MEASUREMENT OF BACTERIAL PRODUCTION AND BACTERIVORY WITHIN A PLANKTONIC FOOD WEB IN A PRODUCTIVE TEMPERATE CONTINENTAL SHELF ECOSYSTEM: METHOD VALIDATION AND ECOLOGICAL IMPACT

Marine heterotrophic bacteria are the most abundant, diverse, and metabolically active organisms in the ocean and while abundances are routinely measured in oceanographic surveys, measurements on growth and bacterivory rates by protists are sparse. The Northeast Shelf Long-Term Ecological Research (NES-LTER) project routinely measures the growth of marine phytoplankton and grazing rate by protists and recently added bacterial growth and bacterivory measurements. To achieve this, we 1) identified the appropriate Flow Cytometer cell concentration range; 2) validated the method using dilution levels and microscopy to cross-validate; and 3) determined a reliable analysis duration with SYBR-Green DNA Stain. We found that using a bacterial concentration of < 500 cells µL^-1 avoids instrument over-saturated and subsequent underestimates of bacterial concentrations. Despite these steps, we observed a 33% underestimation of bacteria using the flow cytometer when compared to microscope counts (R²=0.999). Nonetheless, flow cytometry was more precise across replicates than microscopy (%CV Microscope=9%; %CV Guava=1%). Finally, we determined that SYBR-Green is viable for analysis up to 70 minutes after staining. Following method validation, we successfully quantified bacterial growth and bacterivory rates along the NES-LTER transect for the first time. This places these rates within the larger context of the planktonic food web and allows them to be included as routine measurements within the NES-LTER project, building on the knowledge that the NES-LTER project has cultivated.

Presentation Preference: Poster

Primary Presenter: Alexandra Sinno, Univeristy of Rhode Island Graduate School of Oceanography (alexandra_sinno@uri.edu)

Authors:

Alexandra Sinno, University of Rhode Island  (alexandra_sinno@uri.edu)

Susanne Menden-Deuer, University of Rhode Island, Graduate school of Oceanography  (smenden@uri.edu)

Pierre Marrec, University of Rhode Island, Graduate School of Oceanography  (pmarrec@uri.edu)