Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item INTERACTIONS BETWEEN NITROGEN AND TEMPERATURE ON THE METABOLISM OF THE RED-TIDE MIXOTROPHIC DINOFLAGELLATE KARENIA SPP. IN SUPPORT OF PREDICTIVE MODELS: IMPLICATIONS FOR BLOOM DYNAMICS ON THE WEST FLORIDA SHELF(2023) Ahn, So Hyun; Glibert, Patricia; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The toxic mixotrophic dinoflagellate Karenia spp. forms blooms almost annually in the Gulf of Mexico, especially on the West Florida Shelf (WFS). Blooms typically initiate in early fall but can persist from months to years. Daily, Karenia vertically migrates to the surface water during the day, possibly experiencing changes in temperature, light, nitrogen (N), and prey type and availability. Therefore, this dissertation aimed to examine the interplay between Karenia’s photo-autotrophic and phago-mixotrophic metabolism and the short-term fluctuations in environmental conditions to understand how these factors may relate to the conditions under which Karenia spp. are found in the WFS.Title of Dissertation: INTERACTIONS BETWEEN NITROGEN AND TEMPERATURE ON THE METABOLISM OF THE RED-TIDE MIXOTROPHIC DINOFLAGELLATE KARENIA SPP. IN SUPPORT OF PREDICTIVE MODELS: IMPLICATIONS FOR BLOOM DYNAMICS ON THE WEST FLORIDA SHELF So Hyun (Sophia) Ahn, Doctor of Philosophy, 2023 Dissertation directed by: Professor Patricia M. Glibert, Marine Estuarine Environment Sciences A culture of K. mikimotoi balanced photon flux pressure (light availability) with consumption in overall metabolism when pulsed with 15N-NO3-, 15N-NH4+, or 15N-urea over the range of 15-25°C as shown by photosynthetic fluorescence. However, when shifted to 30°C, cells were significantly stressed, but urea-enriched cells showed a smaller decline in fluorescence, implying that urea might induce a photoprotective mechanism by increasing metabolic “pull.” Studies conducted with natural K. brevis winter and summer populations during 2021 showed that thermal history played a critical role. Unusually, summer blooms had higher biomass but were stressed photosynthetically and nutritionally. However, 15N-urea enriched summer cells had higher uptake rates as well as carbon (C) and N cell-1, especially in warmer waters, showing differential thermal responses based on N forms. Mixotrophy grazing measurements showed that K. brevis grazed both the picoplankter Synechococcus as well as the cryptophyte Rhodomonas. Grazing did not selectively target specific qualities of Synechococcus (based on differing N and P of the prey growth media), but ingestion rates were a function of prey-to-grazer ratios (R2=0.76) as well as prey amounts (R2=0.71). NanoSIMS confirmed 15N incorporation from Synechococcus in K. brevis. In natural communities of K. brevis, ingestion rates were also significantly related to prey-to-grazer ratios (p < 0.01) and by temperatures (p < 0.05) to a lesser degree (R2= 0.75) when incubated at ambient (24°C) and ambient temperature ± 5°C (19, 29°C). The grazer effects on the photosynthetic performance of grazer and prey were also examined. Grazing on Synechococcus indirectly reduce the photosynthetic performance of prey, especially at warmer temperatures but had little or no effect on the photosynthesis of K. brevis itself.Item HARMFUL ALGAE IN CHESAPEAKE BAY: A STUDY FOCUSED ON KARLODINIUM VENEFICUM APPLYING TIME SERIES, PHYSIOLOGICAL, AND MODELING APPROACHES(2018) Lin, Chih-Hsien; Glibert, Patricia M.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Harmful algal blooms (HABs) are expanding worldwide. The harmful dinoflagellate Karlodinium veneficum is of concern because its toxigenic properties cause fish kills. Despite considerable study on nutrient-HAB relationships, there is a lack of data on HAB nutrient physiology because of the complexity of HAB nutrition. Many bloom-forming harmful algae consume particulate prey when nutrients are not available in the dissolved form. The goal of this dissertation was to apply statistical time series analysis, together with a series of laboratory experiments, and multi-nutrient quota models to improve our understanding and predictive capability of this important HAB species. Statistical time series analysis of K. veneficum abundance in Chesapeake Bay showed the predictive power of multiplicative factors (i.e., physical factors, nutrients, and prey) and the importance of temporal lags in some of these factors in bloom promotion. In laboratory experiments, feeding rates were determined for K. veneficum on prey when both were in varying nutritional conditions. Highest feeding rates were found for K. veneficum initially under low nitrogen:phosphorus condition and fed nitrogen-rich prey. Based on these data, a conceptual model was developed of mid-Bay summer K. veneficum blooms that incorporates the role of prey with a high nitrogen:phosphorus ratio originating from river inputs and a source inocula of K. veneficum from southern Bay waters with a lower nitrogen:phosphorus content. Further laboratory experiments were conducted using multi-wavelength fluorometry to measure growth, grazing and photo-physiology of K. veneficum with single and multiple prey species. Growth of K. veneficum increased with increasing prey concentrations of the cryptophyte Rhodomonas salina, but declined with Synechococcus as the prey. Subsequent multi-nutrient mechanistic modeling was undertaken, simulating the growth of dinoflagellate K. veneficum and its common prey, Rhodomonas. The model was run varying nutrient ratios (molar nitrogen:phosphorus of 4, 16 and 32) and temperatures. The modeled biomass of K. veneficum was highest when they consumed prey under high nitrogen:phosphorus conditions. When nutrients were in balanced proportions, lower biomass of the dinoflagellate was attained at all temperatures in the model. This study underscores the importance of considering prey and their nutritional quality, as well as dissolved nutrients, in modeling HAB dynamics.