This work reports the development of an analytical methodology for the analysis of PCB congeners based on integrating relative retention data provided by other researchers. The retention data were transposed into a multiple retention marker system which provided good precision in the calculation of relative retention indices for PCB congener analysis. Analytical run times for the developed methodology were approximately one hour using a commercially available GC capillary column. A Tracor Model 700A Hall Electrolytic Conductivity Detector (HECD) was employed in the GC detection of Aroclor standards and environmental samples. Responses by the HECD provided good sensitivity and were reasonably predictable. Ten response factors were calculated based on the molar chlorine content of each homolog group. Homolog distributions were determined for Aroclors 1016, 1221, 1232, 1242, 1248, 1254, 1260, 1262 along with binary and ternary mixtures of the same. These distributions were compared with distributions reported by other researchers using electron capture detection as well as chemical ionization mass spectrometric methodologies. Homolog distributions acquired by the HECD methodology showed good correlation with the previously mentioned methodologies. The developed analytical methodology was used in the analysis of bluefish (Pomatomas saltatrix) and weakfish (Cynoscion regalis) collected from the York River, lower James River and lower Chesapeake Bay in Virginia. Total PCB concentrations were calculated and homolog distributions were constructed from the acquired data. Increases in total PCB concentrations were found in the analyzed fish samples during the fall of 1985 collected from the lower James River and lower Chesapeake Bay. Comparisons between the homolog distribution patterns in the fish samples with the previously mentioned Aroclor distribution patterns suggests a different source of PCBs for different areas. Sediments, oysters (Crassostrea virginica) and brackish water clams (Rangia cuneata) collected from the tidal James River in 1986 were also analyzed. Total PCB concentrations and homolog distributions were calculated for all samples. Sediment total PCB concentrations were relatively constant over the sampling range except in the region of the turbidity maximum which were significantly higher. Total PCB concentrations in the Rangia from the region of the turbidity maximum were the highest of all the biota samples. Rangia homolog distribution patterns from this area were distinctly different from the sediment distribution patterns or the other Rangia distribution patterns in this segment of the river. Alteration of the endemic distribution pattern may be due to physical-chemical processes occurring within the turbidity maximum.

Field tethering experiments in seagrass beds of Bahia de la Ascension, Mexico examined the impact of different-sized artificial shelters upon survival of three juvenile size-classes of the Caribbean spiny lobster, Panulirus argus. The artificial shelters were concrete structures (casitas) that simulate lobster dens. In the tethering experiments, spiny lobster survival was generally higher in smaller than larger casitas, though the effect depended upon the relationship between lobster and shelter size. Thus, spiny lobster survival depends not only upon the availability of shelter, but also on the scaling between shelter size and lobster size. These results suggest that placement of appropriately-scaled artificial shelters in nursery habitats where natural shelter is scarce is likely to augement habitat carrying capacity and therefore lobster production by increasing protection from predators. Field enclosure experiments examined the effects of spiny lobster size, social condition (i.e. presence or absence of conspecifics), shelter size, and predation risk (i.e. presence or absence of a major predator, the nurse shark Ginglyostoma cirratum) upon den choice by juvenile and adult P. argus. to corroborate the findings of the enclosure experiments, seasonal, size-specific abundance patterns of P. argus were quantified in the field by deploying artificial lobster shelters (casitas) of different sizes in two habitats that differed primarily in the potential for gregarious interactions. The experimental and observational field results were strikingly similar. Social condition and the scaling of lobster size to shelter size jointly regulated den choice patterns of adult and juvenile Panulirus argus in the field experiments and observations; lobsters also displayed marked size-specific behavioral flexibility in den choice according to social condition and predation risk. When conspecific densities and predation risk were low, lobsters resided primarily in smaller shelters; when conspecific densities were high and predation risk was low, lobsters resided predominantly in large shelters offering the highest potential for gregariousness; and, when predation risk was high, irrespective of conspecific densities, lobsters shifted to gregarious habitation in smaller, safer shelters. Hence, this study provides an empirical and conceptual framework for identifying how variations in the availability of resources, such as conspecifics and appropriately scaled refuges, influence the distribution and abundance of social, shelter-dwelling species.

