The local phytoplankton community in Shizugawa Bay, Japan, from 2021 to 2022: analysis by DNA metabarcoding

This study was conducted in Shizugawa Bay, located on the north-eastern coast of Japan, to determine phytoplankton assemblages. Metabarcoding with the <i>PsbA</i> gene and environmental surveys were conducted from May 2021 to January 2022. PCA results showed that phytoplankton assemblages changed with the environmental parameters, such as water temperature and salinity, indicating a clear seasonal pattern. The relative abundance was dominated by Chlorophyta (annual mean 34.9%) &gt; Bacillariophyta (29.1%) &gt; Haptophyta (17.8%) &gt; Dinophyceae (11.7%). It is suggested that many species of Chlorophyta remain without being filtered by shellfish because the dominant representatives were pico-prasinophytes, which are of small size and are difficult for shellfish to capture. Bacillariophytes are thought to have been consumed preferentially since they are known to be a good food source for adult shellfish. Among Dinophyceae, <i>Dinophysis</i> spp. (causing diarrheal poisoning) were dominant throughout the period, while <i>Alexandrium</i> spp. (causing paralytic poisoning) showed relatively low abundance. <i>Phaeocystis</i> spp. (including some toxic species) were the dominant haptophytes. Cyanobacteria tended to appear particularly in summer although their mean relative abundance was less than 3%. Although the data are limited, they provide a useful snapshot of phytoplankton assemblages in Shizugawa Bay and the environmental factors that affect them.