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MEPS 712:49-65 (2023)  -  DOI:

Photoperiodism and overwintering in boreal and sub-Arctic Calanus finmarchicus populations

Estelle Coguiec1,*, Kim S. Last2, Jonathan H. Cohen3, Laura Hobbs2, Marvin Choquet4,5, Elizaveta Ershova6, Jørgen Berge1,7, Malin Daase1

1Department of Arctic and Marine Biology, UiT the Arctic University of Norway, 9019 Tromsø, Norway
2The Scottish Association for Marine Science, Oban, Argyll PA37 1QA, Scotland
3School of Marine Science and Policy, University of Delaware, Lewes, Delaware 19958, USA
4Faculty of Biosciences and Aquaculture, Nord University, Bodø, Norway
5Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden
6Institute for Marine Research, Bergen, Norway
7Centre for Autonomous Marine Operations and System (AMOS), Department of Biology, Norwegian University of Science and Technology, NTNU, Trondheim, Norway
*Corresponding author:

ABSTRACT: The copepod Calanus finmarchicus, a key species in the North Atlantic, generally spends the non-productive season by descending into deep waters and entering diapause, a physiological state characterized by reduced metabolism and arrested development. In the open ocean, overwintering depths are below 600 m, where temperature and light conditions are favourable to initiate diapause. However, C. finmarchicus has also been reported diapausing in areas with shallow water depth such as fjords, coastal waters and shelf seas. In these environments, the temperature and light conditions are different, and it has been hypothesized that under such conditions C. finmarchicus may remain active throughout winter. Here, we investigated changes in the swimming activity of C. finmarchicus from shallow fjords in the eastern North Atlantic during overwintering in response to ambient photoperiod. We conducted monthly experiments with populations from 2 fjords from different latitudes (sub-Arctic Ramfjord, 69°N and boreal Loch Etive, 56°N), measuring the locomotor activity of individual C. finmarchicus stage CVs exposed to a natural light:dark cycle. At both locations, peaks in activity in response to the light cycle were observed to shift from nocturnal during the early overwintering phase to diurnal during mid and late overwintering phase, with a minimal intensity observed during the mid-overwintering phase. In Ramfjord, activity and rhythmicity were generally lower than in Loch Etive. We conclude that C. finmarchicus remains active throughout its overwintering period when in shallow (<200 m) locations but down-regulates its locomotor activity during the main overwintering phase, which we describe as a winter resting state as distinct from classical diapause.

KEY WORDS: Locomotor activity · Latitudinal seasonality · Lipid · Overwintering · Zooplankton

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Cite this article as: Coguiec E, Last KS, Cohen JH, Hobbs L and others (2023) Photoperiodism and overwintering in boreal and sub-Arctic Calanus finmarchicus populations. Mar Ecol Prog Ser 712:49-65.

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