Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item DRIVERS OF EPIBENTHIC BIODIVERSITY AND ABUNDANCE IN BARROW CANYON, CHUKCHI SEA UTILIZING DROP CAMERA VIDEO DATA(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.Item An evaluation of methods for measuring phytoplankton and ecosystem status in the Chukchi Sea(2020) Neeley, Aimee Renee; Harris, Lora A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation represents a three-pronged approach for evaluating ecosystem-level changes in the Chukchi Sea: 1) evaluation of uncertainties in field measurements of absorption 2) direct measurements of phytoplankton taxonomy and the community’s interaction with the environment and 3) apply existing and new remote sensing tools to measure ecosystem-level changes over large spatio-temporal scales. The first and final chapters provide context for the dissertation and conclusions. The second chapter quantifies the magnitude of uncertainty within multiple methods for measuring particle absorption. The light field exiting the surface ocean is measured by satellite instruments as ocean color and is impacted by water column absorption. Biogeochemically-relevant products, such as phytoplankton and particle absorption are derived from the light field using algorithms. Therefore, accurate measurements of absorption are critical to algorithm development and validation. I employed a multi-method approach to estimate the precision of measuring optical density of particles on a filter pad using two common spectrophotometric methods, and assessed the uncertainty of the computational techniques for estimating ap. The uncertainty ranged from 7.48%-119%. Values of ap at 555 nm and 670 nm exhibited the highest values of uncertainty. Poor performance of modeled ap compared to measured ap suggests the uncertainties are propagated into bio-optical algorithms. The third chapter investigates the consequences of earlier seasonal sea ice retreat and a longer sea-ice-free season on phytoplankton community composition. The timing of sea ice retreat, light availability and sea surface stratification largely control the phytoplankton community composition in the Chukchi Sea. This region is experiencing a significant warming trend, decrease in sea ice cover, and a documented decline in annual sea ice persistence and thickness over the past several decades. I applied multivariate statistical techniques to elucidate the mechanisms that relate environmental variables to phytoplankton community composition in the Chukchi Sea using data collected during a single field campaign in the summer of 2011. Three phytoplankton groups emerged that were correlated with sea ice, sea surface temperature, nutrients, salinity and light. The fourth chapter evaluates a new remote sensing tool for its utility to trace trends in ocean color over the summer months, 2003-2018, in the Chukchi Sea. The apparent visible wavelength reduces an ocean color spectrum to one number that represents the apparent color of the water. Median trend analysis of apparent visible wavelength and Chlorophyll a indicated that an ecosystem-level change in phytoplankton and nonalgal particles has occurred, correlated with the loss of sea ice.Item Implications of Ocean Acidification for Three Pacific Arctic Bivalve Species(2016) Goethel, Christina Leigh; Grebmeier, Jacqueline M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sea ice retreat, seawater warming, and now ocean acidification are recognized as physical stressors impacting the productive benthic communities on the shallow continental shelves of the northern Bering and Chukchi Seas, particularly calcifying organisms like bivalves that are prey items for benthivorous predators including walruses, eiders, and bearded seals. Using time-series benthic faunal collections and laboratory experiments, my research: 1) evaluates the abundance and dominant size class of Macoma calcarea in the northern Bering Sea and the southeastern Chukchi Sea during summer months from 1998-2014, and 2) investigates the effects of ocean acidification on growth and oxygen consumption of two size classes of three dominant bivalve species, M. calcarea, Astarte montagui, and Astarte borealis. Results suggest a northward shift in bivalve distribution (p < 0.01) and a recent size reduction at both sites. Experimental results suggest that one dominant size class (2.1-3 cm) will be more susceptible to ocean acidification.Item CALORIC CONTENT OF BERING AND CHUKCHI SEA BENTHIC INVERTEBRATES(2012) Wilt, Lisa Marie; Grebmeier, Jacqueline M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Extensive seasonal sea ice reduction has highlighted the need to evaluate the status and potential long term changes of highly productive benthic communities in the Pacific Arctic Region. Walrus that use sea ice to access offshore feeding areas are now being forced to haul out on land for part of the year, requiring them to forage for benthic prey from closer to shore. To explore this energetic problem, I conducted a caloric survey of benthic invertebrates, and evaluated relationships between caloric content and environmental variables. Latitude was the strongest non-taxonomic dependency for caloric content (ANOVA p=0.003 with taxon dependencies, p<0.001 without). Cluster analysis revealed caloric densities were higher in offshore, high nutrient Bering Sea Anadyr Water, and lower in nearshore, low nutrient Alaska Coastal Water. An evaluation of preservation techniques indicated formalin fixation increased infaunal caloric content (p<0.001), suggesting caution while converting traditional benthic population studies to caloric values.