Gene editing is revealing how corals respond to warming waters. It could transform how we manage our reefs



Mikaela Nordborg/Australian Institute of Marine Science, Author provided

Dimitri Perrin, Queensland University of Technology; Jacob Bradford, Queensland University of Technology; Line K Bay, Australian Institute of Marine Science, and Phillip Cleves, Carnegie Institution for Science

Genetic engineering has already cemented itself as an invaluable tool for studying gene functions in organisms.

Our new study, published in the Proceedings of the National Academy of Sciences, now demonstrates how gene editing can be used to pinpoint genes involved in corals’ ability to withstand heat stress.

A better understanding of such genes will lay the groundwork for experts to predict the natural response of coral populations to climate change. And this could guide efforts to improve coral adaptation, through the selective breeding of naturally heat-tolerant corals.

A threatened national treasure

The Great Barrier Reef is among the world’s most awe-inspiring, unique and economically valuable ecosystems. It spans more than 2,000 kilometres, has more than 600 types of coral, 1,600 types of fish and is of immense cultural significance — especially for Traditional Owners.

But warming ocean waters caused by climate change are leading to the mass bleaching and mortality of corals on the reef, threatening the reef’s long-term survival.




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


Many research efforts are focused on how we can prevent the reef’s deterioration by helping it adapt to and recover from the conditions causing it stress.

Understanding the genes and molecular pathways that protect corals from heat stress will be key to achieving these goals.

While hypotheses exist about the roles of particular genes and pathways, rigorous testings of these have been difficult — largely due to a lack of tools to determine gene function in corals.

But over the past decade or so, CRISPR/Cas9 gene editing has emerged as a powerful tool to study gene function in non-model organisms.

CRISPR: a technological marvel

Scientists can use CRISPR to make precise changes to the DNA of a living organisms, by “cutting” its DNA and editing the sequence. This can involve inactivating a specific gene, introducing a new piece of DNA or replacing a piece.

In our 2018 research, we showed it is possible to make precise mutations in the coral genome using CRISPR technology. However, we were unable to determine the functions of our specific target genes.

For our latest research, we used an updated CRISPR method to sufficiently disrupt the Heat Shock Transcription Factor 1, or HSF1, in coral larvae.

Based on this protein-coding gene’s role in model organisms, including closely related sea anemones, we hypothesised it would play an important role in the heat response of corals.

Injection going into coral egg.
We injected CRISPR components into the fertilised eggs of the coral species Acropora millepora to inactivate the HSF1 gene.
Phillip Cleves/Carnegie Institute for Science, CC BY-NC-ND

Past research had also demonstrated HSF1 can influence a large number of heat response genes, acting as a kind of “master switch” to turn them on.

By inactivating this master switch, we expected to see significant changes in the corals’ heat tolerance. Our prediction proved accurate.




Read more:
What is CRISPR, the gene editing technology that won the Chemistry Nobel prize?


What we discovered by injecting coral eggs

We spawned corals at the Australian Institute of Marine Science during the annual mass spawning event in November, 2018.

We then injected CRISPR/Cas9 components into fertilised coral eggs to target the HSF1 gene in the common and widespread staghorn coral Acropora millepora.

_Acropora millepora_ coral colony during a mass spawning event.
Acropora millepora colonies can be found widely on the Great Barrier Reef. They reproduce sexually in ‘mass spawning’ events.
Mikaela Nordborg/Australian Institute of Marine Science, Author provided

We were able to demonstrate a strong effect of HSF1 on corals’ heat tolerance. Specifically, when this gene was mutated using CRISPR (and no longer functional) the corals were more vulnerable to heat stress.

Larvae with knocked-out copies of HSF1 died under heat stress when the water temperature was increased from 27℃ to 34℃. In contrast, larvae with the functional gene survived well in the warmer water.

Let’s understand what we already have

It may be tempting now to focus on using gene-editing tools to engineer heat-resistant strains of corals, to fast-track the Great Barrier Reef’s adaptation to warming waters.

However, genetic engineering should first and foremost be used to increase our knowledge of the fundamental biology of corals and other reef organisms, including their response to heat stress.

