MEES Theses and Dissertations
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Item Interactions between an estuarine submersed plant bed and its physical and biogeochemical environment: Seasonal and spatial variation(2009) Gruber, Renee Kirstin; Kemp, William M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Annual cycles of growth and morphology were analyzed in a bed of the canopy-forming submersed aquatic vegetation (SAV) species, Stuckenia pectinata, in relation to seasonal water quality conditions in a Chesapeake Bay tributary. A rapid accumulation of aboveground plant material occurred during the spring period of high water clarity, which aided plants in circumventing light limitation during the summer period of low water clarity. During summer, this SAV bed strongly attenuated wave energy, which contributed to growth-promoting feedback effects that improved light and nutrient availability for plants. Modification of hydrodynamic conditions also resulted in several negative feedback effects on SAV growth. Feedbacks were regulated by plant stand size and density and seasonal changes in plant canopy architecture. The findings of this study illustrate the significant impacts SAV beds can have on their local environment, improving conditions and resulting in plant growth that could not otherwise occur in this degraded system.Item Organic nitrogen and carbon transformations in a stream network of Chesapeake Bay watershed(2009) Delaney, Katie M.; Kaushal, Sujay S; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increased export of anthropogenically-derived nitrogen in streams has contributed to increased water quality problems. I investigated in-stream transformations of nitrogen and carbon at the benthic habitat and reach network scale. Both indicated large transformations of dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) along the Gwynns Falls urban stream network. In-stream transformation of DON and DOC declined from headwaters to outflow, with a mean 23% removal of DOC and 57% removal of DON. Transformation rates ranged from in-stream internal loading of 28 g/m2/day to in-stream removal of 740 g/m2/day for DOC (mean: uptake 64 g/m2/day) and in-stream internal loading of 4.8 g/m2/day to in-stream removal of 74 g/m2/day for DON (mean: uptake 3.5 g/m2/day). Urban stream networks may act as both "transporters" and "transformers" of nitrogen and knowledge regarding in-stream N transformations is critical in predicting the sources and removal of nitrogen en route to adjacent tidal waters.Item Predation by eastern mudminnows (Umbra pygmaea) on macroinvertebrates of temporary wetlands(2009) Lombardi, Susan Elizabeth; Lamp, William O.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fish play a substantial role in aquatic food webs, yet the effect of feeding activities of small stream fish that enter seasonally-flooded temporary wetlands during periods of hydrologic connectivity is not well understood. In this study, eastern mudminnows (Umbra pygmaea) were introduced to a fishless wetland in Caroline County, Maryland, and the aquatic macroinvertebrate community did not significantly change within two weeks. Gut contents of mudminnows collected from the wetland and a stream consisted primarily of dipteran larvae; ostracods were also a common food source for wetland mudminnows. Common prey not found in gut contents but present in the wetland were tested as food, and all taxa were consumed in a no-choice predation experiment. Mudminnows have the potential to directly affect multiple trophic levels and subsequent ecosystem functioning through predatory interactions with sustained hydrologic connectivity between fish sources and temporary wetlands.Item An RNA:DNA-based index of growth in juvenile Atlantic menhaden (Brevoortia tyrannus): laboratory calibration and field assessment(2009) Edwards, Jason Lee; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atlantic menhaden (Brevoortia tyrannus) is an ecologically and economically important species in the mid-Atlantic coastal ecosystem. Its population dynamics are influenced by growth and survival during juvenile occupancy in estuarine nursery habitats. Therefore, quantifying production of potential nursery areas is important to understanding population processes and defining essential fish habitat for this species. Based on laboratory growth experiments, an RNA:DNA-based growth model was developed for young-of-the-year menhaden. The temporal response of RNA:DNA to changes in feeding condition was also quantified in the laboratory. Results of these investigations indicate RNA:DNA as a reliable tool for estimating recent growth and condition in relation to habitat residency. RNA:DNA-based estimates of growth were combined with site-specific abundance estimates to evaluate the spatiotemporal variability in production of potential menhaden nursery habitats. Site-specific production estimates exhibited high spatiotemporal variability suggesting menhaden utilize a mosaic of habitats to promote production, rather than specific sites consistently generating high levels of production.Item PATTERNS OF WETLAND PLANT SPECIES RICHNESS ACROSS ESTUARINE RIVER GRADIENTS(2009) Sharpe, Peter James; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)It is widely accepted that in coastal wetlands a negative relationship exists between plant species richness (number of species) and salinity. However, the distribution of species richness across estuarine