The diet of the copepod Calanus varies dramatically across the Pacific, with bacteria dominating in tropical waters and dinoflagellates in the Arctic.
Analysis of carbon and nitrogen isotope ratios in essential amino acids traced the copepod's diet across a broad region from tropical to Arctic waters.
In the tropical and subtropical Pacific, nitrogen-fixing and heterotrophic bacteria made up about half of the basal diet, while in the Bering Strait and Chukchi Sea, dinoflagellates accounted for more than 50 percent, with total eukaryotic microalgae reaching roughly 80 percent.
These shifts indicate that warming-driven changes in stratification and nutrient dynamics are reshaping planktonic food webs, with potential cascading effects on marine biodiversity and biogeochemical cycles.