Nitrate uptake by Karenia brevis. II. Behavior and uptake physiology in a nitrate-depleted mesocosm with a bottom nutrient source

Karenia brevis may optimize growth by alternately maximizing exposure to light, migrating up into an oligotrophic water column during the day, and to nutrients (nitrate), by migrating down to the sediment-water interface at night. Understanding how cell behavior contributes to the acquisition of light and nutrients that are separated in space is critical to understanding how K. brevis populations persist in oligotrophic environments. In response to previous modeling efforts that parameterized cell physiology and behavior in nitrate- replete conditions, we examined similar cellular characteristics in a stratified 1.5 m deep mesocosm. The upper 2/3 of the mesocosm, encompassing the surface and middle samples, was nitrate depleted (