11 billion pieces of plastic bring disease threat to coral reefs



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A plastic bottle trapped on a coral reef.
Tane Sinclair-Taylor, Author provided

Joleah Lamb, Cornell University

There are more than 11 billion pieces of plastic debris on coral reefs across the Asia-Pacific, according to our new research, which also found that contact with plastic can make corals more than 20 times more susceptible to disease.

In our study, published today in Science, we examined more than 124,000 reef-building corals and found that 89% of corals with trapped plastic had visual signs of disease – a marked increase from the 4% chance of a coral having disease without plastic.

Globally, more than 275 million people live within 30km of coral reefs, relying on them for food, coastal protection, tourism income, and cultural value.

With coral reefs already under pressure from climate change and mass bleaching events, our findings reveal another significant threat to the world’s corals and the ecosystems and livelihoods they support.




Read more:
This South Pacific island of rubbish shows why we need to quit our plastic habit


In collaboration with numerous experts and underwater surveyors across Indonesia, Myanmar, Thailand and Australia, we collected data from 159 coral reefs between 2010 and 2014. In so doing, we collected one of the most extensive datasets of coral health in this region and plastic waste levels on coral reefs globally.

There is a huge disparity between global estimates of plastic waste entering the oceans and the amount that washes up on beaches or is found floating on the surface.

Our research provides one of the most comprehensive estimates of plastic waste on the seafloor, and its impact on one of the world’s most important ecosystems.

Plastic litter in a fishing village in Myanmar.
Kathryn Berry

The number of plastic items entangled on the reefs varied immensely among the different regions we surveyed – with the lowest levels found in Australia and the highest in Indonesia.

An estimated 80% of marine plastic debris originates from land. The variation of plastic we observed on reefs during our surveys corresponded to the estimated levels of plastic litter entering the ocean from the nearest coast. One-third of the reefs we surveyed had no derelict plastic waste, however others had up 26 pieces of plastic debris per 100 square metres.

We estimate that there are roughly 11.1 billion plastic items on coral reefs across the Asia-Pacific. What’s more, we forecast that this will increase 40% in the next seven years – equating to an estimated 15.7 billion plastic items by 2025.

This increase is set to happen much faster in developing countries than industrialised ones. According to our projections, between 2010 and 2025 the amount of plastic debris on Australian coral reefs will increase by only about 1%, whereas for Myanmar it will almost double.

How can plastic waste cause disease?

Although the mechanisms are not yet clear, the influence of plastic debris on disease development may differ among the three main global diseases we observed to increase when plastic was present.

Plastic debris can open wounds in coral tissues, potentially letting in pathogens such as Halofolliculina corallasia, the microbe that causes skeletal eroding band disease.

Plastic debris could also introduce pathogens directly. Polyvinyl chloride (PVC) – a very common plastic used in children’s toys, building materials like pipes, and many other products – have been found carrying a family of bacteria called Rhodobacterales, which are associated with a suite of coral diseases.

Similarly, polypropylene – which is used to make bottle caps and toothbrushes – can be colonised by Vibrio, a potential pathogen linked to a globally devastating group of coral diseases known as white syndromes.

Finally, plastic debris overtopping corals can block out light and create low-oxygen conditions that favour the growth of microorganisms linked to black band disease.

Plastic debris floating over corals.
Kathryn Berry

Structurally complex corals are eight times more likely to be affected by plastic, particularly branching and tabular species. This has potentially dire implications for the numerous marine species that shelter under or within these corals, and in turn the fisheries that depend on them.




Read more:
Eight million tonnes of plastic are going into the ocean each year


Our study shows that reducing the amount of plastic debris entering the ocean can directly prevent disease and death among corals.

The ConversationOnce corals are already infected, it is logistically difficult to treat the resulting diseases. By far the easiest way to tackle the problem is by reducing the amount of mismanaged plastic on land that finds its way into the ocean.

