Biology Theses and Dissertations
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Item STUDIES ON THE GNRH/GTH SYSTEM OF FEMALE STRIPED BASS (Marone saxatilis): EFFECTS OF GNRH AGONJST THERAPY AND COMPARISON OF REPRODUCTIVE ENDOCRINE PARAMETERS BETWEEN WILD AND CAPTIVE FISH(1999) Steven, Colin R.; Zohar, Yonathan; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)In the striped bass (Marone saxatilis), and many other commercially important fish species, captivity results in an inability to complete final oocyte maturation (FOM), ovu lation , and spawning. We hypothesize that this effect is mediated by a disruption of the hypothalamo-pituitary-gonadal (HPG) axis at the level of the gonadotropin -releasing hormones (GnRHs). To confirm this hypothesis research was conducted focused on three objectives: First, to complement the battery of assays previously developed for analysis of the GnRH/GtH system in striped bass, an RNAse protection assay was developed to measure specific expression of the three forms of GnRH in striped bass (salmon GnRH, chicken GnRH-If and seabream GnRH). Secondly, effects of GnRH agonist-induced ovulation on the HPG axis of captive striped bass was examined by comparison of several reproductive endocrine parameters between females sampled at four stages of oocyte development. Finally, differences were examined between the reproductive endocrine status of wild and captive female striped bass. We conclude that sbGnRH is the most important form for the preovulatory release of pituitary GtH-II in striped bass. We suggest that captive females synthesize levels of GnRH mRNA that are comparable to their wild counterparts, however fail to release adequate quantities of bioactive GnRH within the pituitary to stimulate completion of FOM. This data may indicate that regulation of sbGnRH in striped bass occurs via post-transcriptional/ translational mechanisms. Furthermore, the presence of salmon GnRH in the pituitaries of captive fema les may be indicative of a possible role for salmon GnRH in the regulation of FOM.Item Adenyl Cyclase and Its Relationship to Insect Diapause in the European Corn Borer, Ostrinia Nubilalis (Hubner)(1978) Gelman, Dale Berkman; Lockard, J. David; Hayes, Dora K.; Botany and Science Teaching; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The purpose of this study was to determine if there is a link between adenyl cyclase activity and the diapause condition in the European corn borer, Ostrinia nubilalis. Insects inhabiting those latitudes where cold and warm seasons alternate with one another have evolved mechanisms which allow them to remain dormant (in a state of diapause) during the winter months of the year. Photoperiod, as well as temperature and humidity, has been shown to control the onset, maintenance and termination of insect diapause. In recent years, evidence supporting a role for the cyclic AMP system, including adenyl cyclase, as well as a role for one or more biogenic amines in the pathway between light reception and the neuroendocrine regulation of the insect life cycle and in the multitude of neuroendocrine pathways controlling insect growth and metamorphosis has been accumulating. In light of this evidence, it was decided to investigate the effects of two light regimens, short day (diapausing-inducing) and long day (pupation-inducing), on adenyl cyclase activity of various stages of fifth instar European corn borer larval heads, and to determine the effects of the biogenic amine neurotransmitters, norepinephrine, octopamine, and dopamine on this activity. Adenyl cyclase activity was measured by a modification of the method of Krishna, et al., (1968). A summary of the results follows. In head extracts of fifth instar European corn borer larvae reared under both long day and short day photoperiodic regimens, adenyl cyclase activity in the presence of sodium fluoride increased as the larvae progressed through early, middle and mature stages. In long day larval heads, activity decreased in late prepupae and reached a low in pharate pupae. In contrast, adenyl cyclase activity in short day larval heads peaked in early diapause and then returned to prediapause levels during late diapause. Norepinephrine significantly enhanced adenyl cyclase activity only in early diapause larval head extracts, while octopamine significantly enhanced adenyl cyclase activity in head extracts of late short day mature and early diapause larvae. Dopamine was ineffective as an activator. An analysis of the combined effect of neurotransmitter and developmental stage revealed that in general, a given neurotransmitter in combination with short day larval head extracts resulted in higher adenyl cyclase levels than that neurotransmitter in combination with long day