UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
2 results
Search Results
Item The Role of Connectivity and Spatial Structure on the Population Dynamics of Marine Fishes(2023) Arai, Kohma Herbert; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Migrations regulate population structure, which can play an important role in conferring stability at aggregate scales via asynchronous responses of population sub-components to perturbation; however, little is known about the importance of spatial structure in population persistence in fishes. My dissertation aims to explore the role of spatial structure on the population dynamics of marine fishes. Two species that exhibit different types of population structure were considered: (i) Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic, comprised of two components that have distinct spawning regions off Canada (northern contingent) and the US (southern contingent); and (ii) striped bass (Morone saxatilis) in the Hudson River (HR), which exhibit early-life partial migration whereby a portion of juveniles remain in their natal freshwater habitats, while others migrate into higher salinity habitats. In Chapter 2, I used otolith stable isotopes (d18O/d13C) to understand contingent mixing of the Northwest Atlantic mackerel over two decades (2000–2019). Prevalent contingent mixing occurred within the US waters, indicating that the northern contingent may provide subsidies to the US mackerel fishery. In Chapter 3, I combined machine learning with otolith d18O isoscapes to predict the geographic origin of the Northwest Atlantic mackerel spanning four decades (1975–2019). Contingent mixing occurred over four decades, including the 1970s when intensive foreign fisheries took place in US waters. Nursery hotspots were detected within spawning regions, but shifted over time. In Chapter 4, for HR juvenile striped bass, I explored the influence of early-life conditions and environmental drivers on partial migration. Otolith chemistry uncovered four dominant early migration modes. Partial migration was associated with larval growth, albeit facultatively controlled by environmental conditions. In Chapter 5, I evaluated how HR striped bass early-stage partial migration influenced recruitment patterns to the adult population over a 3-decade span. As an outcome of partial migration, adults recruited from a variety of nurseries, which exhibited asynchronous dynamics in response to climate variables. Through a comparative analysis of two species that exhibit different types of population structure, I demonstrated how spatial structure can play key roles in the population dynamics of marine fishes, with implications for management and conservation.Item An Integrated Isotopic and Biomarker Analysis of the Glaciogenic Vazante Group, Brazil(2012) Miller, Kristen Elizabeth; Kaufman, Alan J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Vazante Group, a meta-sedimentary succession located in south-central Brazil, contains several intervals of diamictite, interpreted as glacial in origin, bracketed by well-preserved carbonate and shale. This glacial succession was previously associated with the global occurrence of Neoproterozoic low latitude glacial deposits (aka Snowball Earth), and biomarkers (molecular fossils) identified from an organic-rich interval within this succession were used to infer active photosynthesis during the ice age (Olcott et al., 2005). However, new Re-Os and detrital zircon U-Pb ages suggest that the upper Vazante Group is ca. 1.3 to 1.0 billion-years old (Geboy, 2006; Azmy et al., 2008; Rodrigues et al., 2008) and thus may preserve evidence for hitherto unknown Mesoproterozoic ice ages. Within this context, I present biomarker and time-series stable isotope data from a basin-wide distribution of pre- and post-glacial sedimentary units in order to i) evaluate the Mesoproterozoic interpretation of this succession, ii) assess the biologic and environmental conditions present when these sediments were deposited, and iii) to understand the co-evolution of life and ocean chemistry in response to rapidly changing environmental conditions. Biomarker distributions and abundances from the Serra do Garrote Formation, a pre-glacial shale, and the Serra do Poço Verde and Lapa formations, both post-glacial shales, show evidence of a diverse microbial community that would have only existed in a redox stratified water column. Additionally, the presence of aryl isoprenoids, biomarkers indicative of green sulfur bacteria, in the Serra do Garrote and Serra do Poço Verde formations suggest that reducing, sulfide-rich water was present in the photic zone. These biomarkers however, are absent from the Lapa Formation suggesting that sulfidic conditions either receded to deeper water or collapsed entirely. Carbon and sulfur isotopic signatures support the conclusions drawn from this biomarker study. Carbon and sulfur trends from the Serra do Garrote and Serra do Poço Verde formations show evidence of a large, anoxic, isotopically stable, dissolved organic carbon pool (relative to inorganic carbon) and extensive bacterial sulfate reduction of a small, oceanic sulfate reservoir. The Lapa Formation, on the other hand, displays evidence for a smaller, isotopically responsive, dissolved organic carbon pool. The carbon isotopic compositions of carbonates from these three units are consistent with other Mesoproterozic successions supporting the geochronological age constraints. Taken together, biomarker and time-series stable isotope data from the upper Vazante Group map a transition from a sulfide-rich, stratified, water column to one that, while still stratified, was no longer sulfidic. This environmental transition occurred in response to consecutive Mesoproterozoic ice ages.