Suspension Regulation in Positively Buoyant Marine Diatoms

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This research program will determine the role of internal ionic regulation in maintaining the positive buoyancy of large oceanic diatoms, Rhizosolenia, using a combined laboratory and field program. Previous work has shown that diatoms of the genus Rhizosolenia are positively buoyant, and that this buoyancy can be described by a size- dependant function of cell sap density and silicification. This program will follow the buoyancy response of positively buoyant diatoms to light and nutrient (N, P, Si) manipulations. The resulting changes in direction and rate of movement will be related to variations in the cell sap ionic composition and concentration of internal nutrient pools. Diel studies will measure the temporal variation in buoyancy to determine its potential effect on the vertical positioning of cells in relation to life-cycle phenomenon. The potential for vertical migration in these diatoms for utilization of deep nitrate pools will be specifically addressed in laboratory and field experiments. This work represents the first focused analysis of positive buoyancy in diatoms, a class of plankton previously assumed to be incapable of directed upward movement in the euphotic zone.