PHASED CELL-DIVISION IN A NATURAL-POPULATION OF DINOPHYSIS-SACCULUS AND THE IN-SITU MEASUREMENT OF POTENTIAL GROWTH-RATE

A method for the in situ estimation of the potential growth rate of th e dinoflagellate Dinophysis sacculus based on the pattern of cell divi sion and the duration of the cell cycle phases according to the model of McDuff and Chisholm (Limnol. Oceanogr., 27, 783-788, 1982) is propo sed. In order to observe the cell cycle and measure the in situ growth rate of D.sacculus, water samples were taken from Alfacs Bay in the E bro River Delta, Spain, in May and June 1994, and kept in the laborato ry under a light-dark cycle similar to that in the field. The pattern of cell division in the D.sacculus population was established by inten sive sampling over 24 h periods. The maximum frequency of cells underg oing cytokinesis was observed at dawn and that of recently divided cel ls 2 h later. Based on the pattern of cell division and the duration o f the various cell cycle phases, a generation time between 2 and 5 day s was estimated. Subsequently, in situ estimates of the growth rate fo r D.sacculus were carried out in St Caries de la Rapita harbour during October 1995. A mean generation time of 7 days was estimated.