Scientists at the University of Cape Town’s Climate Risk Lab led the study, which analysed data from more than 21 000 species. (Photo by Emmanuele Contini/NurPhoto via Getty Images)
Climate change will continue to create opportunities for marine species to colonise new habitats, even if the world continues to rapidly reduce greenhouse gas emissions, new research has found.
Scientists at the University of Cape Town’s Climate Risk Lab led the study, which analysed data from more than 21 000 species.
Published in Nature Communications, their research showed that the increase in ocean temperatures caused by climate change is projected to create opportunities for marine species to colonise habitats that were previously thermally unsuitable. Other marine species, meanwhile, will be exposed to potentially unsafe temperatures.
The authors analysed when, where, and how fast climate change will cause exposure and create opportunities for global marine biodiversity.
They explained that thermal exposure occurs when a species in a site is exposed to temperatures beyond its realised thermal niche for at least five consecutive years.
A thermal opportunity, on the other hand, arises when the temperature at a previously unsuitable site near the existing range of the species becomes suitable for at least five consecutive years, meaning that the “temperature falls within the realised thermal niche limits of that species”.
The researchers found that shifts in ocean temperatures caused by climate change are already creating opportunities for marine species to colonise new habitats, “potentially remixing” local biodiversity in the process.
These opportunities for colonisation will continue to increase for thousands of species until mid-century, even if greenhouse gas emissions are quickly reduced. But exposure to unsafe temperatures is projected to accelerate later and negatively affect more species, especially if climate change is not controlled.
Particularly sensitive to warming
Although climate change is affecting biodiversity on land and in the ocean, marine organisms have been found to be particularly sensitive to warming.
“For instance, marine ectotherms [their body temperature fluctuates with that of the surrounding environment] tend to fully occupy their potential latitudinal range, indicating that their range boundaries closely track changes in temperature.”
Compared to terrestrial ectotherms, marine ectotherms are also more susceptible to physiological stress from climate change because of their narrower thermal safety margins, meaning “the smaller difference between body temperatures and the upper critical thermal limit of a species”.
The study noted that such sensitivity, coupled with fast climate change and lower constraints on dispersal, has driven range shifts towards newly suitable habitats. “As a result, rates of local extirpation [extinction], colonisation, species richness change and temporal turnover in community composition are higher for heating in the oceans than on land.”
But these changes are not randomly distributed in space and time. “While at the equatorward edge of species ranges climate change is causing abundance declines and local extirpations, abundance increases and the influx of new species have been observed at higher latitudes.”
Given the effect of temperature in determining both high and low-latitude range limits of marine species, equatorward shifts can be strongly influenced by the loss of climatically suitable habitats and poleward shifts “by thermal opportunities arising in previously unsuitable regions”.
Reshaping marine life
“Our findings suggest climate change reshaping many marine life communities can no longer be avoided,” said Andreas Schwarz Meyer, the study’s lead author.
The effects of exposure and opportunity will threaten marine life in different regions over time. Negative effects projected to be associated with exposure to potentially unsafe temperatures are concentrated in the tropics, increasing rapidly after 2050 if global warming continues. In temperate and polar regions, near-term changes to biodiversity are projected to arise more from new opportunities emerging in the next few decades.
“While exposure to unsafe temperatures can lead to local extinction of species, new thermal opportunities can bring non-native species into communities, disrupting ecological balance and reducing important ecosystem services such as food provision for people,” Meyer said.
Although some impacts can no longer be avoided, by rapidly reducing the burning of coal, oil and gas, and halting deforestation, the number of species at risk from increasing ocean temperatures can be significantly reduced.
Limiting global warming well below 2°C is expected to halve the number of opportunities created and reduce the number of species exposed to unsafe temperatures by 100-fold compared to uncontrolled climate change, added Christopher Trisos, the study’s co-author.
“Strong, fast, and sustained climate action is crucial to reducing the severe risk of negative impacts on marine life across Earth’s oceans.”