Hanyang University ERICA Researchers Reported How a Warming Ocean Is Changing the Base of the Marine Food Web

Researchers investigate regional copepod diet differences to investigate effects of climate change on marine food webs

GYEONGGI-DO, South Korea, Nov. 12, 2026 /PRNewswire/ -- Climate change is leading to a warmer ocean, potentially affecting marine food webs. To understand these effects, researchers have developed a new approach, where they analyzed the regional variations in the diet of Calanus copepods sampled across the western North Pacific. Their result, based on isotope fingerprinting, revealed significant regional differences in basal dietary sources. This approach establishes a foundation for investigating changes in planktonic food webs.

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.

Sampling Calanus from tropical waters to the Pacific Arctic during summer and autumn, the researchers analyzed carbon and nitrogen isotope ratios in amino acids to estimate basal diets and nitrogen sources.

The results revealed notable geographical variations in basal diets of the copepods. In warmer tropical and subtropical waters with strong stratification, N₂-fixing and heterotrophic bacteria contributed 19.6 ± 5.8% and 30.6 ± 5.3% to the copepods' diet, with biologically fixed N₂ providing 29.2 ± 7.9% of microalgal nitrogen.

Moving northward into subarctic and Arctic waters, bacterial reliance dropped while eukaryotic microalgae expanded, reaching approximately 80% of basal diets in the Bering Strait and Chukchi Sea. Dinoflagellates alone accounted for 54.4 ± 10.5%, supported by 91.4 ± 2.3% nitrate-derived nitrogen.

"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.

Reference
Title of original paper: Dietary records in cosmopolitan copepod Calanus spp. revealed large contribution of dinoflagellates in subarctic Pacific
Journal: Science Advances 
DOI: 10.1126/sciadv.aed3966

Hanyang University ERICA 
Website: https://www.hanyang.ac.kr/web/eng/erica-campus1

Media Contact:
Jin-Mo An
82-31-400-4947
[email protected]

SOURCE Hanyang University ERICA