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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Food habits, prey selectivity and food resource partitioning of a community of fishes on the outer continental shelf

Sedberry, George R., III 01 January 1980 (has links)
The demersal fish community of the outer continental shelf in the Middle Atlantic Bight consists of resident species, seasonal species with boreal affinities, and seasonal species with warm temperature affinities. Dominant demersal fishes of the outer continental shelf feed primarily on macrobenthic invertebrates, which persist in dense, stable communities. Some dominant predators also feed heavily on fishes, cephalopods, and planktonic invertebrates, at least seasonally. Food habits of the fishes change seasonally, especially at the species level. Food habits of fishes also change considerably with size, with most predators showing distinct feeding stanzas separated by a marked change in feeding strategy. Electivity patterns of predators upon the benthos were varied with respect to prey distribution and abundance patterns. Some dominant benthic species were not selected as food. Other rarer species were preferentially selected. Some prey species that varied in abundance with respect to habitat strata were eaten in proportion to their abundance in most habitats. Others were eaten only where very abundant, or were consumed in moderate amounts regardless of their abundance in the benthos. Several factors may account for these patterns. Most predator species shared many prey species. Overlap in diet among the predators varied seasonally, with overlap relationships changing as species and size class composition of the predators changed. Intra-specific diet overlap between feeding stanzas was low, but higher interspecific overlap occurred between species of similar size. Dietary overlap was lowest in the spring, when planktonic and nektonic organisms were consumed by most size classes of dominant predators. Although many important prey species were consumed by several predators, some were selectively consumed by only a few predators, so that there was never complete dietary overlap between two species.
22

The faunal assemblages, community structure and life history patterns of Decapod crustacea from the Middle Atlantic Bight

Wenner, Elizabeth Lewis. 01 January 1979 (has links)
No description available.
23

Quantifying Spatiotemporal Variability in Zooplankton Dynamics in the Gulf of Mexico Using a Physical-Biogeochemical Model

Unknown Date (has links)
Zooplankton play an important role in global biogeochemistry and their secondary production supports valuable fisheries of the world’s oceans. Coupled physical-biogeochemical models (PBMs) provide a unique oceanographic research tool for studying zooplankton on basin and global scales since zooplankton cannot currently be estimated using remote sensing techniques. However, evaluating the accuracy of zooplankton abundance estimates from PBMs has been a major challenge as a result of sparse ship-based observations. Consequently, zooplankton dynamics have been under studied and under validated in PBMs. In this study, we configure a PBM for the Gulf of Mexico (GoM) and validate simulated zooplankton fields against an extensive combination of in situ biomass and rate measurements. We find that spatial variability in mesozooplankton biomass observed in a multi-decadal database for the northern GoM is well resolved by the model with a statistically significant (p < 0.05) correlation of 0.74. In terms of community composition, the model estimates that large zooplankton (LZ) and predatory zooplankton (PZ) functional groups makes up approximately 40% and 60% of the simulated mesozooplankton biomass respectively, which is further supported by ship-based measurements. Once validated the model was used to investigate mesozooplankton diet and secondary production. Model results of LZ dietary composition suggests that herbivory is the dominant feeding pathway whereas PZ dietary composition is largely carnivorous. Dietary composition is found to be less binary in the oligotrophic GoM where LZ and PZ feed on a combination of phytoplankton and zooplankton. We discuss how already low mesozooplankton biomass in the oligotrophic Gulf (~0.04 mmol N m-3) may become further reduced in the future with important impacts on food availability for higher planktivorous trophic levels such as pelagic larval fish. Such reductions could be expected from increases in thermal stratification as a result of a warming ocean and ensuing increases in bottom-up ecosystem limitation. / A Thesis submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester 2019. / April 17, 2019. / bio-physical model, Gulf of Mexico, larval fish, offline modeling, physical-biogeochemical model, zooplankton / Includes bibliographical references. / Michael Stukel, Professor Co-Directing Thesis; Eric Chassignet, Professor Co-Directing Thesis; Steven Morey, Committee Member; Sven Kranz, Committee Member; Nicholas Cogan, Committee Member.
24

