Marine phytoplankton community structure of the waters of the Argentine Islands (2019-2021)

The variability of phytoplankton community structure was analyzed in the waters of the Argentine Islands in late summer period of 2019, 2020 and 2021, as well as from February 2020 to February 2021. Biodiversity (121 taxa) and phytoplankton structure of the Argentine Islands waters corresponded to earlier studies. The late summer succession in 2019 and 2020 and 2021 was found typical for the waters of the Argentine Islands. Representatives of Bacillariophyceae completely dominated the studied community. Biomass variability was largely determined by large centric diatoms with low specific surface (S/W) values ranging from 70 to 300 m2·kg-1. Higher values of phytoplankton development metrics and a more noticeable presence of haptophyte, cryptophyte and diatom groups with S/W values larger than 700 m2·kg-1 differed 2019 from 2020 and 2021. Lower development metrics and simplified taxonomic structure of phytoplankton were recorded in 2020 – 2021. The decrease in the specific surface of the groups in the late summer periods of 2020 and 2021 was caused both by a decrease in the relative contributions of small-celled Coccolithophyceae and Cryptophyceae and by a general decrease in S/W of these taxa. Characteristic annual phytoplankton development patterns were revealed. The spring phytoplankton development was formed by high abundance of Fragilariopsis with a predominant contribution to the biomass of large centric diatoms. At the beginning of austral summer, the role of flagellates from the genera Cryptomonas (Cryptophyta) and Pyramimonas (Chlorophyta), as well as small flagellates, increased. The late austral summer period was characterized by the dominance of large centric diatoms with a significant presence of small flagellates and a periodic increase in the contribution of Fragilariopsis. The spring-summer succession had common features with the development of phytoplankton in the more northern regions of the Western Antarctic Peninsula (Palmer station), while the late summer phase – with the more southern Rothera station.