Coastal seas around New Zealand are heading into a marine heatwave, again



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This summer, coastal seas to the north and east of New Zealand are even warmer than during last year’s marine heat wave.
from http://www.shutterstock.com, CC BY-ND

Craig Stevens, National Institute of Water and Atmospheric Research and Ben Noll, National Institute of Water and Atmospheric Research

As New Zealanders are enjoying their days at the beach, unusually warm ocean temperatures look to be a harbinger of another marine heatwave.

Despite the exceptional conditions during last year’s heatwave in the Tasman Sea, this summer’s sea surface temperatures to the north and east of New Zealand are even warmer.

The latest NIWA climate assessment shows that sea surface temperatures in coastal waters around New Zealand are well above average. Marine heatwave conditions are already occurring in parts of the Tasman Sea and the ocean around New Zealand and looking to become the new normal.




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


Changing sea surface temperature anomalies (conditions compared to average) in the oceans around New Zealand during the first two weeks of January – comparing 2009 to 2019. Source: NIWA

What’s in a name

Currently, marine heatwaves are defined as periods that last for five or more days with temperatures warmer than the 90th percentile based on a 30-year historical baseline. Given we are likely to experience many more such events as the oceans continue to warm, it is time to understand and categorise the intensity of marine heat.

The names Hurricane Katrina, tropical cyclone Giselle (which sank the ferry Wahine 50 years ago), tropical cyclone Winston give a malevolent personality to geophysical phenomena. Importantly they get graded into categories, so we can rapidly assess their potential impact.




Read more:
Winston strikes Fiji: your guide to cyclone science


An Australian team has developed a classification scheme for marine heatwaves. The team used an approach similar to that used for hurricanes and cyclones – changing conditions can be slotted into to a sequence of categories. At the moment it looks like we are in marine heat wave category one conditions, but potentially entering category two if it continues to warm.

Turning the heat up on marine life

A marine heatwave is potentially devastating for marine ecosystems. It is also an indication that the hidden buffer in the climate system – the fact that the oceans have absorbed 93% of the excess heat – is starting to change. Individual warm seasons have always occurred, but in future there will be more of them and they will keep getting warmer.

The Great Barrier Reef has already been hit hard by a succession of marine heatwave events, bleaching the iconic corals and changing the structure of the ecosystem it supports.




Read more:
The 2016 Great Barrier Reef heatwave caused widespread changes to fish populations


Further south, off Tasmania’s east coast, a number of species that normally occur in tropical waters have extended their range further south. A number of fish species, lobster and octopus species have also taken up residence along the Tasmanian coast, displacing some of the species that call this coast home. Mobile species can escape the warmer temperatures, but sedentary plants and animals are hardest hit.

In New Zealand, aquaculture industries will find it more difficult to grow fish or mussels as coastal waters continue to warm. If the same trends seen off Tasmania occur here, areas with substantial kelp canopies will struggle and start to be replaced by species normally seen further north. But the impacts will likely be very variable because the warming will be heavily influenced by wind and ocean currents and different locations will feel changes to a greater or lesser extent.

NIWA’s research vessel Kaharoa has deployed Argo floats in the Southern Ocean and in waters around New Zealand.
NIWA, CC BY-ND

Predicting the seasons

As important as it is to identify a marine heatwave at the time, reliable predictions of developing conditions would help fishers, aquaculture companies and local authorities – and in fact anyone living and working around the ocean.

Seasonal forecasting a few months ahead is difficult. It falls between weather and climate predictions. In a collaboration between the National Institute of Water and Atmospheric Research and the Australian Bureau of Meteorology, we are examining how well long-term forecasts of ocean conditions around New Zealand stack up. Early forecasts suggested this summer would not be as warm as last year. But it now looks like this summer will again be very warm in the ocean.




