MEES Theses and Dissertations

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    (2022) HOWLADER, ARCHI; NORTH, ELIZABETH; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Salinity is a major environmental factor that influences the population dynamics of fish and shellfish along coasts and estuaries, yet methods for predicting the salinity history at specific sampling stations are not widely available. The specific aim of this research was to predict the history of salinity experienced by juvenile and adult oysters (Crassostrea virginica) collected at sampling stations in Delaware Bay as part of the Selection along Estuarine Gradients in Oysters (SEGO) project. To do so, empirical relationships were created to predict salinity at five oyster bed stations using observing systems data and then applied to construct indices of salinity exposure over an oyster’s lifetime. The desired accuracy was +/- 2 psu. Three independent sources of salinity data were used in conjunction with observing systems data to construct and validate the predictive relationships. Observing systems data from the USGS station at Reedy Island Jetty and continuous near-bottom measurements taken by the U.S. Army Corps of Engineers (ACOE) from 2012-2015 and 2018 were employed to fit nonlinear empirical models at each station. Haskin Shellfish Research Laboratory (Haskin) data were used to evaluate model fit, then ACOE data from 2018 (withheld from model fitting in the validation analysis) and SEGO data from 2021 were used to validate models. The best-fitting models for predicting salinity at the oyster bed stations given the salinity at Reedy Island Jetty were logarithmic in form. The root mean square error (RMSE) of the models ranged from 1.3 to 1.6 psu when model predictions were compared with Haskin data, 0.5 to 1.5 when compared with ACOE data, and 0.6 to 0.8 when compared with SEGO data. All of these models were within the desired accuracy range. Results demonstrate that observing systems data can be used for predicting salinity within +/- 2 psu at oyster bed stations within 39 km in upper Delaware Bay. When these models were applied to estimate low salinity exposure of 2-year-old oysters via the metric of consecutive days below 5 psu, the indices suggested that there could be as much as a 42-day difference in low salinity exposure for oysters at stations 31 km apart. This study helps further our understanding of the salt distribution in Delaware Bay as well as the effect of low-salinity stress on the life cycle and genetic differentiation of oysters. In addition, the approach of using observing systems data to predict salinity could be applied to advance understanding of salt distribution and the effect of low salinity exposure on living resources in other estuaries.
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    Insights into benthic macroinvertebrate ecology in the northern Bering and southern Chukchi Seas from stable isotope analysis
    (2022) Green, Emma Mackenzie; Cooper, Lee W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In the Pacific Arctic Region, the northern Bering Sea and southern Chukchi Sea support large and diverse communities of benthic macroinvertebrates that provide an important link to the pelagic communities and marine mammals that rely on the benthic populations for food. While the abundance and biomass of these benthic macroinvertebrates are well documented, little is known about how benthic macroinvertebrates interact with each other and how these interactions are affected by climate change. I measured the stable isotope composition (bulk δ15N and δ13C values) of similar species collected in 2014, 2016, 2017, and 2021 in the northern Bering and southern Chukchi Seas. Although there was little change over time in either δ15N or δ13C values, both stable isotope ratios were significantly different between stations with differing production phenologies. The southern Chukchi Sea (a productive set of sites with high chlorophyll concentrations throughout the summer) had lower δ15N values and higher δ13C values, while the northern Bering Sea site with production mostly associated with the period of sea ice breakup had higher δ15N values and lower δ13C values. This pattern was observed across similar species and feeding types. The higher δ15N values in the northern Bering Sea could be due to an extra step in the food chain from bacterial reworking. The contrast between these two regions in δ13C might indicate higher primary production in the southern Chukchi Sea compared to the northern Bering Sea. The differing food web dynamics between these two sites highlight the benthic diversity across small scales and similar organisms in Pacific Arctic food webs.
