Chronic ocean heating fuels ‘staggering’ loss of marine life, study finds | Marine life
Chronic warming of the oceans is fueling a “staggering and deeply concerning” loss of marine life, a study finds, with fish levels falling by 7.2% from warming as little as 0.1C per decade.
The researchers examined the annual change in 33,000 populations in the Northern Hemisphere between 1993 and 2021 and isolated the effect of the decadal rate of seafloor warming from short periods such as marine heatwaves. They found that the decline in biomass due to chronic heating reached 19.8% in a single year.
“To put it simply, the faster the ocean floor warms, the faster we lose fish,” said Shahar Chaikin, a marine ecologist at Spain’s National Museum of Natural Sciences and lead author of the study.
“A drop of 7.2% for every tenth of a degree per decade may seem minimal,” he added. “But, compounded over time and across entire ocean basins, this situation represents a staggering and deeply concerning loss of marine life. »
The study, published Wednesday in Nature Ecology & Evolution, also found that marine heat waves caused short-term booms in some populations, masking long-term damage from climate change.
For example, a heatwave that could lead to a decline in sprat populations in the Mediterranean Sea, located at the warm edge of their natural range, would lead to a boom in the North Sea, at the cold edge of their range.
Fish in cold areas are better able to take advantage of these changes than those in warm areas, the researchers found, but these temporary gains in cold water mask a “widespread loss” from ocean warming.
Carlos García-Soto, a scientist at Spain’s National Research Council and co-author of the UN’s global ocean assessment, said the study revealed “worrying” dynamics for ocean governance.
“Global warming reduces fish biomass, while heat waves can generate temporary increases that mask the underlying trend,” said García-Soto, who was not involved in the study. “This combination introduces a clear risk of misinterpretation when making decisions.”
Guillermo Ortuño Crespo, a marine biologist who co-leads a group of deep-sea specialists with the International Union for Conservation of Nature, said the study was “methodologically sound and very valuable” but cautioned against making climate disruption the main explanation for biomass changes in marine species.
“Historically, overfishing has been the main driver of biomass decline in many global fisheries. [and] according to FAO [UN Food and Agriculture Organization] “The proportion of overexploited stocks globally continues to increase,” said Ortuño Crespo, who was not involved in the study. “The current challenge is that this overfishing crisis is further exacerbated by ocean warming and deoxygenation.”
Marine life is extremely vulnerable to temperature changes caused by fossil fuel pollution that clogs the atmosphere. Scientists have repeatedly warned that “every fraction of a degree counts” as temperatures inch dangerously close to the 1.5C threshold at which world leaders have promised to limit global warming by the end of the century.
“Our research proves exactly what this biological cost looks like underwater,” Chaikin said. “If we allow the rate of ocean warming to accelerate by even a tenth of a degree per decade, we expect great losses to global fish populations that no management plan can easily repair. »