Joleah Lamb, Research fellow, Cornell University

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

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How we found 112 ‘recovery reefs’ dotted through the Great Barrier Reef


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Some reefs are strong sources of coral larvae.
Peter Mumby, Author provided

Peter J Mumby, The University of Queensland

The Great Barrier Reef is better able to heal itself than we previously imagined, according to new research that identifies 112 individual reefs that can help drive the entire system towards recovery.

The back-to-back bleaching events in 2016 and 2017 that killed many corals on the Great Barrier Reef have led many researchers to ask whether and how it can recover. Conventionally, we tend to focus on what controls recovery on individual reefs – for example, whether they are fouled by seaweed or sediments.

But in our study, published in PLoS Biology, my colleagues and I stepped back to view the entire Great Barrier Reef as a whole entity and ask how it can potentially repair itself.


Read more: The Great Barrier Reef can repair itself, with a little help from science


We began by asking whether some reefs are exceptionally important for kick-starting widespread recovery after damage. To do this we set three criteria.

First, we looked for reefs that are major sources of coral larvae – the ultimate source of recovery. Every year corals engage in one of nature’s greatest spectacles, their mass reproduction during a November full moon. Fertilised eggs (larvae) travel on ocean currents for days or weeks in search of a new home.

With our partners at the CSIRO we’ve been able to model where these larvae go, and therefore the “connectivity” of the reef. By using this modelling (the Great Barrier Reef is far too large to observe this directly), we looked for reefs that strongly and consistently supply larvae to many other reefs.

Healthy reefs supply far more larvae than damaged ones, so our second criterion was that reefs should have a relatively low risk of being impacted by coral bleaching. Using satellite records of sea temperature dating back to 1985, we identified reefs that have not yet experienced the kind of temperature that causes mass coral loss. That doesn’t mean these reefs will never experience bleaching, but it does mean they have a relatively good chance of surviving at least for the foreseeable future.

Our final criterion was that reefs should supply coral larvae but not pests. Here we focused on the coral-eating crown-of-thorns starfish, whose larvae also travel on ocean currents. We know that outbreaks of these starfish tend to begin north of Cairns, and from that we can predict which reefs are most likely to become infested over time.

Fortunately, many good sources of coral larvae are relatively safe from crown-of-thorns starfish, particularly those reefs that are far offshore and bathed in oceanic water from the Coral Sea rather than the currents that flow past Cairns. Indeed, the access to deep – and often cooling – ocean water helps moderate temperature extremes in these outer reefs, which also reduces the risk of bleaching in some areas.

Using these three criteria, we pinpointed 112 reefs that are likely to be important in driving reef recovery for the wider system. They represent only 3% of the reefs of the Great Barrier Reef, but are so widely connected that their larvae can reach 47% of all the reefs within a single summer spawning season.

Unfortunately, their distribution across the reef is patchy. Relatively few are in the north (see map) so this area is relatively vulnerable.

Black dots show reefs identified as strong sources of coral larvae; grey dots show other reefs.
Hock et al., PLoS Biol.

Our study shows that reefs vary hugely, both in their exposure to damage and in their ability to contribute to the recovery of corals elsewhere. Where these patterns are pretty consistent over time – as is the case for the reefs we identified – it makes sense to factor this information into management planning.

It would be sensible to improve surveillance of these particular reefs, to check that crown-of-thorns starfish do not reach them, and to eradicate the starfish if they do.

To be clear, these are not the only reefs that should be managed. The Great Barrier Reef already has more than 30% of its area under protection from fishing, and many of its other individual reefs are important for tourism, fisheries and cultural benefits.

But the point here is that some reefs are far more important for ecosystem recovery than others. Factoring these patterns into tactical management – such as how best to respond in the aftermath of a cyclone strike – is the next step. It’s a need that has been articulated repeatedly by the Great Barrier Reef Marine Park Authority.


Read more: Coal and climate change: a death sentence for the Great Barrier Reef


Taking the long-term view, the greatest threats to the reef are rising sea temperatures and ocean acidification caused by elevated carbon dioxide levels. This is clearly a challenge for humanity and one that requires consistent policies across governments.

