Microbial trophodynamics in the Delaware Estuary

Abstract

ABSTRACT: The relationship between bacteria, phytoplankton and heterotrophlc microflagellates is examined over large spatial and seasonal scales in the Delaware Estuary, USA. The estuary was sampled along the main salinity axis (0 to 30 ppt), from near Philadelphia to the mouth, between February and Auqust 1985. Samples were analysed for bacterial abundance and production, for heterotrophic microflagellate abundance and grazing rate on bacteria, and for phytoplankton production and biomass. Temperature was a major factor that requlated bacteria and microflaqellates. With the exception of cold peridds, bacterla and microflagellates appeared to respond to phytoplankton production During the spring and summer, bacterial production and microflagellate grazing were highest in the lower estuary, where phytoplankton production was also highest. Bacterial production was on average 23% of the phytoplankton carbon production. In this area of the estuary grazing on bacteria was highest. Bacterivores grazed 95% of the bacterial production. Estimates on the carbon flow from phytoplankton to bacteria and subsequently to microflagellates suggest that bacteria and microflagellates do not return lost phytoplankton production to the main phytoplankton-zooplankton food chain in the Delaware Estuary. Instead, it appears that the primary effect of heterotrophic microbes is the mineralization of organic compounds to their inorganic constituents.