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.
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Item THE ORGANISMAL AND POPULATION EFFECTS OF CLIMATE CHANGE ON JUVENILE BLUE CRAB (CALLINECTES SAPIDUS) IN THE PATUXENT RIVER, CHESAPEAKE BAY(2017) Glandon, Hillary Lane; Miller, Thomas J; Paynter, Kennedy T; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Future climate scenarios predict an increase in temperature and dissolved carbon dioxide (pCO2) of the marine environment in the next century. Calcifying marine invertebrates are thought to be especially vulnerable to increases in pCO2 and although the effect of increasing temperature in many of these taxa is understood, less is known about the interactive effects of these stressors on the physiology of calcifying invertebrates. In the present study, juvenile blue crab (Callinectes sapidus) were exposed predicted future levels of temperature and pCO2 in a 2x2 factorial design for two complete molts (approximately 30 days). Increased temperature caused a significant increase in crab growth rate and food consumption, but at a cost to carapace thickness and chemistry. The carapaces of individuals exposed to increased temperature were significantly thinner and had significantly lower percent high-magnesium calcite (HMC), the mineral from which the carapace derives its strength. Although there was a significant increase in percent HMC in response to increased pCO2, this was paired with an increase in the concentration of magnesium, complicating the overall effect of increased pCO2 on the carapace. The temperature range tested in this study was not large enough to elicit a significant difference in mean oxygen consumption rate. Crabs were resilient to exposure to extremely high levels of pCO2; there was no significant effect of increased pCO2 on crab growth rate, food consumption, or oxygen consumption rate. Individual physiological response data were utilized in concert with historical and predicted water temperatures to determine effects of future predicted increases in water temperature on blue crab overwintering behavior in the Chesapeake Bay. Model data indicated a significant shortening of the overwintering period from approximately 3.5 months currently to between 1.5 and 3 months, depending on the climate model utilized for the predictions. Increases to growing season length, combined with predicted increases in crab growth rate and food consumption, indicate that in the future blue crab will mature faster and may possibly grow year-round, similar to individuals that live in the southern extent of the species’ range.Item Growth and recruitment rates of juvenile blue crabs ( Callinectes sapidus) in Chesapeake Bay(2006-05-25) Puckett, Brandon; Secor, David H.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recent marked declines of the commercially and ecologically important blue crab in Chesapeake Bay have prompted requests for improved scientific information on blue crab population dynamics. I evaluated recruitment rates to blue crab fisheries using three independent approaches: direct observations, length-frequency analysis, and lipofuscin-based ageing. Three cohorts of known-age pond-reared blue crabs were sampled monthly, growth rates were modeled and compared to estimates from length-frequency analysis of field-collected crabs. Mean growth rates for juvenile pond-reared and field-collected cohorts ranged from 0.4 to 1.4 mm/day. A temperature-dependent growth model back-calculated settlement dates and predicted partial recruitments of juvenile winter size distributions. Predictions coincided with observations for wild blue crabs. Lipofuscin accumulated exponentially with age. The high growth rates, rapid recruitment rates, and lipofuscin-based age designations suggest that peeler/soft crab fisheries in the summer and hard crab fisheries in the fall/winter are predominately dependent on recruits less than 18 months of age.Item SPATIAL ECOLOGY OF BLUE CRAB (CALLINECTES SAPIDUS) IN CHESAPEAKE BAY(2004-11-12) Jensen, Olaf Peter; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Spatial heterogeneity is a striking feature of the blue crab life history and fisheries in Chesapeake Bay. However, a quantitative assessment of their spatial distribution and the factors controlling it has been lacking. Based on 13 years of data from a baywide winter dredge survey, geostatistical and two-stage generalized additive models (GAMs) are used to characterize blue crab distributions and investigate environmental factors responsible for the distribution of mature females, respectively. A landscape-based distance metric, the "Lowest-Cost Path" (LCP) distance, is developed as an alternative to Euclidean distance for kriging in estuaries. Estimates of variogram parameters differed significantly between the two metrics but kriging accuracy did not. Geostatistical abundance estimates show significant declines from 1990 to 2002. The observed relationship between changes in distribution and changes in abundance is suggestive of density-dependent habitat selection. Depth and distance from the Bay mouth were the most important predictors of mature female abundance.