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

Bacterial abundance and ³H]thymidine incorporation rates wereused to characterize bacterial distributions and dynamics duringa spring diatom bloom in the coastal plume of the Hudson Riverduring March, 1981. Bacterial abundance did not decline significantlyaway from the plume or across the continental shelf. However,a pronounced gradient was observed for ³H]thymidine incorporation. Following a northeast gale, a bloom of Skeletonema costatumdeveloped in response to coastal upwelling. As the plume becamesaltier, warmer and larger, bacterial abundance averaged 1.3x 10⁹ cells 1^–1. Bacterial incorporation of ³H]thymidineinto cold 5% TCA insoluble materials, bacterial production andspecific growth rates averaged 80–120 pmol 1^–1 d^–1,1.4–2.0 x 10⁹ cells 1^–1 and 1.2–1.5 d^–1.respectively. The mean density of bacteria in the plume didnot change even though growth rates were higher than expectedlosses from sinking, mixing and export. The abundance and production levels of attached bacteria inthe plume were significantly higher than they were in coastalwater outside the plume. In contrast, free bacterial levelswere similar in all regions of the shelf and plume. Bacterialparameters in the plume were not correlated with phytoplanktonpigment concentrations, while significant positive correlationswere found in shelf waters >33 salinity. Thus bacteria werecoupled to phytoplankton in shelf waters but not in the plumewhere allochthonous dissolved matter was probably supportingthe bacteria. ^*Lamont-Doherty Geological Observatory Contribution No. 3459 ²Present address: Department of Microbiology, University ofGeorgia, Athens, GA 30602, USA.