Read more:
This summer’s sea temperatures were the hottest on record for Australia: here’s why


One of the important points to keep in mind is that when we are at the beach, we are sampling only the surface temperature. The same is true of satellites – they monitor less than the top millimetre of the ocean.

Sea surface temperatures are several degrees above normal at the moment. But in deeper waters, because of the high heat content of water, even a tenth of a degree is significant. Temperature in the deeper ocean is monitored by a network of moored buoys on and off the continental shelf along the Australian coast. New Zealand has almost nothing that would be comparable.

Measuring temperature in real time

What we can look to, in the absence of moored buoys, is a fleet of ocean robots that monitor temperature in real time. Argo floats drift with ocean currents, sink to two kilometres every ten days and then collect data as they return to the surface.

These data allowed us to identify that the 2017/18 marine heatwave around New Zealand remained shallow. Most of the warmer water was in the upper 30 metres. Looking at the present summer conditions, one Argo robot off New Zealand’s west coast shows it is almost four degrees above normal in the upper 40 metres of the ocean. On the east coast, near the Chatham Islands, another float shows warmed layers to 20 metres deep. To the south, the warming goes deeper, down to almost 80 metres.

Our work using the Australian Bureau of Meteorology forecast model highlights how variable the ocean around New Zealand is. Different issues emerge in different regions, even if they are geographically close.

The research on categories of marine heatwaves shows we will have to keep shifting what we regard as a heat wave as the ocean continues to warm. None of this should come as a surprise. We have known for some time that the world’s oceans are storing most of the additional heat and the impacts of a warming ocean will be serious.The Conversation

Craig Stevens, Associate Professor in Ocean Physics, National Institute of Water and Atmospheric Research and Ben Noll, Meteorologist/forecaster, National Institute of Water and Atmospheric Research

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

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Antarctic seas host a surprising mix of lifeforms – and now we can map them



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In contrast to common perceptions, Antarctic seafloor communities are highly diverse. This image shows a deep East Antarctic reef with plenty of corals, sponges and brittlestars. Can you spot the octopus?
Australian Antarctic Division

Jan Jansen, University of Tasmania; Craig Johnson, University of Tasmania, and Nicole Hill, University of Tasmania

What sort of life do you associate with Antarctica? Penguins? Seals? Whales?

Actually, life in Antarctic waters is much broader than this, and surprisingly diverse. Hidden under the cover of sea-ice for most of the year, and living in cold water near the seafloor, are thousands of unique and colourful species.

A diverse seafloor community living under the ice near Casey station in East Antarctica.

Our research has generated new techniques to map where these species live, and predict how this might change in the future.

Biodiversity is nature’s most valuable resource, and mapping how it is distributed is a crucial step in conserving life and ecosystems in Antarctica.




Read more:
Explainer: what is biodiversity and why does it matter?


Surprises on the seafloor

The ocean surrounding the Antarctic continent is an unusual place. Here, water temperatures reach below freezing-point, and the ocean is covered in ice for most of the year.

While commonly known for its massive icebergs and iconic penguins, Antarctica’s best-kept secret lies on the seafloor far below the ocean surface. In this remote and isolated environment, a unique and diverse community of animals has evolved, half of which aren’t found anywhere else on the planet.

These solitary sea squirts stand up to half a metre tall at 220m depth in the dark, cold waters of East-Antarctica. Images such as this one were taken with cameras towed behind the Australian Icebreaker Aurora Australis.
Australian Antarctic Division

Colourful corals and sponges cover the seafloor, where rocks provide hard substrate for attachment. These creatures filter the water for microscopic algae that sink from the ocean surface during the highly productive summer season between December and March.

In turn, these habitat-forming animals provide the structure for all sorts of mobile animals, such as featherstars, seastars, crustaceans, sea spiders and giant isopods (marine equivalents of “slaters” or “woodlice”).

The Antarctic seafloor is also home to a unique group of fish that have evolved proteins to stop their blood from freezing.

