Picoplankton community structure at a coastal front region in the northern part of the South China Sea

Abundances of picoplankton groups were determined by flow cytometry in the Northern South China Sea (SCS) in winter 2004 to study the dynamics of picoplankton at a coastal front region. Prochlorococcus is more abundant in relatively high temperature and salinity waters than in nearshore area. Heterotrophic bacteria dominate in total picoplanktonic biomass but keep rather stable in biomass and surface/bottom biomass ratio on both sides of the front. Increases of picophytoplanktonic biomass and their surface/bottom biomass ratio are remarkable mainly owing to the contribution of Synechococcus on the offshore open SCS waters. Temperature is found to limit the growth of Synechococcus and Prochlorococcus. Picoeukaryotes and heterotrophic bacteria are less sensitive to the change in hydrographic conditions across the front. The autotrophic/heterotrophic biomass ratio of picoplankton is lower in eutrophic coastal waters on the nearshore side relative to the offshore and oligotrophic open SCS.