Culturable diversity of Arctic phytoplankton during pack ice melting

Priscillia Gourvil,Ian Probert,Christine Michel,Daniel Vaulot,Florence Le Gall,Adriana Lopes Dos Santos,Dominique Marie,Catherine Gérikas Ribeiro,Margot Tragin,Jody W Deming

doi:10.1525/elementa.401

Abstract

Massive phytoplankton blooms develop at the Arctic ice edge, sometimes extending far under the pack ice. An extensive culturing effort was conducted before and during a phytoplankton bloom in Baffin Bay between April and July 2016. Different isolation strategies were applied, including flow cytometry cell sorting, manual single cell pipetting, and serial dilution. Although all three techniques yielded the most common organisms, each technique retrieved specific taxa, highlighting the importance of using several methods to maximize the number and diversity of isolated strains. More than 1,000 cultures were obtained, characterized by 18S rRNA sequencing and optical microscopy, and de-replicated to a subset of 276 strains presented in this work. Strains grouped into 57 phylotypes defined by 100% 18S rRNA sequence similarity. These phylotypes spread across five divisions: Heterokontophyta, Chlorophyta, Cryptophyta, Haptophyta and Dinophyta. Diatoms were the most abundant group (193 strains), mostly represented by the genera Chaetoceros and Attheya. The genera Baffinella and Pyramimonas were the most abundant non-diatom nanoplankton strains, while Micromonas polaris dominated the picoplankton. Diversity at the class level was higher during the peak of the bloom. Potentially new species were isolated, in particular within the genera Navicula, Nitzschia, Coscinodiscus, Thalassiosira, Pyramimonas, Mantoniella and Isochrysis. Culturing efforts such as this one highlight the unexplored eukaryotic plankton diversity in the Arctic and provide a large number of strains for analyzing physiological and metabolic impacts in this changing environment.

Highlights

Polar algal communities impact (Lutz et al, 2016) and are impacted by (Brown and Arrigo, 2013) ice melting cycles
In the present study, partial 18S rRNA gene sequences and light microscopy were used to characterize 276 Arctic strains obtained during the Green Edge campaign (Supplementary Data S1), 77 and 199 isolated from ice and water samples, respectively (Figure 2)
A significant level of novelty exists within these strains, as almost 60% of the representative sequences of phylotypes did not match any sequence from previously cultured strains (Table 1) and more than 40% did not match any existing sequence from environmental datasets

Summary

Introduction

Polar algal communities impact (Lutz et al, 2016) and are impacted by (Brown and Arrigo, 2013) ice melting cycles. The tight links between phytoplankton diversity/production and sea ice dynamics are beginning to be decoded and seem to be fairly complex (Arrigo et al, 2014; Olsen et al, 2017). Due to increased light availability and vertical mixing, the shrinking of pack ice and the shift from thick multi-year ice to thinner first-year ice has been linked to enhanced Arctic primary production (Arrigo et al, 2008; Brown and Arrigo, 2013). § Sorbonne Université, CNRS, FR2424, Roscoff Culture Collection, Station Biologique de Roscoff, Roscoff, FR increased river run off, leads to an increase in water column stratification which in turn may impact nutrient availability and plankton diversity (Li et al, 2009). Climaterelated changes can increase Arctic vulnerability to invasive species (Vincent, 2010) as the intrusion of warmer waters “atlantifies” the Arctic Ocean (Årthun et al, 2012) and temperate phytoplankton move northwards, replacing Arctic communities (Neukermans et al, 2018)

Objectives

Methods

Results

Discussion

Conclusion