Journal of Oceanography, Vol. 56 (No. 4), pp. 419-427, 2000
Tomoyuki Kasuya*, Takashi Ishimaru and Masaaki Murano
Department of Ocean Sciences, Tokyo University of Fisheries, 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan
(Received 29 October 1998; in revised form 1 November 1999; accepted 22 December 1999)
Abstract: Surveys of the abundance and size composition of the ctenophore Bolinopsis mikadowere conducted in Tokyo Bay over a 5-year period from 1990 to 1994. B. mikadoappeared throughout the year, and its mass occurrence was observed between August and November; annual maximum abundance ranged from 19 to 91 ind. m-2. Water temperature seems to influence the seasonal variation of B. mikadoabundance. Environmental conditions (e.g. rough waters due to a typhoon) and predation by the beroid ctenophore Beroe cucumis appear to affect annual variations of B. mikadoabundance. Size frequency distributions of B. mikadoindicated that its reproduction was most active in summer and fall but occurred throughout the year in Tokyo Bay. A sharp decline of the copepod population in August 1990 was probably due to predation by B. mikadowhich was very abundant at that time; its predatory impact was estimated to be 24 % day-1.