Cell volumes, maximal growth rates of unicellular algae and ciliates, and the role of ciliates in the marine pelagial1,2

A review of growth rates of diatoms and dinoflagellates in light‐saturated, nutrient‐replete cultures at 20°C confirms weak dependence on cell volume or mass. These maximal (intrinsic) rates are not linearly related to surface area or surface‐to‐volume ratio of the cells. The growth of most diatoms is materially faster than that of dinoflagellates; other algae fall in between or below the dinoflagellates. Small ciliates have appreciably higher intrinsic growth rates than algae of the same cell volume. The average food consumption per ciliate in the marine pelagic realm is inferred to be very low, so that the realized specific growth rates are much smaller than the intrinsic potentials. Also, a previously postulated refuge from predation, afforded by small size, is extended down to about 10‐ µ m 3 cell volume.