Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item Investigating the role of the Mid-Atlantic inner continental shelf as a marine finfish nursery: a comparative approach(2010) Woodland, Ryan Jordan; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The paradigm of estuarine-dependence in marine fishes has been challenged by evidence of facultative recruitment by juveniles to both estuarine and inner continental shelf (ICS) nursery habitats. This ecological flexibility suggests that the potential nursery area for marine fishes may be more expansive than previously considered. Two lines of investigation were undertaken to evaluate the overarching hypothesis that ICS habitats serve a nursery function for finfish that also use estuarine nurseries: 1) a direct comparison of seasonal, annual and compositional assemblage structure between an ICS habitat of the Middle Atlantic Bight (Delmarva Peninsula) and an adjacent estuary (lower Chesapeake Bay); and 2) an investigation of trophic structuring within an ICS demersal finfish assemblage with an emphasis on ontogenetic niche. In comparisons between nursery types, there was a strong seasonal similarity in assemblage structure between the estuary and ICS despite significant differences in abundance estimates at the species level. Juvenile trophic niche of two indicator species, bluefish and bay anchovy, was wider and more diverse in the estuary yet physiological condition was similar or higher in the ICS. In focused studies on the ICS food web, diet overlap was common among consumers, yet stable isotope evidence indicated prey resources were partitioned along vertical (trophic position) and horizontal (pelagic-benthic pathway) trophic axes. Benthic and pelagic food webs were tightly coupled in most juvenile phase finfish; yet, this relationship showed signs of decoupling in older age classes, suggesting an increased reliance on benthic trophic pathways with age and size. Several prey species that link pelagic and benthic food webs were shown to be important in the diets of demersal finfish, particularly mysid shrimp. Comparative assemblage and food web studies demonstrated that the ICS functions as summer nursery habitat for a wide variety of temperate marine finfish that also use proximal estuarine nurseries. The contribution of ICS nurseries to annual juvenile production represents a critical, but unknown component of population demographics for many marine species and must be considered to conserve essential fish habitats and account for recruitment variability in fisheries stock assessments.Item Blue Crab Farming on Maryland's Eastern Shore(2009) Donnelly, Justin Michael; Ambrose, Michael A; Architecture; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Biologists speculate that a combination of pollution and overharvesting might soon lead to the extinction of the blue crab in the Chesapeake Bay. This project investigates inland crab farming as a means by which to resurrect the region's dwindling blue crab industry and alleviate pressure on rapidly declining wild fisheries. Although the project transplants the blue crab onto land, it minimizes the impact to the plants and animals displaced. In short, the project asks us to rethink how we fish and how we farm and how they relate. The architectural proposal seeks to establish the general parameters of a heretofore untried blue crab farming operation and to apply these rules to a specific farm project in Dorchester County, Maryland. The final product consists of a series of greenhoused raceways, constructed wetlands, working meadows, a laboratory for rearing crab eggs to juvenile development, a picking/processing facility, restaurant, and modest educational facilities.Item RELATIONSHIPS BETWEEN LARVAL MORPHOMETRICS AND SETTING EFFICIENCY IN THE EASTERN OYSTER, CRASSOSTREA VIRGINICA(2009) Vlahovich, Emily Ann; Meritt, Donald W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In oyster hatcheries, the decision to move larvae from rearing tanks to setting tanks is based on physical and behavioral characteristics. These criteria can suggest conflicting action and a more reliable method may result in higher spat production. I observed hatchery reared Crassostrea virginica larvae, beginning with larvae retained on a 200 µm sieve. Aliquots of larvae were measured or placed in a setting vessel, and the remaining were returned to the culture cone daily. Each day had an associated setting efficiency, loss, and set of larval morphometrics, including shell height and length and eyespot diameter. Day was most strongly correlated with setting efficiency. Eyespot diameter was moderately correlated with setting efficiency, and shell morphometrics were weakly correlated with setting efficiency. I estimated daily spat production, which peaked on day 2. These results suggest spat production may be increased by altering current hatchery methods to consider eyespot diameter or days past retention on a 200 µm sieve when deciding to place larvae in setting tanks.Item CHEMICAL INDUCTION OF SETTLEMENT IN LARVAE OF THE EASTERN OYSTER CRASSOSTREA VIRGINICA (GMELIN)(2009) Grant, Melissa; Meritt, Donald W.