The outlook for coral reefs remains grim unless we cut emissions fast — new research


Morgan Pratchett, ARC Centre of Excellence for Coral Reef Studies, CC BY-ND

Christopher Cornwall, Te Herenga Waka — Victoria University of Wellington and Verena Schoepf, University of AmsterdamThe twin stress factors of ocean warming and acidification increasingly threaten coral reefs worldwide, but relatively little is known about how various climate scenarios will affect coral reef growth rates.

Our research, published today, paints a grim picture. We estimate that even under the most optimistic emissions scenarios, we’ll see dramatic reductions in coral reef growth globally.
The good news is that 63% of all reefs in this emissions scenario will still be able to grow by 2100.

But if emissions continue to rise unabated, we predict 94% of coral reefs globally will be eroding by 2050. Even under an intermediate emissions scenario, we project a worst-case outcome in which coral reefs on average will no longer be able to grow vertically by 2100.

The latter scenarios would have dramatic consequences for marine biodiversity and the millions of people who depend on healthy, actively growing coral reefs for livelihoods and shoreline protection. This highlights the urgency and importance of acting now to drastically reduce carbon dioxide emissions.

Coral reefs are home to more than 830,000 species and provide coastal communities with food and income through fisheries and tourism.

The Great Barrier Reef alone contributes A$6.4 billion to the Australian economy. Critically, coral reefs also protect coastlines from storm surges and create land for many low-lying Indo-Pacific island nations.

Marine heatwaves, caused by ongoing ocean warming, have already had a severe impact on coral reef ecosystems by triggering mass bleaching events. These events are becoming more frequent and intense, and cause mass die-offs across large areas.

Bleaching at the Great Barrier Reef
Marine heatwaves trigger mass bleaching and coral die-offs.
Morgan Pratchett, ARC Centre of Excellence for Coral Reef Studies, CC BY-ND

Ocean acidification also reduces the growth of corals by limiting their ability to build their skeletons from calcium carbonate. Together, these stressors threaten the ability of coral reefs to grow and keep up with sea level rise.

Complex impacts from ocean warming and acidification

Our understanding of how ocean warming and acidification threaten reef-forming species has improved considerably over the past decade. However, understanding how coral reef growth will be altered by climate change is more complex than simply measuring rates of change from individual taxonomic groups of corals.

Our study of 183 reefs worldwide provides the first quantitative estimate of how most of the processes that control reef growth respond to climate change and affect carbonate accumulation and growth rates.

Coral reef
Coral on the Great Barrier Reef during the 2020 bleaching event.
Morgan Pratchett, ARC Centre of Excellence for Coral Reef Studies, CC BY-ND

Reefs grow by layering calcium carbonate, produced either by corals and coralline algae. The amount of calcium carbonate built by these reefs depends on many factors.

Cyclones, waves and currents can flush parts of the reef away. Acidifying ocean water means more dissolves chemically. And there is a biological carbonate exchange, known as bio-erosion. Sponges, parrotfish, sea urchins and algae can all eat it, but then return some as defecated sand.

Depending on which of these processes dominates, coral reefs either grow and accrete vertically, or they start to erode. Most of these processes vary for each reef, and almost all are affected by climate change.




Read more:
The Great Barrier Reef outlook is ‘very poor’. We have one last chance to save it


To complicate matters, the frequency and intensity of marine heatwaves will vary geographically, making it difficult to estimate to what degree coral mass bleaching events will reduce coral cover.

In our research, we applied these local and global processes to 233 locations on 183 distinct coral reefs that vary in their species compositions and physical complexity. We found significant variability in responses to ocean acidification and warming.

Geographical and species variability

We predict coral mass bleaching events will have the largest impact on carbonate production across all sites. The world’s coral reefs have already been transformed dramatically by these events over the past few decades.

Coral bleaching at the Maledives
Coral reef in the Maldives, before coral mass bleachign event.
Chris Perry, CC BY-ND



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


Diver and equipment at a coral reef
Experimental setup used to measure calcification coralline algae on the Great Barrier Reef.
Guillermo Diaz-Pulido, CC BY-ND

We used the documented impacts of the 2016 mass bleaching on the Great Barrier Reef, which affected a large range of reefs with different species compositions, depths and latitudes. During this event, each reef experienced varying heat stress, which manifested in different levels of coral cover loss.

