Influence of different water masses on planktonic ciliate distribution on the East China Sea shelf

Abstract

In summer 2006 and winter 2007, ciliate abundance and biomass were investigated in the East China Sea in connection with water masses, frontal zones, dissolved oxygen and chlorophyll a concentrations, and picoplankton and nanoflagellate abundances. In addition, tintinnid ciliates were identified to species based on lorica morphology. There was no significant difference of ciliate abundance and biomass between Changjiang diluted water (CDW) and shelf mixing water (SMW) in the Changjiang river estuary and its adjacent sea in summer, or among the coastal water (CoW), the SMW and the Kuroshio water (KW) on the shelf in winter. The influence of water masses on ciliate distribution was slight, except that distinct increases in ciliate abundance were observed in the vicinity of frontal structures. Most tintinnids were neritic species, with no discrimination between two water masses in the Changjiang river estuary. However, cosmopolitan and warm water species were very mainly restricted to SMW and KW; neritic species were essentially present in CoW and SMW on the continental shelf.Total ciliate biomass was closely correlated with picoplankton biomass in the CDW and KW. Picoeukaryotes and Synechococcus were the potential food source of ciliates. In winter, within KW, nanoflagellates would play a major role in the transfer of organic matter from picoplankton to ciliates in the microbial community within KW. In the low-oxygen and hypoxia area adjacent to the Changjiang estuary where relatively high ciliate abundance and biomass occurred, heterotrophic bacteria would appear to exhibit a potential prey effect on the distribution of bacterivorous aloricated ciliates and nanoflagellates acting as intermediates between bacteria and tintinnids.