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    (2022) Pfaff, Andrea Ruth; Grebmeier, Jacqueline M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In the Northeastern Chukchi Sea’s Barrow Canyon, modeling indicates that converging currents rapidly downwell high volumes of labile carbon creating a benthic biological hotspot. Utilizing a Drop Camera Video System, this thesis analyzes the epibenthic population across upper Barrow Canyon along the Distributed Biological Observatory transect DBO5. Results show that overall abundance of epibenthic fauna is highly correlated with depth while diversity is correlated with water mass variables such as bottom water temperature, salinity, nutrient concentrations, current speeds, and sediment grain size. Higher taxonomic diversity is found along the inshore slope of Barrow Canyon and correlated with conditions associated with the swifter inshore Alaskan Coastal Water. Taken together these data show that while particulate food and associated epibenthic abundance is highest in the Canyon’s trough, there is a zonation of organisms between the inshore and offshore slope with the inshore slope supporting a higher diversity and predominantly suspension feeding organisms.
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    (2022) Hanacek, Daniella; Staver, Lorie; Cornwell, Jeffrey; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The production of methane in brackish marshes may offset the carbon sequestered by these wetlands. Brackish tidal marshes are widespread in Chesapeake Bay and there exists a need for understanding the carbon balance of these ecosystems. This thesis presents the results of measurements of methane flux, through static flux chamber experiments, and analysis of marsh porewater to examine biogeochemical and plant-mediated drivers of methane flux in marshes of Chesapeake Bay. In addition, there is growing interest from the scientific and resource management community in how natural marshes cycle carbon and whether restored marshes show biogeochemical similarities. Therefore, I tested my hypotheses in the natural marshes of Monie Bay, part of the Chesapeake Bay National Estuarine Research Reserve – Maryland, and in restored tidal marshes created with dredged sediments at Poplar Island. Methane emissions offset annual carbon storage at Monie Bay and Poplar Island by 0.7 and 2.1 percent, respectively, based on average values of annual fluxes. However, there remains uncertainty in the accuracy of this estimate given the spatial and temporal variability in my observed fluxes, and the limited sampling frequency and spatial extent of my study. Within such uncertainty lays a justification for continued long-term monitoring of methane emissions in restored and natural marshes of Chesapeake Bay to resolve this important marsh management question.
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    Evaluating the Consequences of Alternative Atlantic Striped Bass Harvest Control Rules on Their Prey, Atlantic Menhaden
    (2022) Schiano, Samantha E.; Nesslage, Genevieve; Wilberg, Michael; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Harvest control rules (HCRs) are automatic fishery management procedures that are agreed upon in advance and that dictate the rate of fishing that can take place. I evaluated a suite of single species and dynamic multispecies HCRs to evaluate their relative performance in achieving management goals for the striped bass (Morone saxatilis) and Atlantic menhaden (Brevoortia tyrannus) stocks using a linked, age-structured predator-prey simulation model. First, simulation model inputs were updated using the most recent stock assessment information, and striped bass length- and weight-at-age estimates were updated using otolith-based ageing data. Linear models evaluating change in striped bass length- and weight-at-age over time and between sexes identified an increase in size of as much as 30% between 1998 and 2019. Additionally, striped bass continued to grow past age-15, indicating that future striped bass stock assessments should consider expanding the number of ages included in the model. The updated predator-prey simulation model was then used to compare performance of a suite of 27 HCRs. The most influential factor determining performance of striped bass HCRs was striped bass fishing mortality (F). Atlantic menhaden had little effect on striped bass spawning stock biomass (SSB) at both high and low percent composition of Atlantic menhaden in striped bass diets. Traditional single species HCRs performed well, specifically those for which striped bass are managed at or below their target F. Although there was no single HCR that performed well for both stocks given their current reference points, both single species and dynamic multispecies HCRs that involved the “40-10 rule” for striped bass (lower threshold at 10% of unfished SSB and upper threshold at 40% unfished SSB) performed best across all striped bass performance metrics.