This information helped us to calibrate models to predict heat-stress events globally between now and 2100 and to gauge the future magnitudes of heat stress and their impact on our study sites.

We found currently degraded reefs fared poorly in our model, even under lower emissions scenarios. Reefs whose carbonate production was more robust against the effects of climate change tended to be those with high present-day carbonate production rates, higher contributions from coralline algae (which are also vulnerbable, but comparatively more resistant to warming than corals) and low rates of bio-erosion.

Hope for coral reefs

In higher emissions scenarios, even reefs dominated by coralline algae began to suffer as ocean acidification and warming intensified. It is also important to note that such reefs will provide different, and perhaps reduced, services compared to coral-dominated reefs because they are structurally less complex.

People standing on a coal reef
Team members assess coral health during the 2016 bleaching event in the Kimberley, Western Australia.
Christopher Cornwall, CC BY-ND

We did not explore in depth whether remaining coral reef communities could gain tolerance to rising temperatures over time. This could manifest as an increase in the proportional abundance of heat-tolerant species as more heat-sensitive corals die during mass bleaching events.

Surviving corals could acclimatise or even adapt. But whether these mechanisms could provide hope for the continued growth of coral reefs in the future — and if so, to what extent — is largely unknown. Nor can we say if more heat-tolerant corals could sustain similar rates of reef growth and structural complexity.

Coral reef in Chagos
A coral reef in Chagos before a bleaching event in April 2016.
Chris Perry, CC BY-ND

The best hope to save coral reefs and their ecological, societal and economic benefits is to reduce our carbon emissions dramatically, and quickly. Even under our projected intermediate scenarios we expect mean global erosion of coral reefs.

Under the lowest emissions scenario we examined, we expect profound changes in coral reef growth rates and their ability to provide ecosystem services. In this scenario, only some reefs will be able to keep pace with rising sea levels.

We owe it to our children and grandchildren to reduce emissions now, if we have any hope of them witnessing the majestic nature of coral reef ecosystems.The Conversation

Christopher Cornwall, Rutherford Discovery Fellow, Te Herenga Waka — Victoria University of Wellington and Verena Schoepf, Assistant Professor, University of Amsterdam

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

Watching a coral reef die as climate change devastates one of the most pristine tropical island areas on Earth


Sam Purkis, University of MiamiThe Chagos Archipelago is one of the most remote, seemingly idyllic places on Earth. Coconut-covered sandy beaches with incredible bird life rim tropical islands in the Indian Ocean, hundreds of miles from any continent. Just below the waves, coral reefs stretch for miles along an underwater mountain chain.

It’s a paradise. At least it was before the heat wave.

When I first explored the Chagos Archipelago 15 years ago, the underwater view was incredible. Schools of brilliantly colored fish in blues, yellows and oranges darted among the corals of a vast, healthy reef system. Sharks and other large predators swam overhead. Because the archipelago is so remote and sits in one of the largest marine protected areas on the planet, it has been sheltered from industrial fishing fleets and other activities that can harm the coastal environment.

But it can’t be protected from climate change.

A diver carries a plastic pipe for measuring while swimming over a variety of corals
A diver documents the coral reefs in the Chagos Archipelago.
Khaled bin Sultan Living Oceans Foundation

In 2015, a marine heat wave struck, harming coral reefs worldwide. I’m a marine biologist at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, and I was with a team of researchers on a 10-year global expedition to map the world’s reefs, led by the Khaled bin Sultan Living Oceans Foundation. We were wrapping up our work in the Chagos Archipelago at the time. Our report on the state of the reefs there was just published in spring 2021.

As the water temperature rose, the corals began to bleach. To the untrained eye, the scene would have looked fantastic. When the water heats up, corals become stressed and they expel the tiny algae called dinoflagellates that live in their tissue. Bleaching isn’t as simple as going from a living coral to a bleached white one, though. After they expel the algae, the corals turn fluorescent pinks and blues and yellows as they produce chemicals to protect themselves from the Sun’s harmful rays. The entire reef was turning psychedelic colors.

Two bright pink coral mounds
Just before they turned white, the corals turned abnormally bright shades.
Phil Renaud/Khaled bin Sultan Living Oceans Foundation

That explosion of color is rare, and it doesn’t last long. Over the following week, we watched the corals turn white and start to die. It wasn’t just small pieces of the reef that were bleaching – it was happening across hundreds of square miles.

