Potential overestimation of bacterial respiration rates in oligotrophic plankton communities

Adequate bacterial respiration (BR) estimations are necessary to understand the flow of carbon through marine plankton food webs. A considerably higher bacterial contribution to total microbial plankton community respiration (CR) has been observed in oligotrophic systems compared to more productive systems. Classical BR estimation procedures, typically oxygen consumption measurements, comprise pre-incubation filtration to separate bacteria from the rest of the plankton community and long incubation times (24 h). The resulting disruption of the community linkages over long time periods might affect BR measurements, especially in oligotrophic systems characterized by tightly coupled microbial food webs. In this study, BR data were compiled from 2 con trasting environments: the highly productive R a de Vigo (NW Spain) and the North Atlantic oligotrophic gyre. Standard procedures or in vivo electron transport system (ETS) activity (non prefiltered and short-time incubation) procedures were used to obtain a total of 209 BR estimations. Bacterial contribution to plankton CR was significantly higher in oligotrophic than in highly productive conditions (155% and 42%, respectively) when using standard procedures, while similar values were observed (31% and 30%) with in vivo ETS procedures. The relation between plankton CR and BR along the studied productivity gradient suggests that bacterial contribution to total CR varies less than previously assumed with an average value approximating 30% through different trophic situations.