Most Antarctic fish have evolved ‘anti-freeze blood’ allowing them to survive in water temperature below zero degrees C.
Australian Antarctic Division

Mapping biodiversity is hard

Biodiversity is a term that describes the variety of all life forms on Earth. The unprecedented rate of biodiversity loss is one of the biggest challenges of our time. And despite its remoteness, Antarctica’s biodiversity is not protected from human impact through climate change, pollution and fisheries.




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Although scientists have broadly known about Antarctica’s unique marine biodiversity for some time, we still lack knowledge of where each species lives and where important hotspots of biodiversity are located. This is an issue because it hinders us from understanding how the ecosystem functions – and makes it hard to assess potential threats.

Why don’t we know more about the distribution of Antarctic marine species? Primarily, because sampling at the seafloor a few thousand metres below the surface is difficult and expensive, and the Antarctic continental shelf is vast and remote. It usually takes the Australian Icebreaker Aurora Australis ten days to reach the icy continent.

A selection of the diverse and colourful species found on the Antarctic seafloor.
Huw Griffiths/British Antarctic Survey

To make the most of the sparse and patchy biological data that we do have, in our research we take advantage of the fact that species usually have a set of preferred environmental conditions. We use the species’ relationship with their environment to build statistical models that predict where species are most likely to occur.

This allows us to map their distribution in places where we have no biological samples and only environmental data. Critically, until now important environmental factors that influence the distribution of seafloor species have been missing.




Read more:
Antarctica has lost 3 trillion tonnes of ice in 25 years. Time is running out for the frozen continent


Using predictions to make a map

In a recent study, we were able to predictively map how much food from the ocean-surface was available for consumption by corals, sponges and other suspension feeders at the seafloor.

The science behind linking food-particles from the ocean surface to the biodiversity of Antarctic seafloor fauna. Satellites (1) can detect the amount of algae at the ocean-surface. Algae-production is particularly high in ice-free areas (2) compared to under the sea-ice (3). Algae sink from the surface (4) and reach the seafloor. Where ocean-currents are high (5), many corals feed from the suspended particles. In areas with slow currents (6), particles settle onto the seafloor and feed deposit-feeding animals such as seacucumbers.
Jansen et al. (2018), Nature Ecology & Evolution 2, 71-80.

Although biological samples are still scarce, this allowed us to map the distribution of seafloor biodiversity in a region in East Antarctica with high accuracy.

Further, estimates of how and where the supply of food increased after the tip of a massive glacier broke off and changed ocean conditions in the region allowed us to predict where abundances of habitat forming fauna such as corals and sponges will increase in the future.

Colourful and diverse communities are also found living in shallow waters.
Australian Antarctic Division

Antarctica is one of the few regions where the total biomass of seafloor animals is likely to increase in the future. Retreating ice-shelves increase the amount of suitable habitat available and allow more food to reach the seafloor.

For the first time in history, we now have the information, computational power and research capacity to map the distribution of life on the entire continental shelf around Antarctica, identify previously unknown hotspots of biodiversity, and assess how the unique biodiversity of the Antarctic will change into the future.


The Conversation


Read more:
How a trip to Antarctica became a real-life experiment in decision-making


Jan Jansen, Quantitative Marine Ecologist, University of Tasmania; Craig Johnson, Professor, University of Tasmania, and Nicole Hill, Research fellow, University of Tasmania

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

King tides and rising seas are predictable, and we’re not doing enough about it


Mark Gibbs, Queensland University of Technology

Recent king tides have again caused significant damage to coastal assets in Australia and New Zealand. This time the combination of large tides and coastal storms damaged properties on Torres Strait islands and in Nelson and other coastal areas of New Zealand. It is increasingly recognised worldwide that, despite many coastal adaptation plans being developed, the implementation of these plans is lagging.

King tides occur several times a year when the Moon is slightly closer to the Earth (so they’re sometimes called perigean spring tides). This means king tides are predictable, as are rising sea levels. The combination, along with sporadic storm events, will lead to increasing flooding of our coastal cities.




