No description available.

No description available.

No description available.

Throughout the salt marshes of the US Atlantic Coast, ribbed mussels (Geukensia demissa, Dillwyn, 1817) and smooth cordgrass (Spartina alterniflora Loisel) form an important mutualistic relationship. Spartina provides habitat and promotes settling of ribbed mussels, which, in turn, stabilize and fertilize the Spartina and sediment. This relationship, however, is at risk of interruption due to sea level rise, erosion, and coastal development. Among the most at-risk segments of the marsh, the front (waterward) edge of the marsh is also where ribbed mussels and their ecosystem services are concentrated. Despite their importance of ribbed mussels to the salt marsh ecosystem, very little is known about the spatial distribution. in order to address these questions, we had the following objectives: 1) to identify spatial factors influencing mussel distribution across the landscape, 2) to quantify the contribution of ribbed mussels to nitrogen removal in the presence of Spartina, and 3) to assess how the distribution of the population and its ecosystem services are likely to change by the year 2050. We conducted field work in the summers of 2015 and 2016 to survey ribbed mussel populations in 30 marshes around the Chesapeake Bay. Ribbed mussel population density and distribution was positively related to the number of Spartina stems, the exposure of the site, and to a minor degree, the amount of agriculture within 300 m. The amount of forested land cover within 60 m was negatively related to ribbed mussel density. With these factors, we built a model to estimate ribbed mussel populations in the first two meters (edge) of the marsh, and estimated the presence of 805 million mussels along the edges of Virginia's marshes. Sediment core incubations revealed that when ribbed mussels are integrated with Spartina, the ammonium and particulate removal is enhanced, relative to when mussels occur separately, but that the overall rates vary dramatically by the location of the marsh whence the cores were collected. Spatial application of a 0.62 m sea level rise scenario and local erosion rates altered the distribution of both marshes and ribbed mussels. Overall, ribbed mussel abundance declined by 3.6% between 2018 and 2050; however, most locations saw moderate to large declines, while a very few locations saw very large increases (> 100%). Declines in abundance were greatest in urban areas dominated by fringing marsh and extensive shoreline armoring, while gains were greatest in agricultural areas with extensive marshes. The projected redistribution of mussels by 2050 will have important implications for water quality improvement goals that will need to be addressed by local and state authorities. This dissertation has focused on the seascape ecology and management of ribbed mussels in the Chesapeake Bay. The work has demonstrated the importance of applying spatial techniques to study and understand organisms and ecosystems at the interface between land and water. Only through further study and proactive planning will we be able to plan for and address the coming impacts of anthropogenic climate change and sea level rise.

The incidence of tick-borne diseases is on the rise in the US and around the world, due in part to emerging pathogens. However, the environmental drivers affecting these pathogens remain unclear. Most research on the topic in the US has focused on Borrelia burgdorferi, which causes Lyme, but it is unknown if the same conditions that affect B. burgdorferi also affect other pathogens, which may be carried by other ticks or reservoirs. The answer will help determine generalizable principles in tick-borne pathogen ecology, if they exist, as well as better manage for tick-borne pathogen risk in areas at risk from new and often unfamiliar pathogens. One such pathogen in the eastern US is Ehrlichia chaffeensis, which is transmitted by the lone star tick (Amblyomma americanum) and is the causative agent of monocytic ehrlichiosis, a potentially fatal illness. Here, I examine spatial and temporal variation in E. chaffeensis prevalence in southeastern Virginia and how this is influenced by the environment. in Chapter 1, I used four years of data to ask how E. chaffeensis prevalence changed between years and how this was affected by seasonal weather patterns. Using mixed-effect models, I related E. chaffeensis occurrence to temperature, humidity, vapor-pressure deficit, and precipitation up to 21 months prior to sampling. Annual prevalence varied significantly from 0.9% - 3.7%, and was positively affected by temperatures during the previous winter (i.e. before the current cohort of nymphs hatched). I hypothesize this is because winter temperature affects reservoir host mortality or natality, which would in turn affect the availability of naïve reservoir hosts in the spring. Regardless of mechanism, my findings have implications for the future because winters in this region are predicted to grow warmer, which could increase E. chaffeensis prevalence. in Chapter 2, I used five years of field data to ask how landscape context affects spatial variation in the prevalence of E. chaffeensis and interannual occupancy dynamics of its vector, A. americanum. Under a Bayesian framework, I created a metric- and scale-optimized model to relate E. chaffeensis prevalence and A. americanum turnover to the availability, quality, and fragmentation of habitat. Prevalence was highest and turnover was lowest in areas of low forest cover and low edge density, dominated by deciduous trees. Thus, highest disease risk is predicted in areas of forested areas that are either isolated or abutted against impermeable boundaries, both characteristic of many parks. Many of my results highlight the complexity of tick-borne disease dynamics and the challenges inherent to the subject; some results ran counter to my predictions and E. chaffeensis prevalence remains rare, which makes it challenging to model. That said, my work also represents important progress in an often-neglected area of tick-borne disease ecology. to my knowledge, this is the first study to address temporal variation in E. chaffeensis prevalence, and is one of few studies to relate E. chaffeensis prevalence to landscape context at a scale relevant to the pathogen's hosts and to disease-risk management.