Chesapeake Bay is possibly the largest summer nursery for Carcharhinus plumbeus in the western Atlantic. Longline sampling conducted from 1990--1999 was used to delineate this nursery spatially and temporally. Catch data from 83 longline stations sampled throughout the Virginia Chesapeake Bay were analyzed as a function of nine physical and environmental variables to delineate this nursery spatially. Tree-based models determined which variables best discriminated between stations with high and low catches and indicated that complex distribution patterns could be adequately modeled with few variables. The highest abundance of juvenile sharks was predicted where salinity was greater than 20.5 and depth was greater than 5.5 meters. Longline data from 100 sets made at two standard stations in the lower Bay indicated that immigration occurred in late May and early June and was highly correlated with increasing water temperature. Emigration from the estuary occurred in late September and early October and was highly correlated with decreasing day length. Between 1995 and 2000, 1846 juvenile C. plumbeus were tagged. With two exceptions, recaptures made in summer months were within 50 kilometers of the tagging location. Those recaptured in winter months were caught between 200 and 830 kilometers from the tagging location and indicated that the coastal waters of North Carolina and South Carolina serve as important winter nurseries from late October until May. Tag recaptures made in subsequent summers suggest that most juvenile sandbar sharks return to the same summer nurseries annually. Ultrasonic telemetry was used in investigate the diel activity patterns of juvenile C. plumbeus in Chesapeake Bay. Ten sharks were tracked for 10 to 50 consecutive hours. Swimming direction was correlated with mean direction of 2 tidal currents. Mean activity space was conservatively estimated to be 110 km2, which is two orders of magnitude greater than that reported for other carcharhiniform species. Swimming depth ranged from surface to 40 meters and was significantly deeper during the day (12.8 meters) than during the night (8.5 meters). This diel activity pattern and large activity space is hypothesized to be an adaptation for foraging on patchy prey in a productive, yet dynamic, temperate estuary.

Complex oyster reefs created by the Eastern oyster, Crassostrea virginica, though once prominent features of the Chesapeake Bay region, have become relatively scarce in comparison to historic descriptions. This decline, caused by a combination of overfishing, disease, habitat destruction and pollution, this decline continues despite substantial restoration efforts that have spanned decades. In response to this decline, the states of Virginia and Maryland considered the intentional introduction of the non-native Suminoe oyster, C. ariakensis. Previous studies questioned the reef-building capability of this Crassostrea species, which may affect its habitat function. Through a combination of field and mesocosm studies, I examined the possibility that this non-native oyster species would provide an ecologically-functional equivalent of the native oyster species if introduced into Chesapeake Bay. Habitat complexity and associated benthic communities of experimental triploid C. virginica and C. ariakensis reefs were investigated at four sites of varying salinity, tidal regime, water depth, predation intensity and disease pressure in the Chesapeake Bay region (Virginia and Maryland). Four experimental treatments were established at each site: C. virginica; C. ariakensis; 50:50 of C. virginica: C. ariakensis; and shell only. Abundance, biomass, species richness, evenness, dominance and diversity of reef-associated fauna were evaluated in relation to habitat location and oyster species over a period of 21 months. Habitat complexity varied spatially, although no differences among complexity indices were associated with oyster species. Increases in vertical reef heights and surface rugosity were observed over time for all experimental reefs, and treatment effects were observed after 19 months of development, when C. ariakensis reefs exceeded the vertical heights of C. virginica reefs, removing any doubt regarding the Suminoe oyster's reef-building capability. Spatial comparisons of reef-associated macrofauna suggested functional equivalency between oyster species with respect to habitat at intertidal locations (where C. ariakensis survival was low), and at subtidal sites of low salinity. at subtidal locations of higher salinities, however, the numbers of organisms associated with C. virginica reefs per unit of oyster biomass were significantly greater than the numbers of organisms associated with C. ariakensis. Multivariate analyses of data from subtidal high salinity sites also revealed unique communities associated with C. virginica treatments, while mixed oyster species assemblages were functionally equivalent to mono-specific C. ariakensis experimental treatments. Temporal comparisons at one mesohaline subtidal site revealed that the observed effects of oyster species on habitat function in higher salinity locations are inconsistent over time and likely overshadowed by seasonal larval recruitment dynamics and local hydrodynamics. Though a common oyster reef trophic cascade between juvenile oysters, C. virginica; mud crabs, Panopeus herbstii; and oyster toadfish, Opsanus tau was successfully replicated during mesocosm trials, specific trophic interactions were not significantly affected by oyster substrate species or habitat complexity (as it was defined within the constraints of the experiment). Together, these experiments represent the first effort to quantify the potential habitat function of C. ariakensis in Chesapeake Bay, and provide evidence of species-specific similarities and differences in reef-associated communities.