Not only will this help us more accurately predict the natural response of coral reefs to a changing climate, it will also shed light on the risks and benefits of new management tools for corals, such as selective breeding.

It is our hope these genetic insights will provide a solid foundation for future reef conservation and management efforts.The Conversation

During mass spawning events, corals release little balls that float to the ocean’s surface in a spectacle resembling an upside-down snowstorm.

Dimitri Perrin, Senior Lecturer, Queensland University of Technology; Jacob Bradford, , Queensland University of Technology; Line K Bay, Principal Research Scientist and Team Leader, Australian Institute of Marine Science, and Phillip Cleves, Principal Investigator, Carnegie Institution for Science

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

Ocean warming threatens coral reefs and soon could make it harder to restore them



Climate-driven ocean warming threatens healthy coral reefs, like this one in Hawaii.
Shawna Foo, CC BY-ND

Shawna Foo, Arizona State University

Graphic stating that at 86.9 degrees Fahrenheit, the chance of transplanted corals surviving falls below 50%

CC BY-ND

Anyone who’s tending a garden right now knows what extreme heat can do to plants. Heat is also a concern for an important form of underwater gardening: growing corals and “outplanting,” or transplanting them to restore damaged reefs.

The goal of outplanting is to aid coral reefs’ natural recovery process by growing new corals and moving them to the damaged areas. It’s the same idea as replanting forests that have been heavily logged, or depleted farm fields that once were prairie grasslands.

I have studied how global stressors such as ocean warming and acidification affect marine invertebrates for more than a decade. In a recently published study, I worked with Gregory Asner to analyze the impacts of temperature on coral reef restoration projects. Our results showed that climate change has raised sea surface temperatures close to a point that will make it very hard for outplanted corals to survive.

Coral gardening

Coral reefs support over 25% of marine life by providing food, shelter and a place for fish and other organisms to reproduce and raise young. Today, ocean warming driven by climate change is stressing reefs worldwide.

Rising ocean temperatures cause bleaching events – episodes in which corals expel the algae that live inside them and provide the corals with most of their food, as well as their vibrant colors. When corals lose their algae, they become less resistant to stressors such as disease and eventually may die.

Hundreds of organizations worldwide are working to restore damaged coral reefs by growing thousands of small coral fragments in nurseries, which may be onshore in laboratories or in the ocean near degraded reefs. Then scuba divers physically plant them at restoration sites.

Outplanting is the process of transplanting nursery-grown corals onto reefs.

Outplanting coral is expensive: According to one recent study, the median cost is about US$160,000 per acre, or $400,000 per hectare. It also is time-consuming, with scuba divers placing each outplanted coral by hand. So it’s important to maximize coral survival by choosing the best locations.

We used data from the National Oceanic and Atmosphere Administration’s Coral Reef Watch program, which collects daily satellite-derived measurements of sea surface temperature. We paired this information with survival rates from hundreds of coral outplanting projects worldwide.

We found that coral survival was likely to drop below 50% if the maximum temperature experienced at the restoration site exceeded 86.9 degrees Fahrenheit (30.5 degrees Celsius). This temperature threshold mirrors the tolerance of natural coral reefs.

Globally, coral reefs experience an annual maximum temperature today of 84.9˚F (29.4˚C). This means they already are living close to their upper thermal limit.

When reefs experience temperatures only a few degrees above long-term averages for a few weeks, the stress can cause coral bleaching and mortality. Increases of just a few degrees above normal caused three mass bleaching events since 2016 that have devastated Australia’s Great Barrier Reef.

Map of global sea surface temperatures, color coded to show bleaching risks.
Sea surface temperatures on Aug. 3, 2020, measured from satellites. Warning = possible bleaching; Alert Level 1 = significant bleaching likely; Alert Level 2 = severe bleaching and significant mortality likely.
NOAA Coral Reef Watch

Warmer oceans

Climate scientists project that the oceans will warm up to 3˚C by the year 2100. Scientists are working to create coral outplants that can better survive increases in temperature, which could help to increase restoration success in the future.