Read more:
Hurt by sea: how storm surges and sea-level rise make coastal life risky


Higher sea levels, whether creeping (associated with anthropogenic climate change) or transient (episodic storm events), have impacts on both private and public property and assets. What is now mostly nuisance flooding will become more problematic, and the ever-increasing global damage bill from disaster will continue to mount.

According to the global re-insurer Munich Re, losses from natural disasters in 2017 totalled US$330 billion, the second highest on record. Almost half of these losses (41%) were uninsured.

Who’s responsible for adaptation plans?

In keeping with the theory that risk is best managed by those closest to the risk, local government in Australia is the level of government best suited to managing such local risks. In response to the increasing threat from rising sea levels, many local government councils around Australia have developed coastal climate adaptation plans.

Federal and state governments clearly also have roles to play in managing coastal inundation. The federal government is often the insurer of last resort, especially for public infrastructure.


Read more: Coastal communities, including 24 federal seats at risk, demand action on climate threats

Read more: Coastal law shift from property rights to climate adaptation is a landmark reform


In Queensland, the state government has implemented the successful QCoast2100 program. This is helping local governments to develop adaptation plans all along the state’s coastline.

It is increasingly recognised that many of the plans developed in the past contain overcomplicated analyses of oversimplified adaptation options. Instead, we need less complicated ways of determining the most suitable adaptation option and assessments that consider more tailored and considered options, which will then be more readily implementable.

What are the options?

Coastal climate adaptation options tend to fall into one of three categories:

  • retreat – relocate assets and structures inland or to higher ground
  • protect – mostly by building engineered seawalls, although green infrastructure can also be implemented
  • accommodate – live with the hazard but reduce the vulnerability of structures and assets.

Retreat makes intuitive sense: relocating assets out of harm’s way reduces their vulnerability. However, this approach has proved politically problematic, especially for private buildings.

Most communities are familiar with seawalls and other forms of coastal protection. Others fundamentally disagree with the principle of hard coastal protection measures.




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The third adaptation option, accommodating sea-level rise, is becoming the most popular approach in many nations, including the low-lying Netherlands. However, this approach is probably the least understood in Australia and rarely appears as the preferred option in Australian coastal adaptation plans.

This option includes making existing structures less vulnerable. This might involve relocating electrical and air-conditioning services and switchboards higher in existing buildings. Over time, vulnerable sites can be repurposed with less vulnerable land uses and structures.

This is different from pre-emptively evicting and relocating entire communities from vulnerable locations – the retreat option. The retreat option is most easily implemented immediately after major flooding that has led to significant damage.

Plans must consider the politics

Early coastal adaptation plans commonly advocated mass pre-emptive coastal retreat, but local government often ended up shelving or rejecting such recommendations. Instead, councils simply commissioned the construction of small local seawalls in areas at risk of erosion.

More developed and recent coastal adaptation plans consider finer spatial scales. What they still often don’t do is consider more sophisticated and politically informed adaptation options and approaches.

Hence adaptation planning is still often best characterised as the “plan and forget” approach. These plans typically lack monitoring and evaluation and a realistic implementation strategy.

The ConversationIncreased flooding of our coastline is inevitable and happening. Therefore, adaptation planning needs to consider more nuanced options that are likely to be more politically palatable and implementable.

Mark Gibbs, Director, Knowledge to Innovation; Chair, Green Cross Australia, Queensland University of Technology

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

How to tackle the rising tide of poaching in Australia’s tropical seas


Steven Purcell, Southern Cross University and Hampus Eriksson, University of Wollongong

High-value marine species in waters off northern Australia are at increasing risk of poaching by foreign fishing crews, according to figures from the Australian Fisheries Management Authority. The number of foreign fishing boats caught in Australian waters increased from six in 2014–15 to 20 in 2015–16.

