Browsing by Author "Silliman, Brian R"
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Item Open Access A Preliminary Assessment of the Blue Carbon Capacity of Belizean Mangroves with Ecological, Economic, and Policy Perspectives(2015-04-24) Chang, Sylvia; Green, Ashley; Kelley, EmmaIn recent years, mangrove forests have experienced increasing deforestation rates in Belize due to coastal development. Our client, the Belize Ministry of Forestry, Fisheries, and Sustainable Development, wants to determine the potential for Belizean mangrove blue carbon to provide funding opportunities through international financing schemes for the conservation and enhancement of mangroves. Mangrove forests are coastal wetlands along the intertidal zone of tropical and subtropical coastlines. Mangrove, salt marsh, and seagrass ecosystems have significant abilities to sequester and store carbon in their biomass and sediments – the carbon stored in these coastal ecosystems is referred to as “blue carbon.” The impact of mangrove deforestation on carbon sequestration in Belize could be significant, but little is known about how much carbon is stored in Belizean mangroves. The goal of this project was to provide a preliminary assessment of the potential of blue carbon in Belize. This project was broken down into three objectives: ecology, economic, and policy. The goal of the ecology portion of this study was to provide preliminary estimates of the blue carbon stocks of Belize’s mangroves. This required data on the extent of Belizean mangroves, which were obtained from a 2010 study by Emil Cherrington and colleagues, as well from a 2014 update provided by Mr. Cherrington. Using this spatial data, four different approaches were applied to estimate the mangrove blue carbon stocks. The first was a meta-analysis evaluating the pre-existing knowledge of belowground carbon storage in mangrove ecosystems in the Caribbean. This analysis identified a linear relationship between belowground carbon storage and latitude, which was used to estimate that approximately 9.4 Tg are stored in the belowground blue carbon pool in Belize. The Blue Carbon Initiative’s Coastal Blue Carbon guidebook was used to make another estimate and this method suggests that approximately 23.3 Tg of blue carbon are stored in the mangrove forests of Belize. Using physiographic mangrove type-specific estimates from carbon studies in Mexico (Adame et al. 2013), a third estimate approximated that there are 29.6 Tg of blue carbon stored in the mangrove forests of Belize. The large variation between these initial estimates emphasized the need to complete in-country mangrove blue carbon sampling. Thus, a study was undertaken combining aboveground mangrove biomass data from the University of Belize’s Environmental Research Institute and soil carbon data from a field study we completed in August 2014. Although this estimate is limited in scope due to its inclusion of only two of the four blue carbon pools, this methodology suggests that there are 13.0 Tg of blue carbon stored in Belize’s mangroves. The second goal of this study was to conduct a preliminary economic analysis of the value of the blue carbon stocks and identify the factors influencing the feasibility of a blue carbon offsets project. Having an estimate of the economic costs and benefits for a blue carbon offsets program helps show the net economic value of actions to conserve or enhance mangroves. Economic analysis will help show when carbon payments can justify the cost of changing local behavior and determine how might a carbon payments project might compete with alternative land uses in Belize. Using preliminary carbon stock estimates and project criteria estimates, we conducted a case study of a net present value (NPV) analysis to determine the economic feasibility of a blue carbon offsets project for 25% of the mangroves on Turneffe Atoll. Not surprisingly, the analysis shows that a blue carbon offsets project cannot outcompete coastal development on Turneffe when the cost for land acquisition is high. Under the scenario without accounting for land acquisition cost, a carbon price greater than $10 per tCO2e is necessary to generate enough revenue to sustain the blue carbon project. The potential for Belize to enter the blue carbon market depends on three factors: the future risk of mangrove deforestation, price of land acquisition, and success of blue carbon credits. The bundling of blue carbon credits with payments for ecosystem services is a potential avenue worth exploring for future blue carbon projects. The third and final objective was to complete a preliminary assessment of the status of mangroves and mangrove conservation in Belize and policies that could promote a reduction of emissions generated by destruction of vegetation as well as increase blue carbon sequestration. We provide an assessment of the threats to mangroves and discussed issues confronting mangrove conservation in Belize. This is followed by an outline of the relevant laws, policies, agencies, and actors. We then used the Blue Carbon Policy Framework 2.0 (Herr et al. 2012) - a report that outlines options for the assimilation of blue carbon into existing policy initiatives - to identify specific actions Belize can take at the national level to facilitate blue carbon activities. We also discuss potential sources of funding for blue carbon initiatives in Belize, and potential obstacles to implementing blue carbon initiatives. A literature review coupled with interviews with officials from the Government of Belize, researchers from the field, and non-governmental organization representatives served to inform the development of this section of