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Although numerous studies have been conducted to examine the effects of neuroactive compounds on bivalve larvae, few have identified chemicals capable of inducing settlement behavior in the eastern oyster Crassostrea virginica. In this study, I treated competent C. virginica larvae with select chemicals to identify those which are capable of inducing settlement behavior at an average salinity of 9.6 (±0.1). The compounds γ-aminobutyric acid and acetylcholine chloride, both at 10-4M, did not significantly increase the percentage of larvae exhibiting settlement behavior. As compared with the control, a significant increase in settlement behavior was induced by treatment with 3-isobutyl-1-methylxanthine, 5-hydroxytryptamine, and L-3, 4-dihydroxyphenylalanine all at 10-4M, as well as ammonia as a solution of 7.9mM NH4Cl (pH=8.0). These findings differ somewhat from the results of similar studies involving other species in the Crassostrea genus and may be of value to hatchery personnel or researchers interested in the chemical induction of settlement behavior in the eastern oyster.Item MOLECULAR BASIS OF VIRULENCE IN INFECTIOUS HEMATOPOIETIC NECROSIS VIRUS (IHNV) USING A REVERSE GENETICS APPROACH(2009) Ammayappan, Arun; Vakharia, Vikram N; Veterinary Medical Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Infectious hematopoietic necrosis virus (IHNV) is a pathogen of major economic importance to the aquaculture industry. The long-term goal of our work is to develop a safe and effective recombinant IHNV vaccine and possibly use IHNV as a virus vector to express foreign genes. To achieve this goal, the complete genome of IHNV 220-90 virulent strain was sequenced and characterized. Subsequently, a full-length cDNA clone of IHNV was generated by constructing the full length cDNA clone, between the cytomegalovirus (CMV) promoter and the autocatalytic hammerhead and hepatitis delta virus ribozymes. Transfection of a full-length plasmid, along with the supporting plasmids resulted in the recovery of infectious rIHNV-220-90. Characterization of the rIHNV-220-90 showed that its growth characteristics in tissue culture were comparable to those of the parental virus. The possible role of IHNV proteins in virulence was explored to some extent. For this, the entire genome of attenuated virus (IHNV-61) was sequenced and compared with its virulent strain. The comparative sequencing analysis studies revealed that majority of differences were located in the glycoprotein gene. The M and G genes, and the trailer region between virulent and attenuated viruses were exchanged; recombinant chimeric viruses were recovered and studied for their pathogenicity in rainbow trout. The results obtained from in vivo studies indicate that the glycoprotein plays a major role in IHNV virulence in fish, whereas the M gene and trailer region play a negligible role in virulence of IHNV. The potential of rIHNV to serve as a viral vector was explored by expressing the VP2 protein of IPNV and hemagglutinin-estrase (HE) protein of ISAV. The recovered rIHNV-VP2 and rIHNV-HE viruses stably expressed the VP2 and HE proteins respectively for at least five serial passages and showed characteristics comparable to that of the parental virus, except that there was a one-log reduction in the virus titer. These results demonstrated that the established reverse genetics system can be utilized effectively to examine the molecular determinants of virulence, pathogenesis, and new approaches for vaccine development.Item Behavioral and Neuroendocrine Correlates of Sex Change in the Gilthead Seabream (Sparus aurata)(2009) Reyes-Tomassini, Jose J.; Zohar, Yonathan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sequential hermaphroditism is the most radical form of environmental sex determination observed in fish: functional adult males or females retain their ability to change sex even as adults. Among the factors that affect sex change in these species, the least understood is the social environment. Here, I studied the influences of social context on sex change in the Gilthead Seabream, Sparus aurata, by using the individual‟s dominance rank as an indicator of social status. To understand the role that the brain might play in sex change, I also studied the two main neuroendocrine factors that serve as the sexually differentiated axes of neural plasticity in most teleost species: AVT and GnRH. To do this, I first developed a set of tools designed to address the challenges associated with observing the behavior of aquacultured species. Using these tools, I provide the first in-depth study of seabream captive behavior, including the results of size-matched and sex-matched paired encounters. I found that females are more aggressive than males, but this difference is influenced by gonadal developmental status. I also showed that small but young males are more aggressive than bigger but older females. I cloned the AVT mRNA in seabream, and validated a quantitative assay to measure total brain AVT levels together with GnRH-1, GnRH-2, and GnRH-3 levels. I found that AVT and GnRH-3 levels rise during the onset of the hypothesized sex-change window, and drop to pre-quiescent levels until spawning, when all of these factors seem to increase their expression levels again. I also show for the first time, that GnRH-2 and dominance rank are strongly correlated in seabream during the spawning season but not during quiescence. GnRH-1 was strongly correlated to rank during quiescence but not during spawning. Finally, neither dominance rank nor size were a good predictor of the outcome of sex change, which seems to contradict what has been documented in sequential hermaphrodite reef fishes. I provide a model that accounts for this