These fishers have evidently come to poach species that fetch high prices and have been overfished elsewhere in the Asia-Pacific region. They seek “lootable resources” – species that are attractive to the black market because they are expensive, easy to catch and weakly regulated.

Among the species being targeted are sea cucumbers, giant clams, turtles and sharks (specifically their fins).

Many of these species are listed as vulnerable or endangered by the International Union for Conservation of Nature (IUCN). Some are even protected from trade by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

A long history of poaching

The apprehended vessels have been primarily from Vietnam and Indonesia. Last month, a Vietnamese fishing vessel stopped inside the Conservation Park Zone of the Coral Sea Commonwealth Marine Reserve was found to be carrying 3 tonnes of partially processed sea cucumbers. Dried sea cucumber, called bêche-de-mer, can fetch more than A$300 per kg when sold in China.

The Timor and Arafura Seas have long histories of illegal, unreported and unregulated fishing due to regional fishery expansion and displacement. Some scientists believe the tensions in the South China Sea are pushing Southeast Asian fishermen into Australian waters. It is also possible that Indonesia’s stricter fisheries policy is shifting fishing patterns in the region.

But apart from economic loss as resources are poached from Australian waters, what are the impacts? A new review shows that species such as sea cucumber can play crucial roles in boosting the health of coral reef systems. This is important at a time when reefs are facing intense stress from climate change and coastal development.

Nine species of sea cucumbers from Australian waters were recently declared threatened with extinction globally by the IUCN. Removal of some marine fauna might degrade the resilience of coral reef ecosystems to broad-scale stressors.

What can be done?

In June, Immigration and Border Protection Minister Peter Dutton said: “Preventing illegal fishers from plundering Australia’s well-managed fisheries is every bit as important as stopping the people smugglers and illegal arrivals.”

Although the Australian Border Force has the capacity to apprehend illegal fishing boats, much of the poaching happens on distant coral reefs. One problem is that illegal fishing boats can plunder lootable resources and get out of Australian waters before Border Force can reach them. So while regulation might be well enforced on reefs within the Great Barrier Reef, for instance, offshore reefs are comparably weakly regulated.

But stronger monitoring and enforcement might not be the only solution anyway. My team’s research, which involved interviewing sea cucumber fishers from Fiji, Kiribati, Tonga and New Caledonia, suggests that they see themselves as having few other livelihood options besides fishing. This means that even if their fishery collapsed or was closed down by authorities, they would simply move elsewhere or fish a different species.

Many fishers from Southeast Asia have doubtless been lured to poaching in Australian waters by similar issues. Curbing the rise in poaching therefore requires not only continued enforcement but also, crucially, foreign aid investment that can help these fishers to diversify their livelihoods.

Australia recently reshaped its foreign aid policy to focus predominantly on delivering “economic growth and poverty reduction”. Organisations such as the Australian Centre for International Agricultural Research (ACIAR) are investing in overseas research and development projects to provide more income-generating opportunities in fisheries and aquaculture. Support to Southeast Asian countries makes up 49% of the budget for fisheries and aquaculture projects.

Australia’s approach to reducing poaching of threatened resources should therefore be multifaceted. Helping foreign fishers deal with their own problems of overfishing by giving them more options to earn a living will ultimately help to tackle the root cause of marine poaching.

The Conversation

Steven Purcell, Senior Rearch Fellow in Fisheries Ecology, Southern Cross University and Hampus Eriksson, Senior research fellow, University of Wollongong

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

Rising seas threaten to drown important mangrove forests, unless we intervene


Neil Saintilan; Catherine Lovelock, The University of Queensland, and Kerrylee Rogers, University of Wollongong

Mangroves are some of the world’s most important trees. They provide food and resources for people and animals, protect coasts, and store huge amounts of carbon. The world’s largest mangrove forest – the Sundarbans in the Bay of Bengal – supports millions of livelihoods. In terms of the services they provide, they are worth nearly US$200,000 per hectare per year.

