Nutrition and growth kinetics in nitrogen- or phosphorus-limited cultures of the ‘novel red tide’ dinoflagellate Heterocapsa circularisquama (Dinophyceae)

Abstract

Heterocapsa circularisquama is a dinoflagellate that has only recently been recorded as producing red tides; it causes severe damage to Japanese shellfish aquaculture by killing bivalves. In order to elucidate the mechanism of red tide outbreaks, the nutrition and growth kinetics of H. circularisquama were examined in nitrogen (N)– or phosphorus (P)–limited semicontinuous culture. Inorganic N compounds, such as nitrate, nitrite, and ammonium, were found to be good nitrogen sources for the growth, whereas organic nitrogen (urea and uric acid) was not utilized. Heterocapsa circuiarisquama could successfully use a wide variety of inorganic and organic phosphorus compounds of different molecular structures as the sole P source. Under N-limited steady-state conditions, the dilution rate (= growth rate) as a function of cell nitrogen quota followed the Droop equation. Under P-limited steady state culture too, the dilution rate as a function of cell P quota followed the Droop equation. Kinetic parameters Dm, (the maximum dilution rate) and Kq (minimum cell quota) were 0.9 d−1 and 1.1 pmol N cell−1 for N-limited cultures and 1.1 d−1 and 89.4 fmol P cell−1 for P-limited cultures. The nutrient availability and kinetic parameters of H. circularisquama are compared with other red-tide organisms and the ecological implications of these characteristics are discussed.