head extracts.Item Interannual and Regional Patterns of Abundance, Growth, and Feeding Ecology of Larval Bay Anchovy (Anchoa Mitchilli) in Chesapeake Bay(2003) Auth, Toby D.; Houde, Edward D.; Marine Estaurine and Environmental Science Program; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Patterns in abundance, growth , and feeding by larval bay anchovy were examined in Chesapeake Bay from 1995-1999 to evaluate factors that contribute to variable recruitments of this abundant fish. The patterns were examined in relation to environmental factors, including hydrography and distributions of prey (zooplankton) and a probable predator (ctenophore). Larval abundances, sizes, feeding incidences, and growth rates varied annually and regionally. Averaged over five years, mean abundances in July decreased by almost two orders of magnitude from the mouth (38.l/m2) to the head (0.6/m) of the Bay, a long a declining salinity gradient. Yearly survey, bay-wide mean abundance varied nearly 10-fold; it was highest in 1998 (42. 7 /m2) and lowest in 1996 (4.6/m2). Feeding incidence was highest in 1998 (23%) and lowest in 1996 (9%), and varied regionally from 27% in the upper Bay to 13% in the mid Bay. Larvae fed predominantly during daylight. The most common prey ingested were copepod eggs and various life stages of calanoid copepods (primarily Acarlia Lonsa). Growth rates of larvae also differed annually and regionally. Mean growth rate was highest in 1998 (0.81 mm/d) and lowest in 1999 (0.68 mm/d), and varied regionally from 0.83 mm/d in the upper Bay to 0.71 mm/din the mid Bay. Zooplankton concentration was positively correlated with larval feeding incidence (r = +0.66) and growth rate (r = +0. 72). Larval feeding incidence was strongly correlated (r = +0.93) and summer larval abundance significantly correlated (r = +0.86) with fall recruitment of young-of-the-year bay anchovy.Item The Feeding Habits of the Toadfish (Opsanus Tau) Based on an Analysis of the Contents of the Stomach and Intestine(1951) Chrobot, Raymond J.; Littleford, Robert A.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Opsanus tau, (Linneaus) - the toadfish, inhabits a vast area along the Eastern Sea Coast of North America. It is found from the coast of Maine to the regions of the West Indies. North of Cape Cod, its occurrence is rather rare. As for the Chesapeake localities, according to previous records the toadfish lives in the muddy bottoms of the oyster regions of the Chesapeake Bay, around the mouth of the Potomac River, and elsewhere in the saltwater regions. Many specimens were collected from many localities around Annapolis, Maryland to the entrance of the Bay by Hildebrand and Schroeder (1927). Studies on the feeding habits of the toadfish have not been very extensive over the past years as reviewed in the literature. Little attention has been given to very detailed analyses of this type because of their lack of economic importance. (Hildebrand and Schroeder, 1927) in their mention of the toadfish state that its principal food appears to consist of crustaceans, with a combination of mollusks, or other fish. Small crabs among the crustaceans appeared most frequently in the food, although shrimp (and in the smaller individuals Amphipods) and Isopods also were present. Almost any kind of offal is eaten, and in places where garbage is thrown overboard, toadfish are almost always present in comparatively large numbers. (Linton, 1901) noted that the alimentary canal is chiefly filled with crustacean and molluscan remains and the bones and scales of fishes. He also noted finding a partly digested toadfish in the stomach of another. (Gudger, 1908) stated that their favorite food is young molting blue crab; any crustacean will do, however, or fish or almost any kind of offal. This investigation was concerned with the feeding habits of Opsanus tau in the Chesapeake Bay in the vicinity of Crisfield, Maryland. A somewhat detailed analysis was made in the determination of the specific type of food that was present in the comparison to what has previously been noted. In correlation with previous accounts of notations made on the feeding habits of the toadfish , a definite relation occurred between the analyses presented here with earlier findings.Item THE EFFECT OF SUMMER STORM EVENTS AS A DISTURBANCE ON THE MOVEMENT BEHAVIORS OF BLACK SEA BASS IN THE SOUTHERN MID-ATLANTIC BIGHT(2019) Wiernicki, Caroline Jane; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Storm events are a key disturbance in the Middle Atlantic Bight (MAB), driving thermal, hydrodynamic, and acoustic perturbations on demersal fish communities. Black sea bass are a model MAB species as their sedentary behavior exposes them to storm disturbances. I coupled biotelemetry