Temporal pattern of division in the dinoflagellate genus ceratium and its application to the determination of growth rate

Laboratory experiments using Ceratium furca (Ehr.) Clap. et Lachm. were conducted to determine the chemical composition of C. furca and to evaluate the accuracy of growth rates determined from the maximum observed frequency of division. The chemical composition of C. furca varied more with physiological changes induced by temperature and culture age than it did with photoperiod. Growth rates calculated from the maximum daily frequency of division (F_max) averaged 79.2% of the rate calculated from the increase in cell number under laboratory conditions and the range was 52.9–111.7% (n= 11).The temporal pattern of cell division in marine species of the dinoflagellate genus Ceratium was examined in a combined program of laboratory and field experiments. Cultures of C. furca were grown in an environmental chamber under various conditions of photoperiod and temperature on 24-h light dark cycles. The initiation of division was independent of temperature over the range of experimental conditions examined (15–25°C). Cell division maintained a fairly constant phase relationship with the beginning of the dark period; it was initiated 8.5 to 10.5 h after the lights were extinguished for photoperiods of 16 to 8 h. Division was less synchronous and was initiated earlier in sexual life-history stages than it was in vegetable stages. In oceanic samples (photoperiods of 10.5 to 14 h), the temporal pattern of cell division was similar among all Ceratium species examined, and division occurred at approximately the same time as in laboratory cultures grown under analogous conditions of photoperiod and temperature.