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.

A chart with three overlapping lines, each representing different decades. It shows that between 1955 and 1974, the bell curve is almost flat at the top. For the lines 1975-1994 and 1995-2015, the dip gets progressively deeper, with peaks either side of the centre.
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).

school of tuna fish
The tropical water at the equator is renowned for having the richest diversity of marine life, including large aggregations of tuna fish.
Shutterstock

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 ray with other fish
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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The Conversation


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.

Mass slaughter of wedge-tailed eagles could have Australia-wide consequences


Simon Cherriman, Murdoch University

Last week it was revealed that at least 136 wedge-tailed eagles have been intentionally poisoned in East Gippsland, with concerns that more are yet to be found.

In the past five years I have used satellite tracking devices to research wedge-tailed eagles’ movements across Australia, and I’ve never encountered raptor deaths on this scale.




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It’s been suggested that the birds were killed to protect lambs. Tragically, not only was this illegal cull unnecessary – evidence suggests that eagles do not often kill livestock – but it could also have ecological consequences right across Australia.

Juvenile birds

There are two main categories of wedge-tailed eagles, based on their age class: sedentary breeding adults, which stay in a home range with nest sites; and highly nomadic juvenile birds that can cover huge distances. There are usually fewer adult birds in one place, because they are territorial.

The very high number of birds affected make it likely that they were largely juveniles. There is currently no accurate data on how many wedge-tailed eagles are in Australia, but this single culling event could have serious effects on future generations’ breeding capacity.




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Sites of persecution can have impacts to eagle populations if they become “ecological sinks”. These are places that draw birds in from a wide area, perhaps because of an unnaturally abundant food source, and then result in birds dying. If these ongoing “mortality black holes” cause hundreds of birds to die in relatively short periods of time, this can start impacting the population.

Do eagles kill lambs?

The wedge-tailed eagle is a powerful predator that kills a variety of mammals. Anecdotal observations by landowners describe birds attacking live lambs and even half-grown sheep. There are also cases in the literature of them working in tandem to hunt larger prey such as kangaroos – behaviour that has been widely documented for large eagle species.

However, evidence gathered during extensive research in Australia has shown that in most cases, eagles seen feeding on lamb or sheep carcasses are “cleaning up” after other predators like foxes and crows, which were actually the direct cause of death.

There are no documented cases of wedge-tailed eagles causing significant economic impacts to the sheep industry. But even if they did, there are other options besides culling. Carcasses placed near livestock would provide easier alternative food sources, for example. Shepherds can effectively guard flocks and protect lambs. Finally, given that wedge-tailed eagles are protected, it may be appropriate for the government to pay compensation for livestock losses.




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It must also be emphasised that eagles prey on a range of other species that are considered to be agricultural pests, such as overabundant native kangaroos, cockatoos, and feral species like rabbits and foxes.

The ConversationSome eagles live, and some die. Such is life on this amazing, arid continent. Death itself is a normal ecological phenomenon, but unnatural deaths on such a large scale can have disastrous consequences for long-lived raptors like the wedge-tailed eagle. We must as a community respect the critical role that predators play in the landscape.

Simon Cherriman, Ornithology, Murdoch University

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

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


File 20171114 27595 17nf1pm.jpg?ixlib=rb 1.1
During mass spawning events coral young rise from their parents to ocean surface.
Australian Institute of Marine Science, Author provided

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

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

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


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


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

https://giphy.com/embed/l2QEeZl0oICDd4eqI

Mass spawning after the full moon

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

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

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


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


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

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

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

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

An important date in the scientific calendar

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

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

New tools for coral reef management

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

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


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


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

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

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

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

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

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

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

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

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

Mass extinctions and climate change: why the speed of rising greenhouse gases matters


Katrin Meissner, UNSW Australia and Kaitlin Alexander, UNSW Australia

We now know that greenhouse gases are rising faster than at any time since the demise of dinosaurs, and possibly even earlier. According to research published in Nature Geoscience this week, carbon dioxide (CO₂) is being added to the atmosphere at least ten times faster than during a major warming event about 50 million years ago.

We have emitted almost 600 billion tonnes of carbon since the beginning of the Industrial Revolution, and atmospheric CO₂ concentrations are now increasing at a rate of 3 parts per million (ppm) per year.

With increasing CO₂ levels, temperatures and ocean acidification also rise, and it is an open question how ecosystems are going to cope under such rapid change.

Coral reefs, our canary in the coal mine, suggest that the present rate of climate change is too fast for many species to adapt: the next widespread extinction event might have already started.

In the past, rapid increases in greenhouse gases have been associated with mass extinctions. It is therefore important to understand how unusual the current rate of atmospheric CO₂ increase is with respect to past climate variability.

Into the ice ages

There is no doubt that atmospheric CO₂ concentrations and global temperatures have changed in the past.

