MEPS 674:73-88 (2021)  -  DOI: https://doi.org/10.3354/meps13820

ABSTRACT: In the eastern Bering Sea, lipid-rich copepods in the genus Calanus help to sustain productive fisheries and efficient energy flow through the ecosystem. In summer and autumn, Calanus populations consist primarily of stage C5 copepodites that are storing lipids and preparing for dormancy (diapause). We collected Calanus C5 copepodites from the eastern Bering Sea shelf in early autumn of 2015 and examined whether Calanus species composition, morphometric characteristics, and lipid-related gene expression varied along a north-south gradient. The sampled area exhibited marked differences in temperature, chl a, and Calanus abundance. However, the Calanus population was surprisingly homogeneous, composed almost entirely of C. glacialis, with no evidence for latitudinal trends in prosome size, oil sac fullness, or lipid-related gene expression. Rather than a latitudinal gradient, we found that C. glacialis from 1 southern station near the Pribilof Islands were larger and exhibited lower oil sac fullness and higher expression of lipid storage genes. Gene expression changes across stations were small relative to large shifts associated with shipboard feeding experiments. The similar characteristics of C. glacialis across stations imply that most of the C5 copepodites had experienced favorable growth conditions regardless of their latitudinal location. It remains unknown how environmental conditions affect C. glacialis physiology during other parts of their life cycle or how patterns vary among years. Continued studies of C. glacialis distribution, morphometrics, and gene expression could address these questions and serve as a harbinger for responses to future climatic changes.

KEY WORDS: Bering Sea · Calanus · Copepod · Lipid · Diapause · Genetics · Metabolism