Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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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 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 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 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.Item Mycobacteriosis in Chesapeake Bay striped bass Morone saxatilis(2008-04-22) Stine, Cynthia Bee; Kane, Andrew S.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Striped bass, Morone saxatilis, is an economically and ecologically important species in the Chesapeake Bay and along the East coast of the United States. In 1997 an epizootic of mycobacterial infections was discovered in the Chesapeake Bay stock and subsequent reports indicated that up to three-fourths of subpopulations of striped bass in the Bay were infected, primarily older fish. This study investigated regional and age class differences in mycobacterial infections among younger striped bass in the Chesapeake Bay, and identified putative risk factors for infection. Approximately 2,000 0+ to 3+ age striped bass, a limited number of spawning stock, and bycatch species were evaluated for microbiology, histopathology and parasitology. Mycobacterial isolates were grouped according to gas chromatography fatty-acid methyl-ester profiles and multi-locus sequencing. Twenty-nine groups of mycobacteria were discerned including M. scrofulaceum, M. septicum, M. interjectum, M. triplex/M. montefiorense, M. szulgai, M. moriokaense, M. duvalii, M. avium, M. terrae, M. pseudoshottsii/M. marinum and M. shottsii, and several putative new species. The majority of mycobacteria groups observed had host overlap. Data revealed that prevalence of mycobacterial infection increased with age, up to 59%. Location of capture was associated with higher infection prevalence in fish sampled from the Pocomoke River compared with fish sampled from the Upper Bay (1+), the Choptank River (1+) and the Potomac River (0+, 1+). The presence of copepods, isopods, acanthacephalans, nematodes and trichodinid ciliates was associated with an increased prevalence odds ratio (POR) for mycobacterial infection, while the presence of bacteria other than mycobacteria was associated with a decreased POR for 0+ fish. Gender was not a risk factor for mycobacterial infection, however, gonads from some mature fish were infected. In addition, mycobacterial infections were observed in 12 other Chesapeake Bay fishes, including Atlantic menhaden, Brevoortia tyrannus, an important prey species. Mycobacterial infections in Chesapeake Bay fish appear to be more complex than the one pathogen-one host scenario. Further, vertical and food-borne transmission cannot be ruled out. Future research requires an holistic approach including evaluation of multiple host species in association with water quality and other environmental parameters.Item COMPARISONS OF MACROFAUNA ASSEMBLAGES ON RESTORED AND NON-RESTORED OYSTER REEFS IN MESOHALINE REGIONS OF CHESAPEAKE BAY IN MARYLAND(2008-01-04) Rodney, William Stanley; Paynter, Kennedy T.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recently restored oyster sanctuary reefs in Maryland allowed for a unique opportunity to observe the abundance and species composition of macrofauna assemblages on unexploited reefs with high concentrations of mature oysters and undisturbed reef architecture. These observations provided insights on the potential changes to reef dwelling macrofauna communities and various reef ecological functions resulting from reef restoration. I sampled macrofauna at four restored oyster sanctuary reefs and adjacent non-restored plots located outside sanctuary boundaries. I then compared the effects of study site location and habitat quality (restored vs. non-restored) on macrofaunal density using thirteen response variables. Motile macrofauna density was an order of magnitude higher on restored reefs and sessile macrofauna density was two orders of magnitude higher on restored reefs. Two out of four functional feeding groups: suspension feeders and carnivore/omnivores, were more abundant on restored plots. Results indicate that restoration improved reef ecological structure and function.Item Development of Standardized Antimicrobial Susceptibility Testing Methods and Aeromonas salmonicida Epidemiologic Cutoff Values for Antimicrobial Agents Used in Aquaculture(2007-07-27) Miller, Ron Ashley; Kane, Andrew S; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Pharmacokinetics describes the time course of drug absorption, distribution, metabolism and excretion. Pharmacodynamics is the relationship between unbound drug concentration over time and the resulting antimicrobial effect. Pharmacokinetic/ pharmacodynamic (PK/PD) indices quantify the relationship between pharmacokinetic parameters (i.e., area under the concentration-time curve, AUC) and microbiological parameters (i.e., minimal inhibitory concentrations, MICs), and are used to establish interpretive criteria or clinical breakpoints. The three primary PK/PD indices used are the AUC over 24 h at steady-state/MIC (AUCss/MIC), the peak concentration/MIC (Cmax/MIC), and the percentage of time over 24 hours that the drug concentration exceeds the MIC at steady-state pharmacokinetic conditions (T>MIC). These indices can be used to determine both appropriate dosage regimens and index magnitudes required for efficacy and reduced antimicrobial resistance emergence. The goal of this work was to determine the relevant PK/PD index target (AUCss/MIC) for oxytetracycline (OTC) against Aeromonas salmonicida, causative agent of furunculosis in salmonids. To achieve this goal we first established a standardized MIC testing method for aquatic bacterial pathogens, then used this method to determine the in vitro susceptibility cutoff concentration (epidemiologic cutoff value) for OTC (and three other antimicrobial agents) against 217 A. salmonicida isolates. We conducted additional in vivo studies using rainbow trout to monitor achievable serum OTC concentrations in both healthy and A. salmonicida-challenged fish. We confirmed OTC to be highly efficacious against a susceptible A. salmonicida strain in vivo, and through pharmacokinetics studies, calculated the OTC AUCss in healthy and challenged fish to be 27.2 and 20.1 μg∙h/mL, respectively. The PK/PD index target reported in a neutropenic mouse model as the most applicable to the tetracyclines is an AUCss/MIC of ≥5. Either of the AUCss values divided by the current epidemiologic cutoff value for A. salmonicida isolates (1 μg/mL) yields a product greater than this AUCss/MIC target of ≥5. This work demonstrates PK/PD indices commonly used in studies in mammals to predict therapeutic efficacy can be applied in studies in fish.