What most people think of as a coral is actually many tiny colonial polyps that build calcium carbonate skeletons. With their algae gone, the coral polyps could still feed by plucking morsels out of the water, but their metabolism slows without the algae, which provide more nutrients through photosynthesis. They were left desperately weakened and more vulnerable to diseases. We could see diseases taking hold, and that’s what finished them off.

We were witnessing the death of a reef.

Rising temperatures increase the heat wave risk

The devastation of the Chagos Reef wasn’t happening in isolation.

Over the past century, sea surface temperatures have risen by an average of about 0.13 degrees Celsius (0.23 F) per decade as the oceans absorb the vast majority of greenhouse gas emissions from human activities, largely from the burning of fossil fuels. The temperature increase and changing ocean chemistry affects sea life of all kinds, from deteriorating the shells of oysters and tiny pteropods, an essential part of the food chain, to causing fish populations to migrate to cooler water.

Corals can become stressed when temperatures around them rise just 1 C (1.8 F) above their tolerance level. With water temperature elevated from global warming, even a minor heat wave can become devastating.

In 2015, the ocean heat from a strong El Niño event triggered the mass bleaching in the Chagos reefs and around the world. It was the third global bleaching on record, following events in 1998 and 2010.

Bleaching doesn’t just affect the corals – entire reef systems and the fish that feed, spawn and live among the coral branches suffer. One study of reefs around Papua New Guinea in the southwest Pacific found that about 75% of the reef fish species declined after the 1998 bleaching, and many of those species declined by more than half.

Research shows marine heat waves are now about 20 times more likely than they were just four decades ago, and they tend to be hotter and last longer. We’re at the point now that some places in the world are anticipating coral bleaching every couple of years.

That increasing frequency of heat waves is a death knell for reefs. They don’t have time to recover before they get hit again.

Where we saw signs of hope

During the Global Reef Expedition, we visited over 1,000 reefs around the world. Our mission was to conduct standardized surveys to assess the state of the reefs and map the reefs in detail so scientists could document and hopefully respond to changes in the future. With that knowledge, countries can plan more effectively to protect the reefs, important national resources, providing hundreds of billions of dollars a year in economic value while also protecting coastlines from waves and storms.

We saw damage almost everywhere, from the Bahamas to the Great Barrier Reef.

Some reefs are able to survive heat waves better than others. Cooler, stronger currents, and even storms and cloudier areas can help prevent heat building up. But the global trend is not promising. The world has already lost 30% to 50% of its reefs in the last 40 years, and scientists have warned that most of the remaining reefs could be gone within decades.

Diver with large sea turtle swimming over corals.
The author, Sam Purkis, dives near a hawksbill turtle in the Chagos Archipelago.
Derek Manzello/Khaled bin Sultan Living Oceans Foundation

While we see some evidence that certain marine species are moving to cooler waters as the planet warms, a reef takes thousands of years to establish and grow, and it is limited by geography.

In the areas where we saw glimmers of hope, it was mostly due to good management. When a region can control other harmful human factors – such as overfishing, extensive coastal development, pollution and runoff – the reefs are healthier and better able to handle the global pressures from climate change.

Establishing large marine protected areas is one of the most effective ways I’ve seen to protect coral reefs because it limits those other harms.

The Chagos marine protected area covers 640,000 square kilometers (250,000 square miles) with only one island currently inhabited – Diego Garcia, which houses a U.S. military base. The British government, which created the marine protected area in 2010, has been under pressure to turn over control of the region to the country of Mauritius, where former Chagos residents now live and which won a challenge over it in the International Court of Justice in 2020. Whatever happens with jurisdiction, the region would benefit from maintaining a high level of marine protection.

A warning for other ecosystems

The Chagos reefs could potentially recover – if they are spared from more heat waves. Even a 10% recovery would make the reefs stronger for when the next bleaching occurs. But recovery of a reef is measured in decades, not years.

So far, research missions that have returned to the Chagos reefs have found only meager recovery, if any at all.

We knew the reefs weren’t doing well under the insidious march of climate change in 2011, when the global reef expedition started. But it’s nothing like the intensity of worry we have now in 2021.

