Simulating chemosensory responses of marine microorganisms1

I have studied the nature of chemosensory interactions in situations relevant to aquatic ecosystems by incorporating a model of chemokinesis by laboratory bacteria into a Monte Carlo simulation of bacterial movement around leaky microalgae. I assumed that the concentration field of the substrate around an alga is determined by molecular diffusion. Results of simulations and various theoretical arguments imply that there is a smallest organism size with a radius >2 µ m which bacteria can find using chemosensory responses. Bacteria most easily find algae that are large and have a high specific leakage rate. Because its feeding also involves chemosensing of food items, a copepod’s observed inability to feed on small algae may also be the result of its inability to sense this potential food. The lack of sensory mechanisms to detect small organisms at a distance implies that the sensing of small organisms must, by default, involve physical contact. This inference agrees with filtration mechanisms noted for microzooplankton feeding.