement. This is an important pathway to reduce the risks and impacts of climate change on World Heritage properties.

UNESCO invited all state parties to act on climate change under the Paris Agreement “consistent with their common but differentiated responsibilities and respective capabilities”.

So what are Australia’s responsibilities?

Ley is correct to point out that all 29 World Heritage listed coral reefs, scattered throughout the tropics, are extremely vulnerable to human-caused climate change.

However, Australia is responsible for the world’s largest coral reef system, and has far higher capabilities to reduce greenhouse gas emissions than other, less wealthy countries.

But Australia’s record on protecting ecosystems and people from climate change is comparatively very poor. And despite being responsible for 20 World Heritage Areas, we have one of the highest per capita emission rates in the world.

The federal government continues to spruik a fossil-fuelled, gas-led COVID recovery, with ongoing subsidies for new coal mines. This support for coal and fossil gas is inconsistent with Australia’s commitments to the World Heritage Convention.

Rejecting the science-based assessments by UNESCO is further damaging Australia’s reputation as a laggard on addressing climate change. Surely, Australia can do better.




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The Conversation


Terry Hughes, Distinguished Professor, James Cook University; Jon C. Day, PSM, Adjunct Senior Research Fellow, ARC Centre of Excellence for Coral Reef Studies, James Cook University, and Ove Hoegh-Guldberg, Professor, The University of Queensland

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

Australian government was ‘blindsided’ by UN recommendation to list Great Barrier Reef as in-danger. But it’s no great surprise


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Jon C. Day, James Cook University; Scott F. Heron, James Cook University, and Terry Hughes, James Cook UniversityThe Australian government on Tuesday expressed shock at a draft decision to list the Great Barrier Reef as “in danger”. But the recommendation has been looming for some time.

The recommendation, by the United Nations Educational, Scientific and Cultural Organisation (UNESCO) and the International Union for Conservation of Nature (IUCN), acknowledges Australia’s commitment to implementing the Reef 2050 Plan, an overarching framework to protect the natural wonder for future generations.

But the “outstanding universal value” of the Great Barrier Reef has continued to decline.

The draft decision will now be considered at the World Heritage Committee meeting, to be held online next month. The development is significant for several reasons – not least that Australia’s progress under the Paris Agreement is being linked to its stewardship of the reef.

Last year, severe bleaching struck all three regions of the Great Barrier Reef.
ARC Centre of Excellence for Coral Reef Studies

What did UNESCO say?

In recommending the in-danger listing, UNESCO and IUCN cited a 2019 report by the Great Barrier Reef Marine Park Authority which found the ecosystem’s long-term outlook had deteriorated from poor to very poor. It said global warming had also triggered coral bleaching events in 2016 and 2017 – which were followed by another mass bleaching event in 2020.

The report said Australia’s progress on the Reef 2050 Plan “has been insufficient in meeting key targets”. It said the plan requires stronger and clearer commitments, in particular on urgently addressing threats from climate change, and improving water quality and land management.

Among other recommendations, the draft decision called on the international community to “implement the most ambitious actions to address climate change […] and fulfil their responsibility to protect the Great Barrier Reef”.




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The 2020 coral bleaching event was the second-worst in more than two decades.
ARC Centre of Excellence for Coral Reef Studies

No real surprise

Federal Environment Minister Sussan Ley’s said the government was “blindsided” by the draft recommendation. However the move has been a long time coming.

As noted above, the government’s 2019 Outlook Report documented the impacts and threats to the Great Barrier Reef in no uncertain terms, and identified climate change as the most serious threat.

There were other indicators the recommendation was looming. In 2020, the IUCN World Heritage Outlook listed the Great Barrier Reef as “critical” due to threats including climate change and poor water quality. The rating – the worst on a four-point scale — was a decline from the 2017 rating of “significant concern”.

And in 2018, a report predicted that without major reductions in greenhouse gas emissions, all 29 World Heritage coral reefs, including the Great Barrier Reef, will cease to be “functioning ecosystems by the end of the century”.

Finally in 2012, the World Heritage Committee warned the Great Barrier Reef could be placed on the in-danger list “in the absence of substantial progress”.




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Climate change isn’t the only concern

While climate change is a major concern in the draft decision, it is but one of numerous pressures on the Great Barrier Reef. Poor water quality due to nutrient and sediment runoff – the latter linked to land clearing – are also big problems.