with an oceanographic model, monitoring black sea bass movement behaviors during the summer-fall of 2016-2018. Storm-driven changes in bottom temperature (associated with rapid destratification) had the greatest effects on fish movement and evacuation rates, while the cumulative effects of consecutive storms had little to no observed effect. Storms also generate substantial noise, but the hearing frequencies of black sea bass are currently unknown. I conducted a quantitative literature analysis on fish hearing based on swim bladder elaboration, successfully classifying detected sound frequency ranges among fishes, including black sea bass. Climate change will likely alter the intensity of MAB storms, prioritizing research on their impacts to fish communities.Item EFFECTS OF SEA LEVEL RISE ON TIDAL FRESHWATER, OLIGOHALINE, AND BRACKISH MARSHES: ACCRETION, NUTRIENT BURIAL, AND BIOGEOCHEMICAL PROCESSES(2019) Allen, Jenny; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal wetlands provide critically important ecosystem services such as storm surge and flood attenuation, pollution retention and transformation, and carbon sequestration. The ability of tidal wetlands to maintain surface elevation under accelerated sea level rise is critical for their persistence. Saltwater intrusion can further threaten tidal freshwater marshes by decreasing primary production and organic matter accumulation as well as cause shifts in microbial pathways, leading to increases in organic matter decomposition and an overall decrease in marsh elevation. The objectives of this research were to examine accretion dynamics across the estuarine gradient of the Nanticoke River, a major tributary of the Chesapeake Bay, and determine the relative contribution of organic and inorganic matter to accretion in the marshes; determine the accumulation rates of C, N, and P across the estuarine gradient; and examine the effects of sulfate intrusion on biogeochemical transformations and marsh surface elevation in tidal freshwater marsh soil. Results of the collective studies suggest that the mechanisms controlling accretion dynamics and nutrient accumulation are complex and are likely driven by site-specific factors rather than estuary-wide factors. Accretion rates and nutrient accumulation rates were highly variable across the estuarine gradient, but were largely dependent on both organic matter accumulation and inorganic sedimentation. Only 8 out of the 15 subsites had accretion rates higher than relative sea level rise for the area, with the lowest rates of accretion found in the oligohaline marshes. Organic matter accumulation is especially important in marshes with low mineral sediment supply, particularly mid-estuarine oligohaline marshes, but may not be enough to help keep these marshes above relative sea level. The tidal marshes along the Nanticoke River removed approximately 15% and 9% of the total N and P load entering the system, but their ability to continue to remove nutrients may be compromised due to rising sea levels. Shifts in microbial pathways and increases in organic matter decomposition due to saltwater intrusion further threaten the ability of these marshes to keep pace with sea level rise, potentially resulting in the loss of an extremely valuable ecosystem.Item The long-term change of Chesapeake Bay hypoxia: impacts of eutrophication, nutrient management and climate change(2019) Ni, Wenfei; Li, Ming; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Eutrophication-induced coastal hypoxia can result in stressful habitat for marine living resources and cause great economic losses. Nutrient management strategies have been implemented in many coastal systems to improve water quality. However, the outcomes to mitigate hypoxia have been mixed and usually small when only modest nutrient load reduction was achieved. Meanwhile, there has been increasing recognition of climate change impacts on estuarine hypoxia, given estuaries are especially vulnerable to climate change with multiple influences from river, ocean and the atmosphere. Due to the limitation of observational studies and the lack of continuous historical data, long-term oxygen dynamics in response to the changes of external forces are still not well understood. This study utilized a numerical model to quantitatively investigate a century of change of Chesapeake Bay hypoxia in response to varying external forces in nutrient inputs and climate. With intensifying eutrophication since 1950, model results suggest an abrupt increase in volume and duration of hypoxia from 1950s-1960s to 1970s-1980s. This turning point of hypoxia might be related with Tropical Storm Agnes and consecutive wet years with relatively small summer wind speed. During 1985-2016 when