Dinoflagellate growth rate in water columns of varying turbidity as a function of migration phase with daylight

Abstract

Photosynthetic dinoflagellates occasionally exhibit nonphototactic phase relationships between their diurnal vertical migration and the daylight cycle. The cause of this variability in specific field cases is generally unclear. A computer model, MIGTIM, is reported that incorporates light dependence of the initial slope (α) and maximum photosynthesis (Pmax) of the photosynthesis versus light intensity (P-I) curve. MIGTIM is used to determine the migration phase that optimizes growth rate of sinusoidally migrating populations under different conditions of photosynthetic light dependence, turbidity and migration depth. Migration phase provides little selective advantage for shallow populations or for populations in low turbidity water columns. Migration phase provides a strong selective advantage for deep populations or for populations in high turbidity water columns. A comparison between MIGTIM output and published field observations suggests that field populations experienced optimum growth rate under the observed environmental and biological conditions. The analysis supports the contention that, under appropriate conditions, water column turbidity is an important component of the complex equation that determines migration phase and that this component acts through the organism's cumulative diurnal photosynthetic response.