Biology Theses and Dissertations

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End date: 2009Subject: search.filters.subject.Biology, Oceanography

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    Effect of pH on phytoplankton and bacteria production
    (2009) Johns, Desmond Justine; Stoecker, Diane K; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In recent decades eutrophication has fueled intense phytoplankton blooms that frequently negatively impact ecosystems. Dramatic pH elevations are commonly overlooked during such blooms, which may also be harmful. Cyanobacteria blooms in the Sassafras River, MD were sampled during Autumn 2008 and measured for primary and bacterial production (PP and BP), and differences in bacteria communities composition were examined. pH elevations above 8.8 in the field corresponded to decreased PP, but had no effect on BP. Laboratory experiments demonstrated that negative effects of pH were dependant on light intensity; PP increased with pH at moderate light intensities, but decreased at low irradiance. There was some evidence that BP is affected by high pH, although bacteria community differences as determined by DGGE were not. Negative effects of high pH are probably most important during spring and summer in low salinity environments when pH fluctuations are more common and last longer.
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    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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    Population genetics of the eastern oyster in Chesapeake Bay
    (2008) Rose, Colin G.; Hare, Matthew P; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The eastern oyster, Crassostrea virginica, plays an important role in the ecology of Chesapeake Bay. Its large population size, long larval dispersal stage and potential for high variance in reproductive success is representative of many marine invertebrates. Nevertheless, many important aspects of the oyster's biology remain unclear. I investigated how migration, natural selection, and effective population size have shaped the evolution of Chesapeake oysters. First, I examined aspects of genetic connectivity among oysters from rivers throughout the Bay. A correlation between geographic and genetic distance indicated that oyster larval dispersal tends to be local and that migration between Bay tributaries is rare over an ecological time scale. This result contributes to a growing body of literature indicating that larval dispersal is not passive. Next, I showed that a pattern of non-neutral mitochondrial evolution previously observed in different oyster populations also existed in Chesapeake Bay C. virginica. Tests of selection indicated that the pattern, in which there is an excess of high frequency and low frequency haplotypes and a deficit of intermediate frequency haplotypes, was the result of positive selection on the genome. Demographic explanations appear unlikely to account for the mitochondrial haplotype pattern because nuclear loci exhibited neutral patterns of sequence evolution. Estimates of effective population size were several orders of magnitude smaller than census size, indicating that there was variance in reproductive success (sweepstakes reproduction). Nevertheless sweepstakes reproduction was not so severe that individual cohorts of juvenile oysters exhibited reduced levels of variation compared to the adult population. Finally I evaluated the risks associated with a supplementation program in which hatchery-raised oysters bred for disease tolerance were released into wild oyster populations. The results indicated that following supplementation, the wild effective population size remained large despite the danger of severe genetic bottlenecks. Increased hatchery effective population is suggested to prevent future harm to the wild population.
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    Watershed land use and nutrient dynamics in Maryland Coasal Bays, U.S.A.
    (2008) Beckert, Kristen A.; O'Neil, Judith M.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Upstream and inshore regions of the Maryland Coastal Bays exhibit degraded water quality. Six streams and three shallow bays were sampled in May and July 2006 and 2007 to compare spatial patterns in relation to land use and nutrient loading. St. Martin River, having a high percentage of crop agriculture and a low percentage of forest and wetlands, experienced the most degraded water quality of the three regions, and stream total nitrogen in its watershed was linked to feeding operations and anthropogenic land use. Despite having a much less developed watershed, Johnson Bay experienced degraded water quality, especially in inshore regions. Sinepuxent Bay had the best water quality of the three bays, but still demonstrated anthropogenic impacts. Nutrient loading from land use is directly related to the observed patterns in St. Martin River, while residence time, groundwater flows, and within-bay cycling has led to water quality degradation in Johnson Bay.
