High and fine resolution of bloom dynamics using HPLC analysis in a semi-enclosed harbour

Chemotaxonomic analysis, a functionally efficient method, was performed every week over a year in the semi-enclosed Jangmok Bay to determine the composition of major phytoplankton assemblages, including small phytoplankton. Multiple blooms occurred through a year: two in summer and one in fall. The high abundance of diatoms in summer resulted in an intensive bloom of cryptophytes with a one-week time lag, followed by a dinoflagellate bloom in the fall. Additional microscopic analysis revealed an ecological succession of major phytoplankton species: a bloom of fast-growing Pseudo-nizschia sp. in summer was replaced by a bloom of Cryptomonas sp. one week after the diatom bloom, and then further succeeded to an Akashiwo sanguinea bloom in fall. The dominance of relatively small-sized Cryptomonas sp. led to a mismatch between the microscopic and chemotaxonomic results during the second bloom, indicating size dependence. In contrast, for the Akashiwo bloom, the microscope analysis was significantly underestimated by the chemotaxonomic analysis. Additionally, the ecological traits inherited by bloom-forming species play a role in their bloom dynamics. This study highlighted that the frequent sampling with the rapid HPLC analysis is effective for accurately understanding spatiotemporal variations of blooms, and can be an invaluable strategy for early warning and understanding bloom patterns in changing coastal ecosystems.