Bacterial dynamics and distribution during a spring diatom bloom in the Hudson River plume, USA

Bacterial abundance and [ 3 H]thymidine incorporation rates were used to characterize bacterial distributions and dynamics during a spring diatom bloom in the coastal plume of the Hudson River during March, 1981. Bacterial abundance did not decline significantly away from the plume or across the continental shelf. However, a pronounced gradient was observed for [ 3 H]thymidine incorporation. Following a northeast gale, a bloom of Skeletonema costatum developed in response to coastal upwelling. As the plume became saltier, warmer and larger, bacterial abundance averaged 1.3 × 10 9 cells 1 −1 . Bacterial incorporation of [ 3 H]thymidine into cold 5% TCA insoluble materials, bacterial production and specific growth rates averaged 80–120 pmol 1 −1 d −1 , 1.4−2.0 × 10 9 cells 1 −1 and 1.2−1.5 d −1 . respectively. The mean density of bacteria in the plume did not change even though growth rates were higher than expected losses from sinking, mixing and export. The abundance and production levels of attached bacteria in the plume were significantly higher than they were in coastal water outside the plume. In contrast, free bacterial levels were similar in all regions of the shelf and plume. Bacterial parameters in the plume were not correlated with phytoplankton pigment concentrations, while significant positive correlations were found in shelf waters >33‰ salinity. Thus bacteria were coupled to phytoplankton in shelf waters but not in the plume where allochthonous dissolved matter was probably supporting the bacteria.