Aerial surveys are commonly used to evaluate in-water sea turtle abundances. A correction is applied to account for turtles diving below the observed surface. Historically, observations of summer/fall surfacing behavior were used for this correction, assuming constant behavior among seasons. Using radio/acoustic telemetry, seasonal differences in sea turtle surfacing behavior were determined among Kemp's ridleys and loggerheads. Mean time spent at surface in the spring ranged between 9.9%-30.0% with significant differences among individuals. Observed surfacing times were higher than historic summer/fall observations (Byles 1988; 5.3%), indicating that historic springtime abundances were overestimated by 50%-80%. Aerial surveys (2001-2004) indicated a 65%-75% decline in the Chesapeake Bay sea turtle population since the 1980's. Current sea turtle estimates range between 2,500-5,500 turtles compared to 6,500-9,000 turtles observed in the Lower Bay alone in the 1980's. Satellite telemetry was used to track long-term movements of adult and juvenile turtles utilizing Virginia's waters. Loggerheads and Kemp's ridleys were found to exhibit significant fidelity to Bay and coastal waters south to Cape Hatteras. Several individuals established winter habitat off Cape Hatteras, adjacent to the outer continental shelf and Gulf Stream. Fall migrations commenced when surface temperatures dropped below 20??C. Some turtles migrated south to Georgia, Florida and the Gulf of Mexico. Two turtles were transported by the Gulf Stream to the north Atlantic and the Grand Banks, indicating some plasticity in habitat use. Virginia's pound net fishery was considered a primary source of sea turtle mortality in the 1980's. Fisheries surveys (2000-2002) indicated a significant reductions in fishery effort and hazardous large mesh and string leaders. No subsurface bycatch mortalities were observed during side scan sonar surveys (2001-2002). Pound nets are no longer a significant source of sea turtle mortality in Virginia. Pound net recaptures of live turtles (1979-2002) indicated strong philopatry to specific foraging areas, including strong inter-annual site fidelity. Over 20% of tagged loggerheads were recaptured in study nets during 1-11 seasons. Satellite telemetry was used to track the movements of one adult loggerhead captured multiple times from 1999-2002. Home range analyses indicated a 73.9% overlap in the total range over a three-year period.

A study of the organic matter (OM) sources and biogeochemical and physicochemical sinks was undertaken in the York River estuary, Virginia. The reactivity of dissolved organic carbon (DOC) was enhanced from ∼25--68% by the combined effects of exposure to natural sunlight and bacterial decomposition. In contrast, sunlight exposure decreased the bioreactivity of DOC in the higher salinity lower York by a factor of five. The combined effects of photochemical and bacterial processing were found to modify both the bioavailability and metabolic fate of OM (e.g. respiration vs. biomass). Stable isotopic (delta13C, delta15N) and radiocarbon (Delta14C) values of bacterial nucleic acids were used to estimate the sources and ages of OM assimilated by bacteria in the York and Hudson River estuaries. Bacterial production in freshwater regions of the York was fueled by OM of young, terrigenous origin which accounted for 42--89% of OM assimilated. The remainder (11--58%) of OM assimilated was derived from freshwater algae. In the mid-salinity York, bacterial production was supported by phytoplankton-derived OM in the spring and summer (93--100%) and marsh-derived OM in the fall (73--100%). Isotopic values of bacteria in the lower York suggested production was supported by phytoplankton-derived OM (86--100%) in July and November and algal and marine-like OM (50--69%) in October. In contrast to the young (10--20 yr) OM assimilated by bacteria in the York, production in the Hudson River was subsidized by old (∼1200 BP) terrigenous OM. Higher C:N ratios, lower delta13C and delta 15N values and depletions of total lipid and lipid compound classes in high molecular weight dissolved organic matter (HMW DOM (≥3kDa)) relative to particulate organic matter (POM), suggested differences in the reactivity and cycling of these two OM fractions. Within the dissolved pool, polyunsaturated fatty acids (FA) were a strong predictor of DOC decomposition in bioassays. FA and sterol distributions suggest that POM is derived from phytoplankton/zooplankton sources, while HMW DOM has a bacterial and vascular plant signature. Thus, the physical form of OM (particulate vs dissolved) may affect both the distribution and biogeochemical processing of OM such that terrigenous DOM may be exported, while POM is retained within the estuary.

