New coral bleaching outbreak in NT a worrying sign of our warming oceans



File 20180316 104642 1fga4az.png?ixlib=rb 1.1
The increasingly bleached coral at Black Point on the Cobourg Peninsula is a worrying sign of what’s to come for other coral reefs in Australia.
Alan Withers, Author provided

Selina Ward, The University of Queensland

An outbreak of coral bleaching has been reported over the summer in Gang Gurak Barlu National Park on the Cobourg Peninsula, 60km northeast of Darwin, homeland of several clans of the Iwaidja-speaking Aboriginal people of Western Arnhem Land.

As no formal monitoring or assessment program is in place for these reefs, it’s impossible to gauge the full severity and extent of the bleaching. However, this video from Black Point on the Cobourg Peninsula contrasts the healthy reef in 2015 and the bleached reef in 2018.

Footage courtesy Alan Withers, music from Kai Engel – Anxiety.

The Northern Territory has unique marine ecosystems which are largely untouched and sit in waters receiving flow from untamed rivers. There are extensive coral reefs with abundant breeding turtle populations, saltwater crocodiles and sharks.

In January this year, the water temperature between the Northern Territory and Papua New Guinea reached what the National Oceanic and Atmospheric Administration (NOAA) calls Alert Level 2 – its highest alert for the risk of bleaching and subsequent coral death.

This is an indication of the duration and intensity of a warming event, measured in “degree heating weeks” – the number of degrees above the average summer maximum temperature, multiplied by the number of weeks. Alert Level 2 indicates at least eight degree heating weeks.

This is not the first time coral bleaching has been seen in the NT. Severe bleaching was recorded in seas off Arnhem Land during the global bleaching event in 2015-16.

Increases in sea surface temperature cause mass bleaching events. The bleached corals have lost most of the single-celled algae, called zooxanthellae, that live and photosynthesise inside the coral cells and provide the corals with most of their energy.

The Great Barrier Reef also suffered severe bleaching in 2016. This resulted in 67% mortality in its northern sections, dwarfing the effects of previous bleaching events in 1998 and 2002.




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


Bleaching patterns tell a story

The bleaching patterns of these three events were tightly correlated with degree heating weeks within geographic areas, with the 1998 and 2002 events having prominent effects in the southern areas.

In 2016 the highest degree heating weeks were recorded on the northern stretches of the Great Barrier Reef, where the most severe bleaching occurred. Southern areas experienced temperatures close to average, partly due to cooler water from Cyclone Winston.

In 2017 the Great Barrier Reef experienced another bleaching event that affected northern and central areas. This event was particularly disturbing, as it followed 2016 and, unlike 1998, 2002 and 2016, it was not an El Niño year.

It is vital that reefs have time to recover between bleaching events if they are to avoid becoming degraded. For corals that survive being bleached, full recovery takes time. Reproductive output can be reduced for extended periods, resulting in less successful recruitment.

This, often combined with the increased competition from algae and soft corals, means that replacement of corals that do not survive bleaching events can be slow. Even fast-growing corals require 10-15 years to return to their prebleaching size.




Read more:
Will the Great Barrier Reef recover from its worst-ever bleaching?


Recent analysis has shown that the intervals between bleaching events across the globe have decreased substantially since the 1980s. The median period between bleaching events is now six years. One reason for this is that temperatures in La Niña conditions (when we expect lower temperatures) are now higher than those of El Niño conditions in the 1980s.

This is further evidence that if we continue on our current path of rapidly increasing emissions, it is increasingly likely that bleaching events will occur annually later this century, as predicted by coral scientists last century.

Resilience of reefs

The 2016 bleaching event demonstrated that areas with good water quality and controlled fishing were not protected from bleaching during this temperature anomaly. However, local conditions can be vitally important for recovery in previously bleached areas and to maintain healthy populations prior to bleaching events.

Unfortunately, climate change is not only causing higher temperatures but also increased intensity of storm and cyclone damage, sea level rise and ocean acidification. So we need resilient reefs to cope with these additional challenges.

We can increase the resilience of reefs by improving water quality. We can do this by reducing sediment and nitrogen and phosphorus input and other toxins such as coal dust, herbicides and pesticides, alongside regulating fishing pressure and protecting as many areas as possible.

New management approaches urgently needed

The beautiful reefs of the Northern Territory and the Great Barrier Reef need to be protected. If we wish to enjoy Australia’s reefs in future decades, it is vital that we change our management priorities.

State and federal governments need to give these areas the priority they deserve through marine parks and ranger programs, and regulation of potentially harmful activities. Water quality needs to be funded in a serious manner. Industrial developments, such as port expansions, need to be evaluated with protection of reefs as a primary concern.

The ConversationReducing emissions dramatically is crucial to slowing all the climate change effects on reefs. Australia can lead by example by rapidly moving away from fossil fuels and opening no new coal mines.

Selina Ward, Lecturer, School of Biological Sciences, The University of Queensland

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

Advertisements

Our acid oceans will dissolve coral reef sands within decades



File 20180222 132650 xoo39k.jpg?ixlib=rb 1.1
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.

11 billion pieces of plastic bring disease threat to coral reefs



File 20180125 107967 k398f2.jpg?ixlib=rb 1.1
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.

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


File 20171129 28869 lod9mh.jpg?ixlib=rb 1.1
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


File 20171114 27595 17nf1pm.jpg?ixlib=rb 1.1
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.

https://giphy.com/embed/3o6fJd19E49uAPpkw8

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



File 20170607 29563 agdn8h
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.