Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item EFFECTS OF ENVIRONMENTAL VARIABLES AND CHANGES IN SEASONAL PATTERNS ON SPATIAL DISTRIBUTIONS OF JONAH CRABS (CANCER BOREALIS) AND ATLANTIC ROCK CRABS (CANCER IRRORATUS) IN GEORGES BANK AND THE MID-ATLANTIC BIGHT, USA(2023) Wade, Kaitlynn Jean; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The economic and commercial importance of Jonah crabs (Cancer borealis) and Atlantic rock crabs (Cancer irroratus) has increased greatly in the USA. The objectives of my research were to determine spatial distributions, habitat preferences, and potential seasonal movements of both species. Data were obtained from the offshore Northeast Fishery Science Center bottom trawl surveys. Analyses included kernel density estimates, generalized additive models, empirical cumulative distribution functions, and ANOVAs. The spatial distributions of Jonah and Atlantic rock crabs changed over time during the 1970s – 2000s. Compared to Atlantic rock crabs, Jonah crabs preferred slightly warmer temperatures, deeper depths, and muddier sediments. Seasonally, Jonah crabs were found farther offshore in the winter and closer to shore in the fall and spring. Atlantic rock crabs were found closer inshore in the winter and spring and more offshore in the fall. Both species were found to have different seasonal patterns in the Mid-Atlantic BightItem Influences of the biotic and structural components of Crassostrea virginica on the oyster reef community.(2015) Kesler, Karen Elizabeth; Paynter, Kennedy T; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The hard, complex reef structure created by the eastern oyster, Crassostrea virginica, provides refuge and habitat that protects many organisms, allowing them to settle, survive, and spawn. In addition, oysters create copious amounts of biodeposits, which potentially serve as a basal nutrient resource for the reef ecosystem. I investigated the influence of oyster reef structure and oyster biodeposits on the reef community through a series of field experiments and mesocosm studies. Initially, the communities that colonized live oyster reefs were compared to communities that colonized empty oyster shell reefs, to evaluate the potential influence of live oysters that were actively feeding and creating biodeposits. Community assemblages on the two reef types were similar and no differences were seen with species level comparisons of abundance or biomass between the two treatments. The impact of oyster shell structure on energy transfer up the food chain from the basal resource of oyster biodeposits to the predator, Gobiosoma bosc, through the amphipod, Melita nitida was then investigated. Oyster shell structure effectively provided protection to amphipods, with reduction of predation impacts in high complexity habitats when a predator was present. Next, stable isotope signatures (d13C and d15N) of dominant reef species and basal resources, including oyster biodeposits, were measured seasonally to evaluate the major resource contributors to the reef. Overall, most carbon sources appeared to be pelagic in nature and an additional unidentified carbon source from outside of the oyster reef was incorporated into the food web. Finally, a d15N tracer study, utilizing biodeposits labeled with elevated d15N values, indicated that both Melita nitida and Neanthes succinea could incorporate Crassostrea virginica biodeposits and pass these nutrients to higher trophic levels. These studies suggested that oyster structure played a prominent role in defining the oyster reef community by providing habitat and protection for reef organisms. Mesocosm studies and isotopic analysis indicated that while some deposit feeders could consume oyster biodeposits, biodeposits were likely not a large component of their diet. Overall, these results suggest that structure was the dominant factor driving community organization on the reef, with minimal influence from oyster biodeposits.Item MODELING POTENTIAL HABITAT OF CHESAPEAKE BAY LIVING RESOURCES(2012) Schlenger, Adam James; North, Elizabeth; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A quantitative understanding is needed to identify the impacts of climate change and eutrophication on the habitat of living resources so that effective management can be applied. A systematic literature review was conducted to obtain the physiological tolerances to temperature, salinity, and dissolved oxygen for a suite of Chesapeake Bay species. Information obtained was used to define required and optimal habitat conditions for use in a habitat volume model. Quality matrices were developed in order to quantify the level of confidence for each parameter. Simulations from a coupled oxygen and hydrodynamic model of the Chesapeake Bay were used to estimate habitat volumes of juvenile sturgeon (Acipenser oxyrinchus) and to assess sensitivity of habitat to environmental factors. Temperature and salinity define spring and fall habitat and a combination of salinity, temperature and dissolved oxygen influence habitat in summer. Both fixed criteria and bioenergetics habitat volume models yielded similar results.Item Habitat use of surf scoters wintering in the mesohaline region of the mainstem Chesapeake Bay, Maryland(2007-12-11) Kidwell, David M.; Adams, Lowell W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Surf scoters (Melanitta perspicillata) are common in coastal waters during winter, but remain one of the least studied waterfowl in North America despite indications of a declining population. Surf scoter foraging was investigated in the mesohaline region of the Chesapeake Bay during 2004-2005. The study compared biological and physical characteristics of benthic habitats among scoter feeding and non-feeding sites. Benthic samples were taken seasonally via a Peterson grab. Surf scoters foraged over oyster bar, packed clay and sand habitats, but avoided mud habitats. Clam densities varied seasonally, increasing over winter regardless of scoter foraging activity. Foraging activity appeared to influence hooked mussel densities on hard bottoms. Lack of foraging over mud habitats, where visibility can be limited, suggests that surf scoters may be visual predators and may have been impacted by habitat sedimentation The correlation of hooked mussel with oyster bars suggests that oyster restoration efforts may positively impact surf scoters.