Sinking in freshwater phytoplankton: Some ecological implications of cell nutrient status and physical mixing processes1

Abstract

Sinking rates of Asterionella formosa, Melosira agassizii, Cyclotella meneghiniana, and Scenedesmus quadricauda in stationary and exponential phases of growth are reported. Stationary phase populations sink 4× more rapidly, on the average, than exponentially growing populations. Time series of sinking rates during change from one growth phase to another demonstrate the viability of rapidly sinking cells. A consideration of sinking in Langmuir circulations indicates that the frequently used algebraic relationship between sinking rate and rate of loss of cells from the mixed layer may greatly overestimate loss rates. A theoretical net potential growth curve, that combines both loss from sinking and growth from sinking‐dependent nutrient uptake, demonstrates that nutrient depleted cells may have optimal growth rates (highest fitness) at high sinking rates.