Results 



During the initial survey, it was noted that 

 many intermolt blue crabs had dark brown or 

 mahogany-colored gills which contrasted with 

 the light-colored gills of recently molted crabs. 

 The light- and dark-colored gill material was 

 subsequently divided and analyzed separately. 



The microbiological data from 61 blue crab 

 gill samples collected during five quarterly sur- 

 veys were analyzed statistically using a general- 

 ized analysis of variance (ANOVA) employing 

 the maximum likelihood approach. The depen- 

 dent variables for analysis were the microbial 

 counts on the blue crab gills; independent vari- 

 ables were urban and industrial pollution, salin- 

 ity, season, gill color, and their pairwise inter- 

 actions. In Table 1, the P-values resulting from 

 the analysis of variance indicated that season, 

 gill color, and the interaction of pollution and 

 season affected the total Vibrio and aerobic, 

 heterotrophic bacterial counts. Fecal coliform 

 counts were not significantly affected by any of 

 the variables investigated. 



Graphically displayed in Figure 3 is the effect 

 of season and gill color on total Vibrio and aero- 

 bic, heterotrophic bacterial counts. Dark gills 

 had consistently higher counts, and the counts 

 showed a similar pattern with season. 



Surprisingly, the absence of urban fecal pol- 

 lution had no significant impact on fecal coliform 

 counts in blue crab gills (Table 1). Blue crab gills 

 obtained from St. Helena Sound, a pristine area, 

 yielded high fecal coliform counts, whereas in- 

 tertidal oysters and waters sampled concurrent- 

 ly were relatively free of contamination (Table 

 2). To confirm the identity of the fecal coliforms 

 found in St. Helena Sound, 90 bacteria were 

 isolated from positive EC broth MPN tubes, 

 checked for their Gram reaction, and analyzed 



Table l.—P values resulting from generalized ANOVA of 

 crab gill data. The hypothesis that a factor has an effect on 

 microbial counts in blue crab gills is accepted when P<0.05. 



P-values, dependent variables 



Independent 

 variables 



Heterotrophs 



Vibrio 



Fecal 

 coliforms 



0.233 



0207 



0015 



0.001 



1 



0.036 



1 



1 



1 



1 



0.304 

 0.211 

 0.355 

 0.312 



6- 



5- 



• HETEROTROPHS DARK GUIS 



 HETEROTROPHS LIGHT GUIS 



a VIBRIOS OARK GILLS 



D VIBRIOS LIGHT GILLS 



NOV T 9 7 9 EEB I980 MAY I980 AUG I960 NOV I980 



Figure 3. — Average total Vibrio and heterotrophic bacterial 

 counts per gram of light and dark crab gill tissue from all 

 samples collected from the St. Helena Sound area. 



biochemically with the four reactions which con- 

 stitute the IMViC differential test (American 

 Public Health Association 1976). The sources for 

 the bacterial isolates were blue crab gills (35), 

 water (26), sediment (15), and oysters (14). 

 Ninety-four percent of the isolates were identi- 

 fied as typical Escherichia coli and 6% as typical 

 Enterobacter aerogenes. Twenty fecal coliforms 

 isolated from blue crab gills were also tested 

 with the API 20E system, and all identified as E. 

 coli. Representative samples of blue crab 

 stomach contents analyzed in parallel with the 



Table 2.— Distribution of fecal coliforms in samples collected 

 from St. Helena Sound area. 



'100 ml of water and sediment samples 



888 



