Summer distribution of Noctiluca scintillans and mesozooplankton in the Western and Southern East China Sea prior to the Three Gorges Dam operation

Abstract

This research investigated the distribution and abundance of Dinoflagellate Noctiluca scintillans and mesozooplankton along two transect lines covering the China shelf, slope, the estuaries of the Yangtze River and the Minjiang River, the Northern Taiwan Strait, and the Kuroshio Current region during the summer of 2001. In addition to the regular sampling, 24-h high-frequency sampling at four fixed stations (estuary of the Yangtze River, estuary of the Minjiang River, the Northern Taiwan Strait, and the Kuroshio Current region stations) were also conducted to understand the diurnal vertical migration behavior of zooplankton. Mesozooplankton were dominated by Calanoida (relative abundance, RA 15.74%), Cyclopoida (RA 5.10%), Pteropoda (RA 3.88%), and copepod nauplii (RA 3.42%). Chaetognaths and calanoid copepods were recorded in all samples. Noctiluca scintillans was abundant (RA 51.04%) among all identified organisms in samples at low-salinity stations, particularly in the estuarine region of the Yangtze River. Copepods were the dominant group of mesozooplankton at most stations of the Southwest East China Sea. Our 24-h high-frequency sampling did not reveal any clear diurnal vertical migration behavior of zooplankton. The cluster analysis indicates that differential patterns of the zooplankton community structure in the Southwest East China Sea were related to different water masses. Our results provide useful information on zooplankton community structure in the estuarine region of the Yangtze River and the Southwest East China Sea prior to operation of the Three Gorges Dam.