The IUCN outlook report said climate change is the biggest threat to all the world’s natural heritage places. In this regard, this week’s draft decision sets an important precedent for the World Heritage Committee. It would seem the committee is now prepared to directly address the issue of climate change, after being less so inclined in previous years.

The Reef 2050 Plan does not adequately address the climate change threat. The UNESCO report calls on Australia to correct this, and ensure the plan sufficiently addresses other threats including water quality.

Decisions by the World Heritage Committee are not binding on any country. Still, we expect the committee’s concerns to result in Australia amending the Reef 2050 Plan to better acknowledge climate change as a significant issue.

The draft decision will be considered at the annual meeting of the World Heritage Committee in July, chaired by China and comprising 21 countries.

Two snorkelers
Getting placed on the in-danger list isn’t likely to impact tourism.
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An end to tourism?

The experience of other major tourist destinations suggests an in-danger listing may not damage tourism at the Great Barrier Reef, as some have feared.

Take the Everglades in the United States, Belize in the Caribbean and the Galapagos Islands. An analysis of these World Heritage properties showed no discernible tourism downturn after an in-danger listing. However, if the Great Barrier Reef’s condition continues to deteriorate, industries that rely on a healthy Reef are likely to endure long-term damage.

An in-danger listing is not permanent, nor does it mean the Great Barrier Reef will be permanently removed from the World Heritage list. Currently, 53 World Heritage properties are on the in-danger list; others were taken off the list once concerns were addressed.

The Great Barrier Reef will continue to be harmed until nations collectively adopt more ambitious climate goals, global emissions of greenhouse gases fall to net-zero and sea temperatures stabilise.

Without real and urgent actions at all levels — global, national, and local — the values that make all heritage places special will decline. That makes it less likely that future generations will be able to enjoy these wonders as we have done.




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The Conversation


Jon C. Day, PSM, Adjunct Senior Research Fellow, ARC Centre of Excellence for Coral Reef Studies, James Cook University; Scott F. Heron, Associate Professor, James Cook University, and Terry Hughes, Distinguished Professor, James Cook University

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

Life on the hidden doughnuts of the Great Barrier Reef is also threatened by climate change



A sea cucumber living on the Great Barrier Reef inter-reef seafloor.
Kent Holmes/Nature Ecology and Evolution, Author provided

Mardi McNeil, Queensland University of Technology; Andrew Hoey, James Cook University; Jody Webster, University of Sydney, and Luke Nothdurft, Queensland University of Technology

Mention the Great Barrier Reef, and most people think of the rich beauty and colour of corals, fish and other sea life that are increasingly threatened by climate change.

But there is another part of the Great Barrier Reef that until recently was largely hidden and under-explored.

In the northern section of the Great Barrier Reef Marine Park there are large Halimeda algal habitats called bioherms (also known as doughnuts because of their shape).

They are constructed by a type of algae (Halimeda) with a limestone skeleton. The tops of the bioherms are carpeted by a living meadow of the algae, yet much of the plant community includes other types of green, red and brown algae and some seagrasses.

A type of green seaweed.
Halimeda is a genus of green macroalgae (seaweed).
Mardi McNeil, Author provided

The bioherms cover an area greater than 6,000km², more than twice the area of shallow coral reefs.

Several maps showing the location of the _Halimeda_ bioherms.
The distribution of Halimeda bioherms in the Great Barrier Reef.
Figshare/Mardi McNeil, CC BY

Scientists have known for decades of this unusual inter-reef seafloor habitat that lies between the coast and the outer barrier reefs. But they’ve never investigated the diversity of marine life that lives there, until now.

In a new study published today in Nature Ecology and Evolution, scientists examined the community of plants and animals that inhabit these unique areas.

Let’s go deeper

Most studies of tropical marine biodiversity come from shallow coastal and coral reef habitats. We know a great deal about the biodiversity of these parts of the Great Barrier Reef.

But beyond the vision of scuba divers, deeper inter-reef habitats on the shelf, such as the bioherms, have been largely under-explored.




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In our study, we used a dataset of all the plants and animals recorded from the bioherms and surrounding seafloor habitats. The data came from the Seabed Biodiversity Project, a large study published back in 2007 of the inter-reef biodiversity in the Great Barrier Reef World Heritage Area.

