Bottom-dwelling fish may be less affected by climate change than previously thought, according to a new study.
Older studies connected prolonged periods of warm ocean temperatures to widespread destruction of coral networks, along with massive extinction of reef fish and kelp forests. In other well-documented cases, evidence was found that marine heat waves were responsible for displacing or killing marine life, from plankton to commercially valuable fish stocks.
The earlier results led the research team to expect a similar pattern being repeated again, but most of the heat waves had little discernible effect on sea life.
Recent heat waves have caused ocean temperatures to rise over the summer, but no evidence was found that extreme heat drove colder water fish toward the poles, while many key commercial fisheries were found to be more resilient to heat than had been previously thought.
Study Results Surprise Climate Scientists
An international group of over a dozen researchers analyzed 248 sea bottom heat waves from 1993 to 2019, which included over 80,000 samples taken along the continental shelves of North America and Europe.
The research team reviewed studies of bottom dwelling fish, such as North Atlantic cod and pollock from that period, and compared the data with the water temperature in the preceding months.
Juliano Palacios-Abrantes, a post-doctoral fellow at the University of British Columbia’s Institute for the Oceans and Fisheries and an author of the study, noted that the findings countered previous research on the subject.
Bottom dwelling species like flounder, halibut, rockfish, and the five species of Pacific salmon were found to be generally resilient to higher temperatures for the most part.
This suggests that the ocean may be less vulnerable to some of the effects of warmer temperatures than was previously feared, but that every increase in temperatures was a roll of the dice, according to the scientists.
William Cheung, director of UBC’s Ocean Sustainability and Global Change Institute and another study co-author, told the Times Colonist he was surprised by the results.
He said the data showed that the impact of heat waves on fish was more complex and sporadic than once previously thought and that “in some cases, it has big impacts.”
Mr. Cheung referred to a deadly ocean heat wave known as “The Blob,” which killed 22 percent of biomass off the coast of British Columbia and Alaska between 2014 and 2016.
Fisheries Less Affected by Temperatures
Another author of the report, Malin Pinsky, a biologist at the University of California Santa Cruz, told The Times that “what we find is good news in many ways.”
“We find that fishes, many of which support our most productive fisheries around the world, are more resilient than we previously thought to these heatwaves … many of these are the species that show up on our plates, the bottom-dwelling fishes near our coast,” he said.
“These results really surprised us. We expected that large heatwaves would have clear and large impacts. But that’s not what the data told us, and that’s what we’re reporting. That’s what makes science so interesting, the surprise.”
It is still unknown how bottom dwelling populations survived multiple heat waves without much damage and why they were tougher than had been previously thought.
One theory is that the fish either dove down to cooler depths or escaped by swimming into cooler waters in a search for a climate refuge.
“When ‘The Blob’ happened in the North Pacific, you have reports of species being like kilometers away from where they were ever seen before,” said Mr. Palacios-Abrantes.
He said that many of the previous studies which looked at the impact of marine heat waves may have been too focused on the extremes.
The research team said that the study needed to be expanded to the waters of the Southern Hemisphere, which were mainly left out of the analysis, and finally clarify the results of the recent findings off the waters of North America and Europe.
Species living closer to the surface, such as coral reefs and their local ecosystems, were not included in the study.
The scientists said that a study of deeper-dwelling fish would be next and admitted that their historical analysis still failed to reflect how fish would survive future heat waves.