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    Microcosm Studies of Nutrient Cycling in Bahamian Stromatolites
    (2008-08-13) Jabro, Nicholas; Marinelli, Roberta; Harvey, Rodger; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    I report results of field observations and experiments that examine the oxygen and nutrient fluxes for stromatolites in Highborne Cay in the Exumas, Bahamas. The aim of this study is to determine whether nutrients play a role in the transition of the community structure within the mats that is thought to be responsible for lithification and, ultimately, mat growth and structure. The research includes nutrient monitoring of the sediment and water column, and measures of rates of oxygen and inorganic nutrient exchange from stirred microcosm chamber incubations of mats with varied community structure. On the basis of mat community composition, I hypothesized that different mat types would have different fluxes, and that Highborne mats would be limited by one or more nutrients that efficient recycling within the mats might otherwise help supply. Samples of the four major mat types were sealed in stirred microcosm flux chambers, incubated in a circulating water bath, and sampled for oxygen, NH4, NO3, PO4, and Silicate. Nutrient addition, treatments of PO4 and Si were employed to investigate whether they stimulate primary productivity, signaling that mats are limited in these solutes. Nutrients in Highborne Cay were high in nitrogen relative to P, with N:P as high as 30. There was no difference in nutrient flux or productivity among mat types, and the addition of nutrients did not change mat productivity. These observations suggest that mat development in Highborne Cay is not limited by nutrients, but more likely structured by external physical factors such as the rate of turbulent flow which may limit the recruitment of competitors such as macroalgae and benthic branching diatoms.
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    Bioenergetic and ecological consequences of diet variability in Atlantic croaker Micropogonias undulatus
    (2008-04-26) Nye, Janet Ashley; Miller, Thomas J.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Atlantic croaker Micropogonias undulatus is a commercially and ecologically important bottom-associated fish that occurs in marine and estuarine systems from Cape Cod, MA to Mexico. I documented the temporal and spatial variability in the diet of Atlantic croaker in Chesapeake Bay and found that in the summer fish, particularly bay anchovies Anchoa mitchilli, make up at least 20% of the diet of croaker by weight. The use of a pelagic food source seems unusual for a bottom-associated fish such as croaker, but appears to be a crepuscular feeding habit that has not been previously detected. Thus, I investigated the bioenergetic consequences of secondary piscivory to the distribution of croaker, to the condition of individuals within the population and to the ecosystem. Generalized additive models revealed that the biomass of anchovy explained some of the variability in croaker occurrence and abundance in Chesapeake Bay. However, physical factors, specifically temperature, salinity, and seasonal dynamics were stronger determinants of croaker distribution than potential prey availability. To better understand the bioenergetic consequences of diet variability at the individual level, I tested the hypothesis that croaker feeding on anchovies would be in better condition than those feeding on polychaetes using a variety of condition measures that operate on multiple time scales, including RNA:DNA, Fulton's condition factor (K), relative weight (Wr), energy density, hepatosomatic index (HSI), and gonadosomatic index (GSI). Of these condition measures, several morphometric measures were significantly positively correlated with each other and with the percentage (by weight) of anchovy in croaker diets, suggesting that the type of prey eaten is important in improving the overall condition of individual croaker. To estimate the bioenergetic consequences of diet variability on growth and consumption in croaker, I developed and validated a bioenergetic model for Atlantic croaker in the laboratory. The application of this model suggested that croaker could be an important competitor with weakfish and striped bass for food resources during the spring and summer when population abundances of these three fishes are high in Chesapeake Bay. Even though anchovies made up a relatively small portion of croaker diet and only at certain times of the year, croaker consumed more anchovy at the population level than striped bass in all simulated years and nearly as much anchovy as weakfish. This indicates that weak trophic interactions between species are important in understanding ecosystem processes and should be considered in ecosystem-based management.
