Seasonal and inter-annual variability in bacterial production and biomass in a temperate estuary

Abstract

Areal bacterial production covaried with phytoplankton production in all regions of the Delaware Estuary, although phytoplankton production explained less of the variance in bacterial production upstream (<7‰ salinity) than in the middle and lower estuary. Specific growth rate correlated with temperature when waters were <12°C, but there was no relationship at higher temperatures. Over the entire estuary, the ratio of annual bacterial production to phytoplankton production was 0.4. In the upper estuary bacterial production exceeded phytoplankton production by 1.4-fold, suggesting that allochthonous sources of organic matter are more important than phytoplankton in supporting bacterial growth in this region. During 5 yr of study, the summer average of bacterial abundance and production varied 2-fold, which could largely be explained by the summer phytoplankton production. Even though bacteria and phytoplankton are uncoupled during the change of seasons, year-to-year variation in bacteria is apparently controlled by primary production and the fraction of primary production processed by heterotrophic bacteria is relatively constant. -from Authors