What we found was surprising. An exceptional diversity of marine life and a distinct community was found to be living on the bioherms.

A diverse community

The biodiversity of marine life was up to 76% higher on the bioherms than the surrounding inter-reef habitats. Species richness was especially high for plants and invertebrates.

The average number of fish species per site was about the same in both Halimeda and non-Halimeda habitats. In total, 265 species of fish were observed in the bioherms, including sharks and rays.

Overall, more than 1,200 species of animals were recorded from the bioherms. The majority of these (78%) are invertebrates.

A feather star invertebrate.
Most of the animals living on the Halimeda bioherms are invertebrates, such as this feather star.
Mardi McNeil, Author provided

A distinct community

The composition of plant and animal communities on the bioherms was also distinctly different to the surrounding inter-reef areas.

Some 40% of bioherm species were unique to that habitat in the study area. The community included many sponges, snails and slugs, crabs and shrimps, brittle stars, sea urchins and sea cucumbers.

The fish community on the bioherms was also distinct from surrounding habitats. The two-spot wrasse, threadfin emperor and black-banded damselfish were particularly common.

A small black fish with a yellow tail and a white band near its neck.
A yellowtail angelfish (Chaetodontoplus meredithi) seen in coral waters of the Great Barrier Reef.
Sascha Schultz/iNaturalist.org/FishofAustralia, CC BY-NC

Most interesting about the bioherm fish community was the occurrence of some species such as the yellowtail angelfish generally thought to live mostly on coral reefs. Some of these reef-associated fishes have been increasingly observed in a range of non-reef habitats.

These multi-habitat users may be using the bioherms for shelter, feeding, spawning or as nursery grounds. Understanding the connections between shallow coral reefs and deeper bioherms is important to better understand how the reef and inter-reef habitats function.

An unusual habitat

The Halimeda bioherms are arguably the weirdest habitat in the Great Barrier Reef.

Recent high-resolution seafloor mapping using airborne lasers revealed the bioherms form a seafloor that looks like fields of giant doughnuts 20 metres high and 200 metres across.

The doughnuts are the connected circles on the seafloor in the yellow/green bioherm part. They look quite small but each circle is about 200 metres across.

The tops of the bioherms lie some 25-30 metres below the surface, so can’t be seen from boats passing over.

Deeper water and the remote location has meant the bioherms have been mostly invisible to marine biologists that work on the nearby shallow coral reefs.

Under threat from climate change

We are only just beginning to understand the importance of Halimeda bioherms as a habitat to support biodiversity in the Great Barrier Reef.

But just as the rest of the Great Barrier Reef is likely to be impacted by the effects of climate change, so too are the bioherms.

Potential threats to the bioherms include marine heating, ocean acidification and changes to circulation patterns.




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It has been more than 15 years since the inter-reef Seabed Biodiversity Project. The five-yearly Great Barrier Reef Outlook Report says little is known about any ecological trends in the bioherm habitat.

Our new study provides a baseline of the biodiversity of Halimeda bioherms at a single point in time. But questions remain about the present state of this ecosystem and its resilience on short and long-term physical and biological cycles.

Long-term monitoring of these unique and hidden habitats is critical to more fully understand the overall health of the Great Barrier Reef.The Conversation

Mardi McNeil, Postdoctoral researcher, Queensland University of Technology; Andrew Hoey, Senior Research Fellow, James Cook University; Jody Webster, Professor of Marine Geoscience, University of Sydney, and Luke Nothdurft, Senior Lecturer – Earth Science, Queensland University of Technology

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

‘Severely threatened and deteriorating’: global authority on nature lists the Great Barrier Reef as critical



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Jon C. Day, James Cook University and Scott F. Heron, James Cook University

The Great Barrier Reef is now in “critical” condition and the health of four other Australian World Heritage properties has worsened, according to a sobering report just released by the International Union for Conservation of Nature (IUCN).

The IUCN is the global authority on nature. Its third outlook report marks the first time the IUCN has declared an Australian property as critical, which means its values are severely threatened and deteriorating. The health of the Blue Mountains, Gondwana Rainforests, Shark Bay and the Ningaloo Coast has also been downgraded.




