Community metabolism and energy transfer in the Chesapeake Bay estuarine turbidity maximum

In an effort to identify the key mechanisms controlling biological productivity and food web structure in the Chesapeake Bay estuarine turbidity maximum (ETM), we measured plankton community metabolism on a series of surveys in the upper Chesapeake Bay during the winter and spring of 2007 and 2008. Measured quantities included primary production, bacterial production, planktonic community respiration, and algal pigment concentrations. These measurements revealed a classic minimum in photosynthesis in the vicinity of the ETM. Temporal variability in plankton community metabolism, primary production, respiration, and bacterial production were highest in the southern oligohaline region down-estuary of the ETM and appeared to be driven by dynamic bio-physical interactions. Elevated primary production and community respiration in this region were often associated with the presence of mixotrophic dinoflagellates. The dinoflagellate contribution to primary production and respiration appeared to be particularly large as a result of their mixotrophic capabilities, which allow them to obtain energy both autotrophically and heterotrophically. The present study suggests that mixotrophic dinoflagellates play a key role in the pelagic food web in the oligohaline region of Chesapeake Bay, supplying most of the labile organic matter during late winter and spring and also providing a vector for transferring microbial production to mesozooplankton.