Increasing concern over the global spread of red tides produced by toxic and non-toxic dinoflagellates has focused research interest on physical and biological interactions that influence the accumulation, persistence, and demise of bloom-forming species. The harmful effects imposed by red tides on marine fauna and associated risks to public health and commercial fisheries have also prompted interest in means to detect, predict, and potentially control harmful algal blooms. Recent studies have shown that microparasites, including viruses, bacteria, and protozoa, are abundant in marine environments. Furthermore, parasite-induced mortality of bacterioplankton and phytoplankton can cause population level changes in host abundance on time scales of hours to days. Infection of red-tide dinoflagellates by their parasitic relative Amoebophrya ceratii has been linked to rapid declines in host populations. This parasite has also been implicated as an important factor in preventing bloom formation. while all such infections of free-living dinoflagellates have been attributed to a single species of parasite, recent data suggest that A. ceratii is a species complex composed of multiple host-specific parasites. This research will further the understanding of red-tide ecology by considering the interplay between host specificity and parasitism of bloom-forming dinoflagellates in Chesapeake Bay. It will also help define the complexity of host-parasite interactions in planktonic systems and provide new insight on the role of parasitism in microbial food-web dynamics. Five specific hypotheses will be tested using state-of-the-art morphological and molecular methods.