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The assessment, while chastening, is not surprising. The Great Barrier Reef has endured three mass coral bleaching events in five years, and last summer’s bushfires caused untold damage in the Blue Mountains and Gondwana Rainforests (not to mention the current fires at the reef’s Fraser Island).

Climate change remains the key issue for World Heritage places, not just in Australia but globally. In fact, the IUCN assessment found climate change threatens 11 of Australia’s 16 properties. This raises further questions over our national climate response.

World Heritage: the best of the best

The latest report builds on previous reports from 2014 and 2017, and shows the status and trends of World Heritage properties identified for their outstanding natural values. As the report states:

our ability to conserve these sites is thus a litmus test for the broader success of conservation worldwide.

To qualify for World Heritage listing for natural values, a place must meet one or more of four criteria: exceptional beauty, geology, ecological processes, and species and habitats.

Some properties are also recognised for cultural values and, if they have both, they’re referred to as “mixed”. Across the world there are 252 natural and mixed World Heritage properties, of which 16 are in Australia.

The IUCN is the official advisor on nature to UNESCO’s World Heritage Committee. The IUCN Outlook report involves assessments by hundreds of international experts, who examine the conservation prospects of all natural and mixed World Heritage properties. It focuses on their natural values, the threats to these values and the effectiveness of actions to protect them.

Threats to our iconic places

Climate change is now the most prevalent threat to natural World Heritage sites, and to many cultural sites.

Overall, the report assessed climate change as a high or a very high threat in 83 out of 252 global properties (33%). This rate is double in Australia, with climate change listed as a threat to 69% (11 of 16) of Australian properties.

And when considering the four natural criteria individually, climate change is the greatest threat to each. This is likely to get worse in future, as climate change is expected to affect more than three times the number of properties impacted by any other threat.

For many properties, the deteriorated conservation outlook is the result of accumulated threats. Impacts of climate change, like coral bleaching and bushfires, are often exacerbated by other threats. For example, the federal government’s 2019 Outlook Report for the Great Barrier Reef listed 45 threats including climate change. This included poor water quality from land-based runoff, coastal development and fishing.

Aerial view of seagrass meadows and headlands in Shark Bay
Seagrass meadows and headlands in the World Heritage-listed Shark Bay Conservation Area, now rated as ‘good with some concerns’.
Shutterstock

At the time of writing, the website which provides the full rationale behind the IUCN outlook was not yet publicly available. However the threats facing the five downgraded Australian sites are well documented.

These include marine heatwaves, which lead to coral bleaching in the Great Barrier Reef and Ningaloo. In Shark Bay, marine heatwaves also cause seagrass — critical habitat for a vast diversity of species — to die-off. Poor water quality, such as from urban and agricultural run-off, is another big threat to the Great Barrier Reef.




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‘Bright white skeletons’: some Western Australian reefs have the lowest coral cover on record


More frequent and intense bushfires are a problem for the Blue Mountains, Shark Bay, and Gondwana Rainforests. These ancient rainforests, along with Ningaloo and Shark Bay, also face threats of invasive species, diseases and storms.

Punching below our weight

While there have been some successes globally, the threats facing our heritage places are escalating.

Since the 2017 assessment, of the 252 properties analysed globally, 16 (6%) have deteriorated and only eight (3%) showed improvement. Notably, Australia is punching below its weight, with 31% of properties having deteriorated (5 of 16) and zero with improvement.




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All of Australia’s World Heritage properties are recognised as having “highly effective” or “mostly effective” protection and management activities.

But the deterioration of the Great Barrier Reef, the Blue Mountains, Gondwana Rainforests, Shark Bay and Ningaloo Coast casts doubt on whether these actions are an effective response to threats, especially climate change.

A whale shark
Western Australia’s Ningaloo Coast, now downgraded to ‘good with some concerns’, is famous for its vast diversity of wildlife, including whale sharks.
Shutterstock

Australia’s climate response has been widely criticised, most recently by Christiana Figueres, the former chief of the UN Climate Framework. In a keynote to open the Australian Emissions Reductions Summit yesterday, Figueres said:

I have been pretty vocal about my frustration for so many years of the completely unstable, volatile, unpredictable stand and position on climate change in Australia.

