Characterisation of large zooplankton sampled with two different gears during midwinter in Rijpfjorden, Svalbard

Abstract

During a midwinter cruise north of 80 o N to Rijpfjorden, Svalbard, the composition and vertical distribution of the zooplankton community were studied using two different samplers 1) a vertically hauled multiple plankton sampler (MPS; mouth area 0.25 m², mesh size 200 μm) and 2) a horizontally towed Methot Isaacs Kidd trawl (MIK; mouth area 3.14 m², mesh size 1500 μm). Our results revealed substantially higher species diversity (49 taxa) than if a single sampler (MPS: 38 taxa, MIK: 28) had been used. The youngest stage present (CIII) of Calanus spp. (including C. finmarchicus and C. glacialis) was sampled exclusively by the MPS, and the frequency of CIV copepodites in MPS was double that than in MIK samples. In contrast, catches of the CV-CVI copepodites of Calanus spp. were substantially higher in the MIK samples (3-fold and 5-fold higher for adult males and females, respectively). The MIK sampling clearly showed that the highest abundances of all three Thysanoessa spp. were in the upper layers, although there was a tendency for the larger-sized euphausiids to occur deeper. Consistent patterns for the vertical distributions of the large zooplankters (e.g. ctenophores, euphausiids) collected by the MPS and MIK samplers provided more complete data on their abundances and sizes than obtained by the single net. Possible 460mechanisms contributing to the observed patterns of distribution, e.g. high abundances of both Calanus spp. and their predators (ctenophores and chaetognaths) in the upper water layers during midwinter are discussed.

Seasonal shifts in feeding patterns: Individual and population realized specialization in a high Arctic fish

“…Methot Isaac Kidd (MIK) sampling was performed both in Rijpfjorden in fall and in winter for an adjacent project but the samples were analyzed using different methods and levels of expertise. We therefore prefer to discuss our results by referring to past studies and other manuscripts, which have investigated the community composition and abundance of zooplankton in a range of fjords in Svalbard allowing us to make well‐informed inferences (Bandara et al, ; Błachowiak‐Samołyk et al, ; Cusa, ; Dalpadado et al, ; Geoffroy et al, ; Kraft, Berge, Varpe, & Falk‐Petersen, ). Furthermore, bioenergetic measurements of the potential prey would help elucidate whether, all else being equal, there is an advantage to select for a given prey over other available prey (But see Mayzaud & Boutoute, ).…”

Modeling studies of the bioluminescence potential dynamics in a high Arctic fjord during polar night

“…Basedow et al (2018) observed that the transport of North Atlantic Water into the Arctic is larger during the Polar Night (January) than in May and August, and that there is a strong influx of zooplankton with North Atlantic Water during the Polar Night. They observed an influx of the bioluminescent copepod Metridia longa, which remains active during the Polar Night, and it has a relatively deep distribution (> 150 m; Blachowiak-Samolyk et al 2015, 2017. Indeed, Hop et al 2019 reported similar processes contributed to higher abundance of Metridia longa and ostracods (known to be bioluminescent, e.g.…”

Molecular tools prove little auks from Svalbard are extremely selective for Calanus glacialis even when exposed to Atlantification

“…Then each individual was placed in ethanol for further molecular species identification. Calanus hyperboreus as a deep-water, oceanic species 49 – 51 is very rarely caught in planktonic nets dedicated for sampling mesozooplankton fraction 52 . It is mainly associated with Greenland waters constituing substantial component of chick diets in the eastern 32 , 53 , 54 and northwest Greenland 55 , 56 .…”