Climate change could lead to a decline in omega-3 fats and higher toxin levels in ocean fish, according to a report on the Nautilus website.

Although it had been documented that global warming was causing ocean fish populations to decline, research suggested it might also influence the make-up of fish bodies, the 26 May report said.

By transforming ocean food webs, warmer temperatures could change the amount of minerals and fats that fish get through their diet, potentially affecting their metabolism and ability to excrete toxic substances, Nautilus wrote.

The research – still in the early stages – indicated these changes could lead to a decline in omega-3 fats and higher toxin levels in certain fish species and other kinds of seafood.

As seafood is a key source of protein, omega-3 fats and key minerals such as zinc and iron – providing nourishment to more than 3bn people worldwide – this could have major effects on human health, the report said.

“The potential implications for global nutrient security could be quite large,” Tanika Shalders, a marine scientist at Australia’s National Marine Science Centre at Southern Cross University, was quoted as saying.

The decline in omega-3 fats begins at the bottom of the food web, where marine algae called phytoplankton synthesise two types of fatty acids to build their cell membranes. At cooler temperatures, phytoplankton tend to produce more unsaturated fatty acids such as omega-3s, as they create more flexible membranes that do not freeze up, aquaculture nutrition specialist Stefanie Colombo of Dalhousie University explained.

At warmer temperatures, production shifts to saturated fatty acids that are stiffer and provide more structure. This meant that, as the ocean warmed, phytoplankton would make less healthy omega-3 fats.

In a study conducted in 2016 by Colombo and colleagues, a computer model predicted that global phytoplankton production of docosahexaenoic acid (DHA) – a type of omega-3 – could decline by almost 28% by the end of the century if ocean surface temperatures warmed by 2.5°C, a figure well within the range of current climate trajectories.

That was a concern due to the fact “all other organisms are basically getting their DHA from … phytoplankton as it gets passed through the food chain,” Colombo said.

Oceanic fish rely mainly on plankton to get their DHA – which explains why fish in cooler regions tend to have more omega-3s than tropical species – and fish are our main dietary source of DHA. This fatty acid is one of the most important omega-3s for human health and is linked to a range of benefits, including lower blood pressure, reduced inflammation, and lower risks of dying from heart disease, according to the report.

The global availability of DHA in fish could decline by 10%-58% by 2100, depending on global warming, according to forecasts by Colombo and her colleagues.

Further research was needed to understand the scale of future DHA declines, Colombo added.

To avoid omega-3 deficits, the aquaculture industry was making efforts to make farmed fish more nutritious by feeding them with DHA-rich algae grown on land, although many lower-income countries might not have the resources to do that at the necessary scale, the report said.