When coral restoration experts choose where to outplant, they typically consider what’s on the seafloor, algae that could smother coral, predators that eat coral and the presence of fish. Our study shows that using temperature data and other information collected remotely from airplanes and satellites could help to optimize this process. Remote sensing, which scientists have used to study coral reefs for almost 40 years, can provide information on much larger scales than water surveys.

Coral reefs face an uncertain future and may not recover naturally from human-caused climate change. Conserving them will require reducing greenhouse gas emissions, protecting key habitats and actively restoring reefs. I hope that our research on temperature will help increase coral outplant survival and restoration success.

[Get our best science, health and technology stories. Sign up for The Conversation’s science newsletter.]The Conversation

Shawna Foo, Postdoctoral Research Scholar, Arizona State University

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

With no work in lockdown, tour operators helped find coral bleaching on Western Australia’s remote reefs



Jeremy Tucker, Author provided

James Paton Gilmour, Australian Institute of Marine Science

Significant coral bleaching at one of Western Australia’s healthiest coral reefs was found during a survey carried out in April and May.

The survey took a combined effort of several organisations, together with tour operators more used to taking tourists, but with time spare during the coronavirus lockdown.

WA’s arid and remote setting means many reefs there have escaped some of the pressures affecting parts of the east coast’s Great Barrier Reef), such as degraded water quality and outbreaks of crown of thorns starfish.

The lack of these local pressures reflects, in part, a sound investment by governments and communities into reef management. But climate change is now overwhelming these efforts on even our most remote coral reefs.

Significant coral bleaching has been identified at WA reefs.
Nick Thake, Author provided

When the oceans warmed

This year, we’ve seen reefs impacted by the relentless spread of heat stress across the world’s oceans.

As the 2020 mass bleaching unfolded across the Great Barrier Reef, a vast area of the WA coastline was bathed in hot water through summer and autumn. Heat stress at many WA reefs hovered around bleaching thresholds for weeks, but those in the far northwest were worst affected.

The remoteness of the region and shutdowns due to COVID-19 made it difficult to confirm which reefs had bleached, and how badly. But through these extraordinary times, a regional network of collaborators managed to access even our most remote coral reefs to provide some answers.




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


Australia’s Bureau of Meteorology provided regional estimates of heat stress, from which coral bleaching was predicted and surveys targeted.

At reefs along the Kimberley coastline, bleaching was confirmed by WA’s Department of Biodiversity, Conservation and Attractions (DBCA), Bardi Jawi Indigenous rangers, the Kimberley Marine Research Centre and tourist operators.

At remote oceanic reefs hundreds of kilometres from the coastline, bleaching was confirmed in aerial footage provided by Australian Border Force.

Subsequent surveys were conducted by local tourist operators, with no tourists through COVID-19 shutdown and eager to check the condition of reefs they’ve been visiting for many years.

The first confirmation of bleaching on remote coral atolls at Ashmore Reef and the Rowley Shoals was provided in aerial images captured by Australian Border Force.
Australian Border Force, Author provided

The Rowley Shoals

Within just a few days, a tourist vessel chartered by the North West Shoals to Shore Research Program, with local operators and a DBCA officer, departed from Broome for the Rowley Shoals. These three reef atolls span 100km near the edge of the continental shelf, about 260km west-north-west offshore.

One of only two reef systems in WA with high and stable coral cover in the last decade, the Rowley Shoals is a reminder of beauty and value of healthy, well managed coral reefs.

But the in-water surveys and resulting footage confirmed the Rowley Shoals has experienced its worst bleaching event on record.

The most recent heatwave has caused widespread bleaching at the Rowley Shoals, which had previously escaped the worst of the regional heat stress.
Jeremy Tucker, Author provided

All parts of the reef and groups of corals were affected; most sites had between 10% and 30% of their corals bleached. Some sites had more than 60% bleaching and others less than 10%.

The heat stress also caused bleaching at Ashmore Reef, Scott Reef and some parts of the inshore Kimberley and Pilbara regions, all of which were badly affected during the 2016/17 global bleaching event.

This most recent event (2019/20) is significant because of the extent and duration of heat stress. It’s also notable because it occurred outside the extreme El Niño–Southern Oscillation phases – warming or cooling of the ocean’s surface that has damaged the northern and southern reefs in the past.

