What whales and dolphins can tell us about the health of our oceans



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Dolphins contribute important knowledge about ocean health.
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Stephanie Plön, Nelson Mandela University

From the poles to the equator, marine mammals such as seals, dolphins and whales, play an important role in global ecosystems as apex predators, ecosystem engineers and even organic ocean fertilisers. The ocean off the coast of South Africa is home to a high diversity of these mammals and is recognised as a global marine biodiversity hotspot.

Marine mammals are often referred to as “sentinels” of ocean health. Numerous studies have explored the effects of both noise and chemical pollution, habitat degradation, changes in climate and food webs on these marine apex predators. Yet the interplay of these factors isn’t well understood.

Our research on the unfortunate dolphins incidentally caught in shark nets off South Africa’s KwaZulu-Natal coast has helped fill in some of the gaps. By assessing the health of these dolphins we have provided valuable baseline information on conditions affecting coastal dolphin populations in South Africa. This is the first systematic health assessment in incidentally caught dolphins in the Southern Hemisphere.

But to gain a fuller picture of the health of marine mammals in these waters I am now combining this contemporary field research with historical data, like the collection at the Port Elizabeth Museum Bayworld.

The combination of data on diet, reproduction, population structure and health helps us gain a better understanding of the pressures and changes these apex predator populations face. And it helps us understand it in relation to global change, including both climate change and pressures brought about by human behaviour.

My research sheds light on multiple factors: pollutant levels, parasites, and availability of prey, all have an impact on individuals as well as populations.

Understanding the health of these animals also gives us insight into the state of the world’s oceans. This is relevant because oceans affect the entire ecosystem including food security, climate and people’s health. This degree of connectedness is highlighted by recent discoveries about how whales act as ecosystem engineers.

The accumulation of this knowledge is important because the planet’s oceans aren’t being protected. Recent popular documentaries such as “Sonic Sea” and “Plastic Ocean” have highlighted their exploitation and pollution.

What’s missing

Without baseline knowledge it’s challenging to establish the potential effects that new anthropogenic developments (those caused by human behaviour) have on local whale and dolphin populations.

For example, we know that whales are sensitive to shipping noise, so what potential impact could a new deep water port have on mothers and their calves? Could it drive them away from these nursery areas, or could it lead to an increased risk of whales and ships colliding? To answer this and monitor the change that a new port brings with it, we are investigating the soundscape of two bays in the Eastern Cape (one with a new port, one without) in parallel with baleen whale mother-calf behaviour.

Another example is understanding how changes in the Sardine run over the past 15 years have affected the diets of these mammals. The Sardine run is an annual phenomenon when large shoals of Sardine migrate northwards along the coast into KwaZulu-Natal waters to spawn. Using long-term data and samples from the Port Elizabeth Museum research collection, we have been able to establish that over the the past 20 or so years the main predator in the Sardine run – the long-beaked common dolphin – has shifted its diet to mackerel. Although such changes in diet can have potential impacts on the health of the dolphins, parallel investigations on the trophic level these animals feed at (using isotope data from teeth) and the body condition of the dolphins (using long-term data on blubber thickness), indicated no adverse effects to the dolphins.

Our analysis highlights how marine mammals may be used as indicators of environmental change and why research is important.

Finding answers to intricate questions on environmental change is not always easy. But a better understanding and knowledge of the environment these animals live in has to be incorporated into studies contributing to their conservation and management. Such studies are becoming increasingly relevant as they highlight the fast degradation of the marine environment.

For example, a recent study identified antibiotic resistant bacteria in both sea water samples and exhaled breath samples from killer whales. This suggests that the marine environment has been contaminated with human waste which in turn has significant medical implications for humans.

Gaining such information is particularly important given the rapid changes taking place in the oceans, such as those on South Africa’s southern and eastern coastline. This includes increasing coastal development, new deep water ports being built or expanded, and parts of the deep sea being explored for oil and gas.

