Temperature effects on growth and cell size in the marine calcareaous dinoflagellate Thoracospaera heimii

Growth experiments were carried out on the marine calcareous dinoflagellate Thoracosphaera heimii. Two strains (A603, GeoB 86) of the phototrophic, pr edominantly vegetative coccoid T. heimii were cultured at different tempera ture and nutrient levels. For the temperature experiment a gradient box was developed to allow the simultaneous testing of a wide range of temperature s on phytoplankton. During the investigations T. heimii was growing from 14 to 27 degrees C. Exponential growth rates do not show an unimodal response curve vs. temperature: values rise with increasing temperatures toward max imal growth rates around 27 degrees C. At low temperatures exponential grow th is extremely long (over 50 days). In f/2 culture medium T. heimii (A603) is less efficient at high temperatures than at low temperatures, final yie ld was about five times higher at 16 degrees C than at 27 degrees C. Growth rate and final yield at 27 degrees C are approximately the same for all ex periments, despite different nutrient levels. Mean shell diameters show no clear relation to growth temperature. Calcification of T. heimii shells is inversely related to temperature. (C) 2000 Elsevier Science B.V. All rights reserved.