have been concerned with the presence of specif- 

 ic human or fishery pathogens in the hemo- 

 lymph, necrotic tissue, or gill material (Rosen 

 1967; Williams-Walls 1968; Krantz et al. 1969; 

 Cook and Lofton 1973; Johnson 1976). The state- 

 ment of Tubiash et al. (1975) that the hemolymph 

 of most healthy blue crabs contains a natural or 

 autochthonous bacterial flora has been chal- 

 lenged, and it has been suggested that further 

 experiments using minimally stressed crabs 

 would be needed to substantiate that statement 

 (Johnson 1976). 



This study was designed to determine, season- 

 ally, the natural Vibrio, fecal coliform, and aero- 

 bic, heterotrophic bacterial populations on blue 

 crabs from environments that differed in salin- 

 ity and influx of urban and industrial pollutants. 

 These microbial populations were also compared 

 with those found in intertidal oysters (Cras- 

 sostrea virginica), waters, and sediments col- 

 lected simultaneously with the crabs. Blue crab 

 gills were chosen as a suitable substrate for 

 microbiological investigations because they have 

 direct contact with the environment and are 

 easily sampled and processed for enumeration of 

 their bacterial flora. 



Materials and Methods 



Two South Carolina areas, Charleston harbor 

 and St. Helena Sound, an estuary 35 mi south of 

 Charleston, were surveyed during a 22-mo pe- 

 riod between August 1979 and May 1981 (Fig. 1). 

 Within each area, two sampling stations were 

 selected, representing mean salinities of 10% o 

 and 25% . The Charleston harbor sampling 

 stations were Foster Creek, salinity 10% o , a 

 tributary to the Wando River, which, along with 

 the Ashley and Cooper Rivers, forms Charleston 

 harbor; and Shutes Folly Island, salinity 25%o, 

 situated near the center of Charleston harbor. 

 The oyster beds in both sites are closed to harvest- 

 ing because fecal coliform levels, monitored in 

 the water column and oyster meats by the South 

 Carolina Department of Health and Environ- 

 mental Control, exceed safe limits for harvesting 

 areas. Foster Creek receives negligible industri- 

 al pollution, whereas the Shutes Folly Island sta- 

 tion receives a moderate-to-heavy influx of 

 industrial pollutants. The St. Helena Sound 

 stations were the Ashepoo River at Mosquito 

 Creek, salinity 10%o, and St. Helena Sound at the 

 mouth of Rock Creek, salinity 25%o. Shellfish 

 beds at these stations are open to harvesting, 



with no discernible influx of urban, industrial, 

 or commercial pollutants. Each station was 

 sampled on a quarterly basis to coincide with 

 the highest and lowest temperatures in the 

 water column and during the middle of the 

 two transitional periods in water tempera- 

 tures. 



Blue crabs were captured in commercial-type 

 crab pots baited with fresh fish heads. The crab 

 pots were harvested from 4 to 24 h after being 

 set, dependent on the seasonal rate of blue crab 

 capture. Intertidal oysters and sediments from 

 the oyster beds were collected manually at low 

 tide. Two hundred grams of the top centimeter of 

 sediment were removed with sterile tongue de- 

 pressors and placed in sterile containers. Sur- 

 face water samples (1 m below the surface) were 

 collected with a Niskin 2 sterile bag sampler 

 (General Oceanics, Miami, Fla.) at the site of 

 blue crab collections. All sediment, water, and 

 oyster samples were immediately cooled with 

 ice. Blue crabs were maintained at their in situ 

 temperature by placing them in a thermally in- 

 sulated container. All samples were analyzed 

 within 4 to 8 h. During a survey, two to four rep- 

 resentative composite samples of blue crab gills 

 (dependent on seasonal activity of blue crabs), 

 three oyster composites, and two samples each of 

 sediment and surface water were collected and 

 analyzed for each sampling station. A composite 

 gill sample contained gills from 10 to 12 crabs. 

 Since mature female blue crabs migrate to 

 higher salinities, male blue crabs dominated the 

 population at 10%o salinity and females at 25%o 

 salinity. Whenever possible, blue crabs above the 

 legal harvesting size for South Carolina, 127 

 mm, were sampled. Each survey was completed 

 within 4 d. For monitoring purposes, tempera- 

 ture and salinity of the surface water were mea- 

 sured, using a YSI Model 33 Salinity-Conduc- 

 tivity-Temperature meter (Yellow Springs In- 

 strument Co., Yellow Springs, Ohio). 



Preparation of oyster and water samples for 

 analyses followed standard procedures (Ameri- 

 can Public Health Association 1970, 1976). Cara- 

 paces of the blue crabs were cracked vertically 

 with a blow from a stainless steel knife. The 

 knife did not penetrate into the gut or organs. 

 The carapace was then removed by pulling up on 

 the lateral spines (Fig. 2). Exposed gills were 

 aseptically removed with forceps and placed in 



2 Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



885 