A reef crisis

The impacts from climate change are not restricted to WA or the Great Barrier Reef – a similar scenario is playing out on reefs around the world, including those already degraded by local pressures.

By global standards, WA still has healthy coral reefs. They provide a critical reminder of what reefs offer in terms of natural beauty, jobs and income from fisheries and tourism.

Despite the most recent bleaching, the Rowley Shoals remains a relatively healthy reef system by global standards. But like all reefs, its future is uncertain under climate change.
James Gilmour, Author provided

But we’ve spent two decades following the trajectories of some of WA’s most remote coral reefs. We’ve seen how climate change and coral bleaching can devastate entire reef systems, killing most corals and dramatically altering associated communities of plants and animals.

And we’ve seen the same reefs recover over just one or two decades, only to again be devastated by mass bleaching – this time with little chance of a full recovery in the future climate.

Ongoing climate change will bring more severe cyclones and mass bleaching, the two most significant disturbances to our coral reefs, plus additional pressures such as ocean acidification.

Reducing greenhouse gas emissions is the only way to alleviate these pressures. In the meantime, scientists will work to slow the rate of coral reef degradation though new collaborations, and innovative, rigorous approaches to reef management.The Conversation

James Paton Gilmour, Research Scientist: Coral Ecology, Australian Institute of Marine Science

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

5 big environment stories you probably missed while you’ve been watching coronavirus



Shutterstock

Rod Lamberts, Australian National University and Will J Grant, Australian National University

Good news: COVID-19 is not the only thing going on right now!

Bad news: while we’ve all been deep in the corona-hole, the climate crisis has been ticking along in the background, and there are many things you may have missed.

Fair enough – it’s what people do. When we are faced with immediate, unambiguous threats, we all focus on what’s confronting us right now. The loss of winter snow in five or ten years looks trivial against images of hospitals pushed to breaking point now.




Read more:
While we fixate on coronavirus, Earth is hurtling towards a catastrophe worse than the dinosaur extinction


As humans, we also tend to prefer smaller, short-term rewards over larger long-term ones. It’s why some people would risk illness and possible prosecution (or worse, public shaming) to go to the beach with their friends even weeks after social distancing messages have become ubiquitous.

But while we might need to ignore climate change right now if only to save our sanity, it certainly hasn’t been ignoring us.

So here’s what you may have missed while coronavirus dominates the news cycle.

Heatwave in Antarctica

Antarctica is experiencing alarmingly balmy weather.
Shutterstock

On February 6 this year, the northernmost part of Antarctica set a new maximum temperature record of 18.4℃. That’s a pleasant temperature for an early autumn day in Canberra, but a record for Antarctica, beating the old record by nearly 1℃.

That’s alarming, but not as alarming as the 20.75℃ reported just three days later to the east of the Antarctic Peninsula at Marambio station on Seymour Island.




Read more:
Anatomy of a heatwave: how Antarctica recorded a 20.75°C day last month


Bleaching the reef

The Intergovernmental Panel on Climate Change has warned a global average temperature rise of 1.5℃ could wipe out 90% of the world’s coral.

As the world looks less likely to keep temperature rises to 1.5℃, in 2019 the five-year outlook for Australia’s Great Barrier Reef was downgraded from “poor” to “very poor”. The downgrading came in the wake of two mass bleaching events, one in 2016 and another in 2017, damaging two-thirds of the reef.

And now, in 2020, it has just experienced its third in five years.

Of course, extreme Antarctic temperatures and reef bleaching are the products of human-induced climate change writ large.

But in the short time since the COVID-19 crisis began, several examples of environmental vandalism have been deliberately and specifically set in motion as well.




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


Coal mining under a Sydney water reservoir

The Berejiklian government in New South Wales has just approved the extension of coal mining by Peabody Energy – a significant funder of climate change denial – under one of Greater Sydney’s reservoirs. This is the first time such an approval has been granted in two decades.

While environmental groups have pointed to significant local environmental impacts – arguing mining like this can cause subsidence in the reservoir up to 25 years after the mining is finished – the mine also means more fossil carbon will be spewed into our atmosphere.