But local protection is vital in order to maintain the reef in the best state possible given the global environment. Actions include improvements to the quality of the water emerging from rivers, controlling crown-of-thorns starfish, and maintaining healthy fish populations.

The ConversationThis is an expensive process and resources need to be deployed as effectively as possible. Our results help target management effectively by revealing the underlying mechanisms of repair on the reef. If management can help protect and facilitate corals’ natural processes of recovery, this might go a long way towards sustaining the Great Barrier Reef in an already challenging environment.

Peter J Mumby, Chair professor, The University of Queensland

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

Explainer: mass coral spawning, a wonder of the natural world


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During mass spawning events coral young rise from their parents to ocean surface.
Australian Institute of Marine Science, Author provided

Line K Bay, Australian Institute of Marine Science; Andrew Heyward, Australian Institute of Marine Science, and Andrew Negri, Australian Institute of Marine Science

During the late spring, corals on the Great Barrier Reef release little balls that float to the ocean surface in a slow motion upside-down snowstorm.

These beautiful events are studied avidly by scientists: the tiny bundles will become young corals, and unlocking their secrets is vital to the continuing life of our coral reefs.


Read more: Newly discovered hermit crab species lives in ‘walking corals’


The first major mass spawning of 2017 unfolded last week following the early November full moon, with another spawning event predicted for December.

https://giphy.com/embed/l2QEeZl0oICDd4eqI

Mass spawning after the full moon

Coral species have a varied sex life. The majority of species are simultaneously male and female (hermaphrodites) and typically pack both eggs and sperm (gametes) into tight, buoyant bundles that are released after dark with remarkable synchronisation. The bundles float to the surface and open, allowing the eggs meet compatible sperm.

Less commonly, some coral species have separate sexes, and a few species even release asexually produced clones of themselves. For all species with sexual reproduction fertilised eggs develop into mobile larvae that settle on the sea floor and become polyps: the beginning of a new coral colony on the reef.

Mass spawnings are spectacular events, in which dozens of coral species release their gametes at specific times. Sometimes more than 100 species spawn on a single night, or over a few successive nights.


Read more: Feeling helpless about the Great Barrier Reef? Here’s one way you can help


This iconic celebration of sex on the reef was first described in the central Great Barrier Reef in 1984 by a group of early-career scientists. The discovery earned them a prestigious Australian Museum Eureka Award for Environmental Research in 1992.

The precise timing of this seasonal phenomenon is linked to seawater temperature, lunar phases, and other factors such as the daily cycle of light and dark. Mass coral spawning is the dominant reproductive mode for corals on the Great Barrier Reef, and has also been recorded on reefs around the world.

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The release of egg and sperm bundles is the culmination of many months of development. In years when the full moon falls early in October and November, many colonies are not quite ready and delay spawning for another lunar cycle. That’s why this year will see some action in November and another mass spawning event after the December full moon.

An important date in the scientific calendar

Spawning can be replicated in aquarium settings, which provide unique opportunities to researchers. All three of us work in the Australian Institute of Marine Science’s (AIMS) unique Sea Simulator, where large numbers of coral larvae are produced for scientific experiments.

Scientists from the Institute and around the world work through the spawning nights to collect gamete bundles, separate sperm and fertilise the eggs, then rear millimeter-long larvae and juveniles. Many experiments continue for days, weeks and even years to address critical knowledge gaps in how corals respond to and recover from stress.

New tools for coral reef management

The extensive coral death in the northern Great Barrier Reef following back-to-back bleaching events in 2016 and 2017 highlights the impacts of rapidly changing ocean conditions. AIMS scientists focus on developing ways to help coral adapt and restore damaged reefs.

Corals reefs are at a crossroads, but there is still hope. Experiments during this year’s spawning season will test whether surviving corals from recent bleaching events are naturally adapted to warmer reef temperatures, and if they produce more heat-tolerant young.


