MEES Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/19655

Browse

Start date: 2000End date: 2009

Search Results

Now showing 1 - 10 of 195
  • Thumbnail Image
    Item
    Understanding Maternal Effects as a Recruitment Mechanism in Lake Michigan Yellow Perch (Perca flavescens)
    (2000) Heyer, Christopher James; Miller, Thomas J.; Biology; Marine - Estuarine - Environmental Sciences Program; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)
    Changes that have occurred in the abundance and trait distribution of adult Lake Michigan yellow perch (Perca flavescens) suggest that maternal effects on larval traits may be substantially influencing the recruitment of this heavily exploited species. Maternal effects on yellow perch larvae at hatching and through 32 days post hatch (dph) were investigated in ten maternal lines to test the null hypotheses of no effect of maternal condition on offspring condition at hatching, no persistence of maternal effects under conditions of starvation and high food availability, and no difference in offspring survival under conditions of starvation and high food availability. Maternal effects were detectable at hatching and likely result in differences among females in size, age, gonadal somatic index, and egg production. Maternal effects at hatching were expressed by differences in larval total length, yolk volume, dry weight, and DNA quantity. Maternal effects persisted under conditions of starvation to 6 dph, after which point virtually all larvae had perished. Maternal effects resulted in a twofold difference in resistance to starvation among the maternal lines. Larvae that exhibited the lowest resistance to starvation were long with small yolk volumes, while those exhibiting the highest resistance to starvation were short with large yolk volumes. Under high food availability maternal effects persisted to 32 dph, and resulted in threefold differences in survival among the maternal lines. No clear mechanism was identified to account for these survival differences. The observed maternal effects in Lake Michigan yellow perch may have substantial implications on recruitment.
  • Thumbnail Image
    Item
    Morphology in Urbanized Streams of the Puget Sound Lowland Region
    (2004) Boyle, Pamela; Prestegaard, Karen; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The purpose of this research is to evaluate the effects of urbanization on channel morphology. Three hypotheses are tested: 1) Channel morphology measured from one cross section is not similar to reach-averaged values, 2) Channel shear stress ratios and erosivity increase with urbanization, and 3) Channel morphological complexity decreases with urbanization increases. Results indicate that single cross-section data do not adequately describe channel morphology. Shear stress and bed mobility did not increase with urbanization, perhaps due to the presence of large bed grain sizes that adjust to increases in flow. Similarly, channel complexity did not decrease with increased urbanization. These data indicate that channel changes resulting from urbanization are influenced by sediment supply as well as discharge, and that this should be taken into consideration in restoration design.
  • Thumbnail Image
    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.
  • Thumbnail Image
    Item
    Benthic Oxygen Production in the Choptank Estuary
    (2009) Chick, Christopher Roberts; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Microphytobenthos (MPB) represent an important component of primary production in many coastal estuarine systems. The aim of this study is to determine which variables in the Chesapeake Bay are positively correlated with MPB oxygen production, and based on this correlation to develop a predictive relationship for estimating benthic primary production. Furthermore, this study estimates the proportion of MPB primary production to total primary production in the Chesapeake Bay. Oxygen flux rates were measured in the dark and in the light from sediment cores taken from three sites on the Chesapeake Bay. Flux rates ranged from 6000 mol O2 m-2 h-1 in the light to -3800 mol O2 m-2 h-1 in the dark treatment. From these rates and other measurements, we developed multiple linear regressions using sediment grain type and depth to predict oxygen production seasonally. We applied these relationships to sediment grain-size and bathymetry data using ArcMap software to create a spatial dimension to our predictive relationships. Based on our derived relationship, we estimated summer average benthic daily net production to be 123 ± 962 mg O2 m-2 d-1 between 0-3 meters. For the winter, we estimated the rate to be 152 ± 413 mg O2 m-2 d-1. For spring we had a weaker relationship, but we estimated benthic production to be -257 ± 123 mg O2 m-2 d-1. Using published pelagic data, we created a proportion of benthic to pelagic primary production, and we estimate that MPB provide approximately 12% of total primary production in the mid-bay region. Shallower depths contained a higher proportion of benthic O2 productivity to pelagic O2 production with the contrast peaking during the summer months.
  • Thumbnail Image
    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.
  • Thumbnail Image
    Item
    Genetic Differentiation of Selected Eastern Box Turtle (Terrapene carolina) Populations in Fragmented Habitats, and a Comparison of Road-based Mortality Rates to Population Size
    (2009) Hagood, Susan; Adams, Lowell; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The decline of eastern box turtle populations is associated with habitat loss and fragmentation, lack of recruitment into breeding populations, removal of individuals from the wild for pets, and road mortality. Box turtle populations in many areas of the eastern United States may effectively be isolated as high traffic volumes on roads adjacent to turtle habitats prevent successful dispersal. If so, populations surrounded by heavily used roads may be less genetically diverse than those in relatively intact habitats. I investigated whether populations in three Montgomery County, Maryland parks that were surrounded by roads were genetically differentiated relative to populations in two larger habitats in Maryland's Prince George's and Anne Arundel counties. Sampling was conducted between 2005 and 2008. I used 10 microsatellite markers to compare these populations, and sampled in an additional five sites (two in Maryland, and one each in Pennsylvania, the District of Columbia, and Florida), to better assess population structure. I found little evidence of genetic differentiation among central Maryland populations regardless of the extent of isolation. I attribute these findings to the slow rate of change in turtle evolution; the observed similarities in genetic diversity may reflect past rather than present gene flow. I found moderate to great differentiation in populations separated by substantial distances. To determine whether road mortality exceeds additive mortality levels believed to be a threat to population persistence, I estimated population size in the three Montgomery County, Maryland, parks using mark-recapture techniques, and compared these estimates to the number of dead, injured, and live turtles in or very near roads observed during walking and driving surveys conducted in 2006. Road-based morality rates fell within the range estimated to be inconsistent with population growth in one of the parks. Road mortality appeared to affect females out of proportion to their abundance in the population. Suggestions for reducing box turtle mortality in areas associated with high mortality rates are included.