But these coastal forests are threatened by rising seas and human development. In a study published today in Nature, we show that some of these forests will drown unless we help them.

Catherine Lovelock explains her new mangrove study

Getting to the root of it all

Mangroves grow along tropical coasts. Unique amongst the world’s plants, they can survive in salt water and can filter seawater. The rain of leaf-fall from tropical mangrove forests provides food for crabs and other herbivores, the foundation of a food web that extends to fish (and therefore people) right across the tropics.

One of the distinguishing characteristics of mangroves are their roots, used to anchor the plant on unstable ground and buttress against wind, waves and currents. The form of root architecture varies greatly between families of mangrove, including the dense prop-roots (Rhizophora), cathedral-like buttresses (Bruguiera), and numerous pneumatophores – literally narrow breathing–tubes – of the common grey mangrove of southeast Australia (Avicennia).

Prop roots on a mangrove
Ruth Reef

A high proportion of the living mass of mangroves exists below-ground. This means mangroves are the most efficient ecosystem globally in the capture and sequestration of atmospheric carbon dioxide. The uniquely oxygen-poor, salty characteristics of mangrove soil provides the perfect setting for long-term preservation of carbon below ground. The typical mangrove forest sequesters several times more carbon dioxide than a tropical rainforest of comparable size.

Mangrove roots trap sediment as currents carrying suspended particles are intercepted and slowed. Between the carbon sequestered below-ground, and the sediment trapped within the tangle of roots, mangroves are effectively able to raise the height of the land over time.

Keeping up with rising seas

Analysis of these sediments shows mangroves can deal with low to moderate sea-level rise by building up land. But how will mangroves respond to future rising seas when people are in the way?

We and other colleagues measured how fast mangrove forests in the Indo-Pacific region increase the height of the land. We used a tool called Surface Elevation Table-Marker Horizon, as you see in the video below.

Mangroves also build up land height by accumulating roots below ground. Previous studies have focused on this. Our study, using up to 16 years of data across a range of coastal settings, shows that sediment build up is also important.

We also compared the rate of land height increase in mangroves to local tidal gauges, to assess whether mangroves were keeping pace with the local rate of sea-level rise.

In most cases (90 out of 153 monitoring stations) mangroves were lagging behind. This is not an immediate problem if mangroves are already high enough to delay the effect of expected sea-level rise. However, mangroves at the low end of their elevation are highly vulnerable.

We used this insight to model how long mangroves might survive rising seas across the Indo-Pacific. We used a range of sea-level rise projections from the Intergovernmental Panel on Climate Change, including a low-range scenario (48 cm by 2010), high-range (63 cm by 2100) and extreme (1.4 m by 2100).

Mangrove forests with a high tidal range and/or high sediment supply such as Northern Australia, eastern Borneo, east Africa and the Bay of Bengal proved to be relatively resilient. Most of these forests will likely survive well into the second half of the century under low and moderate rates of sea-level rise.

The prospect of mangrove survival to 2070 under the 63 cm and 1.4 m scenarios was poor for the Gulf of Thailand, the southeast coast of Sumatra, the north coasts of Java and Papua New Guinea and the Solomon Islands.

Dams holding mangroves back

Our results imply that factors that prevent sediment building up may prevent mangroves responding to sea-level rise. This might include dams holding sediment within water catchments.

This impact is already being felt. An 80% reduction in sediment delivery to the Chao Phraya River delta has, for example, contributed to kilometres of mangrove shoreline retreat.

Similar developments are planned for the Mekong River. These threats compound those already being felt, including the widespread conversion of mangrove to aquaculture.

Appreciation of the financial contribution of mangroves has been slowing the trend of decline. However, long-term survival will require planning that includes both the continued provision of sediment supply, and in many cases the provision of retreat pathways, to allow mangroves to respond to sea level in ways they always have.

