The impact of fine-scale turbulence on phytoplankton community structure

Abstract

We examined the effect of fine-scale fluid turbulence on phytoplankton community structure in an idealized, size-structured community model. It has been shown that turbulence can enhance nutrient transport toward a cell, particularly for larger cells in highly turbulent conditions. Our model suggests that under weak grazing pressure the effect of this mechanism on relative phytoplankton fitness and community structure is negligible. Under these conditions, the high nutrient affinity of small cells dominates relative fitness and allows them to outcompete larger cells. In contrast, when grazing pressure is strong, the turbulent enhancement of nutrient uptake and fitness for larger cells can become ecologically significant. Here, increasing turbulence broadens the size range of coexisting phytoplankton and increases the size of the dominant cell type at equilibrium. We also estimate and map open ocean turbulent dissipation rates as a function of climatological surface wind stresses. The turbulent enhancement of nutrient uptake is most likely to be ecologically significant in regions with low nutrient levels, strong grazing pressure, and relatively high turbulence, such as in windier portions of the subtropical gyre or post-bloom conditions at higher latitudes. In these regions, turbulence may help sustain larger cell populations through otherwise unfavorable environmental conditions.