Biology Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2749

Browse

Search Results

Now showing 1 - 10 of 44

Investigating the role of the Mid-Atlantic inner continental shelf as a marine finfish nursery: a comparative approach
(2010) Woodland, Ryan Jordan; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The paradigm of estuarine-dependence in marine fishes has been challenged by evidence of facultative recruitment by juveniles to both estuarine and inner continental shelf (ICS) nursery habitats. This ecological flexibility suggests that the potential nursery area for marine fishes may be more expansive than previously considered. Two lines of investigation were undertaken to evaluate the overarching hypothesis that ICS habitats serve a nursery function for finfish that also use estuarine nurseries: 1) a direct comparison of seasonal, annual and compositional assemblage structure between an ICS habitat of the Middle Atlantic Bight (Delmarva Peninsula) and an adjacent estuary (lower Chesapeake Bay); and 2) an investigation of trophic structuring within an ICS demersal finfish assemblage with an emphasis on ontogenetic niche. In comparisons between nursery types, there was a strong seasonal similarity in assemblage structure between the estuary and ICS despite significant differences in abundance estimates at the species level. Juvenile trophic niche of two indicator species, bluefish and bay anchovy, was wider and more diverse in the estuary yet physiological condition was similar or higher in the ICS. In focused studies on the ICS food web, diet overlap was common among consumers, yet stable isotope evidence indicated prey resources were partitioned along vertical (trophic position) and horizontal (pelagic-benthic pathway) trophic axes. Benthic and pelagic food webs were tightly coupled in most juvenile phase finfish; yet, this relationship showed signs of decoupling in older age classes, suggesting an increased reliance on benthic trophic pathways with age and size. Several prey species that link pelagic and benthic food webs were shown to be important in the diets of demersal finfish, particularly mysid shrimp. Comparative assemblage and food web studies demonstrated that the ICS functions as summer nursery habitat for a wide variety of temperate marine finfish that also use proximal estuarine nurseries. The contribution of ICS nurseries to annual juvenile production represents a critical, but unknown component of population demographics for many marine species and must be considered to conserve essential fish habitats and account for recruitment variability in fisheries stock assessments.
CARBON AND NITROGEN SOURCES AND CYCLING IN PLANKTONIC MARINE ECOSYSTEMS
(2010) Keller, David Peter; Hood, Raleigh R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Carbon and nitrogen are involved in many important biological and environmental processes and can even influence the global climate (i.e. CO2 as a greenhouse gas). In this dissertation the role of dissolved organic matter (DOM) in marine C and N cycling is studied. Research is also presented that looks at phytoplankton as potential sources of C and N in the upper Chesapeake Bay estuary food web. To better understand DOM cycling a model was constructed to simulate dissolved organic carbon (DOC) and nitrogen (DON) cycling in marine surface waters. Using the model DOM cycling was simulated in the context of: (1) a steady- state comparison of idealized oceanic, coastal, and estuarine ecosystems, (2) the seasonal cycle in eutrophic waters, and (3) a focus on the roles of viruses and microzooplankton. The results suggest that DOM cycling is intricately tied to the biomass concentration, ratio, and productivity of phytoplankton, zooplankton, viruses, and bacteria. The first set of simulations highlights the importance of certain processes in each ecosystem. The second set of simulations shows how DOM cycling, particularly the sources of DOM, changes seasonally. The third set of simulations highlights differences in the top-down and bottom-up roles of viruses and microzooplankton and their subsequent effect on DOM cycling and trophic interactions. To better understand C and N cycling in the upper Chesapeake Bay the biomass distribution and floral composition of the phytoplankton community was studied during the winter and spring to determine if phytoplankton could play an important role in the estuarine turbidity maximum (ETM) food web. This research suggests that the general distribution of phytoplankton in the upper Bay is somewhat like a classic estuarine "salt wedge" diagram with two distinct phytoplankton communities separated by a zone of increased mortality due to salinity stress and ETM entrapment. High concentrations of phytoplankton pigment degradation products were often observed in the ETM suggesting that this is an area of high phytoplankton mortality and/or an area where phytoplankton derived particulate organic matter was being concentrated. These results suggest that phytoplankton have the potential to play an important role in C and N cycling and the ETM food web.