Stable Hydrogen and Carbon Isotopic Compositions of Biogenic Methanes

Burke, Roger Allen, Jr. 01 December 1985 (has links)
Stable hydrogen and carbon isotopic compositions of biogenic methanes collected from the sediments of several deep-sea, nearshore marine-estuarine, and freshwater environments were determined. The isotopic compositions of methane samples from eight different DSDP Sites (mean σD-CH4 = -1850>/∞, std. dev. = 70>/∞, n = 75; mean σ13C-CH4 = -71.30/∞, std. dev. = 6.30/∞, n = 44) are generally typical of methane formed via C02 reduction in deep-sea sediments. Methane collected from several freshwater environments was D-depleted (mean σD-CH4 = -3000>/∞ , std. dev. = 260/∞, n = 20) and 13C-enriched (mean σ13C-CH4 = -60.10/∞, std. dev. = 6.10/∞, n = 20) compared to the deep-sea methane. Normally, acetate dissimilation is thought to account for about 60 to 70% of the total methane production in freshwater sediments. Nearshore marine-estuarine methanes appear to be isotopically intermediate (mean σD-CH4 = -2580>/∞ , std. dev. = 230/∞, n = 46; σ13C-CH4 = -61.80/∞, std. dev. = 3.10/∞, n = 46) between deep-sea and freshwater methanes. Variation in the relative importance of the two main methanogenic pathways, acetate dissimilation and C02 reduction, is probably the single most important factor responsible for the differences in methane isotopic compositions among these three different types of environments. Other factors that probably contribute to the methane isotopic differences are temperature, sedimentation rate, organic matter type and amount, concentration of alternate electron acceptors, rate of methane formation and possibly postgenerative isotopic equilibration. Shallow aquatic sediments are thought to be an important source of methane to the atmosphere; the methane produced in these systems, including the ones sampled in this study, is generally substantially more 13C-depleted than expected based on the σ13C of atmospheric methane and the isotopic fractionation associated with the atmospheric sink process. Too few oD data are available to allow evaluation of the role of shallow aquatic sediments in determining atmospheric σD-CH4.
25

Spatial and Temporal Dynamics of Phytoplankton Distribution in a River-Dominated Estuary, Apalachicola Bay, Florida

Unknown Date (has links)
In the shallow, bar-built estuary Apalachicola Bay, the discharge of the Apalachicola River, the largest river in Florida by discharge volume, produces short residence times of water in the Bay and pronounced gradients in salinity and nutrients. This, in combination with wind- and tidal-driven circulation, generates an environment for plankton that is complex and highly dynamic. Understanding these dynamics and the factors controlling them is prerequisite for estimating phytoplankton biomass and productivity in such ecosystems. This research assessed the variability of estuarine phytoplankton in Apalachicola Bay at multiple temporal and spatial scales, utilizing high resolution spatial sampling, dye release experiments monitored with a drone, and a long-term record of water quality. Small-scale chlorophyll a (Chl a) peaks (1.3 ± 0.7 km wide) had steep gradients (3.0 ± 6.0 µg Chl a L-1 km-1) and accounted for 7.7 ± 2.7 % of the biomass observed with a flow-through water quality instrument. Winds, tides, and temperature affected Chl a peak characteristics, while the river plume front was a dynamic location of elevated Chl a. Horizontal dispersion of small-scale inert tracer patches (10-100 m) were faster than phytoplankton reproduction cycles, suggesting that small-scale phytoplankton patches may not be able to outpace physical dispersion in estuaries through growth. The evaluation of a 14-year time series of bay water quality data revealed that extreme river discharge events influenced intra- and interannual variability of Chl a. The nutrient buffering capacity of Apalachicola Bay, in conjunction with longer residence time, increased light penetration, and reduced grazing pressure, may mitigate the reduction of riverine nutrient input during drought. In contrast, tropical storms and high river discharge events may lead to periods of reduced phytoplankton biomass by increasing flushing rates of the estuary and reducing light availability. These new insights into the spatial and temporal variability of phytoplankton distribution and what’s controlling it helps coastal managers to understand how river discharge, winds, and tides affect biomass in bar-built estuaries. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the Doctor of Philosophy. / Spring Semester 2017. / April 13, 2017. / Drought, Estuaries, Phytoplankton, Rhodamine WT, River, Spatial variability / Includes bibliographical references. / Markus Huettel, Professor Directing Dissertation; Thomas Miller, University Representative; Michael Wetz, Committee Member; Kevin Speer, Committee Member; William Landing, Committee Member.
26