To assess these changes and what they mean for the environment, baseline studies need to be carried out so that potential effects can be assessed. Whales and dolphins are increasingly being recognised as indicators of ocean health in this endeavour.

And a continuation of the research we did on dolphins caught in nets will help document the cyclic changes that can be seen as normal variation in a population. This could prove important for assessing future catastrophic events, such as the Deep Horizon oil spill.

What next

The oceans absorb over 25% of the world’s carbon pollution as well as heat generated by global warming. They also produce at least 50% of the planet’s oxygen, and are home to 80% of all life on earth. Yet only 5% of this vital component of our planet has been explored.

The ConversationResearch on whales and dolphins contributes important knowledge about ocean health. Historical data increasingly provides a guideline to teasing out natural variations in populations and assessing the contribution that multiple factors have on these animals. In time, this will ensure that policy makers are being given sound scientific information. It will also provide us with a good barometer of the overall health of our oceans.

Stephanie Plön, Researcher, Earth Stewardship Science Research Institute, Nelson Mandela University

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

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It’s time to speak up about noise pollution in the oceans


It’s time to speak up about noise pollution in the oceans

Christine Erbe, Curtin University

Ask most people about pollution, and they will think of rubbish, plastic, oil, smog, and chemicals. After some thought, most folks might also suggest noise pollution.

We’re all familiar with noise around us, and we know it can become a problem – especially if you live near an airport, train station, highway, construction site, or DIY-enthusiast neighbour.

But most people don’t think that noise is a problem under water. If you’ve read Jules Verne’s Twenty Thousand Leagues Under the Sea you might imagine that, maelstroms excepted, life is pretty quiet in the ocean. Far from it.

When we put a hydrophone (essentially a waterproof microphone) into the water, no matter where in the world’s oceans, it’s never quiet. We hear wind blowing overhead and rain dropping onto the ocean surface – even from hundreds of metres deep. In Australian waters we can also detect the far-off rumbles of earthquakes and the creaking of Antarctic ice thousands of kilometres away.

Wet and noisy

Water is much denser than air, so its molecules are packed tighter together. This means that sound (which relies on molecules vibrating and pushing against one another) propagates much further and faster under water than in air.

This also applies to human-produced sound. Under water we can hear boats and ships and even aeroplanes. Large vessels in deep water can be detected tens of kilometres away. We can be far offshore doing fieldwork, the only people around, with nothing in sight but water in any direction. Yet when we switch the engines off and put a hydrophone into the water, we hear ship noise. Sometimes, whole minutes later, the vessel we heard might appear on the horizon.

Seafarers have known about another source of sound for thousands of years: marine life. Many animals produce sound, from the tiniest shrimp to the biggest whales. Many fish even communicate acoustically under water – during the mating season, the boys start calling. Whales do it, too.

Light doesn’t reach far under water. Near the surface, in clear water, you might be able to peer a few metres, but in the inky depths you can’t see at all. So many marine animals have evolved to “see with sound”, using acoustics for navigation, for detecting predators and prey, and for communicating with other members of their species.

The thing is that man-made sound can interfere with these behaviours.

The effects of noise on marine animals are similar to those on us. If you’ve ever been left with ringing ears after a rock concert, you’ll know that loud noise can temporarily affect your hearing or even damage it permanently.

Noise interferes with communication, often masking it. Can you talk above the background noise in a busy pub? Long-term exposure to noise can cause stress and health issues — in humans and animals alike.

Excessive noise can change marine creatures’ habits, too. Like a person who decides to move house rather than live next door to a new airport, animals might choose to desert their habitat if things get too noisy. The question is whether they can find an equally acceptable habitat elsewhere.

Pile-driving is noisy work.
Christine Erbe, Author provided

There is a lot more research still to be done in this field. Can we predict what noises and vibrations might be released into the marine environment by new machinery or ships? How does sound propagate through different ocean environments? What are the long-term effects on marine animal populations?