Coral reefs are the canary in the coal mine. Humans have collapsed other ecosystems before through overfishing, overhunting and development, but this is the first unequivocally tied to climate change. It’s a harbinger of what can happen to other ecosystems as they reach their survival thresholds.

This story is part of Oceans 21

Our series on the global ocean opened with five in-depth profiles. Look for new articles on the state of our oceans in the lead-up to the U.N.‘s next climate conference, COP26. The series is brought to you by The Conversation’s international network.The Conversation

Sam Purkis, Professor and Chair of the Department of Marine Sciences, University of Miami

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

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.

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.

There’s insufficient evidence your sunscreen harms coral reefs


Terry Hughes, James Cook University

In the face of persistent heatwaves, Australians are reaching for the sunscreen. But you might have heard some mixed messages about its harm to the environment – specifically to coral reefs.

In July 2018, Hawaii passed a law to prohibit the future sale of sunscreens containing benzophene-3 and octinoxate, claiming these two chemicals increase coral bleaching, and have significant harmful impacts on Hawaii’s marine environment.




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Marine heatwaves are getting hotter, lasting longer and doing more damage


In October 2018, the Republic of Palau followed suit, and banned “reef-toxic” sunscreens. Like most reefs throughout the tropics and subtropics, coral reefs in Hawaii and Palau have already severely bleached multiple times during recent, unusually hot summers, causing extensive loss of corals.

Key West, in Florida, may be the latest area to follow this trend, with a proposed ban to be voted on in early February.

However, medical and skin cancer specialists have warned of the public health risks of a ban on widely used sunscreens, describing the prohibition as risky and unjustified, in part because the few studies that have addressed the environmental impacts of sunscreens experimentally “are not representative of real world conditions”.

For example, the way in which coral tissues were exposed to sunscreen in experiments does not mimic the dispersal and dilution of pollutants from a tourist’s skin (and other sources) into reef waters and onto corals growing in the wild.

Experiments that expose corals to sunscreen chemicals typically use far higher concentrations than have ever been measured on an actual reef. A recent review of the amount of benzophne-3 in reef waters found that, typically, concentrations are barely detectable – usually, a few parts per trillion. One much higher report of 1.4 parts per million, in the US Virgin Islands, is based on a single water sample.

The environmental concerns over sunscreens on coral reefs are centred overwhelmingly on just two studies. The first, published in 2008, noted that there was no previous scientific evidence for an impact of sunscreens on coral reefs.

This study exposed small fragments of corals (branch tips) to high levels of benzophenone-3 and other chemicals by incubating them for a few days inside plastic bags. The fragments in the bags quickly became diseased with viruses and bleached. The authors concluded “up to 10% of the world reefs are potentially threatened by sunscreen-induced coral bleaching”.

Bleaching is a stress response by corals, where they turn pale due to a decline in the symbiotic micro-algae that lives inside their tissues. You can make a coral bleach experimentally by torturing it in any number of ways. However, coral bleaching at a global and regional scale is caused by anthropogenic heating, not sunscreen. We know the footprint of bleaching on the Great Barrier Reef in 1998, 2002, 2016 and 2017 is closely matched to where the water was hottest for longest in each event.

Even the most remote reefs are vulnerable to heat stress. The physiological mechanisms and timescale of thermal bleaching due to global heating is very different from the rapid responses of corals to experimental exposure to high concentrations of sunscreen chemicals.

The second and most-widely cited study of sunscreen toxicity on corals is also laboratory-based. Published in 2016, it focused mainly on the responses of the day-old larvae of one coral species, as well as isolated coral cells. This study did not examine intact coral colonies.

The larvae were placed in 2-3 centilitres of artificial seawater containing a range of concentrations of sunscreen chemicals and a solvent to disperse them. After a few hours, the coral larvae became increasingly pale (bleached) with higher concentrations of oxybenzone.




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Why there’s still hope for our endangered coral reefs


This study also measured the concentration of benzophenone in sea water at six locations in Hawaii. These samples were unreplicated (one per location), and all of them had unmeasureable amounts of sunscreen chemicals. In the US Virgin Islands, the authors found higher concentrations of benzophenone at four out of ten locations, although they did not report results for any blank samples (to control for contamination). The study concluded that oxybenzone threatens the resilience of coral reefs to climate change.

