Phytoplankton Composition During the Ice-Free Period of Lakes on Horseshoe Island (Antarctica) by Metagenomic Analysis

The phytoplankton communities in lakes change seasonally within competitive areas, referred to as seasonal succession, which results in high compositional diversity if conditions remain stable. However, glacial lakes are generally far from human and terrestrial influences due to their location so very few species can be identified and large changes in phytoplankton composition cannot be anticipated. Nonetheless, molecular techniques, as well as classical methods, help us to determine the existence of different species. Additionally, these techniques allow us to evaluate the ecology of glacial lakes from different perspectives with developing technology. Horseshoe Island is located in the area known as Marguerite Bay on the Peninsula region in western Antarctica. This study was carried out to determine phytoplankton genome biodiversity by using the metagenomic analysis method used in 18S rRNA, 16S rRNA, and 23S rRNA gene analyses. 16S rRNA and 23S rRNA gene analyses revealed that bacteria belong to broadly distributed Cyanobacteria taxa, whereas 18S rRNA gene analysis revealed other eukaryotic phytoplankton groups. This method was used for the first time for Horseshoe Island lakes (Col 1, Col 2, Skua, and Zano), and species belonging to Cyanobacteria, Chlorophyta, Ochrophyta, and Bacillariophyta were identified. As a result, the phytoplankton genomic diversity of shallow and oligotrophic glacial lakes was determined, and benthic algal species were also identified in the water samples. These results indicate that benthic algae associated with the sediment can also contribute to aquatic phytoplankton communities in addition to oligotrophic lake phytoplankton biodiversity. Cyanobacterial biodiversity can also be recognized as a sentinel by which to monitor adaptation responses to climate change in this rapidly warming region.