Different Biochemical Compositions of Particulate Organic Matter Driven by Major Phytoplankton Communities in the Northwestern Ross Sea.

Naeun Jo,Bo Kyung Kim,Wuju Son,Myung Joon Kim,Kwanwoo Kim,Jeong-Hoon Kim,Hyoung Sul La,Sang Heon Lee

doi:10.3389/fmicb.2021.623600

Abstract

Marine particulate organic matter (POM) largely derived from phytoplankton is a primary food source for upper trophic consumers. Their biochemical compositions are important for heterotrophs. Especially, essential amino acids (EAAs) in phytoplankton are well known to have impacts on the survival and egg productions of herbivorous zooplankton. To estimate the nutritional quality of POM, the biochemical compositions [biomolecular and amino acid (AA) compositions] of POM were investigated in the northwestern Ross Sea during the late austral summer in 2018. Carbohydrates (CHO) accounted for the highest portion among different biomolecules [CHO, proteins (PRT), and lipids (LIP)] of POM. However, the higher contribution of PRT and lower contribution of CHO were observed in the southern section of our study area compared to those in the northern section. The spatial distribution of total hydrolyzable AAs in POM was considerably influenced by phytoplankton biomass, which indicates that the main source of particulate AA was generated by phytoplankton. Our results showed that the relative contribution of EAA to the total AAs was strongly associated with EAA index (EAAI) for determining protein quality. This result indicates that higher EAA contribution in POM suggests a better protein quality in consistency with high EAAI values. In this study, variations in the biochemical compositions in POM were principally determined by two different bloom-forming taxa (diatoms and Phaeocystis antarctica). The southern region dominated majorly by diatoms was positively correlated with PRT, EAA, and EAAI indicating a good protein quality, while P. antarctica-abundant northern region with higher CHO contribution was negatively correlated with good protein quality factors. Climate-driven environmental changes could alter not only the phytoplankton community but also the physiological conditions of phytoplankton. Our findings could provide a better understanding for future climate-induced changes in the biochemical compositions of phytoplankton and consequently their potential impacts on higher trophic levels.

Highlights

Marine particulate organic matter (POM) is derived from a variety of living and non-living sources, including detritus matter, bacterial cells, and phytoplankton (Volkman and Tanoue, 2002)
Our results revealed that the southern region dominated majorly by micro-sized diatoms was positively correlated with PRT, essential amino acids (EAAs), and EAA index (EAAI) indicating a good protein quality, while the relatively solitary P. antarctica-abundant northern region with higher CHO contribution was negatively correlated with good protein quality factors. 1980; Finkel et al, 2010)
Our study found remarkable differences in biochemical compositions of the phytoplankton communities (i.e., CHO-rich vs. relatively higher PRT and good vs. bad protein quality) depending upon the growth phase and community structure of phytoplankton

Summary

Introduction

Marine particulate organic matter (POM) is derived from a variety of living and non-living sources, including detritus matter, bacterial cells, and phytoplankton (Volkman and Tanoue, 2002). Biochemical properties of POM, especially biomolecular and amino acid (AA) compositions, are useful indicators of nutritional quality for higher trophic consumers (Dell’Anno et al, 2000; Lee et al, 2004; Bhavya et al, 2019). The biomolecular composition of phytoplankton has been considered a suitable indicator of the physiological responses of phytoplankton to the limitation of macro and micronutrients (i.e., bioavailable N, P, Si, and Fe) (Morris et al, 1974; Sterner and Elser, 2002; Saito et al, 2008; Moore et al, 2013) and light stress (Morris et al, 1974; Smith and Morris, 1980; Sunda and Huntaman, 1997; Klausmeier et al, 2008) which is connected with their nutritional quality for higher trophic consumers (Bhavya et al, 2019)

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