Trophic Dynamics of Zooplankton Before and After Polar Night in the Kongsfjorden (Svalbard): Evidence of Trophic Position Estimated by δ15N Analysis of Amino Acids

Abstract

In polar ecology, zooplankton diets and survival rates vary according to the seasonality of solar radiation and oceanographic conditions. Each zooplankton species has evolved feeding strategies to survive in the diet-limited conditions of the "polar night." Many zooplankton studies have reported seasonal adaptations in feeding activity during polar night based on their trophic niches. Nitrogen isotope analysis of amino acids has provided improved accuracy in estimates of trophic position (TP) in various marine species. In this study, field work was conducted in Kongsfjorden before (October 2017) and after polar night (April 2018). As representative zooplankton, an amphipod (Themisto abyssorum), euphausids (Meganycitiphanes norvegica and Thysanoessa sp.), a chaetognath (Parasagitta elegans), and copepods (Calanus spp. and Oithona similis) were collected. trophic position values of each taxon were estimated using the nitrogen isotope ratio of glutamic acid (δ 15 N Glu ) and phenylalanine (δ 15 N Phe ). Results showed that TP values of P. elegans were relatively constant, averaging 3.2 in both seasons, likely due to continuous feeding activity during polar night. Trophic position values were also constant for Calanus spp., ranging 2.5-3.0 in both seasons, due to their ability to utilize stored high-energy wax. In contrast, average TP values for O. similis, an omnivorous zooplankton, were 2.9 in October and 2.3 the following April. Trophic position values for O. similis before polar night can be attributed to the relatively high availability of algae during longer periods of daylight. We found that TP variation in zooplankton before and after polar night differed according to feeding activities in diet-restricted circumstances.

Trophic Dynamics of Calanus hyperboreus in the Pacific Arctic Ocean

“…Our data set showed a wider range of TL AA values of C. hyperboreus, from 2.5 to 3.3. A wide TL AA range for Calanus was previously reported in Kongsfjorden, Svalbard (2.5-3.0 of TL AA, Choi et al (2020)). High clearance on a wide range of diet size (20-200 μm) in cultivation experiments (Huntley & Tande, 1987;Levinsen et al, 2000) may contribute to varying TL AA values for C. hyperboreus.…”

Amino acid nitrogen and carbon isotope data: Potential and implications for ecological studies

“…A greater degree of N exchange between Glx and specific AAs (Glx itself, Ala, Asx, Leu, Ile, Pro, and Val, grouped into trophic AA) is a likely explanation for the 15 N enrichment patterns in the trophic AA. This is commonly observed in most animal consumers (Figure 3a ), from zooplankton (e.g., Choi et al, 2020 ; Decima et al, 2017 ; McClelland & Montoya, 2002 ), amphibians, to birds (e.g., Gomez et al, 2018 ; McMahon et al, 2015 ).…”

“…That is, TP Glx‐Phe variance indicates diet specialization strategies to characterize specialist and generalist feeding habits. In populations collected from 16 ecologically varied habitats, Choi et al ( 2020 ) found that specialist consumers (e.g., pike Pseudogobio escocinus ) had a narrower range of TP Glx‐Phe magnitude than did generalist fish (e.g., largemouth bass Micropterus salmoides ). Moreover, obtaining the correct TP AA helps to infer the δ 15 N baseline of local habitats across geographic scales, and ultimately to construct isotope maps to trace migration routes of consumer animals over regions and time periods (Le‐Alvarado et al, 2021 ; Matsubayashi et al, 2020 ).…”

“…et al, 2021). It is applicable for whole bodies (or any proteinaceous tissue types) from environmental samples to zooplankton and higher trophic-level fish and apex predators (Cherel et al, 2019;Choi & Shin, 2021;Choi et al, 2020;Germain et al, 2013;Laiz-Carrión et al, 2019;Mompean et al, 2016;Richards et al, 2020). For obtaining a TP AA estimate, the two reference variables should be involved: the trophic discrimination factors of trophic and source AAs (TDF AA ), respectively, and the producer-specific isotope offset of trophic and source AAs from the isotope baseline information as fixed factors,…”

Winter Carnivory and Diapause Counteract the Reliance on Ice Algae by Barents Sea Zooplankton

“…During winter, some Arctic zooplankton switch from herbivorous to omnivorous or carnivorous diets (Werner and Auel, 2005), while others rely at least partly on their lipid stores built up during the productive season (Hagen and Auel, 2001). The latter is the case for diapausing Calanus copepods (Falk-Petersen et al, 2009;Choi et al, 2020), and has also been described for Antarctic calanoid copepods (Atkinson, 1998). Governed by their energy reserves, Calanus hyperboreus, for example, has the ability to reproduce during winter (Melle and Skjoldal, 1998;Hirche, 2013;Halvorsen, 2015), in contrast to C. finmarchicus, which is not able to reproduce successfully in the high Arctic (Hirche and Kosobokova, 2007).…”