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

• Published in: Polish Polar Research
• Main Authors: Błachowiak-Samołyk Katarzyna, Zwolicki Adrian, Webster Clare N., Boehnke Rafał, Wichorowski Marcin, Wold Anette, Bielecka Luiza
• Format: Article in Journal/Newspaper
• Language: English
• Published: Polish Academy of Sciences 2017
• Subjects: Arctic; Rijpfjorden; zooplankton; vertical distribution patterns; abundance and size; polar night; Geology; QE1-996.5; Svalbard; Midwinter; Kidd; Polar Research; Rijpfjord*; Zooplankton
• Online Access: https://doi.org/10.1515/popore-2017-0023; https://doaj.org/article/1f1c7595559d45d88ff93b6b0cc1e602

During a midwinter cruise north of 80°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 mechanisms 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.