Ocean Warming Is Driving a Dramatic Loss of Marine Life
Chronic ocean heating is causing a “staggering and deeply concerning” decline in marine life, according to a new study. The study found that fish populations can fall by 7.2% for every 0.1°C of ocean warming per decade, highlighting how even small temperature increases are reshaping marine ecosystems.
Scientists warn that sustained ocean warming driven by climate change is already altering fish distribution, threatening biodiversity and destabilising ocean food webs.
Major Study Tracks 33,000 Marine Populations
The research, published in the journal Nature Ecology & Evolution, analysed year-to-year changes in more than 33,000 marine populations across the northern hemisphere between 1993 and 2021.
Unlike many previous studies, researchers focused specifically on the long-term rate of seabed warming rather than short-term fluctuations such as marine heatwaves. Their findings revealed dramatic declines in marine biomass linked directly to sustained temperature increases.
“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.
“A 7.2% decline for every tenth of a degree per decade might sound small,” he added. “But compounded over time, across entire ocean basins, it represents a staggering and deeply concerning loss of marine life.”
In some cases, the loss of marine life due to chronic warming reached as much as 19.8% in a single year.
Marine Heatwaves Can Mask Long-Term Damage
The study also revealed a surprising effect: marine heatwaves can temporarily boost some fish populations, hiding the long-term impacts of climate change.
For example, during a heatwave:
- Sprat populations may decline in the Mediterranean Sea, where temperatures already sit near the upper limit of the species’ natural range.
- At the same time, the same warming event can lead to population increases in the North Sea, where cooler waters lie at the lower edge of the species’ range.
This means short-term gains in colder regions can obscure the wider loss of marine life occurring across the oceans.
Cold-Water Regions May See Short-Term Gains
Researchers found that fish species in colder waters are often better able to take advantage of warming shifts. However, these temporary increases do not compensate for the overall global decline in marine biomass caused by rising ocean temperatures.
In reality, the apparent “booms” in colder seas may simply reflect fish moving away from increasingly inhospitable warm regions.
Scientists Warn of Major Implications for Ocean Management
Experts say the findings highlight serious challenges for ocean conservation and fisheries management.
According to Carlos García‑Soto of the Spanish National Research Council, the research exposes a worrying trend that could complicate global ocean governance.
“Overall warming reduces fish biomass, while heatwaves 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 poor interpretation when taking decisions.”
Meanwhile, marine biologist Guillermo Ortuño Crespo, who works with the International Union for Conservation of Nature, described the study as “methodologically sound and highly valuable”, though he cautioned that climate change should not be seen as the only factor influencing marine biomass changes.
“Historically, overfishing has been the main driver of biomass declines in many of the world’s fisheries [and] according to the FAO [UN Food and Agriculture Organization] the proportion of overfished stocks globally continues to rise,” said Ortuño Crespo, who was not involved in the study. “The current challenge is that this overfishing crisis is being further exacerbated by ocean warming and deoxygenation.”
Why Every Fraction of a Degree Matters
Marine ecosystems are extremely sensitive to temperature changes. Rising ocean temperatures are largely driven by greenhouse gas pollution from fossil fuels, which trap heat in the atmosphere and oceans.
Scientists repeatedly stress that even small increases in global temperature can have severe ecological consequences. The world is now rapidly approaching the 1.5°C global warming threshold, a limit international leaders have pledged to stay below in order to prevent the most dangerous impacts of climate change.
“Our research proves exactly what that biological cost looks like underwater,” said Chaikin. “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.”
For marine life, the latest research shows that every fraction of a degree of warming can accelerate biodiversity loss and disrupt fragile ocean ecosystems.
At Natural World Fund, we believe protecting the ocean is essential to safeguarding the planet’s biodiversity. Rising sea temperatures are already reshaping marine ecosystems and threatening the wildlife that depends on them. By supporting conservation, reducing climate impacts, and restoring healthy seas, we can help ensure marine life has a future in a rapidly changing world.