One positive is that even though noise pollution travels very fast and very far through the ocean, the moment you switch off the source, the noise is gone. This is very much unlike plastic or chemical pollution, and gives us hope that noise pollution can be successfully managed.

We all need energy, some of which comes from oil and gas; most of our consumer goods are shipped across the seas on container vessels; and many of us enjoy eating seafood caught by noisy fishing boats, some of which even use dynamite to catch fish. We want to protect our borders, making naval operations a necessity. Then there’s the ever growing industry of marine tourism, much of it aboard ever-bigger cruise ships which need large ports in which to berth.

There are a lot of stakeholders in the marine environment, and all speak a different language, all make different claims, and all make noise. Knowing precisely how much noise they make, and how it affects marine life, will help to ensure our oceans and their resources last well into the future.


September 3-11 is SeaWeek 2016, the Australian Association for Environmental Education Marine Educators’ national public awareness campaign.

The Conversation

Christine Erbe, Director, Centre for Marine Science & Technology, Curtin University

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

Oil, gas and marine parks really can coexist in our oceans – here’s how


Cordelia Moore, Curtin University; Ben Radford, Australian Institute of Marine Science; Clay Bryce; Hugh Possingham, The University of Queensland; Oliver Berry, CSIRO, and Romola Stewart

When it comes to conserving the world’s oceans, bigger isn’t necessarily better. Globally, there has been an increasing trend towards placing very large marine reserves in remote regions. While these reserves help to meet some conservation targets, we don’t know if they are achieving their ultimate goal of protecting the diversity of life.

In 2002, the Convention on Biological Diversity called for at least 10% of each of the world’s land and marine habitats to be effectively conserved by 2010. Protected areas currently cover 14% of the land, but less than 3.4% of the marine environment.

Australia’s marine reserve system covers more than a third of our oceans. This system was based on the best available information and a commitment to minimising the effects of the new protected areas on existing users. However, since its release the system has been strongly criticised for doing little to protect biodiversity, and it is currently under review.

In a new study published in Scientific Reports, we looked at the current and proposed marine reserves off northwest Australia – an area that is also home to significant oil and gas resources. Our findings show how conservation objectives could be met more efficiently. Using technical advances, including the latest spatial modelling software, we were able to fill major gaps in biodiversity representation, with minimal losses to industry.

A delicate balance

Australia’s northwest supports important habitats such as mangrove forests, seagrass beds, coral reefs and sponge gardens. These environments support exceptionally diverse marine communities and provide important habitat for many vulnerable and threatened species, including dugongs, turtles and whale sharks.

This region also supports valuable industrial resources, including the majority of Australia’s conventional gas reserves.

A 2013 global analysis found that regions featuring both high numbers of species and large fossil fuel reserves have the greatest need for industry regulation, monitoring and conservation.

Proposed and existing state and Commonwealth marine reserves in northwest Australia shown in relation to petroleum leases.
Cordelia Moore

Conservation opportunitites

Not all protected areas contribute equally to conserving species and habitats. The level of protection can range from no-take zones (which usually don’t allow any human exploitation), to areas allowing different types and levels of activities such tourism, fishing and petroleum and mineral extraction.

A recent review of 87 marine reserves across the globe revealed that no-take areas, when well enforced, old, large and isolated, provided the greatest benefits for species and habitats. It is estimated that no-take areas cover less than 0.3% of the world’s oceans.

In Australia’s northwest, no-take zones cover 10.2% of the area, which is excellent by world standards in terms of size. However, an analysis of gaps in the network reveal opportunities to better meet the Convention on Biological Diversity’s recommended minimum target level of representation across all species and features of conservation interest.

We provided the most comprehensive description of the species present across the region enabling us to examine how well local species are represented within the current marine reserves. Of the 674 species examined, 98.2% had less than 10% of their habitat included within the no-take areas, while more than a third of these (227 species) had less than 2% of their habitat included.

