suggest that this is not likely to occur. In both laboratories, 
natural populations of freshwater bloom-forming cyanobacteria 
exposed to salinities as low as 5 o/oo were severely inhibited 
in terms of photosynthesis. 
If bloom-forming cyanobacteria from freshwater regions 
won't survive in moderate and high salinities, can we expect to 
find significant populations of cyanobacteria in the Chesapeake 
Bay? Until a few years ago, most phytoplankton ecologists 
thought that cyanobacteria were not an important component of 
marine phytoplankton communities. However, with the advent of 
epifluorescent microscopy, it quickly became apparent that there 
was an abundant and ubiquitous population of small (ca. 1 urn 
diameter) coccoid cyanobacteria in the world's oceans (Johnson 
and Sieburth, 1979; Waterbury et al., 1979), and that these 
small cyanobacteria were significant contributors to oceanic 
primary production (Li et al., 1983; Platt et al., 1983). Using 
epifluorescent microscopy, coccoid cyanobacteria fluoresce a 
bright crimson-red color under green light excitation while some 
forms fluoresce a gold-orange color under bluelight excitation 
(Haas, 1982). Both forms are easily and accurately quantified 
by this technique. 
Coccoid cyanobacteria in the lower Chesapeake Bay plankton 
community are most abundant during the summer months when water 
temperatures are highest, as shown in Figure 2, which depicts 
phytoplankton abundance data collected by Harold Marshall of Old 
Dominion University at stations in the lower Bay and in the 
lower James River during 1982-83. The cell counts were made 
using inverted microscopy. The data show that picoplankton 
(phytoplankton less than 2 urn in diameter and in this case domi¬ 
nated by cyanobacteria) reached peak abundances of ca. 15xl0 3 
ml -1 during July, August, and September at both stations. The 
lower James River station also illustrates the sequence of a 
spring bloom of relatively large diatoms preceeding the summer 
maximum of picoplankton. 
Figure 3 shows cyanobacterial abundance along the salinity 
gradient of the lower Bay and James River for August 1983. The 
data are from a transect starting in the lower Bay near Cape 
Charles (salinity 23 o/oo), progressing into Hampton Roads (0 km 
and 22 o/oo) and continuing about 75 km upriver past Jamestown 
Island (2 o/oo). Samples were collected from ca. 1 meter depth 
at each station for 14 consecutive days, except for the Cape 
Charles station which was sampled only four times. Cell counts 
were made with epifluorescent microscopy and for the purposes of 
this presentation, the counts for all days were averaged and a 
standard error depicted. In the lower Bay near the Eastern 
Shore, total cyanobacterial counts were nearly 10 6 ml -1 with 
total abundances not changing appreciably upriver. The propor¬ 
tion of orange fluorescing cells, which are the only type found 
104 
