Journal of Oceanography, Vol. 55 (No. 3), pp. 395-406, 1999
Masanobu Kai1, Tamotsu Hara2, Hiroaki Aoyama1 and Nobuo Kuroda3
1Laboratory of Fishery Environment, Aichi Fisheries Research Institute, Miyacho, Gamagori 443-0021, Japan
2Fisheries Promotion Division, Department of Agriculture and Fisheries, Aichi Prefectural Government, 3-1-2 Sannomaru, Naka-ku, Nagoya 460-8501, Japan
3Marine Resources Research Center, Aichi Fisheries Research Institute, Minamichita, Aichi 447-3412, Japan
(Received 16 May 1997; in revised form 18 December 1998; accepted 19 December 1998)
Abstract: In April 1996, a massive algal bloom of the coccolithophorid Gephyrocapsa oceanicadeveloped in both Chita Bay and Atsumi Bay which comprise the bay known as Mikawa Bay of Japan. It was the first record of such a bloom in this area. In Chita Bay, the bloom persisted until the middle of May, however in Atsumi Bay, it remained until early June. From the analysis of salinity, water temperature, and current velocity and direction data, it is considered that the following mechanism accounts for the occurrence and maintenance of the bloom: Before the bloom, the standing crop of phytoplankton was poor, resulting in relatively rich nutrients throughout the bay. Thereafter, with the influx of oceanic water into Mikawa Bay, high salinity occurred firstly in Chita Bay. Under these hydrographic conditions, the bloom occurred first in Chita Bay, and extended throughout the bay with the clockwise circulation of water into Atsumi Bay. In Chita Bay, the bloom was influenced by rainfall and G. oceanicaflowed out from this area. Whereas, in Atsumi Bay, the bloom persisted for longer due to the clockwise circulation and another influx of oceanic water.