Marine life is fleeing the equator to cooler waters. History tells us this could trigger a mass extinction event

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Anthony Richardson, The University of Queensland; Chhaya Chaudhary, University of Auckland; David Schoeman, University of the Sunshine Coast, and Mark John Costello, University of AucklandThe tropical water at the equator is renowned for having the richest diversity of marine life on Earth, with vibrant coral reefs and large aggregations of tunas, sea turtles, manta rays and whale sharks. The number of marine species naturally tapers off as you head towards the poles.

Ecologists have assumed this global pattern has remained stable over recent centuries — until now. Our recent study found the ocean around the equator has already become too hot for many species to survive, and that global warming is responsible.

In other words, the global pattern is rapidly changing. And as species flee to cooler water towards the poles, it’s likely to have profound implications for marine ecosystems and human livelihoods. When the same thing happened 252 million years ago, 90% of all marine species died.

The bell curve is warping dangerously

This global pattern — where the number of species starts lower at the poles and peaks at the equator — results in a bell-shaped gradient of species richness. We looked at distribution records for nearly 50,000 marine species collected since 1955 and found a growing dip over time in this bell shape.

If you look at each line in this chart, you can see a slight dip in total species richness between 1955 and 1974. This deepens substantially in the following decades.
Anthony Richardson, Author provided

So, as our oceans warm, species have tracked their preferred temperatures by moving towards the poles. Although the warming at the equator of 0.6℃ over the past 50 years is relatively modest compared with warming at higher latitudes, tropical species have to move further to remain in their thermal niche compared with species elsewhere.

As ocean warming has accelerated over recent decades due to climate change, the dip around at the equator has deepened.

We predicted such a change five years ago using a modelling approach, and now we have observational evidence.

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For each of the 10 major groups of species we studied (including pelagic fish, reef fish and molluscs) that live in the water or on the seafloor, their richness either plateaued or declined slightly at latitudes with mean annual sea-surface temperatures above 20℃.

Today, species richness is greatest in the northern hemisphere in latitudes around 30°N (off southern China and Mexico) and in the south around 20°S (off northern Australia and southern Brazil).

The tropical water at the equator is renowned for having the richest diversity of marine life, including large aggregations of tuna fish.
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This has happened before

We shouldn’t be surprised global biodiversity has responded so rapidly to global warming. This has happened before, and with dramatic consequences.

252 million years ago…

At the end of the Permian geological period about 252 million years ago, global temperatures warmed by 10℃ over 30,000-60,000 years as a result of greenhouse gas emissions from volcano eruptions in Siberia.

A 2020 study of the fossils from that time shows the pronounced peak in biodiversity at the equator flattened and spread. During this mammoth rearranging of global biodiversity, 90% of all marine species were killed.

125,000 years ago…

A 2012 study showed that more recently, during the rapid warming around 125,000 years ago, there was a similar swift movement of reef corals away from the tropics, as documented in the fossil record. The result was a pattern similar to the one we describe, although there was no associated mass extinction.

Authors of the study suggested their results might foreshadow the effects of our current global warming, ominously warning there could be mass extinctions in the near future as species move into the subtropics, where they might struggle to compete and adapt.

Today…

During the last ice age, which ended around 15,000 years ago, the richness of forams (a type of hard-shelled, single-celled plankton) peaked at the equator and has been dropping there ever since. This is significant as plankton is a keystone species in the foodweb.

Our study shows that decline has accelerated in recent decades due to human-driven climate change.

The profound implications

Losing species in tropical ecosystems means ecological resilience to environmental changes is reduced, potentially compromising ecosystem persistence.

In subtropical ecosystems, species richness is increasing. This means there’ll be species invaders, novel predator-prey interactions, and new competitive relationships. For example, tropical fish moving into Sydney Harbour compete with temperate species for food and habitat.

This could result in ecosystem collapse — as was seen at the boundary between the Permian and Triassic periods — in which species go extinct and ecosystem services (such as food supplies) are permanently altered.

