New research published in the journal Nature finds that despite the devastating impact marine heatwaves may have on marine ecosystems, in general heatwaves have not had lasting effects on ocean waters that are home to many of the world’s most robust fisheries.
The study by a team of researchers funded through FISHGLOB, an international consortium of scientists who collect, curate, share and use date from scientific bottom trawl surveys, looked at how fish biomass and community composition were affected in the year following a marine heatwave. Researchers discovered that in general, marine heatwaves don’t have a major impact on regional fish communities.
“This is the year of marine heatwaves, which now cover nearly half of the world’s oceans,” said Malin Pinsky, a co-author and associate professor of the Department of Ecology and Evolutionary Biology at the University of California Santa Cruz. “Past heatwaves have been tied to mass die offs of ocean life and economic disasters costing billions of dollars. Our paper is the first comprehensive test of heatwave impacts on the ecosystems most important to global fisheries and blue food security.”
In stark contrast to the current concern about heatwaves, “our analysis reveals a silent majority of heatwaves that had no or even positive impacts on these ecosystems,” Pinsky said. “While this ocean resilience is good news, it also means that negative impacts are unpredictable. Each heatwave that hits is like rolling the dice: will it be a bad one or not? We don’t know until it happens, and this uncertainty is difficult for fisheries and coastal economies.”
Pinsky said that to reach the conclusions, researchers assessed the impacts of 248 marine heatwaves along the coasts of North America and Europe from 1993 to 2019, using 82,322 samples from scientific surveys of marine fishes.
“There is an emerging sense that the oceans do have some resilience, and while they are changing in response to climate change, we don’t see evidence that marine heatwaves are wiping out fisheries,” noted lead author Alexa Fredston, an assistant professor of ocean science at University of California, Santa Cruz.
“The oceans are highly variable, and fish populations vary quite a lot. Against that background, we didn’t see evidence of marine heatwaves dramatically reducing the abundance of fish in the temperate oceans,” Fredston said. “Marine heatwaves can drive local change, but there have been hundreds of marine heatwaves with no lasting impacts.”
Researchers also studied whether marine heatwaves were resulting in loss of species associated with cold water and an increase in species associated with warm water, something known as “tropicalization.” Fredston said that while topicalization has been associated with long-term warming of oceans they saw no consistent signature of that associated with marine heatwaves.