Annual phytoplankton dynamics in coastal waters from Fildes Bay, Western Antarctic Peninsula

Abstract

Year-round reports of phytoplankton dynamics in the West Antarctic Peninsula are rare and mainly limited to microscopy and/or pigment-based studies. We analyzed the phytoplankton community from coastal waters of Fildes Bay in the West Antarctic Peninsula between January 2014 and 2015 using metabarcoding of the nuclear and plastidial 18/16S rRNA gene from both size-fractionated and flow cytometry sorted samples. Overall 14 classes of photosynthetic eukaryotes were present in our samples with the following dominating: Bacillariophyta (diatoms), Pelagophyceae and Dictyochophyceae for division Ochrophyta, Mamiellophyceae and Pyramimonadophyceae for division Chlorophyta, Haptophyta and Cryptophyta. Each metabarcoding approach yielded a different image of the phytoplankton community with for example Prymnesiophyceae more prevalent in plastidial metabarcodes and Mamiellophyceae in nuclear ones. Diatoms were dominant in the larger size fractions and during summer, while Prymnesiophyceae and Cryptophyceae were dominant in colder seasons. Pelagophyceae were particularly abundant towards the end of autumn (May). In addition of Micromonas polaris and Micromonas sp. clade B3, both previously reported in Arctic waters, we detected a new Micromonas 18S rRNA sequence signature, close to, but clearly distinct from M. polaris, which potentially represents a new clade specific of the Antarctic. These results highlight the need for complementary strategies as well as the importance of year-round monitoring for a comprehensive description of phytoplankton communities in Antarctic coastal waters.

Spatiotemporal Variations in Antarctic Protistan Communities Highlight Phytoplankton Diversity and Seasonal Dominance by a Novel Cryptophyte Lineage

“…Both our 18S and 16S data sets contained M. polaris and Bathycoccus prasinos ASVs. These two taxa have been reported in the South Shetland Islands, Marguerite Bay ( 16 , 18 ), the Amundsen Sea, and circumpolar waters surrounding Antarctica ( 68 , 69 ). In Fildes Bay (South Shetland Islands) Micromonas had high relative abundances, comprising up to 47% of the total V4 18S amplicons, and a possible new ASV variant (in addition to M. polaris ) was reported ( 18 ).…”

“…Our study location was ∼60 km from a region sampled near Anvers Island ( 14 ), a distinct environment from fjords that has similarities to the Gerlache Strait. Our location was intermediate to the coastal South Shetland Islands ( 15 , 18 , 49 ) and Marguerite Bay ( 16 ), a true bay (not a fjord). The sequence analysis resolution for the two studies of Southern Ocean waters near the South Shetland Islands was most similar to ours, although they used the V4 18S region, not V9.…”

“…Based on multiyear pigment analyses on transects across the region, this shift is thought to be linked to increased warming ( 13 ). Phytoplankton communities have been addressed using the 18S rRNA gene to examine the entire microbial eukaryote community at a general level ( 6 , 14 – 18 ). Most recently, WAP transect data indicated that a single amplicon sequence variant (ASV) dominated the cryptophyte community at the majority of stations, spanning multiple years, with occasional offsets in peak relative abundances with the known Antarctic cryptophyte Geminigera cryophila ( 19 ).…”

Proteorhodopsin Phototrophy in Antarctic Coastal Waters

“…In the WAP region, aerobic anoxygenic phototrophic bacteria account for up to 8% of the community ( 7 ), while photosynthetic cyanobacteria are a minor component of the marine community ( 19 , 44 – 46 ). Thus, photoautotrophy in this system mostly relies on eukaryotic microorganisms, whose activity increases during blooms, like those described during the austral summer in Chile Bay ( 24 , 25 ).…”

Planktonic protist diversity across contrasting Subtropical and Subantarctic waters of the southwest Pacific

“…482 samples were sequenced generating a total of 9166190 reads, with a median sequencing depth across all samples of 18954 reads per sample (range = 6539 – 36551). Obtained sequences were processed using the DADA2 pipeline (Callahan et al 2017) following the procedure described by (Trefault et al 2021). Taxonomic assignation was made against PR2 database version 4.12 (https://pr2-database.org/), yielding 16861 amplicon single variants (ASVs) assigned to protistan taxa.…”