Linking Ecological Function and Ecosystem Service Values of Estaurine Habitat Types Associated with a Barrier Island System

Francis, Jeffrey Michael 14 March 2013 (has links)
Ecosystem services are benefits humans receive as a function of natural processes. Many current studies seek to express these benefits as an economic value per unit of habitat type without quantifying the ecological functions that allow for the provision of ecosystem services. This study is designed to model each habitat type in an effort to explicitly link the major estuarine habitat types of Mustang Island (oyster reefs, seagrass meadows, and intertidal salt marsh) to their contribution to Nitrogen cycling services. First, a dynamic biomass model of each foundational species was created using Simile, a declarative modeling framework. Second, a monthly snapshot of Nitrogen captured in living biomass was used to quantify the contribution of each species to the Nitrogen cycling services. Finally, the amount of Nitrogen captured in living biomass was valued using a replacement cost approach. An effort was also made to link the provision of recreational fishing services provided by each aforementioned habitat type by partitioning travel costs and license sales weighted by the density of fish found in each habitat type. It was found that oyster reefs of Mustang Island contribute $173,000 yr^-1, seagrass meadows contribute $12,054,095 yr^-1, and intertidal salt marshes contribute $5,242,755 yr^-1 in potential Nitrogen cycling services. The total value of recreational fishing services within the study site was calculated to be $83.8 million dollars yr^-1. A portion of the total value was then attributed to each habitat type: Marsh edge: $2 million; Seagrass meadows: $81 million; and Oyster: $81,000 thousand. These efforts have been made to translate ecological function into economic benefit to improve communication among a wide variety of stakeholders that are more likely to understand economic value. Further refinement of both the models and the economic data necessary to support them, will have the potential to improve the applicability and results of these tools. These results, and the modeling framework through which they are calculated, provide a platform to evaluate management relevant scenarios in a simple, flexible manner that may be adjusted and transferred to other study sites given appropriate local data.
27

Impacts of Margalefidinium polykrikoides and Alexandrium monilatum on Oysters Cultured in Lower Chesapeake Bay

Robison, Clara L 01 January 2019 (has links)
Harmful algal blooms (HABs) are expanding globally and are anticipated to continue increasing with climate change. Two dinoflagellate species, Margalefidinium polykrikoides and Alexandrium monilatum, form extensive and dense blooms most summers in the lower Chesapeake Bay. Alexandrium monilatum, which produces the toxin goniodomin A, tends to bloom soon after M. polykrikoides, for which a toxin has not yet been identified. Previous laboratory studies and a more limited number of field studies indicate mortality and pathology in multiple shellfish species associated with exposure to M. polykrikoides and A. monilatum. However, the impacts of sequential exposure to both HAB species on marine organisms in the natural environment are less well understood. Local aquaculturists grow oysters under a variety of conditions that may be differentially impacted by HAB exposure. No extensive and controlled studies have been carried out in lower Chesapeake Bay assessing impacts of sequential exposure to M. polykrikoides and A. monilatum blooms on oysters cultured using different aquaculture strategies. The two main objectives of this study were to: 1) investigate M. polykrikoides and A. monilatum as a potential threat to cultured oysters, and 2) inform mitigation strategies to minimize HAB impacts based on current grow-out methods. To address these objectives, oysters were grown in 2017 and 2018 at sites characterized by differing water energetics and HAB dynamics. At all sites during both summers, oysters were grown intertidally and subtidally, and in 2018 were also grown in floating cages at one site. Water quality parameters were monitored, including cell concentrations of M. polykrikoides, A. monilatum, and two other local HAB species known to negatively impact oysters, Karlodinium veneficum and Prorocentrum minimum, along with oyster health and survival. Blooms of M. polykrikoides and A. monilatum occurred at the study sites, but not the reference site, in summer 2017 with cell concentrations that were lower than those quantified in some previous years. In summer 2018, neither species bloomed, providing the opportunity to assess oysters during both a bloom and a non-bloom year. Overall oyster mortality in both summers was relatively low compared to mortality often seen associated with other oyster stressors such as disease. Results indicated oyster health and survival were more impacted by factors indirectly related to HABs, specifically location factors (i.e. site and placement location), temperature, and DO. In both summers, mortality was significantly higher for intertidal oysters, compared to subtidal oysters, suggesting intertidal placement may incur stress in summer. It is unknown whether this intertidal stress may be further compounded during more HAB-intensive years. The results of this study suggest M. polykrikoides and A. monilatum had little impact on the health and survival of oysters cultured in the lower Chesapeake Bay in the summers of 2017 and 2018. More than one year of bloom data is likely necessary, however, to fully evaluate the impacts of M. polykrikoides and A. monilatum as potential stressors to cultured oysters in the context of inter-annual variability and the expanding distribution of these two HABs in the Chesapeake Bay.
28