Peabody Energy argues this coal will be used in steel-making rather than energy production. But it’s still more coal that should be left in the ground. And despite what many argue, you don’t need to use coal to make steel.




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Albanese says we can’t replace steelmaking coal. But we already have green alternatives


Victoria green-lights onshore gas exploration

In Victoria, the Andrews government has announced it will introduce new laws into Parliament for what it calls the “orderly restart” of onshore gas exploration. In this legislation, conventional gas exploration will be permitted, but an existing temporary ban on fracking and coal seam gas drilling will be made permanent.

The announcement followed a three-year investigation led by Victoria’s lead scientist, Amanda Caples. It found gas reserves in Victoria “could be extracted without harming the environment”.

Sure, you could probably do that (though the word “could” is working pretty hard there, what with local environmental impacts and the problem of fugitive emissions). But extraction is only a fraction of the problem of natural gas. It’s the subsequent burning that matters.




Read more:
Victoria quietly lifted its gas exploration pause but banned fracking for good. It’s bad news for the climate


Trump rolls back environmental rules

Meanwhile, in the United States, the Trump administration is taking the axe to some key pieces of environmental legislation.

One is an Obama-era car pollution standard, which required an average 5% reduction in greenhouse emissions annually from cars and light truck fleets. Instead, the Trump administration’s “Safer Affordable Fuel Efficient Vehicles” requires just 1.5%.

The health impact of this will be stark. According to the Environmental Defense Fund, the shift will mean 18,500 premature deaths, 250,000 more asthma attacks, 350,000 more other respiratory problems, and US$190 billion in additional health costs between now and 2050.

And then there are the climate costs: if manufacturers followed the Trump administration’s new looser guidelines it would add 1.5 billion tonnes of carbon dioxide to the atmosphere, the equivalent of 17 additional coal-fired power plants.




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When it comes to climate change, Australia’s mining giants are an accessory to the crime


And so…

The challenges COVID-19 presents right now are huge. But they will pass.

The challenges of climate change are not being met with anything like COVID-19 intensity. For now, that makes perfect sense. COVID-19 is unambiguously today. Against this imperative, climate change is still tomorrow.

But like hangovers after a large celebration, tomorrows come sooner than we expect, and they never forgive us for yesterday’s behaviour.The Conversation

Rod Lamberts, Deputy Director, Australian National Centre for Public Awareness of Science, Australian National University and Will J Grant, Senior Lecturer, Australian National Centre for the Public Awareness of Science, Australian National University

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.




Read more:
‘This situation brings me to despair’: two reef scientists share their climate grief


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.




Read more:
Attention United Nations: don’t be fooled by Australia’s latest report on the Great Barrier Reef


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.




Read more:
I studied what happens to reef fish after coral bleaching. What I saw still makes me nauseous


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.

I studied what happens to reef fish after coral bleaching. What I saw still makes me nauseous



Victor Huertas, Author provided

Jodie L. Rummer, James Cook University

The Great Barrier Reef is suffering its third mass bleaching event in five years. It follows the record-breaking mass bleaching event in 2016 that killed a third of Great Barrier Reef corals, immediately followed by another in 2017.

While we don’t know if fish populations declined from the 2016 bleaching disaster, one 2018 study did show the types of fish species on some coral reefs changed. Our study dug deeper into fish DNA.

I was part of an international team of scientists that, for the first time, tracked wild populations of five species of coral reef fish before, during, and after the 2016 marine heatwave.

From a scientific perspective, the results are fascinating and world-first.

Marine heatwaves are now becoming more frequent and more severe with climate change. Corals are bleaching, as pictured here.
Jodie Rummer, Author provided

We used gene expression as a tool to survey how well fish can handle hotter waters. Gene expression is the process where a gene is read by cell machinery and creates a product such as a protein, resulting in a physical trait.

We know many tropical coral reef fish are already living at temperatures close to their upper limits. Our findings can help predict which of these species will be most at risk from repeated heatwaves.




Read more:
‘This situation brings me to despair’: two reef scientists share their climate grief


But from a personal perspective, I still feel nauseous thinking about what the reef looked like during this project. I’ll probably feel this way for a long time.