the riverine nutrient inputs were modestly decreased, the simulated bottom dissolved oxygen exhibited a statistically significant declining trend of ~0.01 mgL-1yr-1 which mostly occurred in winter and spring. Warming was found to be the dominant driver of the long-term oxygen decline whereas sea level rise had a minor effect. Warming has overcome the benefit of nutrient reduction in Chesapeake Bay to diminish hypoxia over the past three decades. By the mid-21st century, the hypoxic and anoxic volumes are projected to increase by 10-30% in Chesapeake Bay if the riverine nutrient inputs are maintained at high level as in 1990s. Sea level rise and larger winter-spring runoff will generate stronger stratification and large reductions in the vertical oxygen supply to the bottom water. The future warming will lead to earlier initiation of hypoxia, accompanied by weaker summer respiration and more rapid termination of hypoxia. The findings of this study can help guide climate adaptation strategies and nutrient load abatement in Chesapeake Bay and other hypoxic estuaries.Item Seasonal Migrations of Atlantic Sturgeon and Striped Bass Through the Maryland Wind Energy Area(2019) Rothermel, Ella Rick; Secor, David; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Baseline information is needed on migrations through US Mid-Atlantic Bight shelf waters in advance of offshore wind development. Acoustically-tagged Atlantic sturgeon and striped bass were detected from 2016-2019 in an array of 20 acoustic telemetry receivers centered on the Maryland Wind Energy Area and extending 10-50 km offshore. Both species were transient (mean residency < 3 days), but migration patterns differed seasonally and were related to depth and temperature. Generalized additive models showed that Atlantic sturgeon occur at inshore sites during spring while striped bass shifted toward the outer shelf as inshore waters cooled in winter. The movement of hundreds of tagged striped bass and sturgeon, originating from shelf waters from Maine to South Carolina suggests that the Wind Energy Area is part of a multi-species Atlantic coastal flyway, particularly during spring, fall, and winter periods. Thus, summer presents a potential window for wind tower construction.Item The effect of salinity on species survival and carbon storage on the Lower Eastern Shore of Maryland due to saltwater intrusion(2019) de la Reguera, Elizabeth; Tully, Kate; Palmer, Margaret; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As sea levels continue to rise, coastal ecosystems are vulnerable to saltwater intrusion (SWI), the landward movement of sea salts. Specifically, in coastal farmlands, we expect SWI to drive changes in plant species composition and carbon (C) storage. As soils salinize, standard crops (i.e. corn, soybean, and wheat) can no longer survive and farmers must consider alternatives. Further, transitioning agricultural fields may become C sinks as SWI advances inland and farmlands begin to resemble tidal wetlands. My objectives were to determine: (1) the effect of SWI on the germination of standard and alternative crop species, and (2) the C storage potential of salt-intruded farmlands. Most standard and alternative crops were intolerant to high levels of osmotic and ionic stress at the germination stage. However, sorghum and salt-tolerant soybean showed promise in field experiments. I show that agricultural fields exposed to SWI have a high potential to store C in soils.Item HYDROLOGIC DRIVERS OF SOIL ORGANIC CARBON STORAGE AND STABILITY IN FRESHWATER MINERAL WETLANDS(2019) Kottkamp, Anna Isabel; Palmer, Margaret; Tully, Katherine; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mineral wetlands comprise most of historic wetland loss, yet few studies focus on mineral wetland soil organic carbon (SOC). We explore SOC across continuous hydrologic gradients within and among seasonally flooded mineral wetlands. First, we quantify SOC stabilization (e.g., organo-mineral associations and aggregates) across a wetland–upland gradient. Second, we examine relationships between hydrologic regime and SOC stocks among wetlands. From wetland–upland, saturation was highly variable in the transition zone. Organo-mineral associations peaked in the transition zone while large macroaggregate SOC declined from wetland–upland. Across wetlands, indicators of drying (e.g., minimum water level and summertime recession rate) were more related to SOC than inundation duration. From wetland basin–upland, SOC stocks were significantly related to both mean water level and relative elevation. We highlight relationships between SOC and the dynamic hydrology of wetlands, emphasizing the need for research on how changing hydrologic regime may influence mineral wetland SOC.