Read more: The Great Barrier Reef can repair itself, with a little help from science


This knowledge underpins the development of active reef management tools such as assisted gene flow.

The huge Sea Simulator lets researchers carefully test how corals respond to stress.
Australian Institute of Marine Science, Author provided

Assisted gene flow involves moving heat-tolerant corals (or their young) to reefs that are warming. This technique proposes to improve the overall heat tolerance of local coral populations, to help the buffer the reef against future bleaching events caused by warmer than normal water temperatures.

More local threats to corals include poor water quality and pollution from coastal development. The early stages of a coral’s life are very sensitive to exposure to pesticides, oil spills and sediments from dredging.

Carefully controlled experiments with aquarium-reared coral larvae provide insights into the role of these local pressures on the rate of recovery and replenishment following large-scale disturbances.

The present reality for coral reefs is one of increasing strain from climate change, cyclones, crown-of-thorns starfish predation, and declining water quality. The ability of coral reef ecosystems to recover from these challenges relies on the success of mass coral spawning both on the reef and advances in the laboratory to generate new options to enhance reef resilience.

The ConversationExploring reef restoration and adaptation needs to go hand-in-hand with ongoing (and increasing) efforts in conventional management, such as climate change mitigation, regional management of water quality and control of crown-of-thorns starfish.

Line K Bay, Senior Research Scientist and Team Leader, Australian Institute of Marine Science; Andrew Heyward, Principal Research Scientist, Exploring Marine Biodiversity, Australian Institute of Marine Science, and Andrew Negri, Principal Research Scientist, Australian Institute of Marine Science

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

How to work out which coral reefs will bleach, and which might be spared


Clothilde Emilie Langlais, CSIRO; Andrew Lenton, CSIRO, and Scott Heron, National Oceanic and Atmospheric Administration

Regional variations in sea surface temperature, related to seasons and El Niño, could be crucial for the survival of coral reefs, according to our new research. This suggests that we should be able to identify the reefs most at risk of mass bleaching, and those that are more likely to survive unscathed.

Healthy coral reefs support diverse ecosystems, hosting 25% of all marine fish species. They provide food, coastal protection and livelihoods for at least 500 million people.

But global warming, coupled with other pressures such as nutrient and sediment input, changes in sea level, waves, storms, ventilation, hydrodynamics, and ocean acidification, could lead to the end of the world’s coral reefs in a couple of decades.


Read more: How much coral has died in the Great Barrier Reef’s worst bleaching event?


Climate warming is the major cause of stress for corals. The world just witnessed an event described as the “longest global coral die-off on record”, and scientists have been raising the alarm about coral bleaching for decades.

The first global-scale mass bleaching event happened in 1998, destroying 16% of the world coral reefs. Unless greenhouse emissions are drastically reduced, the question is no longer if coral bleaching will happen again, but when and how often?

To help protect coral reefs and their ecosystems, effective management and conservation strategies are crucial. Our research shows that understanding the relationship between natural variations of sea temperature and human-driven ocean warming will help us identify the areas that are most at risk, and also those that are best placed to provide safe haven.

A recurrent threat

Bleaching happens when sea temperatures are unusually high, causing the corals to expel the coloured algae that live within their tissues. Without these algae, corals are unable to reproduce or to build their skeletons properly, and can ultimately die.

The two most devastating global mass bleaching events on record – in 1998 and 2016 – were both triggered by El Niño. But when water temperatures drop back to normal, corals can often recover.

Certain types of coral can also acclimatise to rising sea temperatures. But as our planet warms, periods of bleaching risk will become more frequent and more severe. As a consequence, corals will have less and less time to recover between bleaching events.

We are already witnessing a decline in coral reefs. Global populations have declined by 1-2% per year in response to repeated bleaching events. Closer to home, the Great Barrier Reef lost 50% of its coral cover between 1985 and 2012.

A non-uniform response to warming

While the future of worldwide coral reefs looks dim, not all reefs will be at risk of recurrent bleaching at the same time. In particular, reefs located south of 15ºS (including the Great Barrier Reef, as well as islands in south Polynesia and Melanesia) are likely to be the last regions to be affected by harmful recurrent bleaching.