Ice sheets, for example, are reliable book-keepers of ancient climate and can give us an insight into climate conditions long before the thermometer was invented. By drilling holes into ice sheets we can retrieve ice cores and analyse the accumulation of ancient snow, layer upon layer.

These ice cores not only record atmospheric temperatures through time, they also contain frozen bubbles that provide us with small samples of ancient air. Our longest ice core extends more than 800,000 years into the past.

During this time, the Earth oscillated between cold ice ages and warm “interglacials”. To move from an ice age to an interglacial, you need to increase CO₂ by roughly 100 ppm. This increase repeatedly melted several kilometre-thick ice sheets that covered the locations of modern cities like Toronto, Boston, Chicago or Montreal.

With increasing CO₂ levels at the end of the last ice age, temperatures increased too. Some ecosystems could not keep up with the rate of change, resulting in several megafaunal extinctions, although human impacts were almost certainly part of the story.

Nevertheless, the rate of change in CO₂ over the past million years was tame when compared to today. The highest recorded rate of change before the Industrial Revolution is less than 0.15 ppm per year, just one-twentieth of what we are experiencing today.

Temperature has oscillated with greenhouse gases.
Kaitlin Alexander, data from: Luthi et al., 2006: http://www.nature.com/nature/journal/v453/n7193/full/nature06949.html Loulergue et al., 2008: http://www.nature.com/nature/journal/v453/n7193/full/nature06950.html Etheridge et al., 1996: http://onlinelibr

Looking further back

To find an analogue for present-day climate change, we therefore have to look further back, to a time when ice sheets were small or did not exist at all. Several abrupt warming events occurred between 56 million and 52 million years ago. These events were characterised by a rapid increase in temperature and ocean acidification.

The most prominent of these events was the Palaeocene Eocene Thermal Maximum (PETM). This event resulted in one of the largest known extinctions of life forms in the deep ocean. Atmospheric temperatures increased by 5-8C within a few thousand years.

Reconstructions of the amount of carbon added to the atmosphere during this event vary between 2000-10,000 billion tonnes of carbon.

The new research, led by Professor Richard Zeebe of the University of Hawaii, analysed ocean sediments to quantify the lag between warming and changes in the carbon cycle during the PETM.

Although climate archives become less certain the further we look back, the authors found that the carbon release must have been below 1.1 billion tonnes of carbon per year. That is about one-tenth of the rate of today’s carbon emissions from human activities such as burning fossil fuels.

What happens when the brakes are off?

Although the PETM resulted in one of the largest known deep sea extinctions, it is a small event when compared to the five major extinctions in the past.

The Permian-Triassic Boundary extinction, nicknamed “The Great Dying”, wiped out 90% of marine species and 70% of land vertebrate families 250 million years ago. Like its four brothers, this extinction event happened a very long time ago. Climate archives going that far back lack the resolution needed to reliably reconstruct rates of change.

There is, however, evidence for extensive volcanic activity during the Great Dying, which would have led to a release of CO₂ as well as the potential release of methane along continental margins. Ocean acidification caused by high atmospheric CO₂ concentrations and acid rain have been put forward as potential killer mechanisms.

Other hypotheses include reduced oxygen in the ocean due to global warming or escape of hydrogen sulfide, which would have caused both direct poisoning and damage to the ozone layer.

These past warming events occurred without human influence. They point to the existence of positive feedbacks within the climate system that have the power to escalate warming dramatically. The thresholds to trigger these feedbacks are hard to predict and their impacts are hard to quantify.

Some examples of feedbacks include the melting of permafrost, the release of methane hydrates from ocean sediments, changes in the ocean carbon cycle, and changes in peatlands and wetlands. All of these processes have the potential to quickly add more greenhouse gases to the atmosphere.

Given that these feedbacks were strong enough in the past to wipe out a considerable proportion of life forms on Earth, there is no reason to believe that they won’t be strong enough in the near future, if triggered by sufficiently rapid warming.

Today’s rate of change in atmospheric CO₂ is unprecedented in climate archives. It outpaces the carbon release during the most extreme abrupt warming events in the past 66 million years by at least an order of magnitude.

We are therefore unable to rely upon past records to predict if and how our ecosystems will be able to adapt. We know, however, that mass extinctions have occurred in the past and that these extinctions, at least in the case of the PETM, were triggered by much smaller rates of change.

Katrin and Kaitlin will be on hand for an Author Q&A between 2 pm and 3 pm AEDT on Thursday March 24. Post your questions in the comment section below.

The Conversation

Katrin Meissner, Associate Professor, Climate Change Research Centre, UNSW Australia and Kaitlin Alexander, PhD Candidate, Climate Change Research Centre, UNSW; ARC Centre of Excellence for Climate System Science, UNSW Australia

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

BP and Dolphin Deaths


The following link is to an article that looks into mass dolphin deaths as a result of the massive BP oil spill in the USA. There is also a link to an online petition.

For more visit:
http://www.care2.com/causes/environment/blog/scientists-link-mass-dolphin-deaths-to-bp-oil-spill/