DIEL PERIODICITY IN GROWTH AND SINKING RATES OF THE CENTRIC DIATOM COSCINODISCUS-CONCINNUS

Growth and sinking rates varied over a 61.4-h period for semicontinuous cultures of the marine diatom Coscinodiscus concinnus grown at light intensities of 48 and 9-mu-Einst m-2 s-1 on a 12L:12D cycle. The time-course of sinking rates showed cyclic fluctuations, with sinking rates generally decreasing during the dark part of the light: dark cycle and increasing in the light period. For most of the experiment, sinking rates varied in phase with growth rates. Changes in cell size during growth did not account for the variation in the observed sinking rates. The periodicity in sinking rate was probably the result of internal density changes in the cells rather than of changes in cell volume or area.