Growth and phosphate uptake kinetics of the toxic dinoflagellate Alexandrium tamarense from Hiroshima Bay in the Seto Inland Sea, Japan

SUMMARY Shellfish poisoning by the toxic dinoflagellate Alexandrium tamarense (Lebour) Balech occurred for the first time in Hiroshima Bay, Japan, in 1992. Oyster culture in the bay produces as much as 60% of the total production in Japan, and it suffered severe damage. In the present study, we experimentally investigated the growth rate and phosphate uptake kinetics of A. tamarense, Hiroshima Bay strain. A short-term phosphate uptake experiment revealed that the maximum uptake rate was 1.4 pmol P cell-1 per h and the half-saturation constant was 2.6 umol L-1. In semicontin-uous culture, the maximum specific growth rate and the minimum phosphorus cell quota were 0.54 day-1 and 0.56 pmol P cell-1, respectively. These uptake rates suggest that A. tamarense is a poor phosphorus competitor compared with other species. However, the large phosphorus storage capacity (Qpmax/qo= 36), the surge phosphorus uptake ability (Vs/Vi= 4.1) and the low growth rate would be advantageous for surviving brief periods of phosphorus limitation which frequently occur in Hiroshima Bay.