Seasonality of Chesapeake Bay Bacterioplankton Species

Bacteria, γ-subclass of Proteobacteria, Vibrio-Photobacterium, Vibrio vulnificus, Vibrio cholerae-Vibrio mimicus, and Vibrio cincinnatiensis in water samples collected from the Choptank River in Chesapeake Bay from 15 April to 16 December 1996 were enumerated using a fluorescent oligonucleotide direct-counting (FODC) procedure. FODC results obtained using a Bacteria taxon-specific probe ranged from one-third the number of to the same number as that obtained by the acridine orange direct count (AODC) procedure. The abundance of individual taxa (per liter) ranged from 0.25 × 10(10) to 2.6 × 10(10) Bacteria, 0.32 × 10(8) to 3.1 × 10(8) γ-Proteobacteria, 0.2 × 10(8) to 2.1 × 10(8) Vibrio-Photobacterium, 0.5 × 10(7) to 10 × 10(7) V. vulnificus, 0.2 × 10(6) to 6 × 10(6) V. cholerae-V. mimicus, and 0.5 × 10(5) to 8 × 10(5) V. cincinnatiensis. The occurrence of all taxa monitored in this study was higher in summer; however, these taxa made up a larger proportion of the Bacteria when the water temperature was low. Large fluctuations in species abundance as well as in percent composition of Vibrio-Photobacterium occurred from week to week, indicating that localized blooms of these taxa occur. The cross-Choptank River transect sample profile of V. vulnificus and V. cholerae-V. mimicus varied significantly in abundance, and trans-Choptank River transect samples revealed a patchy distribution.