apparent contradiction and conclude that the Gilthead seabream remains true to the size-advantage hypothesis of sex allocation theory, if size and dominance are seen as proximate, rather than ultimate, factors.Item QUALITY ASSESSMENT OF ATLANTIC STURGEON (ACIPENSER OXYRINCHUS) SPERMATOZOA UNDER CONDITIONS OF SHORT-TERM STORAGE(2009) Dorsey, Kathryn Michelle; Woods, Curry; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Short-term storage trials were conducted in 2008 and 2009 on Atlantic sturgeon semen obtained from captive males, held at the U.S. Fish and Wildlife Service, Northeast Fish Technology Center, that were hormonally induced to spermiate; and wild males collected during the spawning season from the Hudson River. Samples were stored under refrigeration (4 + 1°C) in treatments consisting of different gaseous environments (oxygen, nitrogen or air) and experimental diluents (Modified Tsvetkova extender, Park & Chapman extender and neat, i.e. undiluted). Analyses of gamete quality were performed on day 0 (pre-treatment), and then every other day for 7 days in 2008 and for 21 days in 2009. Sperm quality parameters evaluated included: viability, motion analysis, curvilinear velocity and cellular ATP levels. Higher gamete quality was maintained when spermatozoa were diluted in the PC extender and stored in the presence of oxygen.Item Assessment of local abundance, demographics, health and exploitation of Chesapeake Bay American eel(2009) Fenske, Kari Hammarsten; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Chesapeake Bay supports the largest U.S. harvest of American eel Anguilla rostrata, yet little is known about the underlying production rates sustaining harvests. Demographic attributes were compared between six sub-estuaries and with an unexploited population in the Hudson River. A mark-recapture experiment in the Potomac River yielded growth, abundance, and production estimates. Sub-estuaries characterized by lower salinity had a lower proportion of females, and American eels were older, slower growing and showed increased parasitism. Female American eels were larger, older, and had higher growth rates than other gender types. Local abundances were 10-fold higher in the Potomac River estuary in comparison to the Hudson River, but growth rates were similar. Mortality rates were twice as high as those in the Hudson River estuary. The production model indicated American eel recruitment and biomass decreased substantially during the past 20 years.Item NAKED GOBIES (GOBIOSOMA BOSC) AS INDICATORS OF OYSTER REEF RESTORATION SUCCESS(2009) Lederhouse, Terra Marie; Paynter, Kennedy T; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Naked gobies (Gobiosoma bosc) are the most abundant resident fish on oyster reefs in the Chesapeake Bay and serve as a critical trophic link between the benthic and pelagic communities. Their response to oyster restoration may therefore be a useful indicator of ecosystem functioning. Experiments were conducted from 2005-2006 in the Severn and Patuxent Rivers to determine the response of naked gobies to increasing availability of oyster substrate. Naked gobies and other resident macrofauna were collected from experimental oyster reefs, constructed using adult oysters of various densities, loose oyster shell, and ambient sediment. Naked goby abundance, length, dry weight, and biomass increased with the availability of oyster substrate and were positively correlated with the abundance of other resident macrofauna. Individual dry weight and biomass were greater on reefs with a high density of oysters than on control plots, and may therefore serve as important indicators of oyster reef habitat quality.Item THE DISTRIBUTION OF CALLINECTES SAPIDUS MEGALOPAE AT THE MOUTHS OF CHESAPEAKE AND DELAWARE BAYS: IMPLICATIONS FOR LARVAL INGRESS(2009) Biermann, Jeffery Lee; North, Elizabeth W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Transport of Callinectes sapidus (blue crab) megalopae from the continental shelf into estuaries may influence recruitment variability of this economically important species. This research seeks to determine the vertical distribution of C. sapidus megalopae near the mouths of Chesapeake and Delaware Bays, and thereby infer swimming behaviors that may influence ingress to these estuaries. Megalopae and physical conditions were sampled at locations from ~10 km inshore of the estuary mouths to ~40 km offshore in coastal shelf waters in September 2005 and 2006. Megalopae were present in greater abundance and at shallower depths during night compared to day at all locations, suggesting a diurnal effect on distribution within the estuary and on the continental shelf. Unlike previous studies, offshore distributions did not indicate surface oriented behavior. Within the mouth of Delaware Bay, limited evidence suggests that megalopae presence in the upper portion of the water column increases in response to nocturnal flood tides. Results suggest photoinhibited swimming near the mouths of Chesapeake and Delaware Bays. In context of previous laboratory studies, these findings indicate that estuarine chemical cues at very low concentrations may induce changes in megalopae behaviors and stimulate molting at least 40 km offshore of estuarine mouths. Results suggest wind-forcing and density-induced subtidal flow are more likely mechanisms for ingress to Chesapeake and Delaware Bays than tidal-transport.
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