From: Journal of Oceanography, Vol. 55, pp. 395 to 406. 1999
Title: A Massive Coccolithophorid Bloom Observed in Mikawa Bay, Japan
By: MASANOBU KAI1, TAMOTSU HARA2, HIROAKI AOYAMA1 and NOBUO KURODA3

Gephyrocapsa oceanica Kampter is distributed throughout tropical and temperate oceans. Concentrations of 105 cells/l or more are usually restricted to marginal seas (Okada and Honjo, 1975), upwelling (Smayda, 1966) and boundary (Blackwelder, 1984) regions in low latitudes. Unlike E. huxleyi, it is uncommon on record as monospecific blooms. Blackburn and Cresswell (1993) reported a massive bloom of G. oceanica in Australian waters, and suggested a mechanism for the bloom. In the coastal waters of Japan, G. oceanica is the most common Coccolithophorid (Okada and Honjo, 1975), and mono-specific blooms have been recognized in a few instances. In April 1976, G. oceanica bloomed extensively in Ise Bay with a concentration of 1.8-104 cells/ml (Ishimaru, 1990). In recent years, similar blooms were observed in both Tokyo and Sagami Bays in May 1995, however, no scientific reports about those blooms have been published to date. In April 1996, a massive bloom of G. oceanica was observed in Mikawa Bay. Coccolithophorid blooms have not occurred previously in Mikawa Bay, making the bloom we describe here the first occasion. The bloom colored the entire bay to a milky green; and the cell concentrations were more than 1-104 cells/ml for a month, reaching a maximal concentration of 7.4-104 cells/ml. Such high densities and long duration of a mono-specific bloom of G. oceanica have not been recorded in any previous studies in the world. This paper reports the processes of that massive bloom of G. oceanica in Mikawa Bay, and discusses the mechanism of its development and persistence.