MEES Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/19655
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Item DIMETHYSULFONIOPROPIONATE (DMSP) AND DMSP-LYASE IN CNIDARIAN ALGAL SYMBIOSES(2010) Yost, Denise Marie; MITCHELMORE, CARYS L; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dimethylsulfoniopropionate (DMSP) is a multifaceted sulfur compound produced by several groups of marine phytoplankton, macroalgae and higher plants. Additionally, DMSP cleaving enzymes (most of which are thought to be DMSP-lyases) are known to exist in many species of marine phytoplankton, macroalgae and bacteria. Endosymbiotic dinoflagellate microalgae (genus Symbiodinium) of reef-building corals produce high intracellular levels of DMSP. The existence of DMSP-lyase(s) in Symbiodinium was, until recently, unknown. The function(s) of the DMSP/DMSP-lyase system in cnidarian-algal symbioses is poorly understood. Chapter one introduces coral symbioses, DMSP and the potential roles of the DMSP/DMSP-lyase system in cnidarian-algal symbioses. Chapter two describes the first evidence for in vivo DMSP-lyase activity in several isolated Symbiodinium strains, revealing varying levels of DMSP and DMSP-lyase activity. These results prompted further characterization of Symbiodinium DMSP-lyases. Enzyme assay optimization and substrate kinetics experiments found the measured activity of DMSP-lyase enzymes to be affected by permeabilization buffers, pH, temperature and potential oxidative stress effects (chapter three). Prior to investigations of field-collected intact corals, methods for DMSP analyses were optimized in the laboratory to address the inherent complexities of the coral holobiont. This work compared several preparation techniques for the analysis of particulate (algae only, DMSPp) and total (coral tissue and algae, DMSPt) DMSP in several species of stony corals (chapter four). Field-collected corals in chapter five showed DMSPp and DMSPt responses when exposed to the oxidative stressor, copper. The second field study (chapter six) describes how DMSPp and DMSPt concentrations within five prominent Bermudian corals changed with water depth. Finally, chapter seven presents a synthesis examination of the potential functional attributes and significance of the DMSP/DMSP-lyase system in cnidarian-algal symbioses. The factors influencing variable DMSP production and accumulation as well as differences in DMSP-lyase activity are discussed in light of methodological limitations, the biology and physiology of symbiont and coral, Symbiodinium phylotype and environmental variables. The results of this research highlight the existence of DMSP-lyases in Symbiodinium and provide insight into the partitioning of DMSP in cnidarian-algal symbioses, furthering our understanding of the production and potential turnover of DMSP while recognizing the limitations inherent in such investigations.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 An RNA:DNA-based index of growth in juvenile Atlantic menhaden (Brevoortia tyrannus): laboratory calibration and field assessment(2009) Edwards, Jason Lee; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atlantic menhaden (Brevoortia tyrannus) is an ecologically and economically important species in the mid-Atlantic coastal ecosystem. Its population dynamics are influenced by growth and survival during juvenile occupancy in estuarine nursery habitats. Therefore, quantifying production of potential nursery areas is important to understanding population processes and defining essential fish habitat for this species. Based on laboratory growth experiments, an RNA:DNA-based growth model was developed for young-of-the-year menhaden. The temporal response of RNA:DNA to changes in feeding condition was also quantified in the laboratory. Results of these investigations indicate RNA:DNA as a reliable tool for estimating recent growth and condition in relation to habitat residency. RNA:DNA-based estimates of growth were combined with site-specific abundance estimates to evaluate the spatiotemporal variability in production of potential menhaden nursery habitats. Site-specific production estimates exhibited high spatiotemporal variability suggesting menhaden utilize a mosaic of habitats to promote production, rather than specific sites consistently generating high levels of production.Item A von Bertalanffy Based Model for the Estimation of Oyster (Crassostrea virginica) Growth on Restored Oyster Reefs in Chesapeake Bay(2008-02-21) Liddel, Michael Keith; Paynter, Kennedy T; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A model to estimate the mean monthly growth of Crassostrea virginica oysters in Chesapeake Bay was developed. This model is based on the classic von Bertalanffy growth function, however the growth constant is changed every monthly timestep in response to short term changes in temperature and salinity. Using a dynamically varying growth constant allows the model to capture seasonal oscillations in growth, and growth responses to changing environmental conditions that previous applications of the von Bertalanffy model do not capture. This model is further expanded to include an estimation of Perkinsus marinus impacts on growth rates as well as estimations of ecosystem services provided by a restored oyster bar over time. The model was validated by comparing growth estimates from the model