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    Infaunal Effects on Permeable Sediment Processes
    (2008-04-22) Waldbusser, George; Marinelli, Roberta L.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The role of infauna on permeable sediment processes is poorly understood due to methodological limitations and a lack of empirical data. The interactions among porewater flows, sediments, and biogenic structures present a physically and biogeochemically complex sedimentary environment in which traditional measurement techniques and heuristic models are of minimal applicability. Chapter one provides an executive summary of this research. The second chapter describes a field investigation of the impact of the common lugworm and two species of thalassinid shrimp on porewater transport and chemistry in permeable sediments. In this work, novel experimental methods are employed to measure infaunal effects on porewater transport and chemistry. This experiment found differential effects of each taxon on porewater transport and solute chemistry that were highly related to infaunal functional characteristics, and independent of sediment properties. Results from the field study prompted a laboratory microcosm study of lugworm effects on permeable sediment solute fluxes, presented in chapter three. Flow-through sediment microcosms mimicked tidal draining of intertidal flats and measured the effects of lugworms on sediment biogeochemistry. Lugworms were found to significantly alter solute fluxes as well as stoichiometric ratios from the microcosms. The potential ecosystem consequences of stoichiometric changes to regenerated solutes are explored with a new metric. Finally, chapter four presents a synthesis examination of the infaunal functional attributes important to permeable sediment processes with a multi-site, multi-species field investigation. Head-down deposit feeders were found to have similar effects on advection and chemistry, whereas other infauna had differential effects linked to the composition and morphology of the burrow/tube. The mechanisms by which different infauna may affect permeable sediment properties are discussed, and include consideration of covariates such as organism activity and density. The results from this research highlight the importance of infauna to permeable sediment processes, while recognizing the limitations of their effects under different physical regimes. Benthic infauna play a significant role in the biogeochemistry of common permeable sediment habitats in coastal and near-shore environments. The results presented herein suggest the loss of large bioturbating infauna from permeable sediments due to human activities may result in significant changes to coastal biogeochemical cycles.
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    Taxonomy and Ecophysiology of Pseudo-nitzschia in the Chesapeake Bay
    (2007-12-12) Thessen, Anne Elizabeth; Stoecker, Diane K; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Pseudo-nitzschia is a diatom genus known to produce the neurotoxin, domoic acid (DA), which causes Amnesic Shellfish Poisoning (ASP) and Domoic Acid Poisoning (DAP). Field studies were conducted in the Chesapeake Bay to determine which species were present, their toxicity and their spatial and temporal distribution. Strains were isolated from the Chesapeake Bay region and growth and toxin content were studied. The effect of rapid increases in light at low temperatures on toxin production physiology was investigated. Toxic Pseudo-nitzschia is present in the Chesapeake Bay; however, abundance and toxin production are highly variable. Six species of Pseudo-nitzschia were identified: P. pungens, P. calliantha, P. subpacifica, P. cuspidata, P. fraudulenta and P. multiseries. The most abundant species was P. calliantha. Pseudo-nitzschia abundances were associated with low temperature (2-21°C) and high salinity (6-32) and were highest in winter and spring. Compared to other diatom species, Pseudo-nitzschia abundances were low, rarely present above 1000 cells mL-1 and they did not occur as monospecific blooms. Low Pseudo-nitzschia abundances and low, irregular domoic acid concentrations may partially explain the lack of documented toxic events in the Chesapeake Bay. Growth rate and toxin content of strains of Pseudo-nitzschia exposed to different nitrogen sources and irradiances varied significantly, even among strains of the same species isolated from the same water sample. Strain-level differences were responsible for most of the variability in growth rate and toxin content. Sequences of the internal transcribed spacer (ITS) and large subunit (LSU) rRNA matched morphological species definitions, but offered no explanation for the physiological variability. Populations of Pseudo-nitzschia in the mid-Atlantic coastal zone appear to be comprised of numerous ecotypes that require sorting in the future. The hypothesis that DA is produced as an energy modulation strategy when the light and dark reactions of photosynthesis are decoupled was tested by exposing exponentially growing P. multiseries to a rapid increase in irradiance at a low temperature. High light and low temperature conditions increased nitrate (NO3‾) uptake, nitrite (NO2‾) and ammonia (NH4+) release and decreased DA production by the cells. These results could have important implications for natural populations of Pseudo-nitzschia at times of low temperature and high light fluctuations, such as during spring blooms and upwelling events. This thesis answered several questions about Pseudo-nitzschia populations in the Chesapeake Bay area and their ecophysiology, but raised many more. Physiological adaptations and biogeography of Pseudo-nitzschia and DA content of Chesapeake bivalves should be studied further to contribute to the development of predictive models for Pseudo-nitzschia bloom formation and toxin production.