The changes we describe will also have profound implications for human livelihoods. For example, many tropical island nations depend on the revenue from tuna fishing fleets through the selling of licenses in their territorial waters. Highly mobile tuna species are likely to move rapidly toward the subtropics, potentially beyond sovereign waters of island nations.

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Similarly, many reef species important for artisanal fishers — and highly mobile megafauna such as whale sharks, manta rays and sea turtles that support tourism — are also likely to move toward the subtropics.

The movement of commercial and artisanal fish and marine megafauna could compromise the ability of tropical nations to meet the Sustainable Development Goals concerning zero hunger and marine life.

Is there anything we can do?

One pathway is laid out in the Paris Climate Accords and involves aggressively reducing our emissions. Other opportunities are also emerging that could help safeguard biodiversity and hopefully minimise the worst impacts of it shifting away from the equator.

Currently 2.7% of the ocean is conserved in fully or highly protected reserves. This is well short of the 10% target by 2020 under the UN Convention on Biological Diversity.

Manta rays and other marine megafauna leaving the equator will have a huge impact on tourism.
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But a group of 41 nations is pushing to set a new target of protecting 30% of the ocean by 2030.

This “30 by 30” target could ban seafloor mining and remove fishing in reserves that can destroy habitats and release as much carbon dioxide as global aviation. These measures would remove pressures on biodiversity and promote ecological resilience.

Designing climate-smart reserves could further protect biodiversity from future changes. For example, reserves for marine life could be placed in refugia where the climate will be stable over the foreseeable future.

We now have evidence that climate change is impacting the best-known and strongest global pattern in ecology. We should not delay actions to try to mitigate this.

This story is part of Oceans 21

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

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Anthony Richardson, Professor, The University of Queensland; Chhaya Chaudhary, , University of Auckland; David Schoeman, Professor of Global-Change Ecology, University of the Sunshine Coast, and Mark John Costello, Professor, University of Auckland

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

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Drilling for oil in the Great Australian Bight would be disastrous for marine life and the local community

A recent poll showed seven out of ten South Australian voters are against drilling in the Great Australian Bight.
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Sarah Duffy, Western Sydney University and Christopher Wright, University of Sydney

The Great Australian Bight is home to a unique array of marine life. More than 85% of species in this remote stretch of rocky coastline are not found anywhere else in the world. It’s also potentially one of “Australia’s largest untapped oil reserves”, according to Norwegian energy company Equinor.

Equinor has proposed to drill a deepwater oil well 370km offshore to a depth of more than two kilometres in search of oil.

But a recent poll showed seven out of ten South Australian voters are against drilling in the Bight. And hundreds of people recently gathered on an Adelaide beach in protest.

Their main concerns include the lack of economic benefits for local communities, more fossil fuel investment, weak regulation and the potential for an oil spill, devastating our “Great Southern Reef”.

Drilling in the Great Australian Bight has occurred since the 1960s, but never as deep as what Equinor has proposed.

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The Coalition government argues the project will improve energy security and bring money and jobs to the region. Labor announced recently that, if elected, it would commission a study on the consequences of a spill in the region.

So what’s the worst that could happen?

As discussed in a Sydney Environment Institute workshop in April, drilling in the Bight would have disastrous environment and economic implications.

A spill could leak between 4.3 million barrels and 7.9 million barrels – the largest oil spill in history, according to estimates from the 2016 Worst Credible Discharge report, authored by Equinor and its former joint-venture partner, BP.

The Bight is a wild place, with violent storms and strong winds and waves. The geography is remote, unmonitored, largely unpopulated and lacks physical infrastructure to respond effectively to an oil spill.

In such an event, Equinor has said it would take 17 days to respond in a best-case scenario. The worst-case scenario is 39 days, and the goal scenario is 26 days.

In modelling for the worst-case scenario, the company predicts the oil from a spill could even reach from Albany in Western Australia to Port Macquarie in New South Wales.