Flipper-tagging, aerial surveys, and satellite telemetry was used to investigate the occurrence, migratory routes, distances traveled, swimming speeds, diving behavior, and the relation of water temperature to movements and timing of migration of wild loggerhead (Caretta caretta) and Kemp's ridley (Lepidochelys kempii) sea turtles. The behavior and movements of head-started loggerhead turtles was investigated with satellite telemetry and compared to wild turtles. Flipper-tagged loggerhead and Kemp's ridley turtles inhabit Chesapeake Bay during the warm months and many return in subsequent seasons. Aerial surveys showed that loggerhead turtles migrate from south of Cape Hatteras to northern waters during May and June, and return to the south of Cape Hatteras in the autumn, usually during October or November. Satellite telemetry supported aerial survey data, and showed that loggerhead and Kemp's ridley turtles migrate nearshore to the south of Cape Hatteras in the autumn, although one loggerhead became pelagic in the North Atlantic. Kemp's ridleys and some loggerheads migrate as far south as Florida for the winter months, while some loggerheads overwinter in the Gulf Stream off North Carolina. Loggerheads which returned to Chesapeake Bay used similar migratory routes during the northerly and southerly migrations. Loggerhead and Kemp's ridley turtles spent up to 94% of 12 h periods submerged (ridley mean = 81%, loggerhead mean = 88%), and mean dive durations ranged from 13 to 124 min (ridley mean = 66 min, loggerhead mean = 74 min), making 13 to 38 dives over a 12 h period (ridley mean = 25, loggerhead mean = 25). Temperatures measured by satellite transmitters attached to Kemp's ridley turtles ranged from 13-23 C (mean = 17 C), while loggerhead temperatures ranged from 6-33 C (mean = 20 C). Movements of turtles appear to be mitigated by temperatures about 15 C. Movements and diving behavior of head-started loggerheads were different than wild turtles. Some head-started turtles entered the Gulf Stream and traveled eastward across the Atlantic, while others wandered in various directions. Head-started loggerheads made more (mean = 69) and shorter dives (mean = 21 min) over a 12 hr period than wild turtles, and spent significantly less time submerged (mean = 54%) than wild turtles.

The relationship between wetland polycyclic aromatic hydrocarbon (PAH) concentrations and adjacent land use was assessed using surface sediments, sediment cores and global information systems (GIS) in the Elizabeth River, Virginia, an urbanized subestuary of the Chesapeake Bay. Wetlands adjacent to parking lots and petroleum industrial sites exhibited the highest PAH concentrations of all land uses in surfaces sediment and historically. Automobile and coal are the dominant sources of PAHs in wetland sediments historically as determined by relative concentration, fingerprinting and source specific compounds. An analysis of variance (ANOVA) test used to compare sixteen surface sediment sites based on land use revealed significant differences in wetland surface sediment PAH concentration. Multi-family and single-family residential, rural, undeveloped, commercial, petroleum industrial and non-petroleum industrial most accurately identified distinct land use categories in the watershed. Source assessments revealed little variability between sites, which is indicative of one atmospheric source of PAHs to wetland surface sediments. Concentration magnitude and source similarities implicate percent impervious surface and proximity to sources as having a major influences on PAH input to wetlands. GIS and surfaces sediment PAH concentrations were used to assess wetland area, adjacent land use in addition to PAH storage, distribution and input at the micro (site) and macro (watershed) scales. Despite urban wetlands having the largest concentration of PAHs a disproportionately low number of associated wetlands resulted in lower PAH storage at the macro scale. Residential, urban and rural wetlands contained the largest amounts of PAHs respectively. Wetland migration and erosion make wetlands dynamic sinks that constantly release and accumulate contaminants as they migrate shoreward to keep pace with sea level rise. In the urban Elizabeth River over 75% of wetlands are not able to migrate as a result of upland development. A conceptual model depicting wetland migration with developed and undeveloped uplands, and variable PAH source in sediments indicate wetlands can act as sources or sinks of slowly degrading contaminants. PAH flux measurement determined from wetland surface sediment concentrations and accretion rates showed PAH flux to all wetlands were exponentially higher than atmospheric deposition.

The sensory capabilities of settlement-stage fishes are unknown but this information is necessary to studies of larval settlement and recruitment. The morphology of the cephalic lateral line, eye and external olfactory organ of thirteen species of settlement-stage Caribbean labroids was described. Scanning electron images of the cephalic lateral line neuromasts, lateral line canals and olfactory epithelia and histological studies of the retinae and morphological measurements of visual acuity were used to assess the level of sensory development attained at settlement. The sensory capabilities of settlement-stage fishes are discussed in relation to the possible cues settlement-stage fishes may be using to locate a reef and microhabitat within the reef system. In addition sensory development is discussed in relation to interspecific variation in settlement behavior, settlement-site selection, possible evolutionary life history strategies and morphological constraints on sensory development and settlement. development and settlement.