In conclusion, there is actually no direct evidence to demonstrate that bleaching due to global heating is exacerbated by sunscreen pollutants. Similarly, there is no evidence that recovery from thermal bleaching is impaired by sunscreens, or that sunscreens cause coral bleaching in the wild.The Conversation

Terry Hughes, Distinguished Professor, James Cook University

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

The science and art of reef restoration



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Silent Evolution by Jason deCaires Taylor. Taylor makes sculptures and sinks them beneath the sea to create artificial reefs.
© Jason deCaires Taylor

Adam Smith, James Cook University and Ian McLeod, James Cook University

Coral reefs around the world are in crisis. Under pressure from climate change, overfishing, pollution, introduced species and apathy, coral colonies and fish communities are steadily deteriorating.

Coral cover in the Great Barrier reef has declined by an alarming 50% since the 1980s. Some leading scientists believe that the Great Barrier Reef is at a terminal stage.




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$500 million for the Great Barrier Reef is welcome, but we need a sea change in tactics too


One way to address this is through reef restoration. At its simplest, this involves the addition of coral or habitat to a reef. It’s generally undertaken on existing coral reefs, but can also be done on rocky reefs or bare sand.

We have looked back through the decades to celebrate the history of reef restoration, not just in science but also in art, business and politics.

Gardener, by Jason deCaires Taylor.
© Jason deCaires Taylor

Band-aid or reef revolution?

Just as there is no magic solution in human healthcare, there is likewise no magic solution in caring for corals. You do what you can with the resources you have.




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Some scientists have argued that reef restoration is a Band-Aid for the enormous problems that reefs face. We can agree with this point of view, but there are times when a band aid is very useful – and may prevent much more serious injuries.

Reef restoration makes an important local difference, as seen here at Koh Tao, Thailand.
Author provided

Earlier this year the federal government allotted an unprecedented A$500 million dollars to the Great Barrier Reef. This included A$100 million focused on restoration to improve the health of the reef.

Reef restoration science and projects complement community efforts. There is an increasing focus on addressing local issues such as water quality, overfishing, and outbreaks of crown-of-thorns starfish.




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When scientists, industry and government work with local communities we can accelerate the recovery of local reefs.

To do this, we need people who want to make a difference. Once we recognise a degraded ecosystem, we work to reduce stress (like pollution in the water) and add new habitat or helpful species.

Artist Jason deCaires Taylor builds breathtaking underwater sculptures that double as artificial coral reefs.

The history of reef restoration

People have been restoring ecosystems and degraded land for thousands of years. Reef restoration, on the other hand, is relatively new and rarely documented.

Our research indicates that in the modern era there have been three major waves of reef restoration. The first wave started in the 1970s and ‘80s, as scientists were able to easily SCUBA dive and new protective legislation was introduced around the world. This largely involved the addition of new habitats. These could be coral transplants, or artificial constructs likes shipwrecks, concrete pipes, tyres and a purpose built structure called a reef ball.

The second wave from 2000-2010 was associated with scientists and conservationists responding to local concerns from cyclone damage, overfishing, introduced species and over-crowding at tourism sites, particularly in the Caribbean. Restoration methods at this point expanded to removing items as well as adding them, including algae, crown-of-thorns and lionfish.

Reef restoration has evolved over decades.
Author provided

The third wave, from 2016, has focused on new scientific technology such as micro-fragmentation: breaking coral into small pieces so it grows faster. It also emphasises partnerships between government-business-community to reduce threats and restore reefs.

This era also sees a huge increase in communication. Increasingly, we are influenced by social sciences and marketing rather than science and biology in our search for coral reef solutions. Organisations such as Rare, Citizens of the GBR and Reef Check are using citizen scientists, campaigns and pledges to reduce human impact and improve reefs’ health. As an example, the rapid phase out of plastic bags has been led by social media – not science.

Celebrating the Reef restoration Leaders

Documenting the history of reef restoration is important because it allows us to understand our past and be more informed and inspired to take action in the future.

Sculpture at the Underwater Museum at Lanzarote Rubicon.
© Jason deCaires Taylor

The great men and women in our history were innovators who responded to crisis and went against convention by restoring reefs.

We reviewed academic literature and conducted a global survey to find the pioneers who led reef restoration science, management, business and communication. These include Drs Austin Bowden-Kerby, David Vaughan, Todd Barber, Barach Rinkievich and Kristen Marhaver.




