Characteristics of the Biochemical Composition and Bioavailability of Phytoplankton-Derived Particulate Organic Matter in the Chukchi Sea, Arctic

Bo Kim,Jong-Ku Gal,Sun-Yong Ha,Sung-Ho Kang,Kyoung-Ho Cho,Youngju Lee,Jinyoung Jung

doi:10.3390/w12092355

Abstract

Analysis of the biochemical composition (carbohydrates, CHO; proteins, PRT; lipids, LIP) of particulate organic matter (POM, mainly phytoplankton) is used to assess trophic states, and the quantity of food material is generally assessed to determine bioavailability; however, bioavailability is reduced or changed by enzymatic hydrolysis. Here, we investigated the current trophic state and bioavailability of phytoplankton in the Chukchi Sea (including the Chukchi Borderland) during the summer of 2017. Based on a cluster analysis, our 12 stations were divided into three groups: the southern, middle, and northern parts of the Chukchi Sea. A principal component analysis (PCA) revealed that relatively nutrient-rich and high-temperature waters in the southern part of the Chukchi Sea enhanced the microphytoplankton biomass, while picophytoplankton were linked to a high contribution of meltwater derived from sea ice melting in the northern part of the sea. The total PRT accounted for 41.8% (±7.5%) of the POM in the southern part of the sea, and this contribution was higher than those in the middle (26.5 ± 7.5%) and northern (26.5 ± 10.6%) parts, whereas the CHO accounted for more than half of the total POM in the northern parts. As determined by enzymatic hydrolysis, LIP were more rapidly mineralized in the southern part of the Chukchi Sea, whereas CHO were largely used as source of energy for higher trophic levels in the northern part of the Chukchi Sea. Specifically, the bioavailable fraction of POM in the northern part of the Chukchi Sea was higher than it was in the other parts. The findings indicate that increasing meltwater and a low nutrient supply lead to smaller cell sizes of phytoplankton and their taxa (flagellate and green algae) with more CHO and a negative effect on the total concentration of POM. However, in terms of bioavailability (food utilization), which determines the rate at which digested food is used by consumers, potentially available food could have positive effects on ecosystem functioning.

Highlights

In terms of bottom-up controls, phytoplankton is key organism that serves as a primary producer and primary food source for organisms at higher trophic levels in the foodwebs of aquatic ecosystems.Climate change enhances the sea ice melting in the Arctic Ocean with increasing concerns about primary production and nutrient cycling
Since sea-surface temperature and salinity are strongly affected by sea ice and related meltwaters, brine rejection, continental runoff, and the heat flux in the Arctic Ocean [51], we assumed that the temperature and salinity at the surface were representative of the ambient water conditions
The cluster analysis of the surface potential temperature and salinity data allowed the identification of the three types of regions in the Chukchi Sea: cluster 1 was located at a latitude of approximately 66–70 ◦ N; cluster 2 was located at a latitude of 74.7–78 ◦ N and included the Chukchi Borderland; cluster

Summary

Introduction

In terms of bottom-up controls, phytoplankton is key organism that serves as a primary producer and primary food source for organisms at higher trophic levels in the foodwebs of aquatic ecosystems.Climate change enhances the sea ice melting in the Arctic Ocean with increasing concerns about primary production and nutrient cycling. Sea ice loss reduces surface albedo and enhances light penetration, creating irregularities on the timing and the duration of phytoplankton blooms [1,2]. These conditions can create discontinuity between the available food resources and the nutritional demands of higher. Water 2020, 12, 2355 producers [1], including higher trophic level organisms [3], and affect the energy flow of the entire arctic food web. LIP, PRT, and CHO play roles in the structural components and energy storage of marine organisms [9,10], accounting for up to 90% of the weight in algae [11]

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