Culturable diversity of Arctic phytoplankton during pack ice melting

Abstract

14Massive phytoplankton blooms develop at the Arctic ice edge, sometimes extend- 15 ing far under the pack ice. An extensive culturing effort was conducted before and 16 during a phytoplankton bloom in Baffin Bay between April and July 2016. Differ-17 ent isolation strategies were applied, including flow cytometry cell sorting, man-18 ual single cell pipetting and serial dilution. Although all three techniques yielded 19 the most common organisms, each technique retrieved specific taxa, highlight-20 ing the importance of using several methods to maximize the number and diver-21 sity of isolated strains. More than 1,000 cultures were obtained, characterized by 22 18S rRNA sequencing and optical microscopy and de-replicated to a subset of 23 276 strains presented in this work. Strains grouped into 57 genotypes defined by 24 100% 18S rRNA sequence similarity. These genotypes spread across five divi-25 sions: Heterokontophyta, Chlorophyta, Cryptophyta, Haptophyta and Dinophyta. 26 Diatoms were the most abundant group (193 strains), mostly represented by the 27 genera Chaetoceros and Attheya. The genera Rhodomonas and Pyramimonas were 28 the most abundant non-diatom nanoplankton strains, while Micromonas polaris 29 dominated the picoplankton. Diversity at the class level was higher during the 30 peak of the bloom. Potentially new species were isolated, in particular within the 31 genera Navicula, Nitzschia, Coscinodiscus, Thalassiosira, Pyramimonas, Man-32 toniella and Isochrysis.33

Temporal dynamics and biogeography of sympagic and planktonic autotrophic microbial eukaryotes during the under-ice Arctic bloom

“…For example, some cryptophyte species like B. frigidus have been characterized as euryhaline, growing at salinities ranging from 5 to 35 (Daugbjerg et al 2018). The B. frigidus ASV_c699cb1809 and ASV_f8124a0c4a were 100% similar to the sequences obtained from the strains CCMP2045 (GQ375264) and RCC5289 (OR736128), isolated from Baffin Bay waters (Daugbjerg et al 2018) and sea ice, respectively (Ribeiro et al 2020). The latter ASV (ASV_f8124a0c4a) was flagged as an indicator of ice (Figure 5A) and showed a restricted polar distribution (Figure 6) which suggests that it probably represents an ice ecotype.…”

“…It is noteworthy that among the 1 000 genera catalogued by Fourtanier and Kociolek (1999) and Fourtanier and Kociolek (2003), only 197 have reference 18S rRNA sequence (Guillou et al 2012). About 50% of the most abundant ASVs in our study have a cultured representative (Figure 5), indicating that culturing methods have been able to capture the diversity among abundant arctic taxa (Balzano et al 2017;Potvin and Lovejoy 2009;Ribeiro et al 2020;Supraha et al 2022). However, this is not the case for the rarer taxa (Figure S6), highlighting the need for renewed culturing efforts and development of isolation methods to fill this gap.…”