Into the abyss

Few industries in this region operate in depths greater than 200 metres. Therefore, the habitats and biodiversity most at risk are those exposed to human activity on the continental shelf, at these shallower depths.

However, the research also found that three-quarters of the no-take marine reserves are sited over a deep abyssal plain and continental rise within the Argo-Rowley Terrace (3,000-6,000m deep). These habitats are unnecessarily over-represented (85% of the abyss is protected), as their remoteness and extreme depth make them logistically and financially unattractive for petroleum or mineral extraction anyway.

The majority of the no-take marine reserves lie over a deep abyssal plain.
Cordelia Moore

Proposed multiple-use zones in Commonwealth waters provide some much-needed extra representation of the continental shelf (0-200m depth). However, all mining activities and most commercial fishing activities are permissible pending approval. This means that the management of these multiple-use zones will require some serious consideration to ensure they are effective.

A win for conservation and industry

An imbalance in marine reserve representation can be driven by governments wanting to minimise socio-economic costs. But it doesn’t have to be one or the other.

Our research has shown that better zoning options can maximise the number of species while still keeping losses to industry very low. Our results show that the 10% biodiversity conservation targets could be met with estimated losses of only 4.9% of area valuable to the petroleum industry and 7.2% loss to the fishing industry (in terms of total catch in kg).

Examples of how the no-take reserves could be extended or redesigned to represent the region’s unique species and habitats.
Cordelia Moore

Management plans for the Commonwealth marine reserves are under review and changes that deliver win-win outcomes, like the ones we have found, should be considered.

We have shown how no-take areas in northwest Australia could either be extended or redesigned to ensure the region’s biodiversity is adequately represented. The cost-benefit analysis used is flexible and provides several alternative reserve designs. This allows for open and transparent discussions to ensure we find the best balance between conservation and industry.

The Conversation

Cordelia Moore, Research Associate, Curtin University; Ben Radford, Research scientist, Australian Institute of Marine Science; Clay Bryce, Senior Project Manager; Hugh Possingham, Director ARC Centre of Excellence for Environmental Decisions, The University of Queensland; Oliver Berry, Senior Research Scientist, CSIRO, and Romola Stewart, Adjunct Research Fellow, The University of Queensland

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

Ocean acidification: the forgotten piece of the carbon puzzle


Ellycia Harrould-Kolieb, University of Melbourne

Ocean acidification – the rise in ocean acidity due to the increased absorption of carbon dioxide (CO₂) – is often thought of as consequence of climate change. However, it is actually a separate, albeit very closely-related problem.

Ocean acidification is often referred to as “the other CO₂ problem” because, like climate change, it is primarily a result of the increased emissions of this gas. Despite their common driver, though, the processes and impacts of ocean acidification and climate change are distinct. It should not be assumed that policies intended to deal with the climate will simultaneously benefit the oceans.

The current emphasis of global climate policies on a warming target is a case in point.

A narrow focus on temperature stabilisation, for example, opens the door for policy interventions that prioritise the reduction of greenhouse gases other than carbon dioxide. This is because non-CO₂ greenhouse gases — like methane and nitrous oxide, which can arise from agricultural and industrial processes — typically have a higher global warming potential and might even be less costly than CO₂ to reduce.

In addition, several geoengineering schemes have been proposed to reduce the impacts of a warming climate. Yet such schemes often do nothing to address emissions, and may even exacerbate carbon absorption in the oceans.

Reducing CO₂ — the only long-term solution

The most important step in addressing both climate change and ocean acidification, and ultimately the only way to avoid the most serious impacts of both, is the reduction of carbon dioxide emissions.

Long-term policy targets designed to guide emission reductions to a level that would avoid unacceptable consequences should consider both ocean acidification and climate change. Interestingly, it is in doing this that we see the solutions to these two global issues converge.

