Rising ocean temperatures around the world due to climate change are causing marine animals, birds and plants to flee from the equator towards the north and south poles
- Study looked at population numbers of marine lifeforms over 100 years
- Found animals and plants are now migrating to the north of their territory
- Scientists believe this is due to warming global ocean temperatures
- Waters are so warm near the equator that it is intolerable for many species
Species that live in the world’s oceans are fleeing towards the Earth’s poles in a desperate attempt to escape rising water temperatures closer to the equator.
Researchers studied more than 300 species — including plants, mammals and birds — to see where the majority of species are living today.
The study looked at more than 100 years worth of data and discovered that populations are now blossoming closer to the poles.
At the same time, population numbers of marine creatures and plants are dwindling near the equator, as they struggle to adapt to warmer waters.
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Scientists assessed more than 100 years of data looking at where populations of various marine life is thriving. They found animals are now favouring the polar ends of their natural ranges. Pictured, diagram showing the range of two species (discs) and the sites at different latitudes where data on population numbers was gathered
All animals and plants that live in the oceans have a natural range in which they have adapted to survive in.
These often span vast areas, with some species having a range of hundreds of miles.
But when academics from the universities of Bristol and Exeter studied the oceanic life, they found a shift in where the populations were thriving in favour of the polar ends of these ranges.
The team believes the study, published in the journal Current Biology, indicates rising temperatures have led to widespread changes in population size and distribution of marine species.
Martin Genner, an evolutionary ecologist at the University of Bristol and senior study author, said: ‘The main surprise is how pervasive the effects were.
‘We found the same trend across all groups of marine life we looked at, from plankton to marine invertebrates, and from fish to seabirds.’
The world’s oceans have warmed by an average of 1°C since pre-industrial times, the researchers said.
To find out how this temperature change has affected marine life, the team reviewed 540 published records of species abundance changes.
This allowed them to gauge occupancy trends over time and show the latitude favoured by species.
They found certain species to be thriving in the cooler regions of the oceans, with rising temperatures opening up previously inaccessible habitats.
For example, the researchers said, the populations of Adelie penguins was declining near the equator but increasing towards the polar regions.
They found conditions of habitats near the equator were too warm to tolerate.
The study found certain species are thriving in the cooler regions of the oceans, with rising temperatures opening up previously inaccessible habitats. For example, the researchers said, the populations of Adelie penguins (pictured) is declining in abundance near the equator but increasing in abundance towards the polar regions
Louise Rutterford, a study author based at both Exeter and Bristol universities, said: ‘Some marine species appear to benefit from climate change, particularly some populations at the poleward limits that are now able to thrive.
‘Meanwhile, some marine life suffers as it is not able to adapt fast enough to survive warming, and this is most noticeable in populations nearer the equator.
‘This is concerning as both increasing and decreasing abundances may have harmful knock-on effects for the wider ecosystem.’
Changes in distribution are likely to continue, however, as marine warming is predicted to increase up to 1.5°C over pre-industrial levels by 2050.
Mr Genner said: ‘This matters because it means that climate change is not only leading to abundance changes, but intrinsically affecting the performance of species locally.
‘We see species such as Emperor penguin becoming less abundant as water becomes too warm at their equatorward edge, and we see some fish such as European seabass thriving at their poleward edge where historically they were uncommon.’
WHAT ARE MARINE HEATWAVES AND WHAT DO WE KNOW ABOUT THEM?
On land, heatwaves can be deadly for humans and wildlife and can devastate crops and forests.
Unusually warm periods can also occur in the ocean. These can last for weeks or months, killing off kelp forests and corals, and producing other significant impacts on marine ecosystems, fishing and aquaculture industries.
Yet until recently, the formation, distribution and frequency of marine heatwaves had received little research attention.
Climate change is warming ocean waters and causing shifts in the distribution and abundance of seaweeds, corals, fish and other marine species. For example, tropical fish species are now commonly found in Sydney Harbour.
But these changes in ocean temperatures are not steady or even, and scientists have lacked the tools to define, synthesize and understand the global patterns of marine heatwaves and their biological impacts.
At a meeting in early 2015, we convened a group of scientists with expertise in atmospheric climatology, oceanography and ecology to form a marine heatwaves working group to develop a definition for the phenomenon: A prolonged period of unusually warm water at a particular location for that time of the year. Importantly, marine heatwaves can occur at any time of the year, summer or winter.
