Peter Countway, PhD

Senior Research Scientist
Microbial Ecologist
Phone: +1 (207) 315-2567, ext. 302

For media inquiries, please contact


BA, Zoology, University of New Hampshire, 1990

MS, Marine Science, College of William and Mary, 1999

PhD, Biology, University of Southern California, 2005

Research Interests

My research encompasses the fields of marine microbial diversity, ecology, and physiology, using molecular and genomic approaches.

My most recent work focuses on protistan diversity and activity in the benthos and water column surrounding deep-sea hydrothermal vents in the Gulf of California and the East Pacific Rise. He worked for five years as an oceanographic research technician at the Bermuda Biological Station, participated in more than 50 oceanographic cruises, and logged four dives in the research submersible Alvin as part of his deep-sea research.

Outreach Website



  • Lie A. A. Y., Liu Z., Hu S. K., Jones A. C., Kim D. Y., Countway P. D., Amaral-Zettler L. A., Cary S. C., Sherr E. B., Sherr B. F., Gast R. J., Caron D. A. (2014) Investigating microbial eukaryotic diversity from a global census: Insights from a comparison of pyrotag and full-length sequences of 18S rRNA genes. Applied and Environmental Microbiology 80:4363-4373
  • Kim D. Y., Countway P. D., Jones A. C., Schnetzer A., Yamashita W., Tung C., Caron D. A. (2014) Monthly to interannual variability of microbial eukaryote assemblages at four depths in the eastern North Pacific. ISME Journal 8:515-530


  • Coyne, K. J., Countway, P. D., Pilditch, C., Lee, C., Caron, D. A. & Cary, S. C. 2013. Diversity and distributional patterns of ciliates in Guaymas Basin hydrothermal vent sediments. The Journal of Eukaryotic Microbiology, 60:433-447


  • Caron, D. A., Countway, P. D., Jones, A. C., Kim, D. Y. & Schnetzer, A. 2012. Marine Protistan Diversity. In: Carlson, C. A. & Giovannoni, S. J. (eds.) Annual Review of Marine Science, Vol 4. Annual Reviews, Palo Alto. 4:467-493
  • Howard, M. D. A., Jones, A. C., Schnetzer, A., Countway, P. D., Tomas, C. R., Kudela, R. M., Hayashi, K., Chia, P. & Caron, D. A. 2012. Quantitative Real-Time Polymerase Chain Reaction for Cochlodinium fulvescens (Dinophyceae), A Harmful Dinoflagellate from California Coastal Waters. Journal Of Phycology, 48:384-393
  • Kim, D. Y., Countway, P. D., Yamashita, W. & Caron, D. A. 2012. A combined sequence-based and fragment-based characterization of microbial eukaryote assemblages provides taxonomic context for the Terminal Restriction Fragment Length Polymorphism (T-RFLP) method. Journal Of Microbiological Methods, 91:527-536


  • Garneau, M. E., Schnetzer, A., Countway, P. D., Jones, A. C., Seubert, E. L. & Caron, D. A. 2011. Examination of the Seasonal Dynamics of the Toxic Dinoflagellate Alexandrium catenella at Redondo Beach, California, by Quantitative PCR. Applied and Environmental Microbiology, 77:7669-7680
  • Kim, D. Y., Countway, P. D., Gast, R. J. & Caron, D. A. 2011. Rapid Shifts in the Structure and Composition of a Protistan Assemblage During Bottle Incubations Affect Estimates of Total Protistan Species Richness. Microbial Ecology, 62:383-398
  • Schnetzer, A., Moorthi, S. D., Countway, P. D., Gast, R. J., Gilg, I. C. & Caron, D. A. 2011. Depth matters: Microbial eukaryote diversity and community structure in the eastern North Pacific revealed through environmental gene libraries. Deep-Sea Research Part I-Oceanographic Research Papers, 58:16-26
  • Steele, J. A., Countway, P. D., Xia, L., Vigil, P. D., Beman, J. M., Kim, D. Y., Chow, C. E. T., Sachdeva, R., Jones, A. C., Schwalbach, M. S., Rose, J. M., Hewson, I., Patel, A., Sun, F. Z., Caron, D. A. & Fuhrman, J. A. 2011. Marine bacterial, archaeal and protistan association networks reveal ecological linkages. ISME Journal, 5:1414-1425