“Meeting and beating” Australia’s 2030 emissions targets has been the Morrison government’s catch-cry. But the target lacks ambition and the government hasn’t ruled out using Kyoto carry-over credits to help meet it. The government has also refused to commit to a target of net-zero emissions by mid century, in contrast to the policies of many of our international peers.

Management of non-climate stressors is, and will remain, essential to halt the decline of the values of our properties. But Australia must adopt more ambitious climate goals to avoid losing those values that make our heritage places special, preserving them for future generations.




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The Conversation


Jon C. Day, PSM, Post-career PhD candidate, ARC Centre of Excellence for Coral Reef Studies, James Cook University and Scott F. Heron, Associate professor, James Cook University

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

The first step to conserving the Great Barrier Reef is understanding what lives there


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Tom Bridge, James Cook University; Andrea Quattrini, Smithsonian Institution; Andrew Baird, James Cook University, and Peter Cowman, James Cook University

Look at this photo of two coral skeletons below. You’d be forgiven for thinking they’re the same species, or at least closely related, but looks can be deceiving. These two species diverged tens of millions of years ago, probably earlier than our human lineage split from baboons and macaques.

Two white branches of coral
The skeletons of two staghorn coral species with the same ‘bottlebrush’ growth form. They might look similar, but they’re not closely related.
source, Author provided

Scientists have traditionally used morphology (size, shape and colour) to identify species and infer their evolutionary history. But most species were first described in the 19th century, and based solely on features of the coral skeleton visible under a microscope.

Morphology remains important for species recognition. The problem is we don’t know whether a particular morphological feature reflects species ancestry, or evolved independently.

Our new study examined the traditional ideas of coral species and their evolutionary relationships using “phylogenomics” – comparing thousands of DNA sequences across coral species.

Our results revealed the diversity and distributions of corals are vastly different to what we previously thought. It shows we still don’t know many fundamental aspects about the corals on Great Barrier Reef.




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We just spent two weeks surveying the Great Barrier Reef. What we saw was an utter tragedy


And after three mass bleaching events in five years, not having a handle on the basics could mean our attempts to intervene and help coral survive climate change may have unexpected consequences.

An international team of scientists have developed a new genetic tool that can help them better understand and ultimately work to save coral reefs.

How do we know which species is which?

Despite being one of the best-studied marine ecosystems on Earth, there are fundamental knowledge gaps around the Great Barrier Reef, including:

  1. how many coral species live there?
  2. how do we identify them?
  3. where are they found across the vast Great Barrier Reef ecosystem?

Finding the answers to these questions starts with accurate “taxonomy” – the science of naming and classifying living things.

Identifying species based on how similar they look may seem straightforward. As Darwin famously said, closely related species often share morphological features because they inherited them from a common ancestor.




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However, this can be misleading if two unrelated species independently acquire similar features. This process, called convergent evolution, often occurs when different species are faced with similar ecological challenges.

A classic example of convergent evolution is dolphins and the prehistoric ichthyosaurs. These animals are unrelated, but share many similarities since they both occupy a similar ecological niche.

Ichthyosaurs dominated the world’s oceans for millions of years.

At the other end of the spectrum, morphology can vary considerably within a single species. An alien taxonomist visiting Earth could be forgiven for describing the Chihuahua and the Irish Wolfhound as two distinct species.

Bringing coral taxonomy into the 21st century

We used molecular phylogenetics, a field of research that uses variations in DNA sequences to reconstruct genealogies. From corals to humans, molecular phylogenetics has revolutionised our understanding of the origins and evolution of life on Earth.

Molecular approaches have revolutionised our understanding of the diversity and evolution of corals, shedding light on deeper branches in the coral “tree of life”. But within hyper-diverse, ecologically-important coral groups, such as the staghorn corals from the genus Acropora, we are still in the dark.




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If we can put a man on the Moon, we can save the Great Barrier Reef


Our new technique addresses this by comparing thousands of key regions across coral genomes (the entire genetic code of an organism) to help identify species in this ecologically important group for the first time. This method will also allow us to identify morphological features that do reflect shared ancestry and help us recognise species when diving in the reef.

About a quarter of all coral species on the Great Barrier Reef are staghorn corals, and they provide much of the three-dimensional structure fishes and many other coral reef animals rely on, just like trees in a forest.

