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.

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    ALTERNATIVE MIGRATORY PATHWAYS OF JUVENILE STRIPED BASS IN THE PATUXENT RIVER ESTUARY, MARYLAND
    (2012) Conroy, Christian William; Secor, David H.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Although highly migratory striped bass Morone saxatilis utilize spatially diverse and dynamic estuarine systems as nurseries, early dispersal behaviors have remained largely unknown. Using otolith chemistry, we identified consistent migratory and residence behaviors in juvenile striped bass year classes. Migrants were further separated by size and age into contingents that shared similar ontogenetic dispersal thresholds. We identified a small group of larval dispersers that moved to mesohaline waters prior to reaching 6 mm. Resident juveniles experienced better early growth that migrants. Small migrants had the lowest growth rates prior to dispersal, but afterward showed enhanced growth rate. Positive growth inflections were also observed for a group of migrants that reinvaded freshwater at larger sizes. Striped bass migration seems to be controlled by individual growth trajectories, where movement is driven by poor growth in the natal habitat.
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    Epifaunal Disturbance By Periodic Low Dissolved Oxygen: Native Versus Invasive Species Response
    (2005-07-22) Jewett, Elizabeth Bromley; Sebens, Kenneth P; Hines, Anson H; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Invasive species and low dissolved oxygen (DO) threaten the biodiversity and ecosystem health of estuaries worldwide. To test the hypothesis that exposure to low DO reduces resistance of epifaunal community to invasion in the Chesapeake Bay, we conducted experiments using standardized settling panels, including 1) controlled experiments exposing epifaunal communities to low DO; 2) measurement of the short term response of motile and sessile epifauna to low DO; 3) survey of multiple sites in which community structure was correlated with low DO and other environmental variables; and 4) evaluation of the biological and structural effects of an invasive hydroid and a cryptogenic tunicate, both with high tolerance for low DO, on recruitment and development of epifauna. Periodic hypoxia was correlated with an increased cover of the native serpulid polychaete, <i>Hydroides dianthus </i>. Cover of invasive and cryptogenic species increased with exposure to moderate low DO. Cover and incidence of bryozoans, sabellid polychaetes, and cnidarians differed among DO treatments. Nematodes, caprellids, and harpacticoid copepods vacated epifaunal communities in response to low DO. In the multi-site survey, > 50% cover of invasive and cryptogenic species was associated with exposure to chronic low DO. Six of eight sites in the survey experienced periodic low DO (< 4 mg/l), but only one experienced chronic low DO ( > 40% of days below 4 mg/l DO). Shifting cover of <i>Hydroides dianthus </i>, barnacles, and invasive species was correlated (> 50%) with percent of days experiencing low DO. Epifaunal heterogeneity reflected environmental differences among sites. Species richness and diversity at local sites declined with increasing abundance of certain taxa in higher salinity, higher diversity areas. Heightened cover of <i>Molgula manhattensis</i>, <i>Hydroides dianthus</i> or barnacles led to reduced local diversity but regional species diversity was maintained through environmental heterogeneity across sites. Conversely, in lower salinity, lower diversity zone, <i>Cordylophora caspia</i>, an invasive hydroid, had a positive effect on some species. Temporal and spatial shifts in cover of dominant species and in species diversity in response to low DO disturbance and other environmental factors may facilitate persistence of less competitive native or invasive species.