salinity gradients has not been closely examined. I hypothesized that plant species richness in coastal marshes (i.e., wetlands dominated by herbaceous plants) would follow a non-linear pattern with increased distance (salinity) downriver (Chapter 2). To test this hypothesis I conducted detailed marsh vegetation surveys along ≈ 50 km estuarine river gradients of the Nanticoke and Patuxent Rivers, MD/DE. I further hypothesized that the observed patterns of plant species richness on the Nanticoke and Patuxent Rivers could be accurately predicted by a mid-domain effect (MDE) model independent of measured abiotic factors using RangeModel 5.0 (Chapter 3). Lastly, I theorized that Marsh mesocosms subjected to intermediate salinity and inundation would exhibit significantly higher biomass and plant species richness compared to mesocosms subjected to extreme salt/fresh and flooding regimes utilizing a controlled greenhouse experiment (Chapter 4). I found that plant species richness can vary in both a linear (Patuxent River) and non-linear (Nanticoke River) pattern along an estuarine gradient. The MDE model did not explain a high proportion of the observed richness patterns for either river system compared to abiotic factors like porewater salinity. The controlled marsh mesocosm experiment supported the non-linear pattern of plant species richness observed along the Nanticoke River gradient, but did not show a significant difference in plant biomass or richness/diversity between purely fresh and low-salinity marsh mesocosms (α = 0.05). The results of this research suggest that tidal marsh plant richness/diversity patterns do not always conform to a simple linear relationship with increasing salinity and that the MDE is not as important of a mechanism in these communities compared to porewater salinity or flooding frequency. Furthermore tidal low salinity marshes exposed to elevated salinity and flooding frequencies are likely to see a shift in their plant community structure to more salt tolerant plants and less rich/diverse communities assuming they can accrete at a rate equal to or exceeding the present rates of sea-level rise in the Chesapeake Bay.Item HOW DENDRITIC ECOLOGICAL NETWORKS STRUCTURE THE DISTRIBUTION AND MOVEMENT OF STREAM SALAMANDERS(2009) Grant, Evan; Palmer, Margaret A; Nichols, James D; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Research in population biology is concerned with factors affecting the change in a population over time, including births, deaths, immigration and emigration. Despite the potential importance of dispersal, empirical data on movement are lacking in many systems. Hence, there is a large body of theory on dispersal that remains to be tested in real biological systems. In particular, many organisms exist in ecological networks with the complex geometry common to caves, plants and streams. This alternative network topology might influence population and community-level patterns and processes. Chapter 1 introduces the concept of the "dendritic ecological network," highlighting special properties and characteristics useful for understanding community and population-level processes. Of most interest for this dissertation is how the rigid spatial structure and branching topology may have implications for patterns of population distribution and the evolution of movement behaviour in stream organisms. In chapters 2 and 3, I investigate patterns of stream salamander distribution, which may be related to the spatial configuration of stream habitat branches. First, I determined the sampling methods suitable for estimating the probability a site is occupied by one of three stream salamander species. I then applied these methods to investigate occupancy patterns, in relation to stream spatial layout across two mid-Atlantic regions. I found that all three species have higher occupancy in streams with a confluent, firs-order stream, though the strength of this association seems to be related to life history characteristics. Finally, in chapters 4 and 5, I sought to identify movement pathways for larval, juvenile and adult Desmognathus stream salamanders. First, I tested my marking method on larval individuals, and found that the visual implant elastomer marks can be retained through metamorphosis. Then, using individual mark-recapture and multistate modeling, I found that stream salamanders move during the juvenile stage, with both an upstream-biased movement, and a proportionally large probability of moving overland to an adjacent stream reach. The chapters in this dissertation combine empirical investigations of the patterns and pathways of stream salamander movement. Taken together, they elucidate the underlying importance of dendritic ecological networks, and provide direct evidence of dispersal in stream salamanders.Item Light available to the seagrass Zostera marina when exposed to currents and waves(2009) McKone, Katie Lynn; Koch, Evamaria W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aquatic organisms are regularly exposed to varying degrees of hydrodynamic forces such as currents and waves. Seagrasses, which are rooted in the sediment, have flexible leaves, allowing them to sway back and forth with waves and deflect with currents. Furthermore, seagrasses can acclimate to local hydrodynamic forces exerted upon them by changing their morphology, which may benefit the organism via reduced drag, but may also bring disadvantages such as increased self-shading. We examined