In terms of spatial distribution, the phytoplankton pigment ratios and community composition (which was strongly influenced by environmental conditions) showed patterns similar to the T – S properties (Figs. 6 and 7). In coastal areas of the YS the concentrations of N, P and Si compounds are high, reflecting the effects of the Changjiang effluent plume, surface runoff from the west and east coasts, and circulation in the YS. However, because of the unique basin topography and strong tidal currents, the YSCWM is fringed by typical tidal mixing fronts, which separate the cold, stratified water at the off- shore side from the warm, well-mixed, shallow water on the other side. Thus, significantly lower nutrient and Chl a concentrations are observed on the surface of the YSCWM area than in the surrounding water in summer. In the present study, much evidence was presented of the YSCWM area behaving differently from the rest of the sampled region, especially with regard to phytoplankton community structure (Figs. 2 – 8).