Community Metabolism and Energy Transfer in the Chesapeake Bay Turbidity Maximum in 2007 and 2008
(2010) Lee, Dong-Yoon; Hood, Raleigh R.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The estuarine turbidity maximum (ETM) is a zone of elevated organic matter concentrations and it is an important habitat for bacteria, zooplankton, and early-life-stages of fish. In an effort to identify the key mechanisms controlling production, we measured plankton community metabolism on a series of high-resolution spatial surveys in the upper Chesapeake Bay. The spatial patterns of metabolism revealed the highest primary production and community respiration rates downstream of the ETM region, and net heterotrophy in winter and spring. Also, strong correlations between plankton community metabolism and phytoplankton pigment concentrations, including chlorophyll-a and dinoflagellate indicating pigment peridinin, were observed. These correlations suggest that mixotrophic dinoflagellates were key organisms linking detrital and algal organic matter to higher trophic levels. It is hypothesized that the physiological advantages of mixotrophic dinoflagellates (i.e., autotrophic, heterotrophic) combined with the physical conditions in the ETM which enhance the quantity and quality of organic matter give rise to the high secondary production in the upper Chesapeake Bay.
The influence of episodic river flow events on striped bass (Morone saxatilis) spawning in Chesapeake Bay, USA
(2010) Jahn, Ginger Lee; North, Elizabeth W.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The upper Chesapeake Bay is an important and dynamic nursery habitat for striped bass (Morone saxatilis) eggs and larvae. The hypothesis that pulses in flow cause temperature changes that cue striped bass spawning was evaluated with field surveys and historical data analyses. Water temperatures in April and May were negatively correlated with river flow (1956-2002), suggesting that water temperatures decrease during flow events and then increase as flow diminishes, potentially providing a cue for spawning. Survey data from the upper bay in 2007 and 2008 were analyzed in conjunction with historical data on striped bass eggs in tributaries of Chesapeake Bay. Results suggest that increasing water temperatures are the dominant cue for striped bass spawning. Temperature increases after pulsed flow events may cue striped bass spawning and may result in more favorable prey abundances and better larval survival compared to years when spawning is cued by water temperature increases alone.
Effect of pH on phytoplankton and bacteria production
(2009) Johns, Desmond Justine; Stoecker, Diane K; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
In recent decades eutrophication has fueled intense phytoplankton blooms that frequently negatively impact ecosystems. Dramatic pH elevations are commonly overlooked during such blooms, which may also be harmful. Cyanobacteria blooms in the Sassafras River, MD were sampled during Autumn 2008 and measured for primary and bacterial production (PP and BP), and differences in bacteria communities composition were examined. pH elevations above 8.8 in the field corresponded to decreased PP, but had no effect on BP. Laboratory experiments demonstrated that negative effects of pH were dependant on light intensity; PP increased with pH at moderate light intensities, but decreased at low irradiance. There was some evidence that BP is affected by high pH, although bacteria community differences as determined by DGGE were not. Negative effects of high pH are probably most important during spring and summer in low salinity environments when pH fluctuations are more common and last longer.
THE DISTRIBUTION OF CALLINECTES SAPIDUS MEGALOPAE AT THE MOUTHS OF CHESAPEAKE AND DELAWARE BAYS: IMPLICATIONS FOR LARVAL INGRESS
