Climate change is causing warming in the oceans, which can have significant effects on marine food webs. Rising ocean temperatures can intensify seawater stratification, a process in which ocean water forms layers of different densities that mix less readily. This can reduce the supply of nutrients to surface waters and favor smaller phytoplankton species that are better adapted to low-nutrient conditions. Phytoplankton support zooplankton, which in turn transfer energy to fish and other animals. Changes in phytoplankton communities can therefore lead to cascading effects in marine food webs.
In the western North Pacific, changes in ocean temperatures, circulation patterns, and sea-ice cover are causing changes in phytoplankton ecosystem structure. However, how contributions of different microscopic food sources to zooplankton vary across these regions, remain poorly understood.
To address this gap, a research team led by Professor Kyung-Hoon Shin from the Department of Marine Science and Convergent Technology at Hanyang University in South Korea analyzed the cosmopolitan calanoid copepod Calanus spp., a zooplankton that is a key source of food for fishes and sea birds, making it an ideal indicator of basal resource composition and nitrogen pathways. “Our objective was to quantify how nutrient sources and primary-producer communities shape zooplankton diets and nitrogen transfer pathways across the dynamic western north Pacific,” explains Prof. Shin. “To this end, we utilized a new dual-isotope approach for estimating the diet of Calanus.” Their study was made available online in Volume 12, Issue 38 of Science Advances on September 18, 2026.
The researchers sampled Calanus across the western North Pacific during summer and autumn, covering a broad region from tropical and subtropical waters, the subarctic Pacific, to the Bering Strait and southern Chukchi Sea in the Pacific Arctic Ocean. They analyzed carbon and nitrogen isotope ratios in essential amino acids from Calanus spp. tissue. These chemical signatures helped them estimate the contributions of different basal food sources and investigate the nitrogen sources supporting microalgae.
The results revealed notable geographical variations in basal diets of the copepods. In tropical and subtropical Pacific, which have strong surface stratification and low phytoplankton amounts, N2-fixing bacteria and heterotrophic bacteria accounted for 19.6 ± 5.8% and 30.6 ± 5.3%, respectively, of the basal diet. Further north, in regions of the subarctic Pacific, the contribution of N2-fixing bacteria and heterotrophic bacteria decreased, while those of eukaryotic microalgae, such as diatoms and dinoflagellates, increased. Notably, in the Bering Strait and Chukchi Sea, dinoflagellates made up more than half (54.4 ± 10.5%) of the basal diet, while the total eukaryotic microalgae contribution rose to approximately 80%.
The researchers also found that the estimated contribution of dinoflagellates was strongly correlated with the protist contribution inferred from nitrogen isotope ratios. N2 sources supporting microalgae also varied regionally: biologically fixed N2 was more dominant in the tropical Pacific, accounting for 29.2 ± 7.9% of the nitrogen source, while nitrates were the primary source in the Pacific Arctic Ocean, accounting for an estimated 91.4 ± 2.3%.
“Our results demonstrate that combining carbon and nitrogen isotope ratios in Calanus spp. is a robust framework for understanding dietary records,” remarks Prof. Shin. “Importantly, our study shows how warming-driven changes in stratification and nutrient dynamics are reshaping planktonic food webs. This will have cascading consequences for marine biodiversity, biogeochemical cycling, and ecosystem resilience.”
In summary, this study offers an innovative method to track dietary sources of zooplankton, establishing a foundation for investigating how climate change may affect marine food webs.
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Reference
DOI: 10.1126/sciadv.aed3966
About Hanyang University ERICA
Hanyang University ERICA (Education Research Industry Cluster at Ansan) is a prominent research-focused campus established in 1979 in Ansan, South Korea. ERICA offers undergraduate and graduate programs. ERICA is renowned for its active industry-university cooperation, offering students hands-on experience through partnerships with various industries. This ensures that graduates are well-prepared to meet societal needs and excel in their respective fields. With state-of-the-art facilities and a supportive learning environment, Hanyang University ERICA empowers students to pursue their passions and contribute meaningfully to society, staying true to the university's founding philosophy of "Love in Deed and Truth."
Website: https://www.hanyang.ac.kr/web/eng/erica-campus1
About the Author
Prof. Kyung-Hoon Shin is currently a Professor at the Department of Marine Science and Convergence Engineering and a Director of the Global Science Research Center for Marine Material Cycle Processes at Hanyang University. His research group is developing approaches to assess organic biogeochemical cycles and marine food web structure through compound-specific isotope technology for advanced ocean science and environmental ecology. Prof. Shin’s group is also developing lipid biomarker analytical skills and their applications for carbon cycle and nitrogen source identification in marine and environmental science. Prof. Shin has served as Vice President of the Korean Academy of Marine Science and has been a Distinguished Fellow of the Academy since 2021.
Science Advances
Observational study
Animals
Dietary records in cosmopolitan copepod Calanus spp. revealed large contribution of dinoflagellates in subarctic Pacific
18-Sep-2026
The authors declare that they have no competing interests