Cross-shelf Distribution of Summer Dinoflagellate Abundance in the East China Sea and Its Correlation to Environmental Factors

Abstract

Two cruises were conducted to the East China Sea in July 2002 to investigate the cross-shelf distribution of pelagic dinoflagellates and its relationship to environmental factors. Samples for cell abundance and species composition were collected by oblique tows from 30 m depth to sea surface. In most cases, dinoflagellate abundance in the study area was between 3.0 and 11.0 cells L^(-1) with high values occurring at coastal and upwelling stations. The dinoflagellate community was dominated by species belonging to Ceratium, Prorocentrum, and Protoperidinium. A total of 3 dinoflagellate assemblages with characteristic distribution patterns were identified using the methods of correlation and cluster analysis. The Coastal-upwelling Assemblage was the numerically abundant group with C. furca and Prorocentrum micans as the representative species. In contrast, C. teres was the representative species in the Oceanic Assemblage, and cell abundance of this assemblage was high in Kuroshio but declines steadily toward the coastal zone. The Irregular Assemblage contained only a few species, and its distribution varied substantially between cruises. Correlation analysis between cell abundance and environmental factors, such as nutrient concentration and water temperature, indicated that Coastal-upwelling assemblage was composed of cosmopolitan species that grow actively in nutrient-rich regions. On the other hand, the majority of species in the Oceanic Assemblage are tropical in nature, and their high abundance in Kuroshio is probably a result of northward transportation mediated by current systems.