Introduction

Recent evidence demonstrates that the microbial food web (MFW), composed of a wide array of prokaryotic and eukaryotic microorganisms, creates and processes the bulk of primary production in most aquatic systems.  Protists (unicellular eukaryotic microorganisms) play a central role in this complex and dynamic system Despite their widely recognized importance, the relationship between diversity and ecosystem functions of protists remains poorly understood.  Protists demonstrate a variety of nutritional strategies and adaptations, including mixotrophy. In addition, physiological rates of their natural populations can be related to cell taxonomy more than to cell size.  These adaptations make application of the traditional trophic level concepts within the MFW difficult.  Therefore, examination of relationships between the structure and function of protistan communities is paramount for understanding and predicting ecosystem-level processes in the aquatic environment. 

Traditionally, protist identification methods have relied on the microscopic observation of their cell structures.  However, due to the cryptic nature, small size, and variable morphology of many protistan taxa their diversity may not always be determined accurately by microscopy.  Recent advances in molecular techniques, have allowed for new ways to assess microbial diversity.  The small subunit (18S) rDNA has regions that are highly conserved and are therefore used extensively for phylogeny at higher taxonomic levels.  Despite its demonstrated potential, this approach still requires work, and many taxa, including some important members of the MFW, have not been characterized with molecular tools. 

The goals of this research project sponsored by the Microbial Observatories Program of the National Science Foundation are: (1) to characterize protist composition, abundance, and dynamics in Old Woman Creek in relation to  environmental parameters, and (2) to improve our ability to detect protist diversity by refining the molecular techniques and combining them with advanced microscopy.