We used to think that Micronesia’s reefs would be among the first to die off, because the climate is warming faster there than in many other places. But our research, published today in Nature Climate Change, shows that the overall increase in temperature is not the only factor that affects coral bleaching response.

In fact, the key determinant of recurrent bleaching is the natural variability of ocean temperature. Under warming, temperature variations associated with seasons and climate processes like El Niño influence the pace of recurrent bleaching, and explain why some reefs will experience bleaching risk sooner than others in the future.

Different zones of the Pacific are likely to experience differing amounts of climate variability.
Author provided
Degrees of future bleaching risk for corals in the three main Pacific zones.
Author provided

Our results suggest that El Niño events will continue to be the major drivers of mass bleaching events in the central Pacific. As average ocean temperatures rise, even mild El Niño events will have the potential to trigger widespread bleaching, meaning that these regions could face severe bleaching every three to five years within just a few decades. In contrast, only the strongest El Niño events will cause mass bleaching in the South Pacific.

In the future, the risk of recurrent bleaching will be more seasonally driven in the South Pacific. Once the global warming signal pushes summer temperatures to dangerously warm levels, the coral reefs will experience bleaching events every summers. In the western Pacific, the absence of natural variations of temperatures initially protects the coral reefs, but only a small warming increase can rapidly transition the coral reefs from a safe haven to a permanent bleaching situation.


Read more: Feeling helpless about the Great Barrier Reef? Here’s one way you can help


One consequence is that, for future projections of coral bleaching risk, the global warming rate is important but the details of the regional warming are not so much. The absence of consensus about regional patterns of warming across climate models is therefore less of an obstacle than previously thought, because globally averaged warming provided by climate models combined with locally observed sea temperature variations will give us better projections anyway.

The ConversationUnderstanding the regional differences can help reef managers identify the reef areas that are at high risk of recurring bleaching events, and which ones are potential temporary safe havens. This can buy us valuable time in the battle to protect the world’s corals.

Clothilde Emilie Langlais, research scientist at CSIRO Oceans and Atmosphere, CSIRO; Andrew Lenton, Senior Research Scientist, Oceans and Atmosphere, CSIRO, and Scott Heron, Physical Scientist, National Oceanic and Atmospheric Administration

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

Huge restored reef aims to bring South Australia’s oysters back from the brink



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Mud oysters played a largely unappreciated part in Australia’s history.
Cayne Layton, Author provided

Dominic McAfee, University of Adelaide and Sean Connell, University of Adelaide

The largest oyster reef restoration project outside the United States is underway in the coastal waters of Gulf St Vincent, near Ardrossan in South Australia. Construction began earlier this month. Some 18,000 tonnes of limestone and 7 million baby oysters are set to provide the initial foundations for a 20-hectare reef.

The A$4.2-million project will be built in two phases and should be complete by December 2018. The first phase is the 4-hectare trial currently being built by Primary Industries and Regions South Australia; the second phase will see the reef expand to 20 hectares, led by The Nature Conservancy.

Some of the 18,000 tonnes of limestone destined for the seafloor.
D. McAfee

Just 200 years ago the native mud oyster, Ostrea angasi, formed extensive reefs in the Gulf, along more than 1,500km of South Australia’s coastline. Today there are no substantial accumulations of mud oysters anywhere around mainland Australia, with just one healthy reef remaining in Tasmania.

This restoration project aims to pull our native mud oyster back from the brink of extinction in the wild, and restore a forgotten ecosystem that once teemed with marine life.

More than just seafood

Oysters played a large role in Australia’s colonial history. When European settlers first arrived they had to navigate a patchwork of oyster reefs (also called shellfish reefs) that filled the shallow waters of our temperate bays. These enormous structures could cover 10 hectares in a single patch, providing an easily exploited food resource for the struggling early settlers. Oyster shell was burned to produce lime, and the colony’s first buildings were built with the help of oyster cement.

