Marine heatwaves threaten global biodiversity

Extreme weather events occur in the oceans as well as the atmosphere. Marine heatwaves – periods of unusually high temperatures – are increasing in frequency, with 54% more heatwave days per year from 1987–2016 than from 1925–1954, yet their impacts on species and ecosystems are poorly known.

A new paper, co-authored by University of Canterbury scientist Dr Mads Thomsen, recently published online in Nature Climate Change is the first to compare the strength and impacts of prominent marine heatwaves, reporting negative impacts on a broad range of marine organisms, possibly with major socioeconomic ramifications.

The global study, led by Dr Dan Smale of the Marine Biological Association (United Kingdom) and involving scientists from seven countries including Aotearoa New Zealand, found that marine heatwaves vary in their physical manifestations, yet they all affect important biological organisms and alter the functioning of ecosystems.

The research team documented trends and attributes of prominent marine heatwaves across ocean basins, and their biological impacts on species and ecosystems. They found that many regions within the Pacific, Atlantic, and Indian Oceans are particularly vulnerable to future marine heatwaves, because of overlapping levels of high biodiversity, other types of human impacts and a prevalence of species found near their warm-thermal limits. Although the analysed marine heatwaves varied in strength and spatial extents, effects were generally harmful across biological processes and organisms, including critical species like corals, seagrasses and kelps.

“Marine ecosystems face many threats, such as invasions by non-native species, overfishing, acidification and pollution, but shorter periods of unusually high temperatures is now also a well-documented cause of rapid biological changes, sometimes leading to loss of habitat, reduced fisheries or even local extinctions,” says marine biologist Dr Mads Thomsen, from the University of Canterbury’s College of Science.

Dr Thomsen says analysing extreme temperature events on a global scale turned out to be surprisingly relevant for local research in New Zealand, which last year experienced the hottest summer on record. So far, these very recent strong heatwaves from New Zealand have, in contrast to the heatwaves analysed in the Nature Climate Change publication, not been studied much, he says.

“However, early evidence suggests rapid changes to local marine systems, including plankton, fish and kelp. Indeed, a key take-home message from the Nature Climate Change publication is that many more studies should report on temperature-driven rapid biological changes with rigorous scientific methods, to improve our ability to understand and predict future ecosystem functioning.”

The authors conclude that climate change will continue to increase the frequency and strengths of heatwaves and that associated impacts on marine habitats will likely have wide-reaching and cascading effects on the functions these habitats provide.

DOI: 10.1038/s41558-019-0412-1 (https://www.nature.com/articles/s41558-019-0412-1)

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