Countries have largely agreed that there is a desire to limit global temperature increases to no more than 2℃ above pre-industrial temperatures. This is a desire that requires us to drastically reduce our carbon dioxide emissions. Indeed, the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report found that for a 66% chance of remaining below 2℃ we can emit less than 1,010 billion tonnes of carbon dioxide, or about one-third of our carbon budget.

In fact, such a target is in line with the most ambitious atmospheric carbon concentration scenario (called RCP2.6) used by the IPCC to model climate impacts.

A recent study in the journal Science conducted by J.P. Gattuso and colleagues modelled this same IPCC scenario and found that exceeding it would have wide-ranging consequences for marine life, marine ecosystems, and the goods and services they supply to humanity. However, as with climate change, many of the worst impacts of rising acidity could be avoided by following or remaining below this trajectory.

The most critical feature of this scenario with regards to ocean acidification is a reduction of carbon dioxide to net zero emissions by no later than 2070.

But, as Gattuso’s team importantly note, even achieving zero emissions within this timeframe would not prevent substantial ocean acidification. Coral reefs and shellfish populations will remain especially vulnerable.

This is true for climate change impacts as well. And it is the reason that many, particularly those living in developing and low-lying island states, wish to see the long-term goal for global temperature rise reduced to 1.5℃.

In effect, this means that reducing net carbon dioxide emissions to zero must happen even sooner than 2070. Ocean acidification, therefore, provides the impetus for additional urgency in agreeing to stringent timeframes for reducing CO₂ emissions.

Net zero emissions on the table at Paris?

We are fast approaching the next round of climate talks on the UN Framework Convention on Climate Change in Paris. If we are to see any meaningful global climate pact emerge, ocean acidification must sit firmly alongside climate change on the negotiation table.

Given the double threat that ocean acidification and climate change poses to some of the most vital goods and services underpinning human welfare, including food security, economic development, and the viability of ecosystems, it is crucial that world leaders set sharp emission reductions square in their sights.

Promisingly, up for negotiation in Paris is language that could see parties agreeing to net zero emissions. This would indeed be a very welcome, and ultimately necessary, development.

The Conversation

Ellycia Harrould-Kolieb, PhD Candidate, School of Geography & Australian-German Climate and Energy College, University of Melbourne

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

Microbes: the tiny sentinels that can help us diagnose sick oceans


Katherine Dafforn, UNSW Australia; Emma Johnston, UNSW Australia; Inke Falkner, and Melanie Sun, UNSW Australia

Microbes – bacteria and other single-celled organisms – may be tiny, but they come in huge numbers and we rely on them for clean water, the air we breathe and the food we eat.

They are nature’s powerhouses but they have often been ignored. We previously lacked the capacity to appreciate truly their diversity, from micro-scales right up to entire oceans.

Recent advancements in genetic sequencing have revealed this diversity, and our research, published in Frontiers in Aquatic Microbiology this week, shows how we can use this information to understand human impacts on an unseen world – making microbes the new sentinels of the sea.

A sea of microbes

The great majority of bacteria and other microbes are extremely beneficial, performing vital roles such as recycling nutrients.

The number of bacteria on Earth is estimated at 5×10³⁰ (or 5 nonillion, if you prefer), and many of them live in the ocean. There are 5 million bacteria in every teaspoon of seawater, and more bacteria in the ocean than stars in the known universe.

Guess how many microbes?
Victor Morozov/Wikimedia Commons, FAL

There are yet more bacteria in the world’s soils and sediments, with estimates of between 100 million and 1 billion bacteria per teaspoon. These sediments are vital for recycling nitrogen, particularly in coastal sediments closest to human populations. Without bacteria and other microbes, sediments would turn into unsightly, pungent piles of waste.

Microbial services are not limited to recycling. Many microbes, including cyanobacteria, function like tiny plants by using sunlight to produce oxygen and sugars. Due to their extraordinary number in the world’s oceans, the amount of oxygen these organisms produce is equal to that of all plants on land.

