Productivity and population diversity of marine organotrophic bacteria in enclosed planktonic ecosystems

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Abstract
Enclosed ecosystem experiments with marine plankton were carried out in Rosfjord, Norway, March-April, 1979. Results from studies on planktonic bacteria in natural communities and cultures of phytoplankton contained in 1-m diameter flexible plastic bags are reported and these are compared to observations in the surrounding sea. Emphasis was on organotrophic bacteria and their diversity dynamics, particularly in relation to phytoplankton. Five previously isolated strains of bacteria were followed by immunofluorescent staining on membrane filters, and the populations of chromobacteria, bdellovibrios and luminescent bacteria were assayed by specific methods. Secondary productivity of total bacterial populations was estimated from growth rate measurements in filtered seawater and compared to net primary production. Possibly as much as 1/3 of the net production was ultimately consumed by the bacteria. The highly dynamic state of organotrophic bacterial populations and diversity in the sea are demonstrated, and the roles of substrate quality and concentrations of potential bacterial grazers in population regulation are discussed.