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 a new study published in Nature Ecology & Evolution. The research reveals that fish levels fall by 7.2% with as little as 0.1C of warming per decade, based on an analysis of 33,000 populations in the northern hemisphere between 1993 and 2021.
Key Findings on Seabed Warming and Fish Biomass
Researchers isolated the effect of the decadal rate of seabed warming from short-term shifts like marine heatwaves. They found that the drop in biomass from chronic heating can reach as high as 19.8% in a single year. Shahar Chaikin, a marine ecologist at the National Museum of Natural Sciences in Spain and the study's lead author, stated, "To put it simply, the faster the ocean floor warms, the faster we lose fish."
Chaikin emphasized that while a 7.2% decline per tenth of a degree per decade might sound small, it compounds over time and across entire ocean basins, representing a significant loss of marine life. The study also uncovered that marine heatwaves lead to short-term booms in some populations, which mask the long-term harm from climate breakdown.
Impact of Marine Heatwaves and Regional Variations
For example, a heatwave could cause sprat populations to fall in the Mediterranean Sea, at the warm edge of their natural range, while leading to a boom in the North Sea, at the cold edge. Fish in cold areas are better able to capitalize on these shifts than those in warm areas, but these temporary gains hide the "widespread loss" due to ocean warming.
Carlos García-Soto, a scientist at the Spanish National Research Council and co-author of the UN's world ocean assessment, noted that the study reveals a "concerning" dynamic for ocean governance. He explained, "Overall warming reduces fish biomass, while heatwaves can generate temporary increases that mask the underlying trend. This combination introduces a clear risk of poor interpretation when taking decisions."
Challenges from Overfishing and Climate Change
Guillermo Ortuño Crespo, a marine biologist who co-directs a high seas specialist group with the International Union for Conservation of Nature, praised the study as "methodologically sound and highly valuable" but cautioned against attributing biomass changes solely to climate breakdown. He pointed out that historically, overfishing has been the main driver of declines in many fisheries, and according to the UN Food and Agriculture Organization, the proportion of overfished stocks globally continues to rise.
Ortuño Crespo added, "The current challenge is that this overfishing crisis is being further exacerbated by ocean warming and deoxygenation." Marine life is extremely vulnerable to temperature shifts caused by fossil fuel pollution, with scientists warning that "every fraction of a degree matters" as global temperatures approach the 1.5C threshold.
Implications for Future Ocean Management
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." This study underscores the urgent need for integrated strategies to address both climate change and overfishing to protect marine biodiversity.