Rewind to November 2015

We were prepared. Back then we didn’t know the reef was about to bleach and lead to widespread ecological devastation. But we did anticipate that 2016 would be an El Niño year. This is a natural climate cycle that would mean warm summer waters in early 2016 would stick around longer than usual.

But we can’t blame El Niño – the ocean has already warmed by 1°C above pre-industrial levels from continued greenhouse gas emissions. What’s more, marine heatwaves are becoming more frequent and severe with climate change.

Given this foresight, we took some quick liver biopsies from several coral reef fish species at our field site in December 2015, just in case.

Coral bleaching at Magnetic Island, March 2020.
Victor Huertas, Author provided

A couple months later, we were literally in hot water

In February 2016, my colleague and I were based on Lizard Island in the northern part of the Great Barrier Reef working on another project.

The low tides had shifted to the afternoon hours. We were collecting fish in the shallow lagoon off the research station, and our dive computers read that the water temperature was 33°C.




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We looked at each other. These are the temperatures we use to simulate climate change in our laboratory studies for the year 2050 or 2100, but they’re happening now.

Over the following week, we watched corals turn fluorescent and then bone-white.

The water was murky with slime from the corals’ immune responses and because they were slowly exuding their symbiotic zooxanthellae – the algae that provides corals with food and the vibrant colours we know and love when we think about a coral reef. The reef was literally dying before our eyes.

A third of the corals on the Great Barrier Reef perished after the 2016 heatwave.
Jodie Rummer, Author provided

Traits for dealing with heatwaves

We sampled fish during four time periods around this devastating event: before, at the start, during, and after.

Some genes are always “switched on”, regardless of environmental conditions. Other genes switch on or off as needed, depending on the environment.

If we found these fish couldn’t regulate their gene expression in response to temperature stress, then the functions – such as metabolism, respiration, and immune function – also cannot change as needed. Over time, this could compromise survival.




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


The plasticity (a bit like flexibility) of these functions, or phenotypes, is what buffers an organism from environmental change. And right now, this may be the only hope for maintaining the health of coral reef ecosystems in the face of repeated heatwave events.

So, what were the fish doing?

We looked at expression patterns of thousands of genes. We found the same genes responded differently between species. In other words, some fish struggled more than others to cope with marine heatwaves.

Ostorhinchus doederleini, a species of cardinalfish, is bad at coping with marine heatwaves.
Göran Nilsson, Author provided

The species that coped the least was a nocturnal cardinalfish species (Cheilodipterus quinquelineatus). We found it had the lowest number of differentially expressed genes (genes that can switch on or off to handle different stressors), even when facing the substantial change in conditions from the hottest to the coolest months.

In contrast, the spiny damselfish (Acanthochromis polyacanthus) responded to the warmer conditions with changes in the expression of thousands of genes, suggesting it was making the most changes to cope with the heatwave conditions.

What can these data tell us?

Our findings not only have implications for specific fish species, but for the whole ecosystem. So policymakers and the fishing industry should screen more species to predict which will be sensitive and which will tolerate warming waters and heatwaves. This is not a “one size fits all” situation.

One of the species that showed the least amount of change under warming was Cheilodipterus quinquelineatus.
Moises Antonio Bernal de Leon, Author provided

Fish have been on the planet for more than 400 million years. Over time , they may adapt to rising temperatures or migrate to cooler waters.

But, the three recent mass bleaching events is unprecedented in human history, and fish won’t have time to adapt.




Read more:
Attention United Nations: don’t be fooled by Australia’s latest report on the Great Barrier Reef


My drive to protect the oceans began when I was a child. Now it’s my career. Despite the progress my colleagues and I have made, my nauseous feelings remain, knowing our science alone may not be enough to save the reef.

The future of the planet, the oceans, and the Great Barrier Reef lies in our collective actions to reduce global warming. What we do today will determine what the Great Barrier Reef looks like tomorrow.The Conversation

Jodie L. Rummer, Associate Professor & Principal Research Fellow, James Cook University

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

Meet the super corals that can handle acid, heat and suffocation


Resilient corals are offering hope for bleached reefs.
Emma Camp

Emma F Camp, University of Technology Sydney and David Suggett, University of Technology Sydney

Climate change is rapidly changing the oceans, driving coral reefs around the world to breaking point. Widely publicised marine heatwaves aren’t the only threat corals are facing: the seas are increasingly acidic, have less oxygen in them, and are gradually warming as a whole.

