Abstract
A biophysical model is used to compare the possible impacts of two different modes of cell orientation: taxis directed and metabolisminfluenced. The included submodels provide wind‐induced turbulent mixing in the Ekman layer based on wind forcing that randomly varies from day to day; a diurnal light cycle of sea‐surface photosynthetically active radiation (PAR) that is influenced by random cloud cover and that attenuates exponentially with depth; cell‐specific respiration and photosynthesis, with the latter incorporating high PAR photoinhibition, diel variability, and sun‐shade acclimation that varies from day‐to‐day; and cell motility with swimming speed that depends on gravity, temperature, and light intensity and with the two different orientation options. Taxis‐directed orientation is based on positive phototaxis during daylight and positive geotaxis at night. Metabolism‐influenced orientation uses a depth threshold to stop descent, sunrise or a cumulative respiration threshold approached at a rate based on the previous day’s PAR exposure to start ascent, a surface response or a photoinhibition threshold to stop ascent, and sunset or a cumulative photosynthesis threshold to start descent. The thresholds act as proxies for various cellular processes including nutrient uptake or metabolic synthesis that may be involved in orientation preference. Under the modeled conditions, cells using metabolism‐influenced regulation of swimming behavior exhibit more uniformly high cumulative primary production than those that do not.