IMPACT OF CELL-SHAPE AND CHAIN FORMATION ON NUTRIENT ACQUISITION BY MARINE DIATOMS

Diatoms have evolved a multitude of morphologies, including highly elo ngated cells and cell chains. Elongation and chain formation have many possible functions, such as grazing protection or effects on sinking. Here, a model of diffusive and advective nutrient transport is used t o predict impacts of cell shape and chain length on potential nutrient supply and uptake in a turbulent environment. Rigid, contiguous, prol ate spheroids thereby represent the shapes of simple chains and solita ry cells. Ar scales larger than a few centimeters, turbulent water mot ions produce a more or less homogeneous nutrient distribution. At the much smaller scale of diatom cells, however, turbulence creates a roug hly linear shear and nutrients can locally become strongly depleted be cause of nutrient uptake by phytoplankton cells. The potential diffusi ve nutrient supply is greater for elongated than for spherically shape d cells of similar volume but lower for chains than for solitary cells . Although the relative increase in nutrient transport due to turbulen ce is greater for chains, single cells still enjoy a greater total nut rient supply in turbulent environments, Only chains with specialized s tructures, such as spaces between the cells, can overcome this disadva ntage and even obtain a higher nutrient supply than do solitary cells. The model results are compared to laboratory measurements of nutrient uptake under turbulent conditions and to effects of sinking.