The sandbar shark, Carcharhinus plumbeus, has a discontinuous cosmopolitan distribution and is exploited throughout much of its range. In the western North Atlantic, it constitutes the majority of the directed commercial fishery. The stock has declined greatly since the fisheries' inception and has not shown signs of recovery despite the implementation of management practices. Like many highly vagile marine species, it is difficult to obtain information about the sandbar shark through direct observation. Therefore, the goal of this dissertation is to use a molecular approach to examine aspects of behavior and reproduction, providing information useful in conservation and management. to this end, I examine the prevalence of genetic polyandry in the western North Atlantic and estimate effective population size and effective number of breeders for the Delaware Bay and Eastern Shore of Virginia nursery grounds. In addition, I look at patterns of philopatry and reproductive periodicity, while on a worldwide scale, assessing both historical and contemporary gene flow. Paternity analysis using microsatellite markers reveals that most females are mate with multiple males during one reproductive period. Despite the high prevalence of genetic polyandry, no direct benefits are detected. The data, however, suggest that males benefit by excluding other males from mating, intimating strong intrasexual competition. The effective number of breeders per nursery ground, estimated using the linkage disequilibrium method, is fairly consistent across years. Comparisons with census size estimates made for Delaware Bay reveal that the two measurements are tightly coupled. The ratio of effective size to census size is 0.45 or higher. This suggests that monitoring of effective population size may be a useful methodology for tracking abundance, and that exploitation may have a direct negative impact on the level of genetic variance. The results suggest that females may stray between nursery grounds found in Delaware Bay, the Eastern Shore lagoons and Chesapeake Bay, as phi st values are nonsignificant and kin groups are detected between as well as within samples. However, true kin groups can not be distinguished from erroneous kin groups because sample size is too small and the loci employed do not have enough power. Even so, the results suggest that female reproductive periodicity in this species needs to be reevaluated. Different patterns of historical dispersal and contemporary gene flow are observed when markers with different modes of inheritance are used to evaluate historical phylogeography. The results suggest that, although females show regional phylopatry, pulses of female dispersal during the Pleistocene may have created the species' current distribution. This dynamic may have been mediated by the changing distribution of nursery habitat caused by the rise and fall of sea level associated with climate change rather than by fluctuating temperature. This idea is supported by the results, which suggest that male mediated gene flow persists long after female gene flow has stopped.

Zooplankton play a key role in the cycling of dissolved organic matter (DOM) and inorganic nutrients. The factors that affect these processes, however, are not fully understood. I measured the effects of various diets on DOM and inorganic nutrient production by the copepod Acartia tonsa and the heterotrophic dinoflagellate Oxyrrhis marina, and explored the mechanisms of nutrient release from copepods. Copepods feeding on a mixed diet, the preferred diet of most copepods, had significantly lower dissolved organic carbon (DOC), ammonium (NH4+), and total dissolved nitrogen (TDN) release rates compared to feeding on a carnivorous or herbivorous diet. Thus, copepod feeding strategy can control the magnitude and composition of regenerated nutrients supplied to bacteria and phytoplankton. Secondly. I determined the effects of non-bloom and bloom concentrations of non-toxic and toxic cultures of harmful algal bloom (HAB) species Prorocentrum minimum and Karlodinium veneficum on grazing and production of DOM and inorganic nutrients by A. tonsa and O. marina. All algal diets deterred grazing, which likely resulted in starvation and subsequent catabolism of grazer body tissue. Additionally, DOM was typically a higher proportion of total dissolved nutrients released by zooplankton while feeding on the toxic algal culture, suggesting algal nutrient quality or direct toxic effects played a role in the differential nutrient release. Low ingestion rates coupled with high nutrient release rates could lead to feedback mechanisms that could intensify HABs. Finally, the various mechanisms of A. tonsa nutrient release, including sloppy feeding, excretion, and fecal pellet leaching, were isolated. Excretion and sloppy feeding were the dominant modes of DOC and NH4+ release, while sloppy feeding and fecal pellet leaching were dominant modes of urea release. A large proportion of ingested PON was lost as dissolved NH4+ and urea from copepods via all release mechanisms. These results have implications for the rapidity and location at which the regenerated nutrients are recycled in the water column. My dissertation results emphasize the importance of diet and release mechanism on the production of nutrients, particularly DOM, by zooplankton, which are important in understanding the recycling and transfer of nutrients and organic matter in marine food webs.

The chemical, physical, and biological factors affecting the bioavailability of humic nitrogen (N) to coastal phytoplankton were examined. Historically, humic substances have largely been considered biologically refractory, and humic-N is though to be unavailable biologically without prior oxidation via photochemical cleavage or remineralization by bacteria. This is due in part to the high aromaticity and low N content of humic substances. This dissertation investigates whether these assumptions are valid, and whether humic substances may be a more important source of N to the coastal phytoplankton community than previously believed. The research consisted of four main parts. First, changes in the structure and N content of humic substances were monitored by forming humics in the laboratory and following the changes in structure and chemical composition as they aged. It was found that as humics age, they become more aliphatic and fulvic-like. It was also determined that the commonly used XAD-8 extraction technique may underestimate the N content of aquatic humics by stripping ammonium (NH4+) from the humic structure. Second, whether or not this underestimation of humic-N has an effect on previously reported rates of photochemical N liberation from humic compounds was investigated. It was found that while the potential for the underestimation of photochemical release exists, previously reported rates are close to correct, largely due to physical and chemical interactions of humic substances with the surrounding environment. Third, the bioavailability of humic-N was examined using a suite of coastal phytoplankton strains. In short, all coastal strains exposed to humic substances could take up humic-N in short-term incubations; an open ocean strain tested did not take up humic-N. Furthermore, younger humics appeared to be more labile than those aged for time periods greater than three months. Finally, the significance of the salinity-mediated release was investigated and found to be a potentially important transport mechanism of NH4 + to the mid-saline regions of the estuary. In conclusion, the combination of chemical, physical, and biological processes occurring in the estuarine and coastal ecosystems suggests that humic substances are highly dynamic, biologically active compounds and not the biologically recalcitrant molecules portrayed in current literature.