  • Thumbnail Image
    Item
    MORPHOLOGY IN URBANIZED STREAMS OF THE PUGET SOUND LOWLAND REGION
    (2004) Boyle, Pamela Roxana; Prestegaard, Karen; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Increased runoff from urbanization may result in erosion to the stream channel and banks, leading to channel incision, bed changes, loss of instream debris and habitat, and an overall reduction of heterogeneity and channel complexity. These impacts are especially evident in low gradient, gravel-bed, meandering streams - the major type of stream in the Puget Sound Lowland region. The failure of many stream restoration projects is due to a lack of understanding of how morphological features of a stream respond to hydrological changes. Single cross-section methods (instead of reach-level) are generally used and may not adequately portray the complexity, or variation, of the stream channel and bed. Three main hypotheses in this thesis are: 1) a single cross-section taken within a reach does not adequately describe a stream compared to a mean value calculated from several measurements; 2) urban streams with more urbanized drainage areas have higher shear stresses, and thus move larger bed particles and have higher reach mobility; and 3) urban channels have less channel complexity than non-urban channels. Results showed that a single cross-section may not adequately describe the morphological variables of a stream reach; however, this method may be appropriate for calculating reach shear stress. In addition, shear stress and mobility were not found to increase with increasing urbanization. Furthermore, complexity was not found to decrease with increasing urbanization. These two latter results indicate that urbanization (or percent imperviousness) alone cannot be used as a variable to investigate changes in stream morphology and hydraulics. In fact, a measure of sediment supply could be considered an additional independent variable by which to study urbanization impacts to streams. Substrate distributions from this thesis also support this finding.
  • Thumbnail Image
    Item
    Interactions between an estuarine submersed plant bed and its physical and biogeochemical environment: Seasonal and spatial variation
    (2009) Gruber, Renee Kirstin; Kemp, William M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Annual cycles of growth and morphology were analyzed in a bed of the canopy-forming submersed aquatic vegetation (SAV) species, Stuckenia pectinata, in relation to seasonal water quality conditions in a Chesapeake Bay tributary. A rapid accumulation of aboveground plant material occurred during the spring period of high water clarity, which aided plants in circumventing light limitation during the summer period of low water clarity. During summer, this SAV bed strongly attenuated wave energy, which contributed to growth-promoting feedback effects that improved light and nutrient availability for plants. Modification of hydrodynamic conditions also resulted in several negative feedback effects on SAV growth. Feedbacks were regulated by plant stand size and density and seasonal changes in plant canopy architecture. The findings of this study illustrate the significant impacts SAV beds can have on their local environment, improving conditions and resulting in plant growth that could not otherwise occur in this degraded system.
  • Thumbnail Image
    Item
    DECIPHERING THE SECRET OF SARCOMERE ASSEMBLY AND DISEASES USING THE ZEBRAFISH MODEL SYSTEM: REGULATION OF MYOFIBRILLOGENESIS BY SMYD1B AND ITS PARTNERS
    (2009) Li, Huiqing; Du, Shao Jun; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Myofibrillogenesis is a process of precise assembly of sarcomeric proteins into the highly organized sarcomeres which are essential for muscle cell differentiation and function. Myofibrillogenesis requires proper folding and assembly of newly synthesized sarcomeric proteins. Mutations of the sarcomeric proteins are known to cause skeletal and cardiac muscle diseases. smyd1b is a skeletal and cardiac muscle-specific gene which encodes two alternatively spliced isoforms, smyd1b_tv1 and smyd1b_tv2. Knockdown of smyd1b (tv1 and tv2) expression resulted in zebrafish larvae without locomotion and heart contraction. Thick filament assembly was significantly disrupted in smyd1b knockdown embryos. Yeast Two-Hybrid study showed that Smyd1 associates with another muscle-specific protein--skNAC, however, skNAC function in muscle cells is unknown. In order to expand the understanding of smyd1b function and study the working mechanism, I further characterized the function of Smyd1b and its partners including skNAC and Hsp90&alpha1 during muscle development, and carried out mechanistic studies using zebrafish as a model system. Our findings show that: 1) In addition to the thick filament, smyd1b plays an important role in the assembly of thin and titin filaments, as well as Z-line and M-line. 2) Knockdown of smyd1b has no effect for heart tube formation; however, it disrupts the myofibril assembly of the cardiac muscle that causes the heart defect. 3) Smyd1b_tv1, but not Smyd1b_tv2 can be localized on the M-line of sarcomeres. 4) Ser225 on Smyd1b_tv1, which is a potential phosphorylation site, is important for the M-line localization of Smyd1b_tv1. 5) Knockdown of smyd1b causes the upregulation of hsp90&alpha1 and unc45b gene expression. 6) hsp90&alpha1 plays an important role for myofibril assembly. 6) Knockdown of smyd1b or hsp90&alpha1 causes the reduction of myosin protein accumulation. 7) Smyd1b_tv1, but not Smyd1b_tv2 associates with the myosin chaperones Hsp90&alpha1 and Unc45b. 8) sknac is required for the thick and thin filaments assembly. 9) Knockdown of sknac causes the reduction of myosin protein accumulation. These studies provide us an in-depth characterization of smyd1b and its partners' function and expands the mechanistic understanding of how smyd1b fulfils its vital role in myofibrillogenesis. Most importantly, this study provides new insights to help us understand the complex process of myofibrillogenesis and sarcomere diseases.
  • Thumbnail Image
    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.