From nutrient-rich to energy-dense but less nourishing—climate change is transforming the composition of ocean food at its source.
Climate change could fundamentally alter the nutritional foundation of the ocean, with new research suggesting that warming waters may turn phytoplankton—the base of the marine food web—into a form of “fast food” with reduced nutritional value.
A study by researchers at the Massachusetts Institute of Technology (MIT), published in Nature Climate Change, finds that rising ocean temperatures could shift phytoplankton composition from protein-rich to carbohydrate-heavy, particularly in polar regions. This transformation could have cascading effects across marine ecosystems and ultimately impact human food systems.
A Shift at the Base of the Food Chain
Phytoplankton are microscopic, plant-like organisms that form the primary food source for a wide range of marine life, including krill, small fish, and jellyfish. These organisms, in turn, sustain larger species and top predators, including humans.
The study suggests that under continued greenhouse gas emissions through 2100, ocean warming will significantly alter the nutritional profile of these organisms. According to the researchers’ model, phytoplankton in polar regions could shift their balance of proteins to carbohydrates and lipids by approximately 20 percent.
“We’re moving in the poles toward a sort of fast-food ocean,” said lead author Shlomit Sharoni, an MIT postdoctoral researcher, in a media statement. “Based on this prediction, the nutritional composition of the surface ocean will look very different by the end of the century.”
Why Nutritional Composition Matters
While previous research has largely focused on how climate change affects phytoplankton populations, this study highlights a less explored dimension: their internal composition.
“There’s been an awareness that the nutritional value of phytoplankton can shift with climate change,” Sharoni said in a media statement, “But there has been very little work in directly addressing that question.”
Phytoplankton are composed of essential macromolecules such as proteins, carbohydrates, and lipids. These components determine their nutritional value for the organisms that consume them. Any imbalance at this foundational level can ripple through the entire food chain.
“Nearly all the material in a living organism is in these broad molecular forms, each having a particular physiological function, depending on the circumstances that the organism finds itself in,” said Mick Follows, professor at MIT.
Warming Oceans, Changing Chemistry
Using a combination of laboratory data and advanced ocean models, the researchers simulated how phytoplankton respond to changing environmental conditions such as temperature, light, and nutrient availability.
Under current conditions, phytoplankton cells are composed of slightly more than 50 percent protein. However, in future climate scenarios where global temperatures rise by around 3°C, this balance shifts significantly.
In polar regions, reduced sea ice allows more sunlight to penetrate the ocean surface, decreasing the need for light-harvesting proteins. At the same time, warmer temperatures and reduced ocean circulation limit the availability of nutrients such as nitrogen and iron.
As a result, protein levels in phytoplankton could decline by up to 30 percent, while carbohydrates and lipids increase.
Uneven Global Impacts
The effects of this shift are not uniform across the globe.
While phytoplankton populations in polar regions may increase, their nutritional quality is expected to decline. In contrast, subtropical regions could see a reduction in phytoplankton populations by up to 50 percent due to reduced nutrient availability.
In these regions, phytoplankton may adapt by moving to deeper waters, where they can access both light and nutrients, potentially increasing their protein content slightly.
Overall, however, the global trend points toward a more carbohydrate-heavy and less nutrient-dense ocean ecosystem.
Early Signs Already Visible
The researchers compared their model with real-world observations from Arctic and Antarctic regions. The findings indicate that this shift is already underway.
“In these regions, you can already see climate change, because sea ice is already melting,” Sharoni said in a statement. “And our model shows that proteins in polar plankton have been declining, while carbs and lipids are increasing.”
Follows added that the implications extend beyond marine ecosystems.
“It turns out that climate change is accelerated in the Arctic, and we have data showing that the composition of phytoplankton has already responded,” he said in a media statement. “The main message is: The caloric content at the base of the marine food web is already changing. And it’s not a clear story as to how this change will transmit through the food web.”
Implications for Marine Life and Humans
The long-term consequences of this shift remain uncertain. Some species may struggle with reduced protein availability, while others that rely on lipid storage could adapt more easily.
However, scientists warn that any disruption at the base of the marine food chain could have far-reaching impacts on biodiversity, fisheries, and global food security.
As the study highlights, climate change is not only altering how much food the ocean produces—but also how nutritious that food is.