New Accomplishments and Approaches for Assessing Protistan Diversity and Ecology in Natural Ecosystems

single-celled, microscopic forms nearly 4 billion years ago. These minute forms constituted all life on the planet for roughly half of Earth’s biological history, and microbes have remained important determinants of organic matter production, trophic transfer, and degradation throughout Earth’s entire history, although more attention and research tend to be focused on charismatic macrofauna. It therefore seems fitting, albeit overdue, that characterizing and understanding the importance of microbial diversity and function in natural ecosystems has become a focal point of ecological research in the 21st century. Microbial ecology has risen to prominence in ecological research from its rather meager status as recently as the middle of the last century. Awareness of the diversity and importance of the larger phytoplankton (e.g., diatoms, dino flagellates) increased rapidly in the early 20th century. However, even for this conspicuous component of aquatic food webs, studies throughout the latter half of that century significantly added to our knowledge of the standing stocks and diversity of these assemblages and initiated our awareness of the presence and importance of cyanobacteria and minute eukaryotic phototrophs (Malone 1971, Olson et al. 1990). Our knowledge of the ecological niches of aquatic bacteria and protozoa progressed more slowly, and with a few notable exceptions, these assemblages remained an ecological footnote relegated to vaguely defined decompositional processes until the last few decades of the 20th century (Pomeroy 1974, Sieburth 1979). Similarly, the ecological roles of soil bacteria and protozoa have been documented for more than a century, yet recognition of the central role that they play in organic matter degradation and nutrient uptake by plants did not improve dramatically until the latter half of the last century (Alexander 1961). Today, microbes in the ocean and in freshwater ecosystems are widely recognized as essential participants in global biogeochemical cycles. These taxa constitute the bulk of the standing stock of biomass in most of the world’s oceans (Caron et al. 1995), and primary production by cyanobac teria and eukaryotic phytoplankton is responsible for roughly half of the organic carbon and oxygen produced on Earth (and for removal of a commensurate amount of carbon dioxide).