Each of these problems reduces coral growth and fitness, making it harder for reefs to recover from sudden events such as massive heatwaves.




Read more:
Acid oceans are shrinking plankton, fuelling faster climate change


Our research, published today in Marine Ecology Progress Series, investigates corals on the Great Barrier Reef that are surprisingly good at surviving in increasingly hostile waters. Finding out how these “super corals” can live in extreme environments may help us unlock the secret of coral resilience helping to save our iconic reefs.

Bleached coral in the Seychelles.
Emma Camp, Author provided

Coral conservation under climate change

The central cause of these problems is climate change, so the central solution is reducing carbon emissions. Unfortunately, this is not happening rapidly enough to help coral reefs, so scientists also need to explore more immediate conservation options.

To that end, many researchers have been looking at coral that manages to grow in typically hostile conditions, such as around tide pools and intertidal reef zones, trying to unlock how they become so resilient.

These extreme coral habitats are not only natural laboratories, they house a stockpile of extremely tolerant “super corals”.

What exactly is a super coral?

“Super coral” generally refers to species that can survive both extreme conditions and rapid changes in their environment. But “super” is not a very precise term!

Our previous research quantified these traits so other ecologists can more easily use super coral in conservation. There are a few things that need to be established to determine whether a coral is “super”:

  1. What hazard can the coral survive? For example, can it deal with high temperature, or acidic water?

  2. How long did the hazard last? Was it a short heatwave, or a long-term stressor such as ocean warming?

  3. Did the coral survive because of a quality such as genetic adaption, or was it tucked away in a particularly safe spot?

  4. How much area does the coral cover? Is it a small pocket of resilience, or a whole reef?

  5. Is the coral trading off other important qualities to survive in hazardous conditions?

  6. Is the coral super enough to survive the changes coming down the line? Is it likely to cope with future climate change?

If a coral ticks multiple boxes in this list, it’s a very robust species. Not only will it cope well in our changing oceans, we can also potentially distribute these super corals along vulnerable reefs.

Some corals cope surprisingly well in different conditions.
Emma Camp, Author provided

Mangroves are surprise reservoirs

We discovered mangrove lagoons near coral reefs can often house corals living in very extreme conditions – specifically, warm, more acidic and low oxygen seawater.

Previously we have reported corals living in extreme mangroves of the Seychelles, Indonesia, New Caledonia – and in our current study living on the Great Barrier Reef. We report diverse coral populations surviving in conditions more hostile than is predicted over the next 100 years of climate change.

Importantly, while some of these sites only have isolated populations, other areas have actively building reef frameworks.

Particularly significant were the two mangrove lagoons on the Great Barrier Reef. They housed 34 coral species, living in more acidic water with very little oxygen. Temperatures varied widely, over 7℃ in the period we studied – and included periods of very high temperatures that are known to cause stress in other corals.

Mangrove lagoons can contain coral that survives in extremely hostile environments, while nearby coral reefs bleach in marine heatwaves.
Emma Camp, Author provided

While coral cover was often low and the rate at which they build their skeleton was reduced, there were established coral colonies capable of surviving in these conditions.

The success of these corals reflect their ability to adapt to daily or weekly conditions, and also their flexible relationship with various symbiotic micro-algae that provide the coral with essential resources.

While we are still in the early phases of understanding exactly how these corals can aid conservation, extreme mangrove coral populations hold a reservoir of stress-hardened corals. Notably the geographic size of these mangrove locations are small, but they have a disproportionately high conservation value for reef systems.




Read more:
Heat-tolerant corals can create nurseries that are resistant to bleaching


However, identification of these pockets of extremely tolerant corals also challenge our understanding of coral resilience, and of the rate and extent with which coral species can resist stress.The Conversation

Emma F Camp, DECRA & UTS Chancellor’s Research Fellow, Climate Change Cluster, Future Reefs Research Programe, University of Technology Sydney and David Suggett, Associate Professor in Marine Biology, University of Technology Sydney

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