Spring distribution of diatom assemblages in the East China Sea

Abstract

The distribution of diatom assemblages in the East China Sea in late spring was investigated in relation to hydrographical characteristics. Using principal component analyses, 3 water types and 4 diatorn assemblages were defined. The distribution pattern of water types showed a 2-layer structure. The nutrient-depleted Surface Water Type forms a layer above the nutnent-laden hlid-Layer Water Type. In addition, the low-salinity eutrophic Coastal Water Type was found near the Changjiang river plume. In general, the distribution of diatom assemblages matches that of water types. The Upwelled Assemblage and the Coastal Assemblage existed respectively in the upwelled Subsurface Kuroshio Water (the Mid-Layer Water Type) and the Changjiang river plume (the Coastal Water Type). A Background Assemblage mlth low standing stock was found over the entire study area in both the Surface Water Type (nutnent limited) and the Mid-Layer Water Type (light lirnited). The Shelf-Break Assemblage was observed near the shelf break, where variations in physical or chemical environments were insignificant. This probably resulted from an upwelling event that had not previously been observed. Our results indicate that a widespread Background Assemblage is the basic diatom distribution pattern in the East China Sea. At locations where a nutrient source becornes available, the Background Assemblage will change into a new assemblage such as the Upwelled Assemblage or the Coastal Assemblage.