Benthic–pelagic coupling in sediment-associated populations of Karenia brevis

Nutrient delivery to populations of Karenia brevis in oligotrophic water columns in the Gulf of Mexico remains uncertain. Aggregations of K. brevis near the sediment–water interface suggest that cells derive nutrients from the sediment. Video of cells near the sediment suggest that cells either access nutrients that flux out of the sediment or migrate into the sediment pores where higher nutrient concentrations exist. Experiments tested K. brevis' ability to migrate into the sediment using chambers divided by a 100 μm mesh overlain with a thin layer of sediment. Since the diel vertical migration of K. brevis typically displays a nocturnal descent, experiments tested migration response at night in response to sub-sediment nutrient sources. The experiments suggest that while the sediment affects the progress of descending cells, migration occurs through thin layers of sediment and increases in response to elevated nutrient concentrations below the sediment. Since all cells found below the sediment had significantly higher C/N ratios than those remaining above the sediment, migration appears related to a cell's internal biochemical state. The vertical migration behavior of K. brevis may help alleviate bottom-up controls and permit populations to persist as vegetative cells near the sediment–water interface.