Abstract

Experiments were conducted to test the possible effects of viral concentrate additions on the respiration rates of both Chaetoceros gracilis and a natural microplankton community (<200 ?m) from a shallow bay located in central-south Chile (Coliumo Bay, 36°32?S, 72°57?W). Each experiment was started by adding 2 ml of viral concentrate to a C. gracilis culture, microplankton community or bacterioplankton community (nominal size 0.2-1.0 ?m) contained in a 125 ml borosilicate bottle. The incubations lasted 24 h at in situ temperatures and included a minimum of five replicates and five controls. Respiration was measured as oxygen consumption using a semi-automatic photometric Winkler method. Samples were taken from the experimental bottles to assess chlorophyll a, ATP concentration and bacterioplankton abundance throughout the incubation period. Our results show that the addition of viral concentrates can affect the respiration rates of both natural microplankton communities and C. gracilis cultures. When subjected to a viral concentrate addition, the respiration rates of the natural microplankton community decreased by 12-50% or increased by 29%, depending on the experiment, whereas bacterioplankton respiration rates increased by 92% and decreased by 78%, and C. gracilis rates increased by ?4% and decreased by ?7%.