The Physiological Effect of Aureococcus anophagefferens ("brown tide") on the Lateral Cilia of Bivalve Mollusks.

The "brown tide" alga, Aureococcus anophagefferens, had no effect on the activity of the lateral cilia of isolated gills of the bivalve mollusks Argopecten irradians, Geukensia demissa, and Mya arenaria. A. anophagefferens caused a significant decrease in the activity of lateral cilia of five other bivalve mollusks, Crassostrea virginica, Ostrea edulis, Mercenaria mercenaria, Modiolus modiolus, and Mytilus edulis. Exposure of isolated gills of M. edulis to the water from which A. anophagefferens had been removed, or to polystyrene beads at the same concentration as A. anophagefferens, had no effect upon the activity of the lateral cilia. Thus, the inhibition of the lateral cilia is not caused by a compound excreted into the water, nor is it the result of the high density of cells. The response of lateral cilia to dopamine was identical to the response to A. anophagefferens; lateral cilia that were inhibited by dopamine were also inhibited by A. anophagefferens. Pretreatment of the gills of M. edulis with the dopamine antagonist ergometrine blocked the inhibition of the lateral cilia by both dopamine and A. anophagefferens. A water-soluble inhibitory compound was released from A. anophagefferens by exposing the cells to amylase, and then removing the cells by filtration. The effect of this inhibitory compound was also blocked by ergometrine. We propose that the isolated gills are digesting the extracellular coat of A. anophagefferens releasing a water soluble dopamine-mimetic compound that causes inhibition of lateral cilia.