Interactions Between HAB Species and Grazers

Copepods and other macrozooplankton reduce their grazing rates when they encounter dense blooms of some toxic dinoflagellates, perhaps as a result of impaired motor control and elevated heart rates. Heterosigma carterae is avoided by zooplankton predators including rotifers, copepods, pilchard larvae, and juvenile menhaden, but the underlying mechanism is unknown. The tintinnid Favella taraikaensis avoids Heterosigma, even when starved, and reverses the beat of its adoral membranelle to reject cells. Further, Heterosigma is a poor food for mussels, clams, and oysters. Chrysochromulina polylepis negatively affects both feeding and growth rate of the tintinnid Favella ehrenbergii. These are but a few examples of how zooplankton can avoid or reject certain HAB species, and how they can be physiologically impaired once they have consumed the toxic algae.