Marine sentinels

Until recently, finding out just how many different types of microbes there are was relatively difficult. How do you identify and study millions of different organisms that are not visible to the naked eye?

Bacteria, for example, had to be grown in the laboratory in large colonies to be seen. But only 1-3% of bacteria can be cultured successfully.

Advances in genetics together with the development of molecular tools have allowed researchers to investigate marine bacteria in their natural environment. Microbial communities can now be grouped by the role they play in ecosystems and how these groups respond to environmental gradients.

We can use these new tools to measure ecosystem health, which is crucial to managing human impacts on our coastlines, particularly in estuaries. Early studies have found shifts in bacterial community composition to be good indicators of contaminants

Different areas of harbours, such as Sydney Harbour, have distinct bacterial communities. These patterns may be driven by circulation. The outer harbour, which is flushed with seawater on every tidal cycle, is dominated by photosynthetic cyanobacteria. The upper harbour, with less flushing and more runoff, is dominated by soil-related bacteria and those adapted to nutrient-rich environments.

In our waterways, pollutants such as metals bind to fine particles and settle as sediment. This exposes sediment-dwelling organisms to a multitude of toxic products. What effect do these toxic substances have on sediment microbes?

Recent evidence from a large survey of eight estuaries suggests that microbes are far more sensitive to contaminants than larger animals and plants. This survey also revealed that toxic substances were linked to changes in community structure and a reduction in community diversity. This is especially alarming given that a diversity of microbes is essential to nutrient recycling.

Diagnosing wounded seas

It would be great if we could use particular microbes to diagnose human impacts. For instance, certain microbes can indicate water quality.

A technique called metagenomics is revealing the true depth of microbial diversity by pooling DNA sequences from all the species in a sample. It then works backwards to construct a genetic overview of the entire community.

However, while metagenomics can give us important information about the identity of microbes in a community, it can’t tell us what they are doing or how their functions change in response to environmental stressors and human activities.

Metatranscriptomics takes the sequencing approach one step further and characterises gene expression in a microbial community, which can be linked to crucial ecosystem services such as nutrient cycling.

Similar to their use for diagnosis of ailments in humans, molecular tools are being used to diagnose human impacts on earth by observing changes in microbes across polluted and unpolluted environments. They can even detect very small amounts of toxic substances. Because of their diversity, they can potentially be used to detect a wide range of human impacts.

This allows us to identify environmental impacts early, potentially limiting greater loss in larger organisms.

With the new tools to “see” microbes and their importance, we are now perfectly poised to advance our understanding of how microbes are responding to environmental change. They are sentinels of our increasingly human-affected waterways.

The Conversation

Katherine Dafforn, Senior Research Associate in Marine Ecology, UNSW Australia; Emma Johnston, Professor of Marine Ecology and Ecotoxicology, Director Sydney Harbour Research Program, UNSW Australia; Inke Falkner, Community Outreach Coordinator for Sydney Harbour Research Program, Sydney Institute of Marine Science, and Melanie Sun, PhD Candidate – Environmental Research, UNSW Australia

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

The oceans are becoming too hot for coral, and sooner than we expected


Ove Hoegh-Guldberg, The University of Queensland

This week, scientists registered their concern that super-warm conditions are building to a point where corals are severely threatened across the tropical Indian, Pacific and Atlantic oceans. They did so after seeing corals lose colour across the three major ocean basins – a sign of a truly momentous global change.

This is only the third global bleaching event in recorded history.

Underwater heat waves

The situation has been worrying scientists like myself for many months. Over the past 12 months, the temperatures of the upper layers of the ocean have been running unseasonably warm. Underwater heatwaves have torn through these tropical regions over summer, and corals across large areas of reef have lost their colour as the algal partners (or symbionts) that provide much of the food for corals have left their tissues. Bereft, corals are beginning to starve, get diseased and die.

