Distribution of Virus-Infected Bacteria in the Western Equatorial Pacific

Abstract

Abstract: Viruses are generally considered an important agent of bacterial loss in diverse marine environments. However, the impact of viruses on bacteria is unknown in the western equatorial Pacific, where surface waters are warm and phytoplankton biomass is low (i.e., oligotrophic). Further, little is known about their importance in the mesopelagial, where bacteria and heterotrophic nanoflagellates are known to be metabolically active. To elucidate the ecological characteristics of viruses in the western equatorial Pacific, abundances of bacteria and viruses were measured, along with frequencies of visibly infected cells (FVIC) and frequencies of dividing cells (FDC) in epipelagic and mesopelagic samples at three stations near the equator from August to September 2002. Measurements of Secchi depth (20 m) and chlorophyll a concentrations (0.07– 0.4 µg chl a liter-1) indicated that the study area was oligotrophic during the investigation. FVIC ranged from 0.4% to 1.8% and 0.5% to 1.8% in the epipelagic an...