the interaction between water flow and morphology of the seagrass Zostera marina, and how this interaction affects light availability to the plant. We also assessed carbon and nutrient content of Z. marina, as the uptake of these constituents has been linked to hydrodynamic conditions and sediment composition. Our results indicate that local hydrodynamics and sediment composition induce morphological variation in the seagrass Z. marina, and that this variation influences light availability to the seagrass canopy.Item INFLUENCE OF MAP RESOLUTION ON SEASCAPE ECOLOGY OF REEF FISH(2009) Kendall, Matthew Sayre; Miller, Thomas J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Characteristics of benthic maps are controlled by the spatial and thematic resolutions used in map production. The implications of these production decisions on the inferences that can be drawn from the maps are poorly understood. I addressed this need by quantifying the differences among common map types, considering how map type affects inferences of fish and benthic communities at the patch level, and then evaluating the influence of map type on ecological neighborhood analysis of reef fish. Results indicated that hard bottom types, especially patch reefs and colonized pavement, were among the most sensitive to changes in spatial resolution of maps. In contrast, linear reef and continuous seagrass features were characterized quite consistently regardless of spatial resolution. Multivariate analyses indicated that both the fish assemblages and benthic characteristics of reef types overlapped considerably. In contrast, shelf position (inside versus outside of lagoons) showed clear differences in both environmental variables and fish assemblage composition. In general, the results of multivariate analyses suggest that knowledge of the overall fish assemblage or fine-scale environmental characteristics could not be used to predict reef type or vice versa. Furthermore, spatial scale of benthic maps did not affect results when analyses were conducted at the patch level. In addition, a multi-scale landscape analysis was conducted wherein correlations between fish assemblages and surrounding landscape variables were measured using univariate linear regression for a range of scales between 25 and 800 m. The strength of the associations as a function of scale exhibited one of 6 response curve forms and was used to identify the scale that best correlates fish with their surrounding habitat. In these analyses, individual landscape variables explained a maximum of only 25% of the variability in fish distributions. Use of different input maps in many of these analyses resulted in a changed perception of either the strength of peak correlation at a given scale, or the scale at which peak correlations occurred. Overall, the findings revealed which aspects of coral reef ecosystems are sensitive to map scale and advise scientists and managers on map production and use in similar settings.Item Reproductive Physiology of the Female Blue Crab, Callinectes sapidus: Spawning Induction and Vitellogenesis(2009) Bembe, Sarah Elizabeth; Chung, J. Sook; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In aquaculture, spawning is the baseline for production; therefore, the optimization of spawning conditions will directly increase production. The current study aims to optimize spawning conditions for Callinectes sapidus using environmental manipulations of photoperiod and temperature for induction while monitoring the physiological vitellogenin (VtG) levels during ovarian development and maturation. The photothermal manipulations for this study resulted in increased spawning events in 21°C temperatures (compared to 11°C and 15°C) and complete darkness (0L:24D; compared to 8L:16D, 16L:8D, and 24L:0D) while 24L:0D and 11°C suppressed spawning. When assessing the VtG levels in the hemolymph prior to, during, and after all spawning events, the VtG showed a decrease prior to spawning, and significant VtG activity was seen in 21°C for all photoperiods. Overall, spawning and vitellogenesis are temperature dependent events with 67% of the females spawning in 21°C. Photoperiod also has an effect on spawning, but not on vitellogenesis.Item Bioenergetic responses of Chesapeake Bay white perch to nursery conditions of temperature, salinity, and dissolved oxygen(2009) Hanks, Deanna McQuarrie; Secor, David H.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Changes in the physical and chemical structure of estuaries affect the habitat availability for anadromous species. White perch, an estuarine species, are among the most abundant and important fishes in the Chesapeake Bay. Here, I evaluate nursery quality for juvenile white perch by measuring metabolic and growth responses over a range of environmental conditions such as salinity, temperature, and dissolved oxygen. Rearing white perch in 10-d trials varying in temperature, salinity and dissolved oxygen conditions, I estimated growth rates, feeding rates, gross growth efficiency, and routine metabolism. Juveniles experienced higher feeding and growth rates in warmer, more oxygenated waters. In hypoxic environments (<40% saturation), metabolic rates increased as much as 4-fold while growth decreased 3-fold and feeding decreased 2-fold. My results indicate that while white perch are well suited to the saline and thermal conditions present in the Bay, nursery habitat value can be substantially curtailed by hypoxia.