Diatoms rapidly alter sinking behavior in response to changing nutrient concentrations

A diatom's sinking speed affects its depth in the water column, which determines its access to light and nutrients. Some large, centric diatom species perform an unsteady sinking behavior in which a cell's sinking speed oscillates over more than an order of magnitude on time scales of seconds. Diatoms are known to decrease mean sinking speeds and the magnitude of unsteady sinking following exposure to nutrient replete conditions over hours to days. Here we show that on shorter time scales of minutes to hours, nutrient deprived Coscinodiscus wailesii cells increase the mean and unsteadiness of their sinking when exposed to increased nutrient concentrations. Cultures exposed to nitrate or silicate‐depleted media followed by a spike of the missing nutrient showed a sinking speed increase within the first 2 h that declined over the next 22 h. Phosphate deprived cultures did not respond similarly to a phosphate spike. In an experiment with an artificial nutricline in which cells encountered a sharp increase in nutrient concentrations over a distance of 10 cm, mean sinking speeds increased eight fold, and sinking unsteadiness increased significantly; these sinking speed changes occurred over 33 min. The contrasting short and long‐term sinking behavior responses seen in this study demonstrates the importance of examining sinking behavior over multiple time scales. Initial fast and unsteady sinking upon encountering increasing nutrient concentrations may help diatoms take advantage of patchy nutrient distributions. Longer term, slow and steady sinking may be beneficial for maximizing light exposure and minimizing energy costs from unsteady sinking.