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An idea without action is just a dream. Similarly, an idea that has not been communicated widely and is not known and adopted by the general community cannot result in changed behaviour. Increasingly we recognise that good science and management is not enough without community support and action.


The authors would like to acknowledge the valuable contribution of Nathan Cook, Senior Marine Scientist at Reef Ecologic, to this article.

A presentation on the history of Reef Restoration will occur at the Great Barrier Reef Restoration Symposium, July 16-19, Cairns.

Thanks to Jason deCaires Taylor for the use of images. See more at underwatersculpture.com.

The ConversationThis article was updated on July 25 to clarify the location of the reef pictured demonstrating the impact of restoration.

Adam Smith, Adjunct Associate Professor, James Cook University and Ian McLeod, Senior Research Scientist – Coastal Restoration, James Cook University

This article was originally published on The Conversation. Read the original article.

Our acid oceans will dissolve coral reef sands within decades



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Researchers studied reef sands at Heron Island, Hawaii, Bermuda and Tetiaroa. In this photo, white areas show the predominance of sand on reefs.
Southern Cross University

Bradley Eyre, Southern Cross University

Carbonate sands on coral reefs will start dissolving within about 30 years, on average, as oceans become more acidic, new research published today in Science shows.

Carbonate sands, which accumulate over thousands of years from the breakdown of coral and other reef organisms, are the building material for the frameworks of coral reefs and shallow reef environments like lagoons, reef flats and coral sand cays.

But these sands are sensitive to the chemical make-up of sea water. As oceans absorb carbon dioxide, they acidify – and at a certain point, carbonate sands simply start to dissolve.

The world’s oceans have absorbed around one-third of human-emitted carbon dioxide.

Carbonate sand is vulnerable

For a coral reef to grow or be maintained, the rate of carbonate production (plus any external sediment supply) must be greater than the loss through physical, chemical and biological erosion, transport and dissolution.

It is well known that ocean acidification reduces the amount of carbonate material produced by corals. Our work shows that reefs face a double-whammy: the amount of carbonate material produced will decrease, and the newly produced and stored carbonate sands will also dissolve.

Researchers used benthic chambers (pictured) to test how different levels of seawater acidity affect reef sediments.
Steve Dalton/Southern Cross University

We measured the impact of acidity on carbonate sands by placing underwater chambers over coral reefs sands at Heron Island, Hawaii, Bermuda and Tetiaroa in the Pacific and Atlantic Oceans. Some of the chambers were then acidified to represent future ocean conditions.

The rate at which the sands dissolve was strongly related to the acidity of the overlying seawater, and was ten times more sensitive than coral growth to ocean acidification. In other words, ocean acidification will impact the dissolution of coral reef sands more than the growth of corals.

This probably reflects the corals’ ability to modify their environment and partially adjust to ocean acidification, whereas the dissolution of sands is a geochemical process that cannot adapt.

Sands on all four reefs showed the same response to future ocean acidification, but the impact of ocean acidification on each reef is different due to different starting conditions. Carbonate sands in Hawaii are already dissolving due to ocean acidification, because this coral reef site is already disturbed by pollution from nutrients and organic matter from the land. The input of nutrients stimulates algal growth on the reef.

In contrast, carbonate sands in Tetiaroa are not dissolving under current ocean acidification because this site is almost pristine.

What will this mean for coral reefs?

Our modelling at 22 locations shows that net sand dissolution will vary for each reef. However, by the end of the century all but two reefs across the three ocean basins would on average experience net dissolution of the sands.

A transition to net sand dissolution will result in loss of material for building shallow reef habitats such as reef flats and lagoons and associated coral cays. What we don’t know is whether an entire reef will slowly erode or simply collapse, once the sediments become net dissolving, as the corals will still grow and create reef framework. Although they will most likely just slowly erode.

It may be possible to reduce the impact of ocean acidification on the dissolution of reef sands, by managing the impact of organic matter like algae at local and regional scales. This may provide some hope for some already disturbed reefs, but much more research on this topic is required.

The ConversationUltimately, the only way we can stop the oceans acidifying and the dissolving of coral reefs is concerted action to lower CO₂ emissions.

Bradley Eyre, Professor of Biogeochemistry, Director of the Centre for Coastal Biogeochemistry, Southern Cross University

This article was originally published on The Conversation. Read the original article.