New Method Developed to Track How Marine Species Respond to Climate-Induced Heatwaves

A coral reef bleached by heat waves caused by the climate crisis. Photo: Faculty of Science, University of Hong Kong

As more solar energy is absorbed by the oceans, on top of higher temperatures which already exist especially in shallower parts of the ocean, the presence of occasional serious marine heatwaves has become more common globally. The consequences of those heatwaves is deadly, not just for coral reefs which are already dying off worldwide at alarmingly high rates, but for all marine organisms.

Depending on the species, those organisms have basically three responses available to them. Via evolutionary change they can attempt to adapt to what global heating is doing to them, they can migrate to cooler waters more like where they can thrive, or they can die off.

Even if they were to survive via evolution or migration or both, those changes will have devastating effects on the ecosystems they used to live within as well as where they migrate to.

The result of all three adaptation responses could in the end be the same: mass extinctions, either of the species under stress or those organisms dependent on them either as food or through some form of symbiotic relationship.

This problem, which in a way is a key to saving the planet from the climate crisis, has driven researchers to attempt to find a way to predict how these heatwaves can impact marine organisms, and suggest ways to help the ecosystems they live within to adapt.

That is what brought together an international team of marine scientists from Hong Kong, Japan, and Canada, led by Dr Bayden D Russell (Associate Director of the Swire Institute of Marine Science and Associate Professor from the School of Biological Sciences, the University of Hong Kong), including Dr Ben Harvey (University of Tsukuba), Dr Katie Marshall and Professor Christopher Harley (University of British Columbia). Together they have developed a promising new framework to allow us to understand the effects of marine heatwaves, but potentially predict their effects before they occur. 

This new method will allow researchers worldwide to identify the key biological traits of marine species in their region and predict how they are likely to be stressed by heatwaves. Most importantly, using this trait-based approach will allow managers and policy makers to identify the key species which are needed to support ecosystem function and develop strategies to help mitigate the damage caused by heatwaves.

Identifying the survivors: the future of marine ecosystems

Marine heatwaves are discrete heating events in which marine waters heat up to 6°C above normal and can last from days to months. Such high temperatures cause stress to animals and seaweeds, often killing them and in some cases driving range contractions to cooler waters. At the same time, tropical species will move into these colder waters as they warm and alter these ecosystems, sometimes irreversibly. The authors identified that key functional traits, such as heat tolerance, dispersal ability, feeding habits, and behavioural traits potentially affecting ecosystem characteristics, could be used to more accurately identify both how species will be affected by heatwaves and how this would change marine ecosystems.

According to the authors, identifying the functional traits of the resident faunal and floral assemblages is crucial for assessing the vulnerability of marine ecosystems to change and for designing effective management, conservation, and restoration plans. Until now, there has been no framework from which to predict the potential effect of marine heatwaves and prepare for their onset. This new approach allows the identification of key species which support complex ecosystems, such as seaweeds, corals, grazing fish or urchins, and to tailor management towards these species to enhance resistance to heatwaves, re-establishment after them, and ultimately support function of coastal ecosystems.

“Unlike the current approach that is used to project the impacts of marine heatwaves, the integration of trait-based approaches at multiple time scales allows us to use measurable and ecologically meaningful features of organisms, from individual physiological responses to biological interactions, to predict ecological patterns in space and time,” said Dr Bayden Russell. “We can now have a better understanding of how extreme events will drive patterns of geographic distribution, local abundance, and functional diversity of important species.”

“Using this approach will enable more targeted management of marine species to enhance community resilience under climate change,” added Dr Ben Harvey.

“Predicting responses to marine heatwaves using functional traits,” the paper describing this research by Ben P. Harvey, Katie E. Marshall, Christopher D. G. Harley, and Bayden D. Russell, was published Trends in Ecology & Evolution, published online on September 27, 2021.