Contrasting Community Composition of Active Microbial Eukaryotes in Melt Ponds and Sea Water of the Arctic Ocean Revealed by High Throughput Sequencing.

Dapeng Xu,Xinran Li,Sung-Ho Kang,Nianzhi Jiao,Hejun Kong,Ying Wang,Jinyoung Jung,Youngju Lee,Eun-Jin Yang,Alan Warren

doi:10.3389/fmicb.2020.01170

Dapeng Xu, Xinran Li + Show 8 more

Open Access

https://doi.org/10.3389/fmicb.2020.01170

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Abstract

Melt ponds (MPs), form as the result of thawing of snow and sea ice in the summer, have lower albedo than the sea ice and are thus partly responsible for the polar amplification of global warming. Knowing the community composition of MP organisms is key to understanding their roles in the biogeochemical cycles of nutrients and elements. However, the community composition of MP microbial eukaryotes has rarely been studied. In the present study, we assessed the microbial eukaryote biodiversity, community composition, and assembly processes in MPs and surface sea water (SW) using high throughput sequencing of 18S rRNA of size-fractionated samples. Alpha diversity estimates were lower in the MPs than SW across all size fractions. The community composition of MPs was significantly different from that of SW. The MP communities were dominated by members from Chrysophyceae, the ciliate classes Litostomatea and Spirotrichea, and the cercozoan groups Filosa-Thecofilosea. One open MP community was similar to SW communities, which was probably due to the advanced stage of development of the MP enabling the exchange of species between it and adjacent SW. High portions of shared species between MPs and SW may indicate the vigorous exchange of species between these two major types of environments in the Arctic Ocean. SW microbial eukaryote communities are mainly controlled by dispersal limitation whereas those of MP are mainly controlled by ecological drift.

Highlights

One of the most characteristic features of the Arctic Ocean is its sea ice cover and annual cycling of freezing and melting of surface snow and sea ice
This study aimed to address the following questions: (1) do Melt ponds (MPs) and sea water (SW) harbor distinct microbial eukaryotic communities and, if so, to what extent do they differ? (2) what are the major processes that control the assembly of microbial eukaryotic communities in MPs and SW?
Water temperatures of the MPs ranged from −1.2 to 0.5◦C (Figure 2A)

Summary

Introduction

One of the most characteristic features of the Arctic Ocean is its sea ice cover and annual cycling of freezing and melting of surface snow and sea ice. Areal coverage of MPs has been estimated to reach up to 80% of the Arctic sea ice in summer (Lüthje et al, 2006). Arctic Ocean Active Microbial Eukaryotes with sea ice/snow, MPs have a lower albedo so they absorb more heat, which constitutes one of the processes responsible for the polar amplification of global warming (Perovich et al, 2002; Flocco et al, 2012). MPs eventually disappear either by percolating through the sea-ice column or merging with sea water (SW) when the bottom of the pond reaches the ocean. They can refreeze as the air temperatures drop again in the winter (Polashenski et al, 2012). Two different types of MP are usually found in the Arctic: open MPs which are connected with seawater and show a high salinity (ca. 29), and closed MPs which comprise mostly freshwater and have a much lower salinity (Gradinger, 2002; Lee et al, 2012)

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