Unusually warm periods can last for weeks or months, killing off kelp forests and corals, and producing other significant impacts on marine ecosystems, fishing and aquaculture industries worldwide (pictured)
With the definition in hand, we were finally able to analyse historical data to determine patterns in their occurrence.
Analysis of marine heatwave trends
Over the past century, marine heatwaves have become longer and more frequent around the world. The number of marine heatwave days increased by 54 per cent from 1925 to 2016, with an accelerating trend since 1982.
We collated more than 100 years of sea surface temperature data around the world from ship-based measurements, shore station records and satellite observations, and looked for changes in how often marine heatwaves occurred and how long they lasted.
This graph shows a yearly count of marine heatwave days from 1900 to 2016, as a global average.
We found that from 1925 to 1954 and 1987 to 2016, the frequency of heatwaves increased 34 per cent and their duration grew by 17 per cent.
These long-term trends can be explained by ongoing increases in ocean temperatures. Given the likelihood of continued ocean surface warming throughout the 21st century, we can expect to see more marine heatwaves globally in the future, with implications for marine biodiversity.
‘The Blob’ effect
Numbers and statistics are informative, but here’s what that means underwater.
A marine ecosystem that had 30 days of extreme heat in the early 20th century might now experience 45 days of extreme heat. That extra exposure can have detrimental effects on the health of the ecosystem and the economic benefits, such as fisheries and aquaculture, derived from it.
A number of recent marine heatwaves have done just that.
In 2011, a marine heatwave off western Australia killed off a kelp forest and replaced it with turf seaweed. The ecosystem shift remained even after water temperatures returned to normal, signalling a long-lasting or maybe even permanent change.
That same event led to widespread loss of seagrass meadows from the iconic Shark Bay area, with consequences for biodiversity including increased bacterial blooms, declines in blue crabs, scallops and the health of green turtles, and reductions in the long-term carbon storage of these important habitats.
Examples of marine heatwave impacts on ecosystems and species. Coral bleaching and seagrass die-back (top left and right). Mass mortality and changes in patterns of commercially important species s (bottom left and right)
Similarly, a marine heatwave in the Gulf of Maine disrupted the lucrative lobster fishery in 2012. The warm water in late spring allowed lobsters to move inshore earlier in the year than usual, which led to early landings, and an unexpected and significant price drop.
More recently, a persistent area of warm water in the North Pacific, nicknamed ‘The Blob’, stayed put for years (2014-2016), and caused fishery closures, mass strandings of marine mammals and harmful algal bloom outbreaks along the coast. It even changed large-scale weather patterns in the Pacific Northwest.
As global ocean temperatures continue to rise and marine heatwaves become more widespread, the marine ecosystems many rely upon for food, livelihoods and recreation will become increasingly less stable and predictable.
The climate change link
Anthropogenic, that is human-caused, climate change is linked to some of these recent marine heatwaves.
For example, human emissions of greenhouse gases made the 2016 marine heatwave in tropical Australia, which led to massive bleaching of the Great Barrier Reef, 53 times more likely to occur.
Even more dramatically, the 2015-16 marine heatwave in the Tasman Sea that persisted for more than eight months and disrupted Tasmanian fisheries and aquaculture industries was over 300 times more likely, thanks to anthropogenic climate change.
For scientists, the next step is to quantify future changes under different warming scenarios. How much more often will they occur? How much warmer will they be? And how much longer will they last?
Ultimately, scientists should develop forecasts for policy makers, managers and industry that could predict the future impacts of marine heatwaves for weeks or months ahead. Having that information would help fishery managers know when to open or close a fishery, aquaculture businesses to plan harvest dates and conservation managers to implement additional monitoring efforts.
Forecasts can help manage the risks, but in the end, we still need urgent action to curb greenhouse gas emissions and limit global warming. If not, marine ecosystems are set for an ever-increasing hammering from extreme ocean heat.
Source: Eric Oliver, Assistant Professor, Dalhousie University; Alistair Hobday, Senior Principal Research Scientist – Oceans and Atmosphere, CSIRO; Dan Smale, Research Fellow in Marine Ecology, Marine Biological Association; Neil Holbrook, Professor, University of Tasmania; Thomas Wernberg, ARC Future Fellow in Marine Ecology, University of Western Australia in a piece for The Conversation.
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