In this dissertation, I experimentally examine predation-induced mortality upon juvenile queen conch, Strombus gigas, and assess the importance of select habitat predator and conch characteristics affecting predation intensity. Experiments were conducted during the summer and early fall of 1987, 1988, 1990 and 1991 in seagrass beds and adjacent sand flats near Lee Stocking Island, Exuma Cays, Bahamas. These experiments indicate that various factors act interactively to produce habitat-specific mortality rates in queen conch due to predation. These include (1) habitat type, whereby seagrass beds offer some protection; (2) local population dynamics, such that populated seagrass beds appear to enhance conch survival; (3) population density in some seagrass beds, such that mortality is inversely density-dependent; (4) conch size, such that larger conch have higher survival rates, depending on the specific type of habitat; and (5) predation intensity and predator guilds, which likely differ across habitats, producing habitat-specific mortality rates. When integrated with complementary studies of queen conch trophodynamics, these results provide critical information regarding key ecological factors affecting conch survival. In particular, results from the hatchery-reared experiments demonstrate the potential use of hatchery-reared stocks in natural habitats, and hence a valuable option for enhancement of fishery stocks throughout the Caribbean. In general, the integration of results obtained in this dissertation, with complementary studies of queen conch trophodynamics, should provide valuable suggestions of queen conch habitats, densities and scales of patchiness producing highest survivorship and growth rates in nature.

Long term trends in juvenile recruitment of oyster, bluecrab, and 24 species of finfish in a large temperate estuary (lower Chesapeake Bay, USA) are coherent across the three major tributaries (the Virginia rivers James, York, and Rappahannock). The driving force for these long term trends is geographically large in scale. Anomalous winters in the mid 1970's, with the warmest years on record followed immediately by the coldest, caused a severe perturbation in population dynamics. The extreme conditions caused the system to shift, with recruitment patterns following temperatures by a one year lag. Following this anomalous episode, smoothed mean winter water temperatures have increased steadily from 1979 until 1995 &\rm (3.9{lcub}-{rcub}5.7\sp\circ C,& long-term T = &\rm 4.6\sp\circ C),& closely followed (with zero lag) by the first principal component (PC) from each set of smoothed biological indices. Annual indices of juvenile abundance (means of log-transformed catch per unit effort) were calculated by river for the James, York and Rappahannock Rivers. Two collections of different temporal lengths are analysed, oyster, bluecrab and 14 species of finfish (1965-1995) and 17 species of finfish (1980-1995), with an overlap of seven species of finfish. The indices are smoothed by loess (locally weighted scatterplot smoother), and analyses are performed on the indices, the loess-smoothed indices, and the residuals. Principal components analysis (PCA) on the indices indicates coherence in the population fluctuations by a relatively small number of PC's. Weak relationships are found in the unsmoothed indices and the residuals. Smoothed long-term trends eliminate much of the noise, thus exposing the underlying behavior of populations. PCA on the loess-smoothed indices were remarkably cohesive, with only three or four PC's significant in each of the six treatments, accounting for 93 to 98% of total variance, with 44 to 70% in PC#1. Correlations on the first PC's of the loess-smoothed indices, between rivers, within and between surveys, yielded 87-99% agreement; such coherence indicates the underlying causal factor is geographically broad. Cross correlations and scatterplots of smoothed winter water temperature and PC#1 identify the lag during the perturbation years.

Relative importance of predator-prey dynamics and several environmental variables in structuring gastropod and bivalve diversity and distribution was investigated in the subtropical seagrass and macroalgal community of Florida Bay, a highly productive system and primary nursery and foraging ground for finfish and invertebrate predators, including the numerically dominant Caribbean spiny lobster, Panulirus argus. The molluscan assemblage, a primary food source for P. argus in particular, is speciose (75 gastropod and 25 bivalve species) and a significant component of epifaunal and infaunal invertebrate assemblages within Florida Bay. Two experimental areas, located within separate basins and each comprised of two experimental sites, were selected within Everglades National Park. Each site consisted of an array of four replicates of each of four structural treatments designed to manipulate predator abundances and composition. The predator guild associated with experimental structures was monitored at periodic intervals (July 1993 to Aug. 1995), at which time benthic suction samples were taken to evaluate diversity, abundance, and distribution of the molluscan assemblage. Experimental areas were significantly different from each other and were representative of separate subenvironments within Florida Bay. Predator abundances were successfully manipulated locally; experimental structures providing more overhead cover attracted significantly more predators. Predator densities were representative of naturally occurring fauna utilizing seagrass beds rather than abnormally high densities reported in studies utilizing artificial reefs. No significant predation impacts by lobster and finfishes on abundance and species richness of the molluscan assemblage were observed. Predation by P. argus and finfishes did not structure gastropod and bivalve mollusc assemblages in these habitats. Area differences, however, had some influence on prey abundance and diversity given the consistent significant area effects prevalent throughout the data. Moreover, lobsters at densities recorded in this study, can not be considered a keystone or even dominant predator in this system Predation in Florida Bay, as in other tropical and sub-tropical systems, is differentiated in time and space, probably due to habitat heterogeneity, spatial and temporal variability in predator and prey abundances, high diversity of prey, and other factors. The Florida Bay benthic community is likely influenced through bottom-up or physical factors and microhabitat characteristics.