Influence of the tidal front on the three-dimensional distribution of spring phytoplankton community in the eastern Yellow Sea

- Physical environment, chlorophyll concentration and phytoplankton community were investigated in the eastern Yellow Sea.
- Three-dimensional structure of phytoplankton communities was identified in the tidal front region.
- Phytoplankton abundance and chlorophyll a concentration were high in the shore side of the front during the spring tide.
- Subsurface maximum of phytoplankton abundance appeared about 64 km away from the front through the middle layer intrusion.
- Profiles of phytoplankton abundance and chlorophyll a concentration were different due to depth-dependent species change.

Hydrographic observation and biological samplings were conducted to assess the distribution of phytoplankton community over the sloping shelf of the eastern Yellow Sea in May 2012. The concentration of chlorophyll a was determined and phytoplankton was microscopically examined to conduct quantitative and cluster analyses. A cluster analysis of the phytoplankton species and abundance along four observation lines revealed the three-dimensional structure of the phytoplankton community distribution: the coastal group in the mixed region, the offshore upper layer group preferring stable water column, and the offshore lower layer group. The subsurface maximum of phytoplankton abundance and chlorophyll a concentration appeared as far as 64 km away from the tidal front through the middle layer intrusion. The phytoplankton abundance was high in the shore side of tidal front during the spring tide. The phytoplankton abundance was relatively high at 10-m depth in the mixed region while the concentration of chlorophyll a was high below the depth. The disparity between the profiles of the phytoplankton abundance and the chlorophyll a concentration in the mixed region was related to the depth-dependent species change accompanied by size-fraction of the phytoplankton community.