Multiscale variability in bacterioplankton abundance, production, and specific growth rate in a temperate salt‐marsh tidal creek

Abstract

Heterotrophic bacterioplankton abundance, production, and specific growth rate in a salt‐marsh tidal creek were measured weekly from April 1991 to September 1992. During the same period, tidal and diel sampling studies were performed in May, June, and October 1991 and May and August 1992. Seasonal variability of bacterial abundance, production, and specific growth rate was regulated by temperature during nonsummer seasons when temperature was <20°C. During summer, bacterial variables were not limited by temperature. Daily variability of bacterial abundance, production, and specific growth rate was regulated interactively by tidal mixing, substrate supply, and temperature over several tidal cycles. Higher bacterial abundance, production, and specific growth rate observed at low tide indicated that bacterial growth rate in the tidal creek was higher than in the adjacent river waters. This pattern might be due to larger nutrient fluxes originating in the tidal creek. Occasionally, the tidal effect was overridden by temperature during study periods when temperature changed dramatically over several tidal cycles. Bacterial diel patterns in production and specific growth rate in the tidal creek occurred only when day‐night temperature differences exceeded 10°C, with maximal values during daytime. Short‐term temperature manipulation experiments suggested that diel patterns in bacterial production and specific growth rate were probably caused by temperature, not light intensity. Thus, temperature regulated both seasonal and diel variations in bacterial production.