Trophic Dynamics of Calanus hyperboreus in the Pacific Arctic Ocean

• Published in: Journal of geophysical research. Oceans 2021-03, Vol.126 (3), p.n/a
• Main Authors: Choi, Hyuntae, Won, Haemin, Kim, Jee‐Hoon, Yang, Eun Jin, Cho, Kyoung‐Ho, Lee, Youngju, Kang, Sung‐Ho, Shin, Kyung‐Hoon
• Format: Article
• Language: English
• Subjects: Abundance; amino acid; Amino acid composition; Amino acids; Aquatic crustaceans; Calanus hyperboreus; Chemical analysis; Chlorophyll; Chlorophylls; Community composition; Composition; Diatoms; Diet; Dynamics; Fatty acid composition; Fatty acids; Food chains; Food webs; Freshwater; Geophysics; Hydrodynamics; Inflow; Inland water environment; Isotope ratios; Isotopes; Marine microorganisms; Markers; Meltwater; Nitrogen; Nitrogen isotopes; Oceans; Pacific Arctic; Phytoplankton; Plankton; Sea ice; Sea ice concentrations; Seawater; stable isotope; Stratification; Summer; trophic level; Trophic levels; Water analysis; Water inflow; Water purification; Zooplankton
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2020JC017063

The zooplankton community composition in the Pacific Arctic Ocean depends heavily on the sea ice and hydrodynamic conditions. The calanoid copepod Calanus hyperboreus is a dominant Arctic zooplankton, but its diet sources in the Pacific Arctic are unclear. C. hyperboreus individuals were collected in the northern Chukchi Sea (NCS) and the northern‐East Siberian Sea (NESS), which display contrasting chlorophyll abundance and sea ice concentration in summer 2018. Nitrogen isotopes of individual amino acid and fatty acid compositions were measured to determine its trophic level (TL) and dominant diet. C. hyperboreus collected in the NCS had higher TL values (3.0 ± 0.2) and a relatively low proportion of C20:5(n‐3). In the NESS, C. hyperboreus had lower TL values (2.7 ± 0.2) and a larger percentage of C20:5(n‐3), suggesting a greater proportion of diatoms in its diet. Spatial TL variations of C. hyperboreus between the NCS and NESS may be caused by variations in phytoplankton composition (micro‐phytoplankton vs. nano‐ and picophytoplankton) as a result of surface seawater stratification triggered by the inflow of sea ice meltwater as well as summer Bering Sea water through the Bering Strait. These results suggest that the filter‐feeding copepod C. hyperboreus could be a useful indicator to understand trophic dynamics in zooplankton food web. Plain Language Summary The Pacific region of the Arctic Ocean experiences different annual volumes of freshwater inflow, resulting in changes to its water‐mass structure. In 2018, we harvested Calanus hyperboreus, a dominant Arctic zooplankton, from the northern Chukchi Sea (NCS) and northern‐East Siberian Sea (NESS). Sea ice concentrations and phytoplankton abundance varied between the regions. We analyzed the fatty acid composition and amino acid nitrogen isotope ratios to determine its diet sources and trophic dynamics, respectively. We found that C. hyperboreus collected in the NCS occupied higher trophic levels and had a low proportion of diatom‐marker fatty acids. In contrast, in the NESS, C. hyperboreus occupied lower trophic levels and had a larger percentage of diatom‐marker fatty acids, suggesting diatom accounted for a large portion of its diet in the NESS compared with the NCS. Analysis of amino acid nitrogen isotope and fatty acid composition of C. hyperboreus revealed a shift in trophic levels and diets, respectively. Key Points The trophic level of Calanus hyperboreus was correlated with the proportion of fa