Review of 489 experiments finds omega-3 in fish could fall 50% under warming above 10°C

What the review found

The review collected and analysed data from 489 experiments involving 132 marine species, including algae, invertebrates and fish. It grouped warming into low (0 to 6°C), medium (6 to 10°C) and high (more than 10°C).

Warming of 0 to 6°C, which can already happen during marine heatwaves, led to 19% lower omega-3 fatty acids in fish in experiments lasting between 24 hours and six months. That does not include the additional warming impact on the nutritional quality of food fish eat, which the study suggests would happen in the wild.

Under high warming of more than 10°C, omega-3 fell by 50% in fish, 34% in algae and 51% in invertebrates. Levels of saturated fats increased by up to 22%. Separately, the review notes that ocean temperatures could rise by 4.1°C by 2100. Since 1980, ocean temperatures have risen by 0.6°C and the number of heatwaves has doubled, the authors wrote.

The review explains the mechanism: warmer water makes cell membranes more fluid, so organisms replace omega-3s with more rigid saturated fats to stabilise them, a process called homeoviscous adaptation. It also found ocean acidification had less impact on fatty acids than warming, suggesting rising temperature is the dominant driver.

Why the loss matters

Seafood is the main source of EPA and DHA for most people, the authors wrote in The Conversation. The body can also make them from ALA, an omega-3 fat found in plants such as linseed and walnuts. EPA and DHA support brain, eye and heart development, reduce chronic inflammation and can reduce the risk of premature births. The authors wrote that these fatty acids are foundational for biological processes in marine organisms and terrestrial vertebrates and are critical for human health.

Marine algae, including seaweeds and diatoms, are among the only forms of life that produce EPA and DHA. Algae form the base of marine food webs and are sources of micronutrients to all animals. Invertebrates such as crabs and starfish obtain EPA and DHA when they eat marine algae. The fats then pass to fish and eventually to people. If the fats are disrupted at any link, less reaches the animals higher up, including humans.

The authors also note that people in tropical regions often have poorer-quality diets and do not consume enough of these omega-3 fats, while people in developed countries are also not eating enough. The problem will be harder to solve if climate change reduces omega-3 in seafood, especially as fish stocks are already under pressure from overfishing and other human impacts.

What the authors say should change

The authors write that experts have called for urgent cuts to greenhouse gas emissions to limit the worst of climate change. They argue the findings can inform fisheries management, aquaculture and public health policy aimed at securing future supplies of these micronutrients. On waste, they note that food processing throws out up to 80% of fish parts. That material could become omega-3 fish oil or aquaculture feed instead.