Abstract
The traditional view is that the Arctic polar night is a quiescent period for marine life, but recent reports of high levels of feeding and reproduction in both pelagic and benthic taxa have challenged this. We examined the zooplankton community present in Svalbard fjords, coastal waters, and the shelf break north of Svalbard, during the polar night. We focused on the population structure of abundant copepods (Calanus finmarchicus, Calanus glacialis, Metridia longa, Oithona similis, Pseudocalanus spp., Microcalanus spp., and Microsetella norvegica) sampled using 64-µm mesh nets. Numerically, copepod nauplii (≥ 50%) and the young developmental stages of small copepods (< 2 mm prosome length as adult) dominated the samples. Three main patterns were identified: (1) large Calanus spp. were predominantly older copepodids CIV–CV, while (2) the small harpacticoid M. norvegica were adults. (3) For other species, all copepodid stages were present. Older copepodids and adults dominated populations of O. similis, Pseudocalanus spp. and M. longa. In Microcalanus spp., high proportion of young copepodids CI–CIII indicated active winter recruitment. We discuss the notion of winter as a developing and reproductive period for small copepods in light of observed age structures, presence of nauplii, and previous knowledge about the species. Lower predation risks during winter may, in part, explain why this season could be beneficial as a period for development. Winter may be a key season for development of small, omnivorous copepods in the Arctic, whereas large copepods such as Calanus spp. seems to be reliant on spring and summer for reproduction and development.
Highlights
Polar environments are characterized by extremes in light conditions, ranging from periods of midnight sun to periods when the sun does not rise above the horizon
Based on copepodid stage composition, we identified three main population structures among the seven dominant copepod species present: (1) populations dominated by near mature stages, copepodid stages CIV and CV (Calanus spp.), (2) populations dominated by adults (M. norvegica), and (3) populations with all copepodid stages present (M. longa, Pseudocalanus spp., Microcalanus spp., and O. similis)
We studied the zooplankton communities of the western Barents Sea and fjords around Svalbard in January during the Arctic polar night and focused on the age structure of the seven most abundant small and large copepod species
Summary
Polar environments are characterized by extremes in light conditions, ranging from periods of midnight sun (polar day) to periods when the sun does not rise above the horizon (polar night). Studies of zooplankton communities during the Arctic polar night have usually been carried out using acoustic instruments (e.g., Berge et al 2009; Darnis et al 2017) or nets with mesh size ≥ 180 μm (e.g., Hirche and Kosobokova 2011; Daase et al 2014, 2018; Webster et al 2015; Kosobokova and Hirche 2016) These gears detect large zooplankton, but small-sized taxa and young small life stages are underrepresented or go undetected (Nichols and Thompson 1991; Nielsen and Andersen 2002; Svensen et al 2019). Knowledge about the small species and life-stage compositions of zooplankton communities in the Arctic during winter is limited (but see Ussing 1938; Digby 1954; Lischka and Hagen 2005, 2016; Arendt et al 2013; Grenvald et al 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