Collectively, these pre-colonial oyster reefs would have rivalled the geographic extent of the Great Barrier Reef, covering thousands of kilometres of Australia’s eastern and southern coastlines.

The history goes back much further too. For thousands of years oyster reefs fed and fuelled trade among Aboriginal communities. Shell middens dating back 2,000 years attest to the cultural importance of oysters for coastal communities, who ate them in abundance and used their shells to fashion fishhooks and cutting tools.

Health oyster reef in Tasmania.
C. Gillies

The insatiable appetite of the newly settled Europeans for this bountiful resource was devastating. Not only were live oysters harvested for food, but the dead shell foundations that are critical for the settlement of new oysters were scraped from the seabed for lime burning. Armed with bottom-dredges a wave of exploitation spread across the coast, first overexploiting oyster reefs close to major urban centres and then further afield. The combination of the lost hard shell bed and increased sediment runoff from the rapidly altered coastal landscape saw oyster populations crash within a century of colonisation.

Today oyster populations are at less than 1% of their pre-colonial extent in Australia. This is not a unique story – globally it is estimated that 85% of oyster habitat has been lost in the past few centuries, making it one of the most exploited marine habitats in the world.

Today, across much of Australia’s east coast you will see Sydney rock oysters encrusting rocky shores, creating a thin veneer around the edge of our bays and estuaries. On the south coast you occasionally see a solitary mud oyster clinging to a jetty pylon. Many Australians don’t realise that this familiar sight represents a mere shadow of the incredible and largely forgotten ecosystems that oysters once supported.

Oysters are an unsung ecological superhero, with the capacity to increase marine biodiversity, clean coastal waters, enhance neighbouring seagrass, reduce coastal erosion, and even slow the rate of climate change. When oysters cement together, their aggregations form habitat for a great diversity of other invertebrates. A 25cm-square patch of oysters can host more than 1,000 individual invertebrates from a range of different biological groups, in turn providing a smorgasbord for fish.

Restoration site, formerly covered with dense oyster habitat.
D. McAfee

A solitary oyster can filter about 100 litres of water a day, which means that en masse they can function as the “kidneys” of our bays, filtering excess nutrients from the water and depositing them on the seafloor. In doing so, they encourage seagrass growth, while their physical structures help to dissipate wave energy and thus reduce the impact of storm surges.

As if all that weren’t enough, oysters are also a carbon sink, building calcium carbonate shells that are buried in the seafloor after death and eventually compacted to rock, thus helping to prevent carbon dioxide from cycling back into the atmosphere.

Building it back

Restoring oyster reefs has the potential to return these ecosystem services and increase the productivity of our coastal ecosystems. The Gulf of St Vincent project came about through an election promise by the South Australian Government to boost recreational fishing. A collaboration between The Nature Conservancy, Yorke Penninsula Council and the South Australian Government will deliver the reef’s foundations, while my colleagues and I at the University of Adelaide are working to ensure that the restored oysters survive and thrive, and that the reef continues to grow.

The ConversationHopefully this is just the beginning for large-scale oyster restoration in Australia, and the lessons learned from this project will guide more restoration projects to improve the health of our oceans. With other restoration projects also underway in Victoria and Western Australia, the tide is hopefully turning for our once numerous oysters.

Dominic McAfee, Postdoctoral researcher, marine ecology, University of Adelaide and Sean Connell, Professor, Ecology, University of Adelaide

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

The world’s coral reefs are in trouble, but don’t give up on them yet


Terry Hughes, James Cook University and Joshua Cinner, James Cook University

The world’s coral reefs are undoubtedly in deep trouble. But as we and our colleagues argue in a review published today in Nature, we shouldn’t give up hope for coral reefs, despite the pervasive doom and gloom.

Instead, we have to accept that coral reefs around the world are transforming rapidly into a newly emerging ecosystem unlike anything humans have experienced before. Realistically, we can no longer expect to conserve, maintain, preserve or restore coral reefs as they used to be.