to oyster shell height observations from a variety of restoration sites in the upper Chesapeake Bay. Without using the P. marinus impact on growth, the model consistently overestimates mean oyster growth. However, when P. marinus effects are included in the model, the model estimates match the observed mean shell height closely for at least the first 3 years of growth. The estimates of ecosystem services suggested by this model imply that even with high levels of mortality on an oyster reef, the ecosystem services provided by that reef can still be maintained by growth for several years. Because larger oyster filter more water than smaller ones, larger oysters contribute more to the filtration and nutrient removal ecosystem services of the reef. Therefore a reef with an abundance of larger oysters will provide better filtration and nutrient removal. This implies that if an oyster restoration project is trying to improve water quality through oyster filtration, it is important to maintain the larger older oysters on the reef.Item Nutrient enrichment effects on mangrove sediments from differing tree height zones in Bocas del Toro, Panama(2008-01-28) Borgatti, Aimee Rachel; O'Neil, Judith M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Red mangrove (Rhizophora mangle L.) forests have distinct tree-height zones, with tall trees fringing the ocean and shorter trees in interior stands. A long-term nitrogen (N) and phosphorus (P) fertilization experiment in Almirante Bay, Bocas del Toro Province, Panama has shown that tree-height zonation is primarily related to nutrient limitation. This experiment was used to test the effects of in-situ nutrient additions and tree zonation on mangrove sediments. The sediments underlying the experimental R. mangle trees were sampled and N2 fixation, 15N, chlorophyll a, percent N and P, and percent organic biomass were quantified. Both N and P additions significantly affected almost every parameter measured in both zones within this experiment. These results are likely to have implications for management since N and P inputs are predicted to increase throughout the tropics and subtropics worldwide.Item Factors Influencing Glutathione S-transferases in Daphnia magna(2006-07-25) Smith, Lisa Stievater; Nelson, Judd; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Glutathione S-transferases (GSTs) are an important family of xenobiotic biotransforming enzymes that can make toxicity tests variable. Daphnia magna is commonly used in ecotoxicology testing because they are easy to culture, have a short life cycle, and reproduce by parthenogenesis. The specific activities of glutathione S-transferases were determined in D. magna of different ages and D. magna with eggs and without eggs in their brood chambers and in both cases there was a significant difference in the specific activity between the groups. D. magna were exposed to clofibrate and it was determined that clofibrate does not significantly alter the specific activities of GSTs in D. magna. Glutathione S-transferases were purified from D. magna using affinity chromatography and then the purified sample was run on a SDS-PAGE gel to determine the molecular weight of the subunits of glutathione S-transferases which fell in the range that was consistent with previous studies.Item PHYSIOLOGICAL AND MOLECULAR ASPECTS OF ORGANELLE SEQUESTRATION IN THE CILIATE MYRIONECTA RUBRA(2005-12-12) Johnson, Matthew David; Stoecker, Diane K; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The phototrophic ciliate Myrionecta rubra was studied in order to understand the role of organelle retention from its prey, Geminigera cryophila (Cryptophyceae). Sequencing of SSU rRNA genes of M. rubra, and a close relative Mesodinium pulex, revealed short (<1600>bp) sequences with high substitution rates. Phylogenetic analysis yielded a basal placement within the ciliates. Application of a fluorescence in situ hybridization probe revealed the genes were expressed in the cytoplasm and nucleoli of the ciliates. Phylogenetic analysis of the chloroplast nucleomorph SSU rRNA gene in M. rubra confirmed their origin to be from G. cryophila. Feeding on G. cryophila was shown to increase growth, which remained constant for 4 weeks of starvation and then declined slowly over time. Chlorophyll a (chl a) synthesis and plastid division decreased faster than growth, resulting in declines in cell pigment over time. During starvation photosynthetic efficiency declined slightly, while overall photosynthesis became uncoupled from growth, resulting in decreased growth efficiencies. While plastids in M. rubra or G. cryophila have equal efficiency at saturating irradiance, they are more efficient in G. cryophila in low light and have a greater overall quantum yield of photochemistry. Lower C-specific photosynthetic rates and chl a:C ratios resulted in lower growth compared to G. cryophila, which was reflected in increased partitioning of C to lipid fractions and lower protein production in M. rubra. A novel process, retention of prey nuclei (PN), was found to occur in M. rubra. G. cryophila nuclei are retained in a transcriptionally active state for >20 days, and remain in the cytoplasm for at least 30 days, apparently with no net division. Cell and plastid division are maximum during PN retention, and decline after PN loss. The PN genes LHCC10 and GAPDH were expressed at levels greater than those observed in G. cryophila. Expression of a plastid (psbA) and nucleomorph (cbbX) gene was also confirmed. M. rubra is a unique phototroph, capable of regulating and dividing certain G. cryophila organelles, and reaching maximum growth potential when PN are present. Feeding on G. cryophila appears to be most important for obtaining PN.Item THE EFFECTS OF FRESHWATER FLOW AND GRAZING ON THE PLANKTON COMMUNITY STRUCTURE OF CHESAPEAKE BAY TRIBUTARIES(2005-05-02) Reaugh, Matthew L.; Roman, Michael R.