The Conversation

Neil Saintilan, Head, Department of Environmental Science; Catherine Lovelock, Professor of Biology, The University of Queensland, and Kerrylee Rogers, ARC Future Fellow, University of Wollongong

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

Warming seas will set marine life on the move, with some good news among the bad


David Schoeman, University of the Sunshine Coast and Jorge García Molinos, Scottish Association for Marine Science

How will climate change affect life in the oceans? In research to be published in Nature Climate Change* we, among several other authors, show that the answer is likely good and bad.

Our study models how species might move in response to different future climate scenarios. The good news is that overall, thanks to species migrations, most places will end up with greater numbers of species. According to our models, climate change is unlikely to directly cause extinction through warming waters for most species, except for those that can’t move or have very narrow thermal tolerances.

The bad news is that there are a few very special places that will lose species – particularly the spectacular ocean ecosystems of what’s known as the Coral Triangle, the epicentre of global marine biodiversity.

First, the good news

As ocean temperatures increase, marine life will likely move towards the poles – animals and plants will expand their ranges. We can already see this happening. In Australia, tropical species of fish are turning up in northern New South Wales.

We wanted to know how this would affect the overall numbers of animals and plants in the oceans – marine biodiversity – and the distinctive communities they comprise. While many things affect where marine life lives – habitat, competition, salinity – most species are affected fundamentally by temperature.

Using temperature to find out where species might move allowed us to look at an unprecedented number of species – nearly 13,000. These included animals and plants as diverse as fish, corals, jellies, snails, clams, crabs, shrimps and seaweeds.

We looked at two different climate scenarios, business as usual (known as RCP8.5) leading to warming of around 2.5ºC by 2100, and a scenario with medium mitigation (RCP4.5) leading to warming of around 1ºC over the same period.

Our model shows how fast different temperature zones will move and to where, using a measure known as “climate velocity”. This is a good way of predicting where species could move because it traces pathways connected by climate.

We should emphasise that our study shows where species could move. Our projections don’t necessarily mean that they will move, nor that they will successfully establish themselves at the locations where they arrive. That depends on a variety of factors, including their specific habitat requirements and how species interact with each other. But studies of invasive species suggest that species that can move will tend to do so.

Overall we found that biodiversity of the oceans will likely increase at local scales. As a result, we anticipate that marine ecosystems will become more similar. For instance, today on the east Australian coast, the types of species found along the central Queensland coast are quite different from those found in central New South Wales. As sea temperatures warm, we expect those boundaries to gradually break down, leading to what we call a “smearing” of biodiversity.

Bad news for the tropics

There are several theories as to why there are so many species in the tropics, and especially the Coral Triangle. Irrespective, we know that this area supports over 500 species of reef-forming corals, together with a massive diversity of fish, including whale sharks, and six of the seven extant species of sea turtles; it is also visited by many species of whales and dolphins. This concentration of marine biodiversity contributes significantly to livelihoods of the region’s 120 million or so human inhabitants.

Species living in tropical seas already live close to their thermal optimum. As temperatures increase, they will exceed the upper thermal limits of some species. When this happens, some species will adapt, for instance by seeking out micro-refuges, such as small patches of cool water caused by upwelling, or they might resort to living in deeper waters, if the water is clear enough.

But in the long term, most species will need to move. The reason we expect marine biodiversity to decrease in the tropics with warming is that there is no place warmer to act as a source of new species to replace those species moving out.

More than 5,000 of the 13,000 species we looked at in our study are found in the coral triangle. According to our projections, approximately 500 to 1,000 of these species will leave the region thanks to warming waters under RCP4.5 and RCP8.5, respectively.

What can we do?

Our modelling shows that the loss of marine life is strongly related to how much we mitigate climate change.

Even if we take only intermediate levels of action (under scenario RCP4.5), we can minimise the damage. But we can’t eliminate it entirely: under the emission-stabilisation RCP4.5 scenario we anticipate that the Coral Triangle will lose roughly half as many species as under the business-as-usual RCP8.5 scenario.