How likely is an oil spill?

Reports from Norwegian regulators, compiled by Greenpeace, reveal Equinor had more than 50 safety and control breaches, including ten oil leaks, in the last three-and-a-half years. Each incident occurred in regulatory environments with stricter conditions than in Australia.

Our independent regulator, NOPSEMA, does not require inspections of wells during construction to ensure they meet safety standards.

This can be disastrous. For instance, the failure to properly construct the Montara Well in the North West Shelf caused the worst oil spill in Australian history.

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NOPSEMA does not have a set standard for well control. This is a risky proposition because in recent years three of the four major international oil spills from well blowouts occurred in exploration wells, the kind planned for the Bight.

And Greenpeace has questioned the independence of NOPSEMA after it was revealed the regulator will speak at an event promoting oil exploration in the Great Australian Bight.

Adding billions to the GDP, but there’s a catch

The Great Australian Bight boasts more marine diversity than the Great Barrier Reef and attracts more than 8 million visitors a year.

Equinor’s proposed project risks local fishing and tourism industries that rely on a pristine natural environment and contribute $10 billion a year to our economy, twice as much as the Great Barrier Reef.

The Great Australian Bight is home to at least 14 schools of bottlenose dolphins.
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A 2018 ACIL Allen report on the economic impact of drilling in the Great Australian Bight suggested Australia’s GDP could gain A$5.9 billion a year if the region turns out to be a major oil field.

But the catch is that this would require 101 oil wells to be successfully drilled, and many of the expected benefits wouldn’t be realised until between 2040 and 2060. What’s more, this windfall wouldn’t reach the pockets of locals, but would largely land in federal government coffers via the Petroleum Resource Rent Tax.

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These predictions are based on optimistic estimates of oil prices, and the report assumes our oil demand will remain on an upwards trajectory, which would mean we breach the Paris targets by a significant margin.

Worryingly, Equinor’s former partner in this venture, energy giant BP, even tried to claim an oil spill would benefit the local economy, and said:

In most instances, the increased activity associated with cleanup operations will be a welcome boost to local economies.

There is little evidence to support the argument that this drilling will lead to better energy security.

Given Australia doesn’t have the capacity to refine oil domestically, it’s likely most, if not all, of the oil extracted would be processed overseas.

From a security point of view, far more impact would come from reducing our reliance on oil through better vehicle emission standards and promoting a system-wide shift to electric vehicles.

No real benefit to the community

The Great Australian Bight is home to Australia’s most productive fishery, which directly employs 3,900 locals. An oil spill would threaten 9,000 jobs in South Australia alone.

By comparison, Equinor claim that the construction phase of the project would create 1,361 jobs, most of which require experience that would not be found in local communities. For instance, fly-in fly-out workers from Adelaide would take ongoing jobs on the rigs.

Equinor has had more than 50 safety and control breaches in the last three-and-a-half years, occurring in stricter regulatory environments than in Australia.
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Equinor has already completed seismic testing, which involves firing soundwaves into the ocean floor to detect the presence of oil and gas. The testing alone has pushed schools of tuna further out to sea, increasing costs and risks for local fisherman.

You decide, is it worth it?

Decisions over resource projects with significant environmental impacts need to be based on a thorough cost-benefit analysis and include the precautionary principle.

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The economic advantage to either local communities or the Australian public from this proposal is in doubt. And Australians are entitled to ask their politicians why so little is demanded of these organisations.

In the lead-up to a critical federal election, we are left to ask why our political leaders are doubling down on a fossil fuel bet with no clear advantages and a significant downside risk.

Sarah Duffy, Lecturer, School of Business, Western Sydney University and Christopher Wright, Professor of Organisational Studies, University of Sydney

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

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

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.

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Explainer: what is biodiversity and why does it matter?

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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.

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

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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.

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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.

