Effect of a harmful dinoflagellate Heterocapsa circularisquama isolated from Omura Bay, Japan on bivalve molluscs and its growth characteristics
2005
Yamatogi, T.(Nagasaki-ken. Inst. of Fisheries (Japan)) | Sakaguchi, M. | Matsuda, M. | Iwanaga, S. | Iwataki, M. | Matsuoka, K.
Heterocapsa circularisquama is a red-tide forming dinoflagellate causing mass mortality of bivalve molluscs in Western Japan. Bioassay on bivalve molluscs was made using two strains of H. circularisquama isolated from Omura Bay, Nagasaki Prefecture in 1999 and 2002. Pearl oyster Pinctada fucata died within 2-3 days after being exposed to 5,000 cells/mL of H. circularisquama. Short-neck clam Ruditapes philippinarum died within 4-6 days after being exposed to 5,000 cells/mL of H, circularisquama. The growth characteristics of H. circularisquama isolated from Omura Bay in 1999 were examined in 54 different combinations of temperature (10-30 deg C and salinity (16-36) under a light intensity of 80 mumol/m2/s. H. circularisquama reproduced at 12.5-30 deg C and 16-36 in salinity. The highest growth rate was obtained at 30 deg C and 32 in salinity. Under the conditions, maximum specific growth rate was 0.91 day-1. The effect of light intensity on the growth of H. circularisquama was examined at seven different conditions ranging from 10 to 140 mumol/m2/s under 14 h light and 10 h dark cycle and 25 deg C. H. circularisquama grew well at a light intensity of 20 mumol/m2/s and higher, then the growth was saturated at 80 mumol/m2/s. Under the conditions of this experiment, the half-saturation constant for growth of light intensity (Ks) and threshold value (Io) were 24.0 mumol/m2/s and 15.5 mumol/m2/s, respectively. The occurrence of H. circularisquama in Omura Bay, Imari Bay and Tachibana Bay was confirmed in the present study by observation of body scale structures.
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