(2009) Biermann, Jeffery Lee; North, Elizabeth W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Transport of Callinectes sapidus (blue crab) megalopae from the continental shelf into estuaries may influence recruitment variability of this economically important species. This research seeks to determine the vertical distribution of C. sapidus megalopae near the mouths of Chesapeake and Delaware Bays, and thereby infer swimming behaviors that may influence ingress to these estuaries. Megalopae and physical conditions were sampled at locations from ~10 km inshore of the estuary mouths to ~40 km offshore in coastal shelf waters in September 2005 and 2006. Megalopae were present in greater abundance and at shallower depths during night compared to day at all locations, suggesting a diurnal effect on distribution within the estuary and on the continental shelf. Unlike previous studies, offshore distributions did not indicate surface oriented behavior. Within the mouth of Delaware Bay, limited evidence suggests that megalopae presence in the upper portion of the water column increases in response to nocturnal flood tides. Results suggest photoinhibited swimming near the mouths of Chesapeake and Delaware Bays. In context of previous laboratory studies, these findings indicate that estuarine chemical cues at very low concentrations may induce changes in megalopae behaviors and stimulate molting at least 40 km offshore of estuarine mouths. Results suggest wind-forcing and density-induced subtidal flow are more likely mechanisms for ingress to Chesapeake and Delaware Bays than tidal-transport.
Population genetics of the eastern oyster in Chesapeake Bay
(2008) Rose, Colin G.; Hare, Matthew P; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The eastern oyster, Crassostrea virginica, plays an important role in the ecology of Chesapeake Bay. Its large population size, long larval dispersal stage and potential for high variance in reproductive success is representative of many marine invertebrates. Nevertheless, many important aspects of the oyster's biology remain unclear. I investigated how migration, natural selection, and effective population size have shaped the evolution of Chesapeake oysters. First, I examined aspects of genetic connectivity among oysters from rivers throughout the Bay. A correlation between geographic and genetic distance indicated that oyster larval dispersal tends to be local and that migration between Bay tributaries is rare over an ecological time scale. This result contributes to a growing body of literature indicating that larval dispersal is not passive. Next, I showed that a pattern of non-neutral mitochondrial evolution previously observed in different oyster populations also existed in Chesapeake Bay C. virginica. Tests of selection indicated that the pattern, in which there is an excess of high frequency and low frequency haplotypes and a deficit of intermediate frequency haplotypes, was the result of positive selection on the genome. Demographic explanations appear unlikely to account for the mitochondrial haplotype pattern because nuclear loci exhibited neutral patterns of sequence evolution. Estimates of effective population size were several orders of magnitude smaller than census size, indicating that there was variance in reproductive success (sweepstakes reproduction). Nevertheless sweepstakes reproduction was not so severe that individual cohorts of juvenile oysters exhibited reduced levels of variation compared to the adult population. Finally I evaluated the risks associated with a supplementation program in which hatchery-raised oysters bred for disease tolerance were released into wild oyster populations. The results indicated that following supplementation, the wild effective population size remained large despite the danger of severe genetic bottlenecks. Increased hatchery effective population is suggested to prevent future harm to the wild population.
Watershed land use and nutrient dynamics in Maryland Coasal Bays, U.S.A.
(2008) Beckert, Kristen A.; O'Neil, Judith M.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Upstream and inshore regions of the Maryland Coastal Bays exhibit degraded water quality. Six streams and three shallow bays were sampled in May and July 2006 and 2007 to compare spatial patterns in relation to land use and nutrient loading. St. Martin River, having a high percentage of crop agriculture and a low percentage of forest and wetlands, experienced the most degraded water quality of the three regions, and stream total nitrogen in its watershed was linked to feeding operations and anthropogenic land use. Despite having a much less developed watershed, Johnson Bay experienced degraded water quality, especially in inshore regions. Sinepuxent Bay had the best water quality of the three bays, but still demonstrated anthropogenic impacts. Nutrient loading from land use is directly related to the observed patterns in St. Martin River, while residence time, groundwater flows, and within-bay cycling has led to water quality degradation in Johnson Bay.
Microcosm Studies of Nutrient Cycling in Bahamian Stromatolites
(2008-08-13) Jabro, Nicholas; Marinelli, Roberta; Harvey, Rodger; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