We can also look at how we manage the world’s oceans. Some regions, such as the northeast Atlantic and eastern Mediterranean, have seen greater impacts from people than others, and some of these overlap with regions likely to be affected by climate change.

Where there is overlap, we can look at alleviating the damage caused by people, such as pollution of coastal waters, or minimising the pressure on key species, for example by reducing fishing pressure on them.

In other areas, such as the poles, there is low human impact, but we project substantial changes in biodiversity. From a conservation perspective, we want representative sections of these areas to remain free from additional human pressure, for instance by using regulation to control future development.

And because climate change doesn’t respect national boundaries, all of these efforts will require international cooperation.

Only in that way will we ensure the seas remain rich and healthy in the future.

We acknowledge the contributions of all co-authors: Jorge Garcia Molinos, Benjamin S. Halpern, David S. Schoeman, Christopher J. Brown, Wolfgang Kiessling, Pippa J. Moore, John M. Pandolfi, Elvira S. Poloczanska, Anthony J. Richardson and Michael T. Burrows

*Update August 25: the paper on which this article is based has not yet been published. The article will be updated when the link is available.

The Conversation

David Schoeman is Associate professor, Biostatistics at University of the Sunshine Coast and Jorge García Molinos is Research Associate Climate Change Ecology at Scottish Association for Marine Science

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

Rising seas could drown turtle eggs: new research


James Whitmore, The Conversation

Immersion in seawater kills sea turtle eggs, suggesting that sea turtles are increasingly at risk from rising seas, according to research published today in Royal Society Open Science.

In a laboratory experiment, researchers immersed green turtle eggs in seawater for varying lengths of time. The researchers tested eggs of various ages, and then counted the number of eggs that hatched. They found that immersion for six hours reduced survival by a third.

The study partly explains reduced numbers turtle of hatchlings recorded at Raine Island, home to the largest population of green sea turtles in the world.

David Pike, lecturer in tropical biology at James Cook University and lead author of the study, said turtle nests low down on beaches could be underwater for six hours during abnormally high “king” tides or storm surges.

Michele Thums, ecologist at the Australian Institute of Marine Science, said that given climate projections for increased severe weather events, this could mean fewer hatchlings survive in the future.

But every beach will see different impacts from rising seas, said Tim Dempster, senior lecturer in marine biology at University of Melbourne.

“You can’t just take [a…] scenario of a certain degree of warming, say that will lead to a certain amount of sea level rise, project how much land will be inundated and then project what proportion of nesting habitat will be affected,” he said.

Turtle embryos need oxygen to develop into baby turtles, and immersion in water prevents oxygen from the soil entering the eggs. The embryos effectively suffocate, a process known as “hypoxia”.

Thums said that while most turtles nest above the high tide line and are rarely immersed for six hours, “there are always inexperienced turtles that will lay further down the beach and also there is competition at high density nesting sites like Raine Island”.

Compared to the rest of the world, green sea turtles on Raine Island have a much lower level of breeding success, which could lead to a large decline in the number of breeding adults in the future.

Pike said the low level of success could be partly explained by inundation, but there were likely other factors at work.

“One possibility is that the sand is full of bacteria from all of the rotting eggs that are beneath the sand, and that any fresh eggs laid there may be exposed to bacteria that overgrow the egg and kill the embryo,” he said.

“Another possibility is that contaminants (heavy metals, pesticides) are being passed from the mother turtle to the eggs, and that may cause the embryos to die.”

The Queensland Department of Environmental Heritage and Protection is currently trying to raise low lying spots on Raine Island by moving sand. The island could lose between 7 and 27% of its area thanks to rising seas.

With Janelle Braithwaite, editor at The Conversation.

The Conversation

James Whitmore is Editor, Environment & Energy at The Conversation.

This article was originally published on The Conversation.
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