Chronic Ocean Heating Fuels 'Staggering' Loss of Marine Life, Study Finds
Chronic ocean heating is driving a "staggering and deeply concerning" decline in marine life, according to new research. The study reveals that fish levels fall by 7.2% with as little as 0.1 degrees Celsius of warming per decade, based on data from the northern hemisphere.
Research Methodology and Key Findings
Researchers analysed year-to-year changes across 33,000 marine populations between 1993 and 2021, isolating the effect of seabed warming from short-term events like marine heatwaves. They discovered that chronic heating can cause biomass drops as high as 19.8% in a single year, underscoring the severe impact of sustained temperature rises.
"To put it simply, the faster the ocean floor warms, the faster we lose fish," said Shahar Chaikin, a marine ecologist at the National Museum of Natural Sciences in Spain and the study's lead author. He emphasised that while a 7.2% decline per tenth of a degree might seem small, it compounds over time and across ocean basins, representing a significant loss of biodiversity.
Masking Effects of Marine Heatwaves
The study, published in Nature Ecology & Evolution, also found that marine heatwaves can create short-term population booms in some areas, masking the long-term harm from climate breakdown. For example, a heatwave might reduce sprat populations in the warmer Mediterranean Sea while causing a boom in the colder North Sea, where fish are better able to capitalise on temperature shifts.
Carlos García-Soto, a scientist at the Spanish National Research Council and co-author of the UN's world ocean assessment, noted that this dynamic poses risks for ocean governance. "Overall warming reduces fish biomass, while heatwaves can generate temporary increases that mask the underlying trend," he said, warning of potential misinterpretation in decision-making.
Overfishing and Climate Change Interplay
Guillermo Ortuño Crespo, a marine biologist with the International Union for Conservation of Nature, praised the study as methodologically sound but cautioned against attributing biomass changes solely to climate breakdown. He highlighted that overfishing remains a primary driver of declines in global fisheries, with the UN Food and Agriculture Organization reporting rising overfished stocks. "The current challenge is that this overfishing crisis is being further exacerbated by ocean warming and deoxygenation," he added.
Vulnerability and Future Implications
Marine life is highly vulnerable to temperature shifts caused by fossil fuel pollution, with scientists repeatedly stressing that every fraction of a degree matters as global temperatures approach the 1.5C threshold. Chaikin concluded, "Our research proves exactly what that biological cost looks like underwater. If we allow the pace of ocean warming to speed up by even a 10th of a degree per decade, we are expecting great losses to global fish populations that no management plan can easily fix."