This is a confronting message. But it also focuses attention on what we need to do to secure a realistic future for reefs, and to retain the food security and other benefits they provide to society.

The past three years have been the warmest on record, and many coral reefs throughout the tropics have suffered one or more bouts of bleaching during prolonged underwater heatwaves.

A bleached coral doesn’t necessarily die. But in 2016, two-thirds of corals on the northern Great Barrier Reef did die in just six months, as a result of unprecedented heat stress. This year the bleaching happened again, this time mainly on the middle section of the reef.

Reefs are being degraded by global pressures, not just local ones.
Terry Hughes, Author provided

In both years, the southern third of the reef escaped with little or no bleaching, because it was cooler. So bleaching is patchy and it varies in severity, depending partly on where the water is hottest each summer, and on regional differences in the rate of warming. Consequently some regions, reefs, or even local sites within reefs, can escape damage even during a global heatwave.

Moderate bleaching events are also highly selective, affecting some coral species and individual colonies more than others, creating winners and losers. Coral species also differ in their capacity to reproduce, disperse as larvae, and to rebound afterwards.

This natural variability offers hope for the future, and represents different sources of resilience. Surviving corals will continue to produce billions of larvae each year, and their genetic makeup will evolve under intense natural selection.

In response to fishing, coastal development, pollution and four bouts of bleaching in 1998, 2002, 2016 and 2017, the Great Barrier Reef is already a highly altered ecosystem, and it will change even more in the coming decades. Although reefs will be different in future, they could still be perfectly functional in centuries to come – capable of sustaining ecological processes and regenerating themselves. But this will only be possible if we act quickly to curb climate change.

The Paris climate agreement provides the key framework for avoiding very dangerous levels of global warming. Its 1.5℃ and 2℃ targets refer to increases in global average land and sea temperatures, relative to pre-industrial times. For most shallow tropical oceans, where temperatures are rising more slowly than the global average, that translates to 0.5℃ of further warming by the end of this century – slightly less than the amount of warming that coral reefs have already experienced since industrialisation began.

If we can improve the management of reefs to help them run this climate gauntlet, then reefs should survive. Reefs of the future will have a different mix of species, but they should nonetheless retain their aesthetic values, and support tourism and fishing. However, this cautious optimism is entirely contingent on steering global greenhouse emissions away from their current trajectory, which could see annual bleaching of corals occurring in most tropical locations by 2050. There is no time to lose before this narrowing window of opportunity closes.

A crisis of governance

Reef governance is failing because it is largely set up to manage local threats, such as overfishing and pollution. In Australia, when the Great Barrier Reef Marine Park Authority was set up in 1976, the objective of managing threats at the scale of (almost) the entire Great Barrier Reef was revolutionary. But today, the scale of threats is global: market pressures for Australian reef fish now come from overseas; port dredging and shipping across the reef are spurred on by fossil fuel exports to Asia; a housing crisis in the United States can batter reef tourism half a world away; and record breaking marine heatwaves due to global warming can kill even the most highly protected and remote corals.

Increasingly, coral reef researchers are turning to the social sciences, not just biology, in search of solutions. We need better governance that addresses both local and larger-scale threats to coral reef degradation, rather than band-aid measures such as culling starfish that eat corals.

In many tropical countries, the root causes of reef degradation include poverty, increasing market pressures from globalisation, and of course the extra impacts of global warming. Yet these global issues desperately need more attention at just the time when some governments are reducing foreign aid, failing to address global climate change, and in the case of Australia and the US, trying to resuscitate the dying fossil fuel industry with subsidies for economically unviable projects.

Effective reef governance will not only require increased cooperation among nations to tackle global issues, as in the case of the Paris climate deal, but will also require policy coordination at the national level to ensure that domestic action matches and supports these larger-scale goals.

The ConversationQuite simply, we can’t expect to have thriving coral reefs in the future as well as new coal mines – policies to promote both are incompatible.

