The uptake of nutrients across the cell surface is the key process in microbe
competition. Competition for nutrients is often thought of in terms of receptor
affinity and receptor uptake on a simple geometry. Diatoms are a diverse and
important group of microbes responsible for 40\% of the oceans' primary
production. Their membranes are covered by a frustule: an intricate,
porous-silica structure. Here, the role of frustules in influencing diffusive
nutrient uptake is examined analytically and numerically. We propose that
distinct structures are specifically adapted to control nutrient movement at the
diatom surface, and find that nanostructures select for different nutrients.
Structurally influenced diffusion is a little studied mechanism influencing
phytoplankton dynamics and competition. The combination of constrained diffusion
and nutrient uptake produces a new and the richest yet explanation for the
morphological diversity of diatom frustules.