Fluctuations of algicidal microorganisms against the harmful dinoflagellate Heterocapsa circularisquama in Ago bay, Mie prefecture, Japan
1998
Imai, I. (Kyoto Univ. (Japan)) | Nakagiri, S. | Nagai, K. | Nagasaki, K. | Itakura, S. | Yamaguchi, M.
In Ago Bay, Mie Prefecture, red tides of the harmful dinoflagellate Heterocapsa circularisquama have recurrently occurred since 1992 and have caused mass mortality of pearl oysters (to do substantial damage to pearl industry). Studies on kill microorganisms against H. circularisquama were carried out for water samples collected in Ago Bay in summer using the newly developed microplate MPN method. A comparison was made on the numbers of killer microorganisms against Chattonella antiqua, Heterosigma akashiwo, gymnodinium mikimotoi, and H. circularisquama using a water sample collected on 16 August 1994, when a red tide of H. circularisquama was observed. The water sample contained H. circularisquama at a density of about 8000 cells.ml(-1). Killer microorganisms against all the four algal species were scarce (1.ml(-1)). Temporal fluctuations of algicidal microorganisms against H. circularisquama and C. antiqua (Raphidophyceae) were investigated during the summer of 1995 to elucidate effects of those microorganisms on H. circularisquama red tides. Killer microorganisms against H. circularisquama were scarce (1.ml(-1)) during the summer of 1995, although vegetative cells of H. circularisquama appeared at rather high density (1493 cells.ml(-1)).(Stn. K3W). Killer microorganisms against C. antiqua were also scarce (maximum 1.52.ml(-1)). Red tides of H. circularisquama tend to last 1 month or more. It is suggested that the scarcity of killer microorganisms against H. circularisquama in the coastal seas such as Ago Bay presumably contribute to maintain red tides of this species for rather long period
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