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Changes in the plankton composition of estuarine systems are often driven by freshwater flow. These changes in species composition and abundance have the potential to affect trophic dynamics within the plankton community. In order to quantify the effects of freshwater flow in estuaries, the structure of the spring plankton community and copepod grazing were examined in an extreme dry (2002) and wet (2003) year in two tributaries of Chesapeake Bay. Increases in phytoplankton and copepod biomass in the wet year were large in comparison to the increase in microzooplankton biomass. Ample abundance of prey and high copepod community grazing potentials indicate that microzooplankton biomass was influenced by strong top-down control in the high flow year. While no evidence of a copepod-microzooplankton-phytoplankton trophic cascade was found, increased top-down control by grazers in combination with increased nutrient supply in wet years may be important in establishing spring phytoplankton blooms in Chesapeake Bay.Item Genetic Diversity and Phytochemistry of Maryland-Grown American Ginseng (Panax quinquefolius L.)(2004-09-16) Schlag, Erin Margaret; McIntosh, Marla S; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)American ginseng (Panax quinquefolius) is a valuable medicinal herb threatened by over-harvest. Because data are insufficient, current attempts to protect diversity and improve cultivation are inadequate. Random Amplified Polymorphic DNA (RAPD) markers were used to estimate genetic diversity and high-performance liquid chromatography (HPLC) was used to characterize root ginsenoside concentrations in wild and cultivated populations of American ginseng in Maryland. Wild populations were less diverse than cultivated and highly differentiated from one another; suggesting that drift was high and gene flow low in wild populations. Exotic plants were genetically and phytochemically distinct from native plants. The main ginsenoside in exotic plants was Re versus Rg1 in native plants. Plants from at least one wild population were genetically and phytochemically similar to exotic plants, suggesting that exotic plants were introduced into wild populations. Thus, native Maryland American ginseng is unique but threatened by drift, isolation and artificial introductions.Item THE POPULATION STRUCTURE OF VIBRIO CHOLERAE IN CHESAPEAKE BAY(2004-06-03) Choopun, Nipa; Colwell, Rita R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The population structure of V. cholerae in Chesapeake Bay, United States, was analyzed and a simple procedure that employed only two biochemical tests in an abbreviated identification scheme, i.e., arginine dihydrolase and esculin hydrolysis, was developed. After enrichment in alkaline peptone water and selective plating on thiosulfate-citrate-bile salts-sucrose agar, all of the sucrose fermenting colonies identified by the two tests were confirmed as V. cholerae by the polymerase chain reaction. A non-redundant collection of 224 V. cholerae strains collected from 1998 through 2000 from Chesapeake Bay was analyzed for phenotype, genotype, and genomic fingerprint. A long-range enterobacterial repetitive intergenic consensus (ERIC) PCR method that was developed for this study provided fingerprint patterns that proved useful in assessing relatedness among the strains. Cluster analysis was done using three different methods and revealed three well separated, primary clusters: Cluster A, consisting of the majority of the isolates, including the toxigenic type strain for the species and luminescent strains of V. cholerae; a smaller Cluster B, with the noteworthy characteristic of low toxR gene homology; and Cluster M, consisting exclusively of V. mimicus. Another primary cluster, Cluster C, was also identified as a single clone of a sucrose-negative, luminescent, toxR-negative strain. Because V. mimicus formed a separate cluster with similar distance values as demonstrated by V. cholerae Cluster B, using both ERIC fingerprinting and DNA-DNA hybridization, and had phenotypic and genotypic traits and 16S rDNA sequences similar to V. cholerae, it is concluded that all of the primary clusters observed in this study, including V. mimicus, belong to a single species, V. cholerae. V. mimicus was judged to be the highest risk group of the non-toxigenic isolates, in terms of susceptibility to CTX-phi and possession of the heat-stable enterotoxin gene (stn). Approximately 11% of the V. cholerae strains that lacked the toxin-coregulated pili (TCP) and 50% of the V. mimicus strains were found to be susceptible to CTX-phi. In addition to the V. cholerae strains in the toxigenic subcluster, luminescent V. cholerae strains represented the next highest risk, since 14% of the luminescent strains were susceptible to CTX-phi and 33% were stn positive.