As the world’s oceans have warmed by one degree Celsius since pre-industrial times, there has been a pervasive shift in abundance of marine life, from plankton and fish to mammals, seabirds and macroalgae.
Populations of plants and sea creatures in cooler waters have grown as previously unliveable habitats become more viable, while those near warmer waters have dropped off.
This finding comes from a global analysis of data for more than 300 marine species collected over the last century and is published in the journal Current Biology.
“Some marine species appear to benefit from climate change, particularly some populations at the poleward limits that are now able to thrive,” says co-lead author Louise Rutterford, from the University of Bristol, UK.
“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.”
Both these trends could have detrimental impacts on species behaviours and the broader ecosystem – including predators, prey and food availability – and point to further loss of marine species as ocean temperatures continue to rise up to 1.5 degrees as projected by 2050.
“We see species such as Emperor penguins becoming less abundant as water becomes too warm at the equatorward edge,” says senior author Martin Genner, “and we see some fish such as European seabass thriving at their poleward edge where historically they were uncommon.”
Other species that are moving from warmer to cooler waters include Atlantic herring and Adèlie penguins.
While the shifts could increase fishing opportunities for warm-water fish in new habitats, it could also create ideal conditions for warm-water parasites to flourish, disrupting aquaculture industries and coastal livelihoods.
The authors had predicted, based on smaller, regional studies, that temperature changes would impact abundance of marine organisms, which function physiologically within slim thermal tolerance limits.
But human activities are impacting the ocean in other ways, causing habitat destruction and climate change-related storms, salinity and acidification, which need to be considered along with a thorough life history plus physiological and ecological characteristics of each species.
To get a clearer, global picture of abundance patterns in relation to ocean temperatures, the team collected data from 540 sets of records from 1991 to 2016.
Their analysis found that, on the whole, species populations were much more likely to have grown towards the poles and diminished near the equator, confirming that warming waters are impacting their survival.
“Thus, our study builds on evidence of climate-associated local abundance changes and sits alongside climate-driven changes in other biological parameters,” the authors write, “such as the overall distributions of species, and shifts in the timing of life history events.”
This is likely to continue, they add, “impacting further on local marine assemblages and the coastal industries that depend on them.”
Natalie Parletta is a freelance science writer based in Adelaide and an adjunct senior research fellow with the University of South Australia.
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