Climate and Bioinvasives drivers of change on South African Rocky shores?

Mead, Angela January 2011 (has links)
Includes abstract. / Includes bibliographical references. / The overall aims of the thesis were to assess spatio-temporal change in macro species assemblages at sites located around the South African coast. Detected changes were considered in parallel with regional patterns of bioinvasion and climate change driven shifts in temperature trends over comparable time scales.
29

Phytoplankton growth and zooplankton grazing in the southern Benguela current

Olivieri, Emilia T January 1985 (has links)
Bibliography: pages 135-146. / The development and production of several phytoplankton communities and the consumption of these communities plankton were investigated in newly by herbivorous mesozooupwelled waters of the southern Benguela Current by means of an electronic counting and sizing technique (Coulter counter). A feasibility study was initiated to test the accuracy of the Coulter counter (Model TAII) in estimating phytoplankton size and biomass in fresh and preserved samples from the Benguela current. Counting phytoplankton using this method gave a higher degree of reproducibility than the inverted microscope method. Certain recommendations as to the counting procedures were made. The counting of preserved samples was shown to introduce artefacts, resulting in a 77 per cent reduction in particle volume after a year of preservation. Correlations of particle volume with chorophyll a, carbon and nitrogen were calculated, with highest correlations occurring between particle volume and chlorophyll a. Particle volume was shown to represent biomass as accurately as any of the other methods.
30

How reliable is morphological species delimitation in kelp? : a study of two closely related South African Ecklonia species

Levy, Sarah Bernadette January 2014 (has links)
Includes bibliographical references. / Ecklonia maxima and Ecklonia radiata are both kelp bed forming macroalgae along the South African coast, and the latter is also found in considerable abundance in Australia and New Zealand. Genetically they exist as two distinct species and can usually be differentiated morphologically, especially when occurring as geographically separate entities. However, they do appear to intergrade when growing together, where plants of apparent intermediate and indeterminate morphology have been observed. This study tested the reliability of morphology in separating these two Ecklonia species across their intraspecific range of morphological variation, from locations where the species co-occur, as well as where they appear in isolation in South Africa (both species) and Australia (E. radiata only). No individual characters reliably separated between species, yet overall size distinctions as well as the morphometric separation of hollow and solid-stiped sporophytes provide good evidence for morphological differentiation of E. radiata and E. maxima. While E. radiata clusters morphometrically, a distinction between Australian and South Africa specimens is observed. In localities where the two species are reported to co-exist morphological distinction is less clear, particularly in deep water at Buffels Bay. The blade morphology of these deep water sporophytes is distinct from both E. radiata and E. maxima across all locations, while overall size distinctions contribute most prominently to the morphological separation of E. radiata and E. maxima at De Hoop. Environmental data in combination with more detailed genetic analyses, especially those aimed at hybrid identification, are necessary to resolve the nature of these subtidal plants as well as to investigate the relationship between genetic differentiation and overlapping morphology in plants at De Hoop.

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