As sea levels rise, coastal salt marshes, and the organisms for which they provision, face existential threats. A first step in understanding how projected marsh loss and reconfiguration may impact obligate species is to define their contemporary distribution and temporal shifts in structure using dynamic occupancy models. While occupancy models have commonly been applied to multi-annual butterfly studies, few have investigated population dynamics within a single-season. Here, we used Bayesian dynamic use models to define within-flight-period trends in adult salt-marsh skipper (Panoquina panoquin) use and state change probability. In doing so, we developed and validated a fully-Bayesian test for closure, and documented the ecology, behavior and detectability of this previously unstudied marsh-specialist butterfly. We found evidence that transects in our study system were open to changes in state across the field season, and, consequently, that transect use probability varied considerably by month from 0.35 to 0.84. Latent salt-marsh skipper phenology and transect quality were better predictors of within-flight-period dynamics than marsh area or isolation. This research highlights how variable population dynamics can be within a period of time commonly assumed to be static.

We examined the use of fringing marshes by herons and shorebirds in the southern portion of Chesapeake Bay. From 13 pairs of natural fringing marshes and nearby, constructed living shoreline marshes, we completed analysis of videos recorded at discrete, 30-minute intervals (dawn, dusk, high tide, low tide) throughout the 2018 and 2019 field seasons (May through August). A total of 684 hours of recording yielded 91 individual observations of birds comprising six species. Spotted Sandpipers (Actitis macularius) were observed most frequently (25), but only at living shoreline marshes. Likewise, 15 of 16 observations of Green Herons (Butorides virescens) were at living shoreline marshes. Great Blue Herons (Ardea Herodias; 19), Great Egrets (Ardea alba; 16), and Yellow-crowned Night Herons (Nyctanassa violacea; 14) were observed at both living shoreline and natural fringing marshes, and a single Willet (Tringa semipalmata) was observed at a living shoreline marsh. Bird species richness was significantly higher at living shoreline marshes relative to natural fringing marshes (2.2 ± 0.26 vs 1.0 ± 0.20, respectively; Wilcoxon signed-rank test, V = 45, p = 0.008). Spotted Sandpipers spent significantly more time on average at living shoreline marshes relative to natural fringing marshes (514 s vs 0 s, respectively; V = 36, p = 0.008), as did Green Herons (341 s vs 4 s; V = 36, p = 0.008). We found, however, no difference in time spent between marsh types for Great Blue Herons, Great Egrets or Yellow-crowned Night Herons. From generalized linear modeling, no models that included time of day, time since high tide, year, or marsh type fit the observational data better than the null model for any species. For Spotted Sandpipers, the model including Julian day yielded a better fit with a positive slope, indicating increased use of living shoreline marshes later in the season of observation. The rocky sills placed in front of constructed living shoreline marshes appear to provide refuge and/or foraging habitat for both Spotted Sandpipers and Green Herons. Because use of living shoreline marshes by other heron and egret species was similar to natural fringing marshes, we conclude that living shorelines as coastal management features provide habitat support for herons and shorebirds at least as well as natural fringing marshes.

