Comparison of phytoplankton macromolecular compositions and zooplankton proximate compositions in the northern Chukchi Sea

Abstract

The macromolecular (proteins, lipids, and carbohydrates) composition of phytoplankton and the proximate (water, proteins, lipids, and ash) and elemental (carbon and nitrogen) compositions of mesozooplankton were determined in the northern Chukchi Sea to establish the relationship between zooplankton and their phytoplankton food source. Among the phytoplankton macromolecules examined in this study, lipids had the highest contents (58.4±8.2%) and proteins had the lowest (16.1±7.3%), which may be a consequence of a nitrogen deficiency in phytoplankton growth during the study period. In contrast, proteins (59.7±10.6% DW) were the major proximate components in the mesozooplankton community, which was dominated by copepods up to 71% of total abundance. The low lipid contents (13.8±12.4% DW) in the mesozooplankton community in this study might be due to the dominance of small species such as Calanus glacialis, which generally have relatively lower lipid contents than large copepods. Moreover, the spawning period of<em> C. glacialis</em> from April to June might be an additional reason for the low lipid contents, because copepods have normally very low lipid contents after spawning. The low lipid contents resulted in a low energy content in this mesozooplankton community in the northern Chukchi Sea. The different biochemical compositions of phytoplankton and zooplankton should be considered in order to understand the impacts of climate change on the quality of prey provided by lower trophic levels and subsequently on Arctic marine ecosystems.