Distribution of Chromophytic Phytoplankton in the Eddy-Induced Upwelling Region of the West Pacific Ocean Revealed Using rbcL Genes.

Laxman Pujari,Jun Sun,Liuyang Li,Chao Wu,Dhiraj Narale,Changling Ding,Guicheng Zhang,Jinjun Kan

doi:10.3389/fmicb.2021.596015

Abstract

Marine chromophytic phytoplankton are a diverse group of algae and contribute significantly to the total oceanic primary production. However, the spatial distribution of chromophytic phytoplankton is understudied in the West Pacific Ocean (WPO). In this study, we have investigated the community structure and spatial distribution of chromophytic phytoplankton using RuBisCO genes (Form ID rbcL). Our results showed that Haptophyceae, Pelagophyceae, Cyanophyceae, Xanthophyceae, and Bacillariophyceae were the dominant groups. Further, chromophytic phytoplankton can be distinguished between upwelling and non-upwelling zones of the WPO. Surface and 75 m depths of a non-upwelling area were dominated by Prochlorococcus strains, whereas chromophytic phytoplankton were homogenously distributed at the surface layer in the upwelling zone. Meanwhile, Pelagomonas-like sequences were dominant at DCM (75 m) and 150 m depths of the upwelling zone. Non-metric multidimensional scaling (NMDS) analysis did not differentiate between chromophytic phytoplankton in the upwelling and non-upwelling areas, however, it showed clear trends of them at different depths. Further, redundancy analysis (RDA) showed the influence of physicochemical parameters on the distribution of chromophytic phytoplankton. Along with phosphate (p < 0.01), temperature and other dissolved nutrients were important in driving community structure. The upwelling zone was impacted by a decrease in temperature, salinity, and re-supplement of nutrients, where Pelagomonas-like sequences outnumbered other chromophytic groups presented.

Highlights

Marine phytoplankton are accountable for half of the world’s primary production
Surface phosphate concentration was below the detection limit at station West Pacific Ocean (WPO)-1 (18°N), WPO-4 (15°N), WPO-5 (11.9°N), and WPO-8 (2°N), whereas the highest concentration was recorded at WPO-6 (8.9°N; 0.11 μmol L−1)
Surface ammonia concentration was below the detection limit at stations WPO-5 (11.9°N) and WPO-7 (2°N), whereas the highest concentration was recorded at WPO-2 (18°N; 1.09 μmol L−1)

Summary

Introduction

Marine phytoplankton are accountable for half of the world’s primary production They are the key players of the global carbon cycle (Falkowski, 1994; Smetacek, 1999). Form I is the most abundant (Tabita, 1999), and it is subdivided into four subclasses, i.e., IA, IB, IC, and ID These genes are divided into the terms ‘green’ and ‘red’ lineages. Earlier studies on functional gene rbcL form ID have emphasized its importance through gene abundance, expression and have provided high-resolution community composition of chromophytic phytoplankton in different marine ecosystems (Pichard et al, 1993; Samanta and Bhadury, 2014). As the rbcL gene is chloroplast encoded, the chloroplast gene copy number swithin chromophytic phytoplankton differ, in diatoms. Diatoms may comprise of up to 2000 chloroplast-encoding rbcL genes in addition to two copies of rbcL gene in their genome (Douglas, 1988)

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