Several aspects of effects of the organophosphate pesticide diazinon on the American oyster Crassostrea virginica Gmelin were investigated. Uptake of diazinon directly from water was compared with uptake of diazinon sorbed to either fine sediment or algae; the primary route of assimilation seems to be from the water. Concentrations of diazinon between 0.91 and 2.03 mg/L inhibit shell growth during 96 hours of exposure; there is a sharp threshold of effect for this response which is probably an indirect one caused by lack of food during shell closure. Acetylcholinesterase inhibition is significant in oyster heart tissue at concentrations of approximately 1 mg/L and greater. Even when inhibition is as great as 72%, however, it is not fatal. During a six-week exposure at high temperatures (22-24&\sp\circ&C), diazinon accelerated depletion of glycogen stores but had no long-term effect on total lipid reserves. Because of the disruption of the energy balance caused by the high temperature, glycogen stores in all oysters were depleted by the end of the period and little reproductive conditioning occurred. There is a suggestion of some early gametogenic activity because there was an increase in total lipid content during the first 21 days in the controls and low dose but not in the two highest doses. This increase may have resulted from conversion of some glycogen to lipid for vitellogenesis. Diazinon is rapidly accumulated and metabolized by oysters. The pesticide and its biotransformation products are quickly eliminated from the animal when exposure ends; more than 90% is removed within two days. A small fraction of the nonpolar byproducts, however, appears to be stored in the lipids. The bioconcentration factor calculated from results of an accelerated uptake test is 56; although this is low compared with that of many compounds, it is higher than that reported for diazinon in other invertebrates.

Differences in zooplankton community structure and diet within the mesopelagic zone (base of euphotic zone to 1000 m) play a key role in affecting the efficiency by which organic matter is exported to depth, but how the structure of mesopelagic food webs change with depth or location is poorly known. I examined how mesopelagic zooplankton affect particle export in an oligotrophic (Hawaii Ocean Time-series site ALOHA) compared to a mesotrophic (Japanese time series site K2) open-ocean system. In the first part of the study, I investigated how fecal pellet characteristics change with depth in order to quantify the extent of particle repackaging by mesopelagic zooplankton. There was significant evidence of mesozooplankton repackaging of sinking particles in the mesopelagic zone, as indicated by presence of new fecal pellet types (as different size, color, or shape) occurring at different depths. Fecal pellets reflected the disparate zooplankton community structure at the two sites, and larger pellets at K2 likely increased transfer efficiency of POC there compared to ALOHA. In the second portion of this study, I analyzed fatty acids (FA) in zooplankton and particles to characterize zooplankton diet and large (>51mum) particles in the mesopelagic zone of these two contrasting regions. Total FA concentration was higher in zooplankton tissue at K2, largely due to FA storage by ontogenetic vertical migrating species there. FA biomarkers that were indicative of particle feeding were also evident at both sites. Finally, I quantified cyanobacteria and small eukaryotic phytoplankton in the guts of mesopelagic zooplankton using light and epifluorescence microscopy to determine if mesopelagic zooplankton mediate the export of small phytoplankton to the deep sea. Cyanobacteria and small, eukaryotic phytoplankton occurred in the guts of nearly all target species sampled from the surface to 1000 m, indicating mesozooplankton grazing on aggregates is a pathway by which export of carbon and picoplankton can be enhanced. Guts of diel vertical migrators still contained picoplankton at their deep, daytime residence depths, indicating active export of these cells. In all three studies it was apparent that carnivory becomes an increasingly important component of mesopelagic zooplankton diet with depth. Evidence included the presence in sediment traps of red fecal pellets produced by carnivores, fatty acids in zooplankton tissue indicative of an increasingly carnivorous diet with depth, and the presence of chitin, gastropod shells, and microzooplankton in mesopelagic zooplankton gut contents. Changes in zooplankton feeding ecology from the surface through the mesopelagic zone, and between contrasting environments, have important consequences for the quality and quantity of organic material transported to the deep sea.

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