The “heatwaves” that are causing the problem are characterised by extremes that are 1-3 degrees C warmer than the long-term average for summer. It doesn’t seem like much but past experience has shown us that exposure to small increases in temperatures for a couple of months is enough to kill corals in great numbers.

In the first global mass bleaching event in 1998, regions such as Okinawa, Palau and north-west Australia lost up to 90% of their corals as temperatures soared.

By the end of 1998 up to 16% of the corals on the world’s tropical reefs had died.

The key concern here is that corals are not an inconsequential part of the biology of the ocean. While geographically insignificant (less than 0.1% of the ocean), coral reefs punch well above their weight in terms of their importance to the ecology of the ocean and to humans.

Over a million species are thought to live in and around coral reefs, while an estimated 500 million people derive food, livelihoods and other benefits from coral reefs throughout the tropics.

Why the heatwaves?

Warm conditions were seen across the ocean in 2014, with an on-again off-again El Niño condition in the Pacific and similar conditions across Indian and Atlantic-Caribbean ocean regions.

As a result, surface waters came close to triggering mass coral bleaching in many places, and did trigger bleaching in many others. The equatorial Pacific, for example, experienced bleaching temperatures from April without relent, generating reports of extensive bleaching and mortality.

One question that is on everyone’s lips is, why the elevated temperatures?

At one level, the drivers for the current global bleaching event are clear. Climate change has been driving up sea temperatures. When natural variability adds to this trend, such as during El Niño, temperatures now exceed the threshold for mass coral bleaching and death.

This explanation has been sufficient for the last couple of decades. I have used it many times.

However, that may be changing as we learn that the intensity of El Niño may well also be vulnerable to changes in average global temperatures. A growing number of studies (see also here) are showing that strong El Niño are becoming more frequent, and climate change is likely a significant driver of this. This and phenomena such as the mysterious warm patch) in the eastern Pacific (nicknamed the “Blob”) suggest the simple model may need to be modified.

The Coral Reef Watch program run by the US National Oceanic and Atmospheric Administration (NOAA) has developed a number of models to estimate the likelihood of mass coral bleaching and mortality, as you can see in the figure below.

Projections of stress – NOAA
NOAA Coral Reef Watch

These models show considerable ability to predict where, when and how severe mass coral bleaching and mortality are likely to be. Looking at these projections reveals the spread of underwater heatwaves and the risk of mass coral bleaching and mortality.

Have we under-estimated the risk of a changing ocean?

Understanding the sensitivity of reef-building corals to elevated temperatures allows us to ask the question: if sea temperatures are increasing, when does it get too hot for corals every year in the future? I did this some years ago and came up with the answer that most oceans get too hot for their corals on a yearly basis by 2040-2050.

At the time, this was quite shocking – the idea that corals would be eliminated by mid-century. All those species, all those resources for people.

The problem is, I was only accounting for a doubling of greenhouse gases, as opposed to the tripling or more under the current business-as-usual approach, and the models used for estimating future sea temperatures didn’t account for more frequent extreme El Niño. And if so, then my original projections of when the oceans become too hot for coral reefs are too optimistic!

The current looming global stress event certainly emphasises this story. As I look at NOAA’s stress maps, I am reminded of the huge and unprecedented experiment that we are running. I am also conscious that the consequences of warming have been underestimated for almost everything we look at. I am compelled to question whether the negotiators headed for meeting in Paris in a month or so really appreciate the urgency.

Do they know that we need to pull the plug immediately on this crazy experiment? Given that the current pledges going into Paris are so woefully inadequate, it would seem not.

Perhaps we now have to hope that the dying gasps of the world’s most diverse marine ecosystem can jolt our negotiators into action. If not, then it would seem that nothing will.

The Conversation

Ove Hoegh-Guldberg, Director, Global Change Institute, The University of Queensland

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