I report results of field observations and experiments that examine the oxygen and nutrient fluxes for stromatolites in Highborne Cay in the Exumas, Bahamas. The aim of this study is to determine whether nutrients play a role in the transition of the community structure within the mats that is thought to be responsible for lithification and, ultimately, mat growth and structure. The research includes nutrient monitoring of the sediment and water column, and measures of rates of oxygen and inorganic nutrient exchange from stirred microcosm chamber incubations of mats with varied community structure. On the basis of mat community composition, I hypothesized that different mat types would have different fluxes, and that Highborne mats would be limited by one or more nutrients that efficient recycling within the mats might otherwise help supply. Samples of the four major mat types were sealed in stirred microcosm flux chambers, incubated in a circulating water bath, and sampled for oxygen, NH4, NO3, PO4, and Silicate. Nutrient addition, treatments of PO4 and Si were employed to investigate whether they stimulate primary productivity, signaling that mats are limited in these solutes. Nutrients in Highborne Cay were high in nitrogen relative to P, with N:P as high as 30. There was no difference in nutrient flux or productivity among mat types, and the addition of nutrients did not change mat productivity. These observations suggest that mat development in Highborne Cay is not limited by nutrients, but more likely structured by external physical factors such as the rate of turbulent flow which may limit the recruitment of competitors such as macroalgae and benthic branching diatoms.
Bioenergetic and ecological consequences of diet variability in Atlantic croaker Micropogonias undulatus
(2008-04-26) Nye, Janet Ashley; Miller, Thomas J.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Atlantic croaker Micropogonias undulatus is a commercially and ecologically important bottom-associated fish that occurs in marine and estuarine systems from Cape Cod, MA to Mexico. I documented the temporal and spatial variability in the diet of Atlantic croaker in Chesapeake Bay and found that in the summer fish, particularly bay anchovies Anchoa mitchilli, make up at least 20% of the diet of croaker by weight. The use of a pelagic food source seems unusual for a bottom-associated fish such as croaker, but appears to be a crepuscular feeding habit that has not been previously detected. Thus, I investigated the bioenergetic consequences of secondary piscivory to the distribution of croaker, to the condition of individuals within the population and to the ecosystem. Generalized additive models revealed that the biomass of anchovy explained some of the variability in croaker occurrence and abundance in Chesapeake Bay. However, physical factors, specifically temperature, salinity, and seasonal dynamics were stronger determinants of croaker distribution than potential prey availability. To better understand the bioenergetic consequences of diet variability at the individual level, I tested the hypothesis that croaker feeding on anchovies would be in better condition than those feeding on polychaetes using a variety of condition measures that operate on multiple time scales, including RNA:DNA, Fulton's condition factor (K), relative weight (Wr), energy density, hepatosomatic index (HSI), and gonadosomatic index (GSI). Of these condition measures, several morphometric measures were significantly positively correlated with each other and with the percentage (by weight) of anchovy in croaker diets, suggesting that the type of prey eaten is important in improving the overall condition of individual croaker. To estimate the bioenergetic consequences of diet variability on growth and consumption in croaker, I developed and validated a bioenergetic model for Atlantic croaker in the laboratory. The application of this model suggested that croaker could be an important competitor with weakfish and striped bass for food resources during the spring and summer when population abundances of these three fishes are high in Chesapeake Bay. Even though anchovies made up a relatively small portion of croaker diet and only at certain times of the year, croaker consumed more anchovy at the population level than striped bass in all simulated years and nearly as much anchovy as weakfish. This indicates that weak trophic interactions between species are important in understanding ecosystem processes and should be considered in ecosystem-based management.

Biology Theses and Dissertations

Browse

Filters

Settings

Sort By

Results per page

Search Results