Muscle and hepatopancreas of blue crabs (Callinectes sapidus), collected from the Elizabeth River, Virginia, contained residues of polycyclic aromatic hydrocarbon (PAHs}, polychlorinated biphenyls (PCBs) and organochlorine pesticides. Analytical procedures involved dichloromethane extraction of lyophilized tissue, followed by molecular size and polarity-based purification of the extract. capillary gas chromatography with flame ionization detection and electrolytic conductivity detection was used for quantitation and tentative identification of the xenobiotic compounds. Mass spectrometry was used for confirmation of these identities. Contaminant concentrations were greater in hepatopancreas than in muscle in crabs from every site examined. Hepatopancreas PAH burdens were as high as 11 mg/kg dry weight, with an accompanying muscle level of 3.1 mg/kg. The PAHs present consisted mainly of alkylated low molecular weight compounds (e.g., acenaphthenes and naphthalenes), except near a creosote-impacted site. At the latter location, unsubstituted, higher molecular weight PAHs (e.g., pyrene and chrysene) dominated. Organochlorines, which included PCBs, 4,4'-DDE, and chlordane were found in lower concentrations. The effect of molting on xenobiotic accumulation in Crustacea was also examined. Molting is essential for crustacean growth and is integral to the reproductive process in some species. Molting and intermolt blue crabs were maintained in cages at the creosoted-impacted Elizabeth River site mentioned above. PAH concentration in muscle and hepatopancreas was measured for both molt groups. Newly molted blue crabs possessed statistically higher tissue burdens than intermolt crabs of three unsubstituted PAHs (cyclopenta(def)phenanthrene, fluoranthene, and pyrene) characteristic of the creosote-contaminated exposure site. Mean concentration of the three PAHs in hepatopancreas was 9560 μg/kg in newly molted crabs and 3360 μg/kg in intermolt crabs. Mean PAH concentration in muscle was 1380 μg/kg in new-molts and 498 μg/kg in intermolts. The elevated tissue burdens may be due to increased water uptake and shell permeability at ecdysis or decreased metabolism of PAH during the molt process. Newly molted blue crabs are regarded as a seafood delicacy and tissue burdens of xenobiotics, such as PAHs, may be of human health concern.

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Various investigations of the population dynamics of blue crabs in Chesapeake Bay indicate that predator-induced mortality in the juvenile phase may determine year-class strength. In a tethering study, which spanned three seasons in shallow-water habitats of the lower York River, daily mortality rates of juvenile crabs were measured across three variables: crab size (30-70 mm carapace width), habitat type (seagrass, mud, and sand), and month (May-November). Vulnerability to predation was consistently lower for larger crabs, approaching a size refuge from predation at approximately 90 mm carapace width. Predation was most intense in unvegetated sand habitats, and significantly lower in seagrass and unvegetated mud. The data also reflected a strong seasonal pattern in predation potential which was correlated with water temperature. Predators contributing to this pattern were identified and assessed using an underwater video-recording system to monitor tethered crabs. While a variety of potential predators appeared and attacked crabs frequently, only two species had a measurable impact on crab survival, adult conspecifics and northern puffers, Sphoeroides maculatus. These results were confirmed in large laboratory tanks using untethered crabs as prey. These studies indicate that the mechanisms behind seasonal variation in predation pressure may include both physiologically-linked activity rhythms and seasonal migration of predators. The potential impact of seasonally-varying predation pressure on the life history of blue crabs was explored in a modeling exercise, using concepts of dynamic optimization. The results suggest that the blue crab may exhibit behavioral adaptations which are reflected in optimal biological timing of recruitment and growth, thereby enhancing survival through the juvenile phase.

The first two chapters of this study examine faunal composition and latitudinal patterns in diversity of fishes in warm-temperate and tropical estuarine waters of the western Atlantic from La Plata River (35&\sp\circ&S), Argentina, to Chesapeake Bay (37&\sp\circ&N), USA (33 faunal reports). Species distributions generally corresponded with previously recognized marine zoogeographic regions, and cluster analyses also showed that faunal similarity among estuarine sampling sites was related to the type of sampling gear used and to the type of habitat that was sampled in each estuary. The total number of fish species reported is positively related to the size of the area sampled and number of individuals collected, although latitude (or temperature related phenomena) played a critical role in determining richness and equitability among species. The results of this study show that interaction between disturbance frequency or magnitude (e.g. temperature and salinity variations) and the rate at which dominance is achieved can result in a predictable pattern of fish species diversity in estuaries. In the last chapter the structure of estuarine fish assemblages in Patos Lagoon (32&\sp\circ&S), Brazil, and York River (37&\sp\circ&N), USA is described using historical bottom trawl data, to examine similarities between geographically isolated fish assemblages. Within broad limits structural assemblage patterns were correlated with temperature changes, although the intensity of seasonal changes differed between them. The lowest winter temperatures in the York River were correlated with a pronounced seasonal species emigration from the estuary, a pattern which was not observed in the more thermally moderate Patos Lagoon. Patos Lagoon was more diverse in terms of equitability and species richness than the York River at any particular point in time, but the seasonal pattern of use of the estuary (i.e. nursery and feeding grounds) was similar between localities, and did not differ from other temperate or tropical estuaries. Comparing fish assemblages using a nondimensional diversity index (i.e, H&\sp\prime&) masks interesting differences in species richness and relative abundance, and measurements of species richness and equitability (rarefaction and relative species rank techniques) independent of sample size should be used in order to determine richness and equitability differences among systems.

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Fecal contamination in estuaries has become an increasing concern worldwide. The use of wetlands for wastewater treatment has expanded due to their natural ability to improve water quality by removing suspended sediments, nutrients, and fecal bacteria. In general, most of the removal occurs through deposition and accumulation in the wetland substrate. This would suggest that wetlands are effective filters for fecal coliform transported from terrestrial environments to surface waters. It has also been hypothesized, however, that wetlands may be an intermittent source of fecal coliform in tidal systems as a result of wildlife deposition and /or accumulation from terrestrial sources. To investigate the role of tidal wetlands in fecal coliform loadings from small estuarine systems, this project examines the difference between monitoring data and modeling data for shellfish growing areas in Virginia. Results suggest that models should treat tidal wetlands as discrete components of contributing watersheds, rather than assuming they can be grouped with forested land areas. Tidal wetlands’ role in fecal coliform transport could be embodied through the net sediment transport between tidal wetland and adjacent coastal water. When the tidal wetland substrate is resuspended, what happens to the water quality? Do tidal wetlands contribute to and how they contribute to the high amount of fecal coliform (FC) in shellfish harvesting zone? To address these questions, Loading Simulation Program C++ (LSPC) and a hydrodynamic model - Tidal Prism Water Quality Model were used to simulate fecal coliform transport through the watershed (including wetlands) and coastal waters with the support of the project of Development of Shellfish TMDLs for Virginia. The error analysis, that is the discrepancy between the model prediction and observation data, will then be used to explore the sinks and/or sources of fecal pollution in tidal marshes. Seasonal variation of fecal coliform concentrations in shellfish growing water and model sensitivity tests will be analyzed and discussed surrounding this issue.