Drought on the Murray River harms ocean life too

The mouth of the Murray River delivers vital nutrients to marine life in the ocean beyond.
SA Water, Author provided

Hannah Auricht, University of Adelaide and Kenneth Clarke, University of Adelaide

Drought in the Murray River doesn’t just affect the river itself – it also affects the ecosystems that live in the ocean beyond.

In a study published in Marine and Freshwater Research today, we found that the very low flows in the river over the past decade reduced the abundance of microscopic marine plants called phytoplankton, which are ultimately the base of all marine food webs.

This shows that the health of the Murray River has a much bigger influence on the marine environment than we previously realised. With climate change poised to make droughts more frequent and severe in the river, it will be crucial to monitor the health not just of freshwater species, but of the local marine ones too.

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Phytoplankton depend on nutrients, which are often delivered to the ocean by rivers. In turn, these tiny plants are a source of food for almost all marine ecosystems. Worldwide, they are responsible for half the production of organic matter on the planet.

In South Australia, a dry period dubbed the Millennium Drought (2001 to 2010) and overallocation of water resources (primarily for agriculture) meant that very little water was delivered from the Murray Mouth to the coastal ocean. Between 2007 and 2010, no water was discharged at all. The water in the river’s lower reaches became much saltier and cloudier.

We used historical flow records and satellite imagery, taken between early 2002 and late 2016, to figure out how much phytoplankton and other organic matter were in the coastal ocean each month. We broke up the area into incremental zones, venturing up to 130km from the river mouth.

We found that during and after high-flow events, Murray River discharge resulted in a huge increase in phytoplankton concentrations – as far as 60km beyond the river’s mouth. Surprisingly, before our research it wasn’t known that the river played such an important role in stimulating phytoplankton growth over such a large area.

The mouth of the Murray River, where sometimes no water flows into the ocean at all.
CSIRO/Wikimedia Commons, CC BY

Armed with an understanding of how river flows influenced phytoplankton growth, we used historic flow records to estimate phytoplankton concentrations back to 1962. Our results showed that large flows used to occur more often and in greater volumes, and consequently that phytoplankton populations would have gone through more frequent and larger booms.

This in turn would have benefited all of the species that ultimately depend on phytoplankton for food, either directly or indirectly. This food web encompasses almost the whole marine ecosystem.

The past affects the future

Water resource management has greatly altered the volume and timing of freshwater discharges from the Murray. The ocean beyond the Murray mouth now receives small and infrequent deliveries of freshwater.

Rainfall and streamflow are decreasing in this already variable region, while temperatures are rising. This means that South Australia is likely to experience more severe and more frequent droughts, which will cause flows from the Murray mouth to decline still further, ultimately reducing phytoplankton abundance.

Previous research had already established the links between river outflows, phytoplankton and health of marine environments and species. But as far as we can tell, no other research has looked at exactly how extended periods of no or low river outflows affect marine ecosystems. This makes it difficult to predict how these systems will respond to climate change.

We believe that reduced Murray River outflows and reduced phytoplankton concentrations would likely have also placed strain on local mulloway fish and Goolwa cockle populations. Juvenile mulloway use river outflows as habitat and environmental cues, and cockles feed on organic material in the water.

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This is why it is so important that the management of the Murray River doesn’t just stop at the river’s mouth, but continues into the ocean beyond. Current plans are focused on restoring flows to support the riparian and wetland ecosystems of the Murray as well as the Lower Lakes and Coorong.

But there has been little recognition of the role of river outflows on the marine environment – let alone in management. Although we might not always think about it, the marine environment is really the end of the river system, and part of a larger global cycle. It would therefore be beneficial if plans extend to monitor the marine ecosystem’s response, both at broad and fine scales, to varying flow events.

It would seem the time is past ripe to call for greater research and consideration on this matter, so that we don’t do further damage to what is actually still a part of the Murray River system, and can improve measures to protect the marine environment.

