Preface. Molecular ecology of aquatic communities: where have we been, why are we here, and where are we going? J.P. Zehr. Plasmid Ecology of Marine Sediment Microbial Communities; J.P. Zehr, P.A. Sobecky. Use of the Polymerase Chain Reaction and Denaturing Gradient Gel Electrophoresis to Study Diversity in Natural Virus Communities; S.M. Short, C.A. Suttle. Flow Cytometry in Molecular Aquatic Ecology; J.L. Collier, L. Campbell. Distribution of Microbial Assemblages in the Central Arctic Ocean Basin Studied by PCR/DGGE: Analysis of a Large Data Set; V.C. Ferrari, J.T. Hollibaugh. Bacterial Populations in Replicate Marine Enrichment Cultures: Assessing Variability in Abundance Using 16S rRNA-Based Probes; J.M. Gonzalez, et al. Diversity of Bacterial Communities in Adirondack Lakes: Do Species Assemblages Reflect Lake water Chemistry? B.A. Methe, J.P. Zehr. New Insights on Old Bacteria: Diversity and Function of Morphologically Conspicuous Sulfur Bacteria in Aquatic Systems; N.D. Gray, I.M. Head. The Distribution and Relative Abundance of Ammonia-Oxidizing Bacteria in Lakes of the McMurdo Dry Valley, Antarctica; M.A. Voytek, et al. Microscopic Detection of the Toluene Dioxygenase Gene and Its Expression Inside Bacterial Cells in Seawater Using Prokaryotic In Situ PCR; F. Chen, et al. Variability in bacterial community structure during upwelling in the Coastal Ocean; L.J. Kerkhof, et al. Application of Molecular Techniques to Addressing the Role of P as Key Effector in Marine Ecosystem; D.J. Scanlan, W.H. Wilson. Immunological and Molecular Probes to Detect Phytoplankton Responses to Environmental Stress in Nature; J. LaRoche, et al. Spatial Scale and the Diversity of Benthic Cyanobacteria and Diatoms in a Salina; U. Nubel, et al. A Rapid Method to Score Plastid Haplotypesin Red Seaweeds and Its Use in Determining Parental Inheritance of Plastids in the Red Alga Bostrychia (Ceramiales); G.C. Zuccarello, et al. Protistan Community Structure: Molecular Approaches for Answering Ecological Questions; D.A. Caron, et al. Molecular and Demographic Measures of Arsenic Stress in Daphnia pulex; C.Y. Chen, et al. Taxonomic and Systematic Assessment of Planktonic Copepods Using Mitochondrial COI Sequence Variation and Competitive, Species-Specific PCR; A. Bucklin, et al. Effects of Stress on Freshwater Invertrebrate Populations of Chironomus tentans: Assaying Sub-lethal Stress Using Heat Shock Protein 70 (HSP-70) Expression; N.K. Karouna-Renier, J.P. Zehr. RNA:DNA ratio and other nucleic acid-based indicators for Growth and Condition of Marine Fishes; L. Buckley, et al.