Terry Hughes, Distinguished Professor, James Cook University, James Cook University and Joshua Cinner, Professor & ARC Future Fellow, ARC Centre of Excellence, Coral Reef Studies, James Cook University

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

Back-to-back bleaching has now hit two-thirds of the Great Barrier Reef


Terry Hughes, James Cook University and James Kerry, James Cook University

Corals on the Great Barrier Reef have bleached again in 2017 as a result of extreme summer temperatures. It’s the fourth such event and the second in as many years, following earlier mass bleachings in 1998, 2002 and 2016. The Conversation

The consecutive bleaching in 2016 and 2017 is concerning for two reasons. First, the 12-month gap between the two events is far too short for any meaningful recovery on reefs that were affected in 2016.

Second, last year’s bleaching was most severe in the northern section of the reef, from the Torres Strait to Port Douglas, whereas this year the most intense bleaching has occurred further south, between Cooktown and Townsville. The combined footprint of this unprecedented back-to-back bleaching now stretches along two-thirds of the length of the Great Barrier Reef.

Last year, after the peak temperatures in March, 67% of the corals died along a 700km northern section of the reef – the single greatest loss of corals ever recorded on the reef.

Further offshore and to the south, most of the bleached corals regained their colour after the 2016 bleaching, and survived. The patchiness of the bleaching means that there are still sections of the Great Barrier Reef that remain in good condition.

It is still too early to tell how many corals will survive or die over the next few months in the central section as a result of this year’s bleaching.

Four major events

Each of the four bleaching events has a distinctive geographic pattern that can be explained by where the water was hottest for sustained periods during each summer.

For example, the southern Great Barrier Reef escaped bleaching in both 2016 and 2017 because the summer sea temperatures there remained close to normal. Similarly, the earlier mass bleaching events in 1998 and 2002 were relatively moderate, because the elevated water temperatures experienced then were lower than those in 2017 and especially 2016.

The marine heatwaves in 1998 and 2016 coincided with El Niño periods, but this was not the case in 2002 or this year, when water temperatures were also abnormally high. Increasingly around the tropics, we are seeing more and more bleaching events, regardless of the timing relative to the El Niño-La Niña cycle. This reflects the growing impact of global warming on these events.

The local weather also plays an important role in determining where and when bleaching occurs. For example, in 2016, ex-Tropical Cyclone Winston came from Fiji to Australia at the end of February as a rain depression, and cooled the southern region of the Great Barrier Reef, saving it from bleaching.

This year, the category 4 Tropical Cyclone Debbie tracked across the reef in late March, close to the southern boundary of the latest bleaching.

But TC Debbie was too far south to prevent the bleaching that was already under way in the reef’s central and northern sections. Instead of helping to ameliorate the bleaching, this powerful cyclone has added to the pressures on some southern reefs by smashing corals and exacerbating coastal runoff.

Prospects for the future

The fallout from this and last year’s events will continue to unfold in the coming months and years. It takes several months for severely bleached corals to regain their colour, or to die. On some reefs in the Great Barrier Reef’s central region, underwater surveys in 2017 are already documenting substantial loss of corals.

The recovery times for northern and now central reefs that have lost many corals will be at least 10-15 years, assuming that conditions remain favourable for corals during that period.

We have a narrowing window of opportunity to tackle global warming, and no time to lose in moving to zero net carbon emissions. We have already seen four major bleaching events on the Great Barrier Reef with just 1℃ of global average warming.

The goals enshrined in the Paris climate agreement, which aims to hold global warming well below 2℃ and as close as possible to 1.5℃, will not be sufficient to restore the Great Barrier Reef to its former glory. But they should at least ensure that we continue to have a functioning coral reef system.

In contrast, if the world continues its business-as-usual greenhouse emissions for several more decades, it will almost certainly spell the end of the Great Barrier Reef as we now know it.

Terry Hughes, Distinguished Professor, James Cook University, James Cook University and James Kerry, Senior Research Officer, ARC Centre of Excellence for Coral Reef Studies, James Cook University

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