Staghorn coral
Staghorn coral from the Houtman Abrolhos Islands.
Thomas Bridge, Author provided

Unfortunately, staghorn corals are also highly susceptible to threats such as thermal bleaching and crown-of-thorns seastar predation. The future of reefs will be heavily influenced by the fate of staghorn corals.

The risk of ‘silent extinctions’

While we don’t yet know how many coral species occur on the Great Barrier Reef or how widespread they are, many species appear to have far smaller ranges than we previously thought.

For example, we now know some of the corals on Lord Howe Island are endemic to only a few reefs in subtropical eastern Australia and occur nowhere else, not even on the Great Barrier Reef. They evolved in isolation and bleach at much lower temperatures than corals on tropical reefs.

An aerial view of Lord Howe Island
Lord Howe Island is home to the world’s southern-most coral reef.
Shutterstock

This means Lord Howe Island’s corals are of far greater conservation concern than currently recognised, because one severe bleaching event could cause the extinction of these species.




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Bleaching has struck the southernmost coral reef in the world


The risk of “silent extinctions”, where species go extinct without even being noticed, is one of the reasons behind the Australian Academy of Science’s Decadal Plan for Taxonomy, which has led to the ambitious goal to document all Australian species in the next 25 years.

Intervening now may have unexpected consequences

In April, the Reef Restoration and Adaptation Program concept feasibility study found 160 possible interventions to help save the Great Barrier Reef. Proposed interventions include moving corals from warm to cooler waters, introducing genetically-engineered heat-tolerant corals into wild populations, and the harvest and release of coral larvae.

Bleached coral
The Great Barrier Reef has undergone yet another mass bleaching event.
Shutterstock

What could go wrong? Well-intentioned interventions may inadvertently threaten coral communities, for example, through introduction or movement of diseases within the Great Barrier Reef. Cane toads are a famous example of unintended consequences: introduced in the 1930s to control an insect pest, they are now wreaking havoc on Australian ecosystems.

Any intervention affecting the ecology of a system as complex as the Great Barrier Reef requires a precautionary approach to minimise the chance of unintended and potentially negative consequences.

What we need, at this time, is far greater investment in fundamental biodiversity research. Without this information, we are not in a position to judge whether particular actions will threaten the resilience of the reef, rather than enhance it.The Conversation

Tom Bridge, Senior Curator – Corals, James Cook University; Andrea Quattrini, Researcher, Smithsonian Institution; Andrew Baird, Professorial fellow, James Cook University, and Peter Cowman, Research Fellow in Ecosystem Dynamics, James Cook University

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

If we can put a man on the Moon, we can save the Great Barrier Reef



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Paul Hardisty, Australian Institute of Marine Science; Christian Roth, CSIRO; Damien Burrows, James Cook University; David Mead, Australian Institute of Marine Science; Ken Anthony, Australian Institute of Marine Science; Line K Bay, Australian Institute of Marine Science; Mark Gibbs, Queensland University of Technology, and Peter J Mumby, The University of Queensland

Scientists recently confirmed the Great Barrier Reef suffered another serious bleaching event last summer – the third in five years. Dramatic intervention to save the natural wonder is clearly needed.

First and foremost, this requires global greenhouse gas emissions to be slashed. But the right combination of technological and biological interventions, deployed with care at the right time and scale, are also critical to securing the reef’s future.




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We just spent two weeks surveying the Great Barrier Reef. What we saw was an utter tragedy


This could include methods designed to shade and cool the reef, techniques to help corals adapt to warmer temperatures, ways to help damaged reefs recover, and smart systems that target interventions to the most strategically beneficial locations.

Research into breeding coral hybrids for heat-stress resistance could help restore parts of the reef.
Marie Roman/AIMS, Author provided

Implementing such measures across the breadth of the reef – the world’s biggest reef ecosystem – will not be easy, or cheap. In fact, we believe the scale of the task is greater than the Apollo 11 Moon landing mission in 1969 – but not impossible.

That mission was a success, not because a few elements worked to plan, but because of the integration, coordination and alignment of every element of the mission’s goal: be the first to land and walk on the Moon, and then fly home safely.

Half a century later, facing the ongoing decline of the Great Barrier Reef, we can draw important lessons from that historic human achievement.

