Protistan Community Structure

Protistan assemblages of aquatic ecosystems are the focus of extensive research in aquatic ecology. One stimulus for this work has been the long-standing recognition that phototrophic protists (the unicellular algae) constitute a major fraction of the primary productivity within aquatic ecosystems. We have learned a great deal about the taxonomic composition and trophic structure of aquatic protistan communities through the application of traditional approaches of morphological analysis and culture. Nevertheless, the tremendous diversity of protistan assemblages and the varied methods required for identifying protistan species and their abundances, biomass, and trophic activity continue to hamper in-depth understanding of the structure and function of these communities. The success of using molecular (genetic/immunological) signatures for assessing the community structure of natural protistan assemblages will ultimately depend on linking these signatures to classical (morphological) species descriptions and to the physiological abilities of protistan phylotypes. Ultimately, molecular approaches, in combination with classical methods, will provide new tools for studying the emergent physiological, ecological, and biogeochemical processes that are created and/or affected by protistan community structure. Probably the most distinct difference between freshwater and marine protistan communities is the restriction of the larger sarcodines (acantharia, radiolaria, and foraminifera) to brackish and marine ecosystems. Modern molecular biological approaches have revealed unexpected, and as yet largely uncharacterized, protistan diversity in a wide variety of ecosystems.