INTRODUCTION

Phage ecology, considering the ecological significance of native viruses in natural aquatic ecosystems, has had a momentous development since the early 1990s, when it was acknowledged that the abundance of viruses in natural aquatic ecosystems was much higher than had been anticipated. During that time new methods and approaches have been applied to the study of viral communities as well as different aspects of viral activity in natural ecosystems. It has been necessary to develop new concepts and models to interpret these new data and knowledge within the context of ecosystem structure and function. Several excellent reviews provide a comprehensive summary and analysis of the data and information that has accumulated (Fuhrman, 1999; Wilhelm and Suttle, 1999; Wommack and Colwell, 2000; Paul et al., 2002; Weinbauer, 2004; Suttle, 2005) and the reader should consult these for a more complete review of the literature. The purpose of the present chapter is to provide a brief overview of contemporary aquatic phage ecology, including a closer look at the extent to which present theory can be claimed to explain the observations now available.

Based on the numerical dominance of prokaryote over eukaryote unicellular organisms in the pelagic environment (a factor of 2–3 orders of magnitude), the usual assumption is that the population of free viruses is dominated by bacteriophages.