Intervening to save the reef

The recently released Reef Restoration and Adaptation Program concept feasibility study shows Australia could feasibly, and with reasonable probability of success, intervene to help the reef adapt to and recover from the effects of climate change.

The study, of which we were a part, involved more than 100 leading coral reef scientists, modellers, economists, engineers, business strategists, social scientists, decision scientists and reef managers.

More than 100 coral reef scientists took part in the feasibility study.
Nick Thake/AIMS, Author provided

It shows how new and existing interventions, supported by the best available research and development, could help secure a future for the reef.

We must emphasise that interventions to help the reef adapt to and recover from climate change will not, alone, save it. Success also depends on reducing global greenhouse emissions as quickly as possible. But the hands-on measures we’re proposing could help buy time for the reef.

Cloud brightening to heat-tolerant corals

Our study identified 160 possible interventions that could help revive the reef, and build on its natural resilience. We’ve whittled it down to the 43 most effective and realistic.

Possible interventions for further research and development include brightening clouds with salt crystals to shade and cool corals; ways to increase the abundance of naturally heat-tolerant corals in local populations, such as through aquarium-based selective breeding and release; and methods to promote faster recovery on damaged reefs, such as deploying structures designed to stabilise reef rubble.

But there will be no single silver bullet solution. The feasibility study showed that methods working in combination, along with water quality improvement and crown-of-thorns starfish control, will provide the best results.

Field testing the heat resistant coral hybrids in the Great Barrier Reef.
Kate Green/AIMS, Author provided

Harder than landing on the Moon

There are four reasons why saving the Great Barrier Reef in coming decades could be more challenging than the 1969 Moon mission.

First, warming events have already driven the reef into decline with back-to-back bleaching events in 2016 and 2017, and now again in 2020. The next major event is now only just around the corner.




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Second, current emission reduction pledges would see the world warm by 2.3-3.5℃ relative to pre-industrial levels. This climate scenario, which is not the worst case, would be beyond the range that allows today’s coral reef ecosystems to function.

Without swift action, the prospect for the world’s coral reefs is bleak, with most expected to become seriously degraded before mid-century.

The Great Barrier Reef has been hit by consecutive bleaching events – restoring it may be harder than landing on the moon.
Shutterstock

Third, we still have work to do to control local pressures, including water quality and marine pests crown-of-thorns starfish.

And fourth, the inherent complexity of natural systems, particularly ones as diverse as coral reefs, provides an additional challenge not faced by NASA engineers 50 years ago.

So keeping the Great Barrier Reef, let alone the rest of the world’s reefs, safe from climate change will dwarf the challenge of any space mission. But there is hope.

We must start now

The federal government recently re-announced A$100 million from the Reef Trust Partnership towards a major research and development effort for this program. This will be augmented by contributions of A$50m from research institutions, and additional funding from international philanthropists.

Our study shows that under a wide range of future emission scenarios, the program is very likely to be worth the effort, more so if the world meets the Paris target and rapidly cuts greenhouse gas emissions.




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What’s more, economic analyses included in the feasibility study show successful Great Barrier Reef intervention at scale could create benefits to Australia of between A$11 billion and A$773 billion over a 60-year period, with much of it flowing to regional economies and Traditional Owner communities.

And perhaps more importantly, if Australia is successful in this effort, we can lead the world in a global effort to save these natural wonders bequeathed to us across the ages. We must start the journey now. If we wait, it may be too late.


The authors gratefully acknowledge the contribution of David Wachenfeld, Chief Scientist of the Great Barrier Reef Marine Park Authority and member of the the steering committee for the development of this program.The Conversation

Paul Hardisty, CEO, Australian Institute of Marine Science; Christian Roth, CSIRO Great Barrier Reef Coordinator & Senior Principal Research Scientist, CSIRO; Damien Burrows, Director of TropWATER, James Cook University; David Mead, Executive Director of Strategic Development at Australian Institute of Marine Science, Australian Institute of Marine Science; Ken Anthony, Principal Research Scientist, Australian Institute of Marine Science; Line K Bay, Senior Research Scientist and Team Leader, Australian Institute of Marine Science; Mark Gibbs, Director, Knowledge to Innovation; Chair, Green Cross Australia, Queensland University of Technology, and 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.

