AME 61:45-56 (2010)  -  DOI: https://doi.org/10.3354/ame01434

ABSTRACT: The present study is the first to simultaneously document the contributions of bacteria, heterotrophic flagellates, ciliates, and naked, planktonic amebas to the carbon (C) budget of an estuarine water column, and is also the first study of protistan bacterivory in the lower Hudson River Estuary (HRE). Observations were collected at a single near-shore location between June 2006 and May 2009. Bacterial counts and biomass varied approximately 1 order of magnitude on different dates, but were comparable to previous studies of the HRE and other estuaries. Of the 3 heterotrophic protist groups enumerated, heterotrophic nanoflagellates were the least variable and generally had the highest biomass (on average equaling 38% of the bacterial biomass). Counts and biomasses of ciliates and amebas were highly variable, ranging over at least 3 orders of magnitude between sampling dates. Much of the variability in ameba abundance was consistent with previous observations of seasonality. Ciliate biomass averaged 8%, and ameba biomass averaged 15% of the bacterial biomass. Thus, at this location, the importance of amebas as micropredators may be comparable to that of the ciliates, a group generally receiving greater research attention. Ameba ingestion rates could not be measured directly but 3 indirect approaches for calculating ingestion rates produced mean values ranging from 1.2 to 2.5 ng C d^–1 ng^–1 ameba biomass. Each approach demonstrated that ameba C consumption at the study location was highly variable, but was at times high relative to the bacterial standing stock. Taken together, these data suggest that amebas may be more common and of greater importance in estuarine C-fluxes than generally appreciated.

KEY WORDS: Amoeboid protists · Bacterivory · Bactivory · Grazing · Microzooplankton · Microbial ecology · Ameba · Amoeba