Seasonality of Chesapeake Bay bacterioplankton species.

Bacteria, gamma-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 x 10(10) to 2.6 x 10(10) Bacteria, 0.32 x 10(8) to 3.1 x 10(8) gamma-Proteobacteria, 0.2 x 10(8) to 2.1 x 10(8) Vibrio-Photobacterium, 0.5 x 10(7) to 10 x 10(7) V. vulnificus, 0.2 x 10(6) to 6 x 10(6) V. cholerae-V. mimicus, and 0.5 x 10(5) to 8 x 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.

Bacteria of the gamma-subclass Proteobacteria associated with zooplankton in Chesapeake Bay.

The seasonal abundance of gamma-subclass Proteobacteria, Vibrio-Photobacterium, Vibrio cholerae-Vibrio mimicus, Vibrio cincinnatiensis, and Vibrio vulnificus in the Choptank River of Chesapeake Bay associated with zooplankton was monitored from April to December 1996. Large (>202- microm) and small (64- to 202- microm) size classes of zooplankton were collected, and the bacteria associated with each of the zooplankton size classes were enumerated by fluorescent oligonucleotide direct count. Large populations of bacteria were found to be associated with both the large and small size classes of zooplankton. Also, the species of bacteria associated with the zooplankton showed seasonal abundance, with the largest numbers occurring in the early spring and again in the summer, when zooplankton total numbers were correspondingly large. Approximately 0.01 to 40.0% of the total water column bacteria were associated with zooplankton, with the percentage of the total water column bacteria population associated with zooplankton varying by season. A taxonomically diverse group of bacteria was associated with zooplankton, and a larger proportion was found in and on zooplankton during the cooler months of the year, with selected taxa comprising a larger percent of the Bacteria in the summer. V. cholerae-V. mimicus and V. vulnificus comprised the bulk of the large and small zooplankton-associated Vibrio-Photobacterium species. In contrast, V. cincinnatiensis accounted for less than 0.1 to 3%. It is concluded that water column and zooplankton bacterial populations vary independently with respect to species composition since no correlation was observed between taxa occurring with highest frequency in the water column and those in association with zooplankton.