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    The effects of low dissolved oxygen on predation interactions between Mnemiopsis leidyi ctenophores and larval fish in the Chesapeake Bay ecosystem
    (2006-11-27) Kolesar, Sarah Elizabeth; Breitburg, Denise L; Boynton, Walter R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Differences in predator and prey tolerances to low dissolved oxygen (DO) concentrations are important to planktonic food webs in seasonally hypoxic environments like Chesapeake Bay. Hypoxia alters field distributions, encounter rates, and predator-prey interactions between hypoxia-tolerant ctenophores, Mnemiopsis leidyi, and less tolerant ichthyoplankton and zooplankton prey. To examine the effect of hypoxia on estuarine food web species' interactions, I conducted medium and small-scale experiments, field sampling, and collaborated on individual-based model development, focusing on ctenophore-larval fish dynamics. Laboratory estimates of clearance rates for ctenophores on bay anchovy (Anchoa mitchilli) eggs and yolk sac larvae, and naked goby (Gobiosoma bosc) feeding larvae were the same at low and high DO. Field sampling for M. leidyi, ichthyoplankton, mesozooplankton, and scyphomedusae (Chrysaora quinquecirrha) during day and night at two sites in the Patuxent River indicated increased abundance of most species in the bottom layer with increasing bottom DO. Vertical overlap between predator and prey pairs also increased with higher bottom DO, increasing potential encounters and predation. Larval fish swimming speeds did not differ significantly with DO, but ctenophores swam significantly faster at intermediate DO (2.5 mg L-1) than at either low or high DO. DO did not significantly affect ingestion. Greater ingestion of fish larvae by ctenophores followed multiple encounters (56%) than initial encounters (10%) at all DO concentrations, highlighting the potential importance of repeated predator-prey interactions. DO did not significantly affect encounter model estimates of ingestion rates. Ingestions averaged 0.4 fish larvae d-1 m-3 for first encounters and 2 fish larvae d-1 m-3 for multiple encounters. Results from laboratory and field studies parameterized a spatially-explicit individual based model of a ctenophore-ichthyoplankton-copepod intraguild predation food web. Ctenophore predation had a bigger effect on survival of modeled ichthyoplankton than did competition between ctenophores and fish larvae for shared zooplankton prey, but competition more strongly affected larval fish growth rates. DO did not alter the relative importance of ctenophore predation and competition, but low DO did decrease larval fish survival and increase growth rates. Results suggest that effects of DO on vertical distribution and species overlap are more important to predation than direct DO effects.
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    Evaluation of agricultural nutrient reductions in restored riparian buffers
    (2006-11-15) sutton, adrienne june; Fisher, Thomas; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Efforts to restore the Chesapeake Bay have focused on reducing agricultural nutrient losses. In particular, riparian buffer restoration has been an important component of nutrient reduction strategies, and one program used extensively to restore riparian vegetation on agricultural land is the Conservation Reserve Enhancement Program (CREP). I evaluated the effect of CREP on water quality on the Delmarva Peninsula by measuring groundwater nutrients under restored buffers on two farms, monitoring stream baseflow in 30 small watersheds (or subbasins), and monitoring stream stormflow in two subbasins. On the farms, nitrate concentrations were lower in the restored buffers than in the non-buffered sites, suggesting that buffer restoration was successful in filtering groundwater nitrate. In groundwater under a 7 year old CREP buffer, dilution by infiltration of rainwater accounted for 56% of the total nitrogen reduction, and denitrification accounted for 15 to 30%. At the watershed scale, CREP restored 1 to 30% of total streamline in 15 agriculturally-dominated subbasins in the Choptank River. However, I did not detect differences in nitrogen concentrations between these subbasins based on the amount of buffer restoration. Nitrogen concentrations actually increased in most of the streams since previous monitoring before restoration; therefore, buffers may not be extensive enough to have measurable affects on baseflow water quality. However, comparison of stormflow between two subbasins revealed significant nutrient differences. Total buffered streamline was greater and more widely distributed in Blockston than in Norwich subbasin. The amount and distribution of CREP may have influenced the stormflow nutrient yields, which were 2 times higher in Norwich versus Blockston. Lastly, I reviewed 20 years of stream monitoring data from German Branch subbasin in the context of all agricultural management practices implemented in the basin. A decade after management, I detected a 33% decrease in phosphorus concentrations in stream baseflow, but no significant changes in nitrogen concentrations. However, the rate of increase of 0.14 mg N L-1 yr-1 prior to management did not continue to present-day baseflow conditions and may have been suppressed by management practices. While these results are somewhat encouraging, complete understanding of watershed-scale effects of riparian buffers will require further interdisciplinary study.