Hannah Auricht, PhD candidate, University of Adelaide and Kenneth Clarke, Researcher, School of Biological Sciences, University of Adelaide

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

Citizen scientist scuba divers shed light on the impact of warming oceans on marine life

A volunteer diver surveys marine life at Lord Howe Island.
Rick Stuart-Smith/Reef Life Survey, Author provided

Madeleine De Gabriele, The Conversation

Rising ocean temperatures may result in worldwide change for shallow reef ecosystems, according to research published yesterday in Science Advances.

The study, based on thousands of surveys carried out by volunteer scuba divers, gives new insights into the relationship of fish numbers to water temperatures – suggesting that warmer oceans may drive fish to significantly expand their habitat, displacing other sea creatures.

Citizen science

The study draws from Reef Life Survey, a 10-year citizen science project that trains volunteer scuba divers to survey marine plants and animals. Over the past ten years, more than 200 divers have surveyed 2,406 ocean sites in 44 countries, creating a uniquely comprehensive data set on ocean life.

Reef Life Survey takes volunteers on surveying expeditions at hard-to-reach coral reefs around the world.
Rick Stuart-Smith/Reef Life Survey, Author provided

Lead author Professor Graham Edgar, who founded Reef Life Survey, said the unprecedented scope of their survey allowed them to investigate global patterns in marine life. The abundance of life in warm regions (such as tropical rainforests and coral reefs) has long intrigued naturalists. At least 30 theories have been put forward, but most studies have been based on relatively limited surveys restricted to a single continent or group of species.

By tapping into the recreational scuba diving community, Reef Life Survey has vastly increased the amount of information researchers have to work with. Professor Edgar and his colleagues provide one-on-one training to volunteers, teaching them how to carry out comprehensive scans of plants and animals in specific areas.

Dr Adriana Vergés, a researcher at the University of New South Wales specialising in the impact of climate change on ocean ecosystems, said that the Reef Life Survey has already substantially improved our understanding of the marine environment.

“For example, Reef Life Survey data has greatly contributed to our understanding of the factors that determine the effectiveness of effectiveness of marine-protected areas worldwide. The team have made all their data publicly available and more and more research is increasingly making use of it to answer research questions,” she said.

Some of the divers have been working with Reef Life Survey for a decade, although others participate when they can. One volunteer, according to Professor Edgar, was so inspired by the project that he began a doctorate in marine biology (he graduated this year).

There’s a strong link between fish numbers and water warmth, which means warming oceans are likely to change global fish distribution.
Rick Stuart-Smith/Reef Life Survey, Author provided

Warming oceans means fish on the move

One of the important insights delivered by the Reef Life Survey datatbase is the relationship between water temperature and the ratio of fish to invertebrates in an ecosystem. Essentially, the warmer the water, the more fish. Conversely, colder waters contain more invertebrates like lobster, crabs and shrimp.

Professor Stewart Frusher, director of the Centre for Marine Socioecology at the University of Tasmania (and a former colleague of Professor Edgar) told The Conversation that he believes we will see wide-scale changes in fish distribution as climate change warms the oceans.

“Species are moving into either deeper water or towards the poles. We also know that not all species are moving at the same rate, and thus new mixtures of ecosystems will occur, with the fast-moving species of one ecosystem mixing with the slower moving of another,” he said.

As species migrate or expand into newly warmed waters, according to Professor Frusher, they will compete with and prey on the species already living in that area. And while it’s uncertain exactly how disruptive this will be, we do know that small ecosystem changes can rapidly lead to larger-scale impacts.

In order to predict and manage these global changes, scientists need reliable and detailed world-wide data. Professor Frusher said that, with research funding declining, scientists do not have the resources to monitor at the scales required.

“Well-developed citizen science programs fill an important niche for improving our understanding of how the earth is responding to change,” he said.

Madeleine De Gabriele, Deputy Editor: Energy + Environment, The Conversation

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

Oceans: Marine Life in Crisis

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.

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.

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