Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item Marine influence on juvenile fish trophic ecology and community dynamics in Maryland's northern coastal lagoons(2013) O'Brien, Michael Henry Patrick; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Marine influence on Maryland's juvenile lagoon fish community was examined under varied levels of internal and external forcing. In 2009, stable isotope analysis showed increasing marine carbon dependency by bay anchovy with decreasing distance to the marine inlet. Following large seagrass losses, no similar trend was detected in 2012. Weakfish showed no structured dependence on marine carbon in either year. Diet contents lacked corresponding year-to-year changes in pelagic versus benthic prey items. In 2009, serial changes with distance to the inlet occurred in species assemblage, which may have been associated with internal seagrass structure. No gradient occurred in 2012. Analysis of a 24-year survey indicated a shift from marine-pelagic to structure-oriented species, associated with increased seagrass and tide level, and decreased North Atlantic Oscillation index. In Maryland's northern lagoon, the strength of marine influence on juvenile assemblages depended on the interplay between internal bay structure and external marine forcing.Item Scales of Variability in the Size Composition and Community Structure of Fishes in Estuarine Ecosystems(2011) Connelly, William John; Houde, Edward D.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fishing, other human activities, and natural perturbations can alter the species composition and size structure of fish communities in coastal ecosystems. Normalized biomass size spectra (NBSS) and other metrics based on size and abundance of fish communities are sensitive to effects of fishing and have been proposed as useful tools for ecosystem-based management. However, these approaches based on size and abundance are unevaluated at temporal and spatial scales relevant for management within estuaries. Because individual species have important ecological and economic value, tracking temporal and spatial changes in the species composition of the fish communities using multivariate analyses, such as principal component analysis (PCA), can facilitate interpretation of patterns observed in the NBSS. A goal of my dissertation was to determine if indicators suitable for ecosystem-based management can be derived from NBSS parameters and other metrics based on size and abundance for estuarine fish and plankton communities at relatively small temporal and spatial scales. Additionally, I sought to elucidate effects of temporal and spatial variability in species composition on community size structure of estuarine fish communities by combining multivariate and NBSS analyses. Analyzing data from multiple fisheries-independent surveys and water quality monitoring programs, the objectives of my dissertation were 1) to describe and quantify the size distribution and community composition of fish and plankton in Chesapeake Bay at temporal scales ranging from months to over a decade and at spatial scales ranging from 18 km to 100 km, 2) to evaluate long-term trends in abundance, size distribution, and species composition of fish communities in Chesapeake Bay and Pamlico Sound, and 3) to analyze environmental variables and their effects on community structure and size distribution of biological communities in the Chesapeake and Pamlico Sound estuaries. Results supported the conclusion that NBSS combined with traditional community analyses permits detection of changes in ecosystem status, facilitates identification the species associated with the observed variability, and provides a framework to establish management reference points.