Climate change is leading to lower numbers of marine life towards the equator – including mammals, birds, fish and plankton – while populations nearer the poles increase

Climate change is leading to lower numbers of marine life towards the equator – including mammals, birds, fish and plankton – while populations nearer the poles increase

By Gege Li
The European seabass is one of the species that is declining in warmer waters and increasing in cooler waters
Fawcitt Nature and Wildlife / Alamy
Climate change is dramatically changing the abundance of marine life around the world. As oceans warm, populations of species that can adapt to elevated local temperatures have increased nearer to the poles, while those that live closer to the equator are shrinking in size.
Martin Genner at the University of Bristol, UK, and his colleagues examined data from 540 previous studies of marine populations affected by warming. The analysis included 304 marine species, including mammals, birds, fish and plankton, and their change in abundance within their usual habitat range.
The researchers found that the warming of oceans by 1°C over the past century has triggered a widespread change in local communities, and those species that were more abundant at the poleward limit of their range seemed to fare better than those nearer the equatorial limit.
This is because the poleward populations can tolerate a slight temperature increase in cold waters, whereas warming in an already warm tropical environment can prove too extreme for other species, says Genner.
The most surprising thing is that [this was the case] for not just a handful of species, but many, many species, says Genner. The trend was strongest for seabirds and bony fish, but applied to all the taxonomic groups that the researchers analysed. In the next 50 years, ocean temperatures are forecast to rise by another 1.5°C, which suggests that this trend could continue.
This change in species abundance has consequences for humans too. For example, UK fisheries may need to shift their focus to farming more warm-water species, such as herring, rather than Atlantic cod, as cod survive better in cold temperatures.
However, broad analyses like this one oversimplify the effects of climate change, says Nova Mieszkowska at the Marine Biological Association in Plymouth, UK. [These analyses] present the big picture, but often gloss over the important details, omitting the often important array of smaller-scale processes and temporal oscillations that also have significant effects on the abundance and distribution of species.
More long-term information covering a wider geographical range is needed, she says.
Journal reference: Current Biology, DOI: 10.1016/j.cub.2020.02.043
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