Diel vertical migration and nocturnal uptake of nutrients by Chattonella antiqua under stable stratification

Abstract

The ecological advantage of diel vertical migration for the nutrition and population growth of the flagellate Chattonella antiqua (Raphidophyceae) was examined in a large, axenic culture tank. Vertically stratified salinity, temperature, PO43, and NO3−, analogous to oceanographic conditions observed in the field with a red tide of this species in the Seto Inland Sea, were simulated in the tank. C. antiqua was capable of migrating through very sharp salinity and temperature gradients (max ΔS = 2.8‰, ΔT = 2°C) between surface and deep waters. At night the population migrated to deep, nutrient‐rich water and took up PO43− and NO3−. During the day it migrated to the nutrient‐depleted surface water and utilized accumulated nutrients for photosynthesis. Uptake of PO43− and NO3− was synchronized, even if only one was limiting in the water column. Under stable stratification of nutrients, diel vertical migration and nocturnal uptake of nutrients in the deep, nutrient‐rich water were essential for C. antiqua to grow at rates comparable with those of coastal diatoms, which have no migratory ability.