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

Abstract

ABSTRACT This study was conducted in Shizugawa Bay, located on the north-eastern coast of Japan, to determine phytoplankton assemblages. Metabarcoding with the PsbA 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%) > Bacillariophyta (29.1%) > Haptophyta (17.8%) > 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, Dinophysis spp. (causing diarrheal poisoning) were dominant throughout the period, while Alexandrium spp. (causing paralytic poisoning) showed relatively low abundance. Phaeocystis 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.