Environmental effects on Calanus finmarchicus abundance and depth distribution in the Barents Sea

Kristina Ø Kvile,Leif C Stige,Irina P Prokopchuk,David Fields

doi:10.1093/icesjms/fsab133

Abstract

Abstract The vertical migrations performed by zooplankton at daily and seasonal scales are important for marine ecosystem dynamics and biogeochemical cycles. We analysed associations between seasonal variation in abundance and depth distribution of the copepod Calanus finmarchicus and temperature and predation pressure from visual (capelin and herring) and non-visual (ctenophores) predators, using data from a &gt; 30-year survey in the southwestern Barents Sea. Calanus finmarchicus abundances were significantly reduced in upper waters with increased capelin biomass, possibly due to a combination of predation mortality and active avoidance of the upper layer. The weighted mean depth of Calanus finmarchicus tended to become shallower, and abundances in deeper layers lower, with a high probability of ctenophore occurrence, possibly due to a predation effect at depth. Temperature influenced the seasonal timing of Calanus finmarchicus, but appeared less important for depth distribution. This study illustrates how climate-driven changes in the physical and biological environment can influence the seasonal and vertical distribution of zooplankton, which has major implications for the flow of energy and nutrients in marine ecosystems.

Highlights

Zooplankton are aquatic animals that spend their lives in the pelagic zone and drift with currents
We revisited a historical dataset of Calanus finmarchicus abundances collected from 1959 to 1992 in the southwestern Barents Sea, and assessed associations between the species’ depth distribution and indices representing inter-annual variation in temperature and predation pressure from visual
The survey data showed that early copepodites were most abundant in the upper layer, which is expected and in accordance with previous studies as these are actively feeding stages (Dale and Kaartvedt, 2000; Daase et al, 2008)

Summary

Introduction

Zooplankton are aquatic animals that spend their lives in the pelagic zone and drift with currents. The copepod Calanus finmarchicus, the dominant mesozooplankter in the North Atlantic Ocean and adjacent subarctic shelf seas, performs large-scale vertical migrations on diel and seasonal scales (Kashkin, 1962; Melle et al, 2014). Such vertical migrations are important for the food availability for predators, which may modify their behaviour in response to the prey’s vertical movement (Hays, 2003; Baumgartner et al, 2011); the drift of zooplankton with ocean currents (Johnson and Checkley, 2004; Johnson et al, 2006); and the transport and recycling of nutrients (Steinberg et al, 2002). Considerable variability in DVM behaviour was observed in the

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Conclusion