Abstract
The cyclopoid copepod Oithona similis is one of the most abundant copepods in the oceans and has a potentially important role in pelagic food webs. However, there is a lack of knowledge on aspects of its biology and function in planktonic communities. In the present study, we aimed to assess and compare the species' trophic role in Greenlandic coastal waters during the winter-spring transition, with a focus on its winter behaviour, when large calanoids are not pres- ent in the surface layer. Two locations were studied: waters offshore from Godthabsfjord (Nuuk) in winter, and Qeqertarsuaq (Disko Bay) in spring (bloom and post-bloom period). The potential prey of adult females of O. similis was quantified, and grazing experiments were conducted to determine the feeding rates of adult females on phytoplankton and protozooplankton >10 μm. The abundance, stage composition, and egg production of O. similis was also investigated. Ciliates were the preferred prey for O. similis, which confirms its importance as a link between the micro- bial food web and higher trophic levels. We observed high egg production rates and efficiencies of O. similis in winter, confirming that it is active and successfully reproductive in food-limited winter conditions. Our results stress that O. similis is a key component of Arctic and subarctic mar- ine communities throughout the year.
Highlights
Most studies on copepods carried out in Arctic and subarctic seas have focused on large calanoid species, such as Calanus spp
The very low chlorophyll a concentrations found (Table 1), with a uniform distribution in the upper 100 m, indicated winter conditions, a situation confirmed by the low diatom concentrations (Fig. 3)
In Disko Bay, the structure of the water column was completely different during the spring bloom and post-bloom
Summary
Most studies on copepods carried out in Arctic and subarctic seas have focused on large calanoid species, such as Calanus spp. Recent investigations have shown the relevance of small copepods in the Arctic (Auel & Hagen 2002, Hopcroft et al 2005, Svensen et al 2011). Despite their size, these copepods are important in terms of abundance, biomass, and production, especially in coastal waters and fjord systems of the northern hemisphere (Nielsen & Andersen 2002, Lischka & Hagen 2005, Arendt et al 2010). From an abundance point of view, small copepods often outnumber larger species (Møller et al 2006, Madsen et al 2008), and in contrast to large calanoids, which spend winter in diapause (Conover 1988, Conover & Siferd 1993), small copepods can be present yearround in polar seas (Ward & Hirst 2007, Dvoretsky & Dvoretsky 2009a).
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