AUTHOR=Choi Hyuntae , Ha Sun-Yong , Lee Seunghan , Kim Jee-Hoon , Shin Kyung-Hoon 

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

JOURNAL=Frontiers in Marine Science

VOLUME=7

YEAR=2020

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2020.00489

DOI=10.3389/fmars.2020.00489

ISSN=2296-7745

ABSTRACT=<p>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 (<italic>Themisto abyssorum</italic>), euphausids (<italic>Meganycitiphanes norvegica</italic> and <italic>Thysanoessa</italic> sp.), a chaetognath (<italic>Parasagitta elegans</italic>), and copepods (<italic>Calanus</italic> spp. and <italic>Oithona similis</italic>) were collected. trophic position values of each taxon were estimated using the nitrogen isotope ratio of glutamic acid (δ<sup>15</sup>N<sub><italic>Glu</italic></sub>) and phenylalanine (δ<sup>15</sup>N<sub><italic>Phe</italic></sub>). Results showed that TP values of <italic>P. elegans</italic> 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 <italic>Calanus</italic> 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 <italic>O. similis</italic>, an omnivorous zooplankton, were 2.9 in October and 2.3 the following April. Trophic position values for <italic>O. similis</italic> 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.</p>