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

Dynamics of heterotrophic bactena and phytoplankton m the Delaware Estuary (USA) were studied over 3 yr along a sampling transect that enconlpassed the enbre sahnity gradient (0 to 32%) Bactenal abundance and chlorophyll a concentration were only weakly correlated (r = 0 17) Area1 bactenal production (from 3H-thymidme and '4C-leucine incorporalon rates) covaned w t h phytoplankton production in all geographic regions of the estuary (r = 0 ?0), although phytoplankton production explained less of the variance in bactenal production upstream (<? %o s a h i t y ) than in the rmddle and lower estuary Specific growth rate correlated with temperature when waters were < 12C but there was no relabonship at h g h e r temperatures (>12"C) Over the entire estuary, the ratio of annual bactenal production to phytoplankton production was 0 4 In contrast, in the upper estuary bactenal production exceeded phytoplankton production by 1 4-fold, suggesting that allochthonous sources of organic matter are more important than phytoplankton in supporting bactenal growth in t h s region Dunng 5 yr of study, the summer average (May to September) of bactenal abundance and production vaned 2-fold, whlch could largely be explained by the summer phytoplankton production Even though bacteria and phytoplankton are uncoupled during the change of seasons, year-to-year vanation in bactena is apparently controlled by pnmary production and the fraction of primary production processed by heterotrophlc bactena is relatively constant