Located at the interface between uplands and surface water networks, headwater wetlands act as a natural filter to improve downstream water quality and play a critical role in maintaining the ecological integrity of downstream aquatic ecosystems. Vulnerable to development pressure, as well as indirect impacts from land use and climate change, the loss and alteration of headwater wetlands has been linked to the loss of biodiversity and regional water quality declines worldwide. The overall goal of this dissertation is to address some of the challenges associated with the management and conservation of headwater wetlands in the coastal plain of Virginia including: the identification of palustrine forested wetlands in flat coastal landscapes (Chapter II); and improved understanding of the impacts of land use (Chapter III) and climate change (Chapter IV) on the hydrologic regime of headwater wetlands. First, a simple model of wetland distribution was developed by characterizing the depth to groundwater using widely available geospatial data, including surface water features and a high-resolution digital elevation model. Comparison with the National Wetland Inventory (NWI) and targeted field validation indicated that this model provides an effective approach to identify palustrine forested wetlands often unmapped by NWI. Results from this study indicate that there may be at least 37% more wetland area than is currently mapped within the study area; and that in the future, modeling approaches should be used in addition to NWI mapping to better understand the full extent and distribution of wetlands in forested areas. The impacts of land use and climate change were then investigated through field studies of headwater wetland hydrology and community composition. Potential differences in headwater wetland hydrology were evaluated through an index of hydrophytic vegetation occurrence, the wetland prevalence index (PI). Changes in PI between sapling and canopy strata, with respect to local land use, indicated that decreased forest cover was associated with a shift in plant community composition, and that increasing road density was associated with a shift towards more upland type species, while increasing agricultural cover was associated with a shift towards more wetland type species. The effects of climate change, including rising temperatures and altered precipitation patterns were evaluated by developing an empirical model of water table depth for coastal headwater wetlands. Wetland water levels were simulated under current and potential future conditions to evaluate the impact of climate change on the hydrologic regime of headwater wetlands. Based on the model scenarios applied in this study, it appears that decreasing water availability may lead to drier conditions at headwater wetlands by the end of the 21st century, with a substantial decline in minimum water levels and a 3-10% decline in average annual percent saturation. Collectively, the results of this dissertation provide practical insights for improving the conservation and management of coastal headwater wetlands. Improved understanding of the extent and distribution of previously unmapped forested wetlands can improve the capacity to monitor wetland loss and degradation. Additionally, clarifying the influence of land use and climate on the hydrologic regime of these wetlands, can help improve the capacity to forecast and then mitigate potential future impacts to wetland hydrology.

No description available.

Ocean acidification (OA) coupled with other stressors, will be detrimental at the species and ecosystem levels. Decreased carbonate ion concentrations negatively impact calcifying species, yet the combined effects of OA and other stressors are less well known, and many studies disregard species interactions. Multi-species studies involving OA and other stressors are crucial to comprehend the full threat of OA. Understanding how OA interacts with other stressors to affect species responses is necessary for future management of exploited species in an altered ecosystem. The objectives of my study were to assess: 1) the effects of long-term exposure to decreased pH and salinity on juvenile blue crab (Callinectes sapidus) carapace strength and pinch force and juvenile hard clam (Mercenaria mercenaria) armor and growth; and 2) the blue crab and hard clam predator-prey interactions under low pH and salinity via filmed mesocosm trials. In 2018 and 2019, I held juvenile blue crab (n = 24–40; 50–80 mm carapace width) and juvenile hard clams (n = 112; 10–15 mm shell length) in mesocosms with crossed pH and salinity treatments for 10 – 11 weeks. I regularly monitored water quality and chemistry and measured clams weekly. After treatment exposure, I assessed crab carapace and claw strength using force meters and imaged clam shells using a scanning electron microscope (SEM) for shell structure and ridge rugosity. In 2018, crab carapace strength increased with size, decreased with treatment exposure time, and was overall stronger after exposure to low pH. In 2019, crab carapace strength was weakest in the low-pH, high-salinity treatment and strongest in the low-pH, low-salinity treatment. In high-pH treatments, carapace strength was similar regardless of salinity. Claw pinch force also increased with size but was weaker in low-pH, in both 2018 and 2019. Moreover, male crabs in 2019 had stronger pinch force than females. Clam growth was negatively impacted by low pH in both years; however, salinity had a more negative impact in 2019 than in 2018. Clam survival followed a similar trend in both years, with survival being lowest in the low-pH, low-salinity treatment and highest in the control treatment. Deterioration of clam shell structure and ridge rugosity (indicative of damage) were also correlated, as both were greatest in the low-pH, low-salinity treatment and lowest in the control treatment. Finally, in 2019, filmed predator-prey mesocosm trials assessed the interaction between blue crabs and hard clams after treatment exposure. Low sample sizes precluded statistical analyses, but trends indicated there was no alteration in the predator-prey relationship under multiple stressors.