Parasitic Dinoflagellates of Marine Ciliates: Their Significance in Microbial Food Webs

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Ciliated protozoa are widely recognized as an important component of planktonic communities and are believed to play a pivotal role in marine microbial food webs. The importance of ciliates as consumers of phytoplankton and, to a lesser extent, bacterioplankton has been well studied and is now generally accepted. Larger zooplankton are usually viewed as the predominant consumers of ciliates, yet there is little evidence that grazing by metazoa has a substantial impact on ciliate populations. Recent studies of the parastiic dinoflagellate Duboscquella cachoni and its tintinnine host Eutintinnus pectinis in Chesapeake Bay indicate that parasitism can have a significant impact on host abundance in coastal environments where E. pectinis densities are sufficiently high to support epizootic infections. Whether parasitism has a strong influence on other estuarine species or on ciliates in the open ocean where host densities are considerably lower is uncertain. The importance of parasitism to the fate of the ciliate protozooplankton in Chesapeake Bay will be evaluated through a combination of field studies to determine host-parasite abundance, species composition, parasite life histories and generation times.