Changes in protistan community structure due to zooplankton predation: Application of molecular tehniques for studying food web dynamics

Protists (microalgae and protozoa) are important components of aquatic plankton communities, yet only limited information is available on the factors influencing biomass and species diversity of protists within natural plankton assemblages. The aim of my study is to examine trophic coupling between protists and metazooplankton in the California coastal ocean by combining traditional methods (light and electron microscopy) with new molecular approaches (based on ribosomal DNA sequence information). I am investigating 1) to what extent protistan biomass contributes to zooplankton diet, 2) if zooplankton selectively prey on certain protistan species or groups, 3) and how zooplankton predation impacts protistan community structure. An initial feeding experiment was conducted in August 2002 to determine changes in protistan community structure as a consequence of copepod predation (data are currently processed). Another feeding experiment is planned for the period of the spring phytoplankton bloom to examine how seasonal changes in protistan biomass and community structure affect zooplankton feeding behavior. A major focus of my second research year is directed towards the design of species-specific probes and their application. This method provides a unique, more rapid and accurate means of assessing the presence and abundance of specific protistan species, and provides information on the trophic interactions and biogeochemical cycling taking place within marine or freshwater ecosystems.