Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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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.Item Predation by eastern mudminnows (Umbra pygmaea) on macroinvertebrates of temporary wetlands(2009) Lombardi, Susan Elizabeth; Lamp, William O.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fish play a substantial role in aquatic food webs, yet the effect of feeding activities of small stream fish that enter seasonally-flooded temporary wetlands during periods of hydrologic connectivity is not well understood. In this study, eastern mudminnows (Umbra pygmaea) were introduced to a fishless wetland in Caroline County, Maryland, and the aquatic macroinvertebrate community did not significantly change within two weeks. Gut contents of mudminnows collected from the wetland and a stream consisted primarily of dipteran larvae; ostracods were also a common food source for wetland mudminnows. Common prey not found in gut contents but present in the wetland were tested as food, and all taxa were consumed in a no-choice predation experiment. Mudminnows have the potential to directly affect multiple trophic levels and subsequent ecosystem functioning through predatory interactions with sustained hydrologic connectivity between fish sources and temporary wetlands.Item ENVIRONMENTAL CONTROLS AND BIOLOGICAL CONSTRAINTS ON RECRUITMENT OF STRIPED BASS MORONE SAXATILIS IN CHESAPEAKE BAY(2008-11-30) Martino, Edward Joseph; Houde, Edward D; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The causes of >30-fold recruitment variability in striped bass Morone saxatilis were investigated in Chesapeake Bay. Factors that affect survival and growth of early-life stages were evaluated through 1) field surveys in 2001-2003 to document spatial and temporal variability in larval and juvenile abundances, 2) synthetic data analyses to provide a longer-term perspective and 3) trophodynamic and growth analyses to document how environmental variability controls and regulates variability in year-class strength. Daily discharge from the Susquehanna River in spring months controlled the distribution and apparent survival of striped bass and other anadromous fish larvae. Control of recruitment in upper Chesapeake Bay includes both direct and indirect effects of hydrological variability on egg and larval survival. In dry years (1999 and 2002), direct effects of biophysical controls resulted in low abundances of striped bass feeding-stage larvae, a consequence of reduced retention of eggs and yolk-sac larvae at the salt front and Estuarine Turbidity Maximum (ETM). The strongest year classes are produced in wet years that have high retention of eggs and yolk-sac larvae (i.e. direct effects), and a spatial and temporal match between feeding larvae and zooplankton prey (i.e. indirect effects). In moderate and high freshwater flow years (1996, 1998, 2001, 2003), indirect trophodynamic effects were most important. Striped bass larvae were strongly associated with the ETM in wet years when zooplankton prey levels also were highest in the ETM. A higher percentage of feeding larvae was observed in a wet year (2003) than in a dryer year (2001) (93% versus 35%) and faster larval growth (58% higher) occurred in the wet year. Inter-annual variability in growth and its effect on larval stage duration and cumulative mortality were sufficient to generate variability of the magnitude observed in juvenile recruitment. A forecasting model developed for age-0 striped bass recruitment that included spring flow and spring temperatures as independent variables has strong predictive capability. Growth of age-0 juveniles was density dependent, leading to diminished juvenile survival in years of high abundance through size-selective overwinter mortality. Through this mechanism, age-0 abundance levels that vary >10-fold are reduced to 3-4-fold variability at age-3. Density dependence regulates dynamics of age-0 juveniles, compensating for coarser controls over recruitment generated by environmental factors during the egg and larval stages.