We just spent two weeks surveying the Great Barrier Reef. What we saw was an utter tragedy



Author supplied

Terry Hughes, James Cook University and Morgan Pratchett, James Cook University

The Australian summer just gone will be remembered as the moment when human-caused climate change struck hard. First came drought, then deadly bushfires, and now a bout of coral bleaching on the Great Barrier Reef – the third in just five years. Tragically, the 2020 bleaching is severe and the most widespread we have ever recorded.

Coral bleaching at regional scales is caused by spikes in sea temperatures during unusually hot summers. The first recorded mass bleaching event along Great Barrier Reef occurred in 1998, then the hottest year on record.




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Since then we’ve seen four more mass bleaching events – and more temperature records broken – in 2002, 2016, 2017, and again in 2020.

This year, February had the highest monthly sea surface temperatures ever recorded on the Great Barrier Reef since the Bureau of Meteorology’s records began in 1900.

Not a pretty picture

We surveyed 1,036 reefs from the air during the last two weeks in March, to measure the extent and severity of coral bleaching throughout the Great Barrier Reef region. Two observers, from the ARC Centre of Excellence for Coral Reef Studies and the Great Barrier Reef Marine Park Authority, scored each reef visually, repeating the same procedures developed during early bleaching events.

The accuracy of the aerial scores is verified by underwater surveys on reefs that are lightly and heavily bleached. While underwater, we also measure how bleaching changes between shallow and deeper reefs.




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Of the reefs we surveyed from the air, 39.8% had little or no bleaching (the green reefs in the map). However, 25.1% of reefs were severely affected (red reefs) – that is, on each reef more than 60% of corals were bleached. A further 35% had more modest levels of bleaching.

Bleaching isn’t necessarily fatal for coral, and it affects some species more than others. A pale or lightly bleached coral typically regains its colour within a few weeks or months and survives.

The 2020 coral bleaching event was the second-worst in more than two decades.
ARC Centre of Excellence for Coral Reef Studies

But when bleaching is severe, many corals die. In 2016, half of the shallow water corals died on the northern region of the Great Barrier Reef between March and November. Later this year, we’ll go underwater to assess the losses of corals during this most recent event.

Compared to the four previous bleaching events, there are fewer unbleached or lightly bleached reefs in 2020 than in 1998, 2002 and 2017, but more than in 2016. Similarly, the proportion of severely bleached reefs in 2020 is exceeded only by 2016. By both of these metrics, 2020 is the second-worst mass bleaching event of the five experienced by the Great Barrier Reef since 1998.

The unbleached and lightly bleached (green) reefs in 2020 are predominantly offshore, mostly close to the edge of the continental shelf in the northern and southern Great Barrier Reef. However, offshore reefs in the central region were severely bleached again. Coastal reefs are also badly bleached at almost all locations, stretching from the Torres Strait in the north to the southern boundary of the Great Barrier Reef Marine Park.



CC BY-ND

For the first time, severe bleaching has struck all three regions of the Great Barrier Reef – the northern, central and now large parts of the southern sectors. The north was the worst affected region in 2016, followed by the centre in 2017.

In 2020, the cumulative footprint of bleaching has expanded further, to include the south. The distinctive footprint of each bleaching event closely matches the location of hotter and cooler conditions in different years.

Poor prognosis

Of the five mass bleaching events we’ve seen so far, only 1998 and 2016 occurred during an El Niño – a weather pattern that spurs warmer air temperatures in Australia.

But as summers grow hotter under climate change, we no longer need an El Niño to trigger mass bleaching at the scale of the Great Barrier Reef. We’ve already seen the first example of back-to-back bleaching, in the consecutive summers of 2016 and 2017. The gap between recurrent bleaching events is shrinking, hindering a full recovery.

For the first time, severe bleaching has struck all three regions of the Great Barrier Reef.
ARC Centre of Excellence for Coral Reef Studies

After five bleaching events, the number of reefs that have escaped severe bleaching continues to dwindle. Those reefs are located offshore, in the far north and in remote parts of the south.

The Great Barrier Reef will continue to lose corals from heat stress, until global emissions of greenhouse gasses are reduced to net zero, and sea temperatures stabilise. Without urgent action to achieve this outcome, it’s clear our coral reefs will not survive business-as-usual emissions.




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The Conversation


Terry Hughes, Distinguished Professor, James Cook University and 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.