Vertical distribution of polycystine radiolarians in the northern East China Sea

• Area located near the Kuroshio Current (KC) has high species diversity.
• In the north East China Sea (ECS) continental shelf radiolarians are absent in surface waters.
• Northern ECS intermediate water is characterized by subarctic radiolarians.
• Excepting the ECS continental shelf, surface water radiolarians seem to be related to the KC water.

The East China Sea (ECS) is a marginal sea influenced by the Kuroshio Current (KC) and by freshwater discharged by the Changjiang River. In this study, the vertical distribution of polycystine radiolarians in the northern ECS was investigated. We collected plankton-tow samples from the water column at five stations in the northern ECS. Stations 11 and 11′ were on the ECS continental shelf, and stations 1, 8, and 12 were in the northeastern ECS, which is influenced by the KC. We identified six distinct depth intervals by a Q-mode cluster analysis. At stations 1, 8, and 12, radiolarians were abundant and species diversity was high. In the surface waters, standing stocks of subtropical species such as Didymocyrtis tetrathalamus, Phorticium pylonium, Pterocanium praetextum, Spongaster tetras tetras, and the Tetrapyle octacantha groups were high, reflecting the influence of the warm KC. In contrast, at intermediate water depths, standing stocks of subarctic radiolarians such as Actinomma leptodermum, Cycladophora bicronis, Haliommetta miocenica, Pseudodyctiophimus gracilipes, and Lithelius minor were relatively high, which may reflect the influence of a subarctic water mass that probably originated in the North Pacific. At stations 11 and 11′ on the shelf, the influence of freshwater from the Changjiang River is high and radiolarians were absent in the upper 20 m of the water column and scarce at depths of 20–100 m; where three species dominated: Archipera triclavigera, Pseudocubus obeliscus, and Cryptogyrus calvatus.