Distribution Patterns of Picosized and Nanosized Phytoplankton Assemblages in the East China Sea and the Yellow Sea: Implications on the Impacts of Kuroshio Intrusion

Kuroshio, the strongest west boundary current of the Pacific Ocean, has significant impacts on the oceanographic conditions and ecological processes of the Pacific-Asian marginal seas through exchange of water, heat, and materials. In two cruises organized in the East China Sea (ECS) and the Yellow Sea in the spring 2014, observations of picosized and nanosized phytoplankton assemblages using flow cytometry reflected potential impacts of Kuroshio intrusion on phytoplankton communities, particularly in the ECS. The distribution pattern of Prochlorococcus in the ECS clearly depicts the intrusion route of Nearshore Kuroshio Branch Current from the main stream of Kuroshio northeast to Taiwan Island to the coastal waters adjacent to the Changjiang River estuary, an important red tide zone in the coastal waters of China. High abundance of photosynthetic nanoeukaryotes in the coastal waters adjacent to the Changjiang River estuary reflects the occurrence of diatom and dinoflagellate blooms during the investigation. The presence of Prochlorococcus in the coastal waters adjacent to the Changjiang River estuary offers a strong evidence that waters and materials associated with Nearshore Kuroshio Branch Current could be transported into the red tide zone adjacent to the Changjiang River estuary and will affect dynamics of harmful algal blooms in this region. Plain Language Summary Kuroshio is the strongest west Pacific boundary current. The oceanographic and ecological processes of Pacific Asian marginal seas are strongly affected by Kuroshio and its branches. During spring 2014, two cruises were conducted in the East China Sea and the Yellow Sea to find out how Kuroshio intrusion influence the environment and phytoplankton there. Four phytoplankton assemblages with different distribution patterns were detected by flow-cytometry. The assemblage with larger cell size (nanoeukaryotes) preferred to live in the coastal waters and reflected harmful algal blooms in the sea area adjacent to Changjiang River estuary. The abundance of the smallest photosynthetic organism Prochlorococcus was the highest where Kuroshio main stream flows by. The distribution pattern of Prochlorococcus in the East China Sea well depicted the route of a branch stretched from Kuroshio to the coastal waters adjacent to Changjiang River estuary (Nearshore Kuroshio Branch Current), and Prochlorococcus could be an indicator to reflect the influence Kuroshio intrusion has on phytoplankton. The results provide important aspect that open ocean could affect coastal ecological problems related to phytoplankton, such as harmful algal blooms.