  • Countway, P. D., Vigil, P. D., Schnetzer, A., Moorthi, S. D. & Caron, D. A. 2010. Seasonal analysis of protistan community structure and diversity at the USC Microbial Observatory (San Pedro Channel, North Pacific Ocean). Limnology And Oceanography, 55:2381-2396
  • Gilg, I. C., Amaral-Zettler, L. A., Countway, P. D., Moorthi, S., Schnetzer, A. & Caron, D. A. 2010. Phylogenetic Affiliations of Mesopelagic Acantharia and Acantharian-like Environmental 18S rRNA Genes off the Southern California Coast. Protist, 161:197-211


  • Caron, D. A. & Countway, P. D. 2009. Hypotheses on the role of the protistan rare biosphere in a changing world. Aquatic Microbial Ecology, 57:227-238
  • Caron, D. A., Worden, A. Z., Countway, P. D., Demir, E. & Heidelberg, K. B. 2009. Protists are microbes too: a perspective. ISME Journal, 3:4-12
  • Caron, D. A., Countway, P. D., Savai, P., Gast, R. J., Schnetzer, A., Moorthi, S. D., Dennett, M. R., Moran, D. M. & Jones, A. C. 2009. Defining DNA-based operational taxonomic units for microbial-eukaryote ecology. Applied and Environmental Microbiology, 75:5797-5808
  • Rose, J. M., Vora, N. M., Countway, P. D., Gast, R. J. & Caron, D. A. 2009. Effects of temperature on growth rate and gross growth efficiency of an Antarctic bacterivorous protist.Isme Journal, 3:252-260
  • Vigil, P., Countway, P. D., Rose, J., Lonsdale, D. J., Gobler, C. J. & Caron, D. A. 2009. Rapid shifts in dominant taxa among microbial eukaryotes in estuarine ecosystems. Aquatic Microbial Ecology, 54:83-100


  • Countway, P. D., Gast, R. J., Dennett, M. R., Savai, P., Rose, J. M. & Caron, D. A. 2007. Distinct protistan assemblages characterize the euphotic zone and dee li sea (2500 m) of the western North Atlantic (Sargasso Sea and Gulf Stream). Environmental Microbiology, 9:1219-1232


  • Countway, P. D. & Caron, D. A. 2006. Abundance and Distribution of Ostreococcus sp. in the San Pedro Channel, California, as Revealed by Quantitative PCR. Applied and Environmental Microbiology, 72:2496-2506
  • Moorthi, S. D., Countway, P. D., Stauffer, B. A. & Caron, D. A. 2006. Use of quantitative real-time PCR to investigate the dynamics of the red tide dinoflagellate Lingulodinium polyedrum.Microbial Ecology, 52:136-150


  • Countway, P. D., Gast, R. J., Savai, P. & Caron, D. A. 2005. Protistan diversity estimates based on 18S rDNA from seawater incubations in the western North Atlantic. Journal of Eukaryotic Microbiology, 52:95-106
  • Countway, P. D. 2005. Doctoral Dissertation: Molecular Ecology of Marine Protistan Assemblages. Dept. of Biology: Marine Biology & Biological Oceanography. University of Southern California


  • Caron, D. A., Countway, P. D. & Brown, M. V. 2004. The growing contributions of molecular biology and immunology to protistan ecology: Molecular signatures as ecological tools.Journal of Eukaryotic Microbiology, 51:38-48


  • Caron, D. A., Countway, P. D., Lambert, S. E., Rose, J. M. & Schaffner, R. A. 2002. Protozoa in marine and estuarine waters. In: Bitton, G. (ed.) Encyclopedia of Environmental Microbiology.John Wiley & Sons, Inc., New York.2613-2626


  • Countway, P. D. 1999. Carbon production and growth physiology of heterotrophic bacteria in a subtropical coral reef ecosystem. M.S. Thesis, Virginia Institue of Marine Science, College of William and Mary