the report. According to the Blue Carbon Initiative, there are three high priority activities national governments should undertake to incorporate blue carbon priorities and activities into climate change mitigation efforts at the national level (Herr and Pidgeon 2012). These activities include: (1) “development of national blue carbon action plans, outlining specific national circumstances, opportunities, needs and limits;” (2) “conducting national scientific carbon, ecological and socio-economic assessments of shallow coastal marine ecosystems;” and (3) “conducting national cost-benefit analysis of including blue carbon activities into national climate change mitigation strategies” (Herr and Pidgeon 2012). In addition to these three high priority activities, the Blue Carbon Initiative brief (Herr and Pidgeon 2012) also describes additional measures developing countries should undertake to ensure mitigation activities at the national level effectively incorporate blue carbon activities. This report identifies specific actions from that brief that are applicable for Belize and provides additional actions we recommend based on our analysis.Item Open Access A Systematic Review of Facilitation in Intertidal Habitats(2021-04-30) Townsend, SamanthaRecent decades have seen an increase in research on positive species interactions, and it is now known that they are ubiquitous in nature. However, these interactions were never intentionally used in beneficial ways. This changed in 2015 when a study revealed that positive species interactions could aid in salt marsh restoration. Since then, the restoration paradigm has shifted from systematically suppressing negative interactions to harnessing nature’s positive interactions, including ecological facilitation. This review investigates the facilitative interactions that have been observed in intertidal habitats, including salt marshes, mangroves, and oyster reefs. I performed a systematic review to highlight the general trends and research gaps in the study of facilitation across these three intertidal habitats. Seventy-eight studies were included in the database, and the earliest study was published in 1984 in a salt marsh. Since then, studies have increased exponentially. The majority were located in mid-latitudes but were spread across six continents and 18 countries. The 78 studies revealed 212 unique, facilitative interactions. One hundred and thirty-two of these interactions were in salt marshes, 77 were in mangroves, and only 3 were in oyster reefs. The majority of interactions involved autotrophs and lower trophic level species. In addition, the majority of facilitative interactions were direct, interspecific, non-trophic, and involved a primary foundation species. The 78 papers in this database revealed some previously unknown trends in intertidal facilitation which can actively be incorporated into restoration projects. However, this study also revealed the major research gaps in the field that need to be filled in order to more thoroughly establish facilitative theory and most effectively include facilitation in intertidal restoration design.Item Open Access An Analysis of Material Use in Living Shorelines(2024-04-25) Exar, LauraCoastal areas are increasingly affected by anthropogenic climate change through aspects such as flooding and storm surge. Historically, hard structural enforcements like seawalls and bulkheads have been utilized to mitigate these hazards, however, these additions are associated with adverse effects, including increased wave energy, erosion to adjacent properties, and maintenance costs. As an alternative to hard structures, nature-based solutions, such as living shorelines, are now being utilized due to their combined coastal protection and biodiversity benefits. Recent literature has highlighted the knowledge gaps surrounding living shoreline design and material use. Here, we utilize a literature review and field experiment to understand material use in living shorelines and how structural heterogeneity can influence species abundance. The literature review results reveal geographic and temporal trends in the materials utilized. Field results show that increasing the surface heterogeneity of artificial structures resulted in increased oyster abundance. These results are crucial for understanding the most appropriate and efficient designs and materials to further living shoreline implementation.Item Open Access Art as a Pathway to Scientific Awareness and Action: Leveraging Art to Communicate Science and Engage Local Communities for the National Estuarine Research Reserve System(2019-04-24) Horton, SavannahScientists are aware of the need to effectively communicate their research to the public, decision-makers, and funders in new and creative ways. Additionally, an ever-growing number of artists are addressing environmental issues, and funders are beginning to see this work as relevant. This is leading to the increase of interdisciplinary collaborations between the arts and sciences. NOAA’s National Estuarine Research Reserve System (NERRS) attempts to address environmental concerns and protect estuaries by partnering with 29 coastal states to monitor estuary health and manage coastal resources. To accomplish their goal of encouraging stewardship of estuaries in local communities, the NERRS is seeking new ways to communicate monitoring data, and the threats that face these crucial ecosystems. NOAA’s Office for Coastal Management and the National Estuarine Research Reserve Association (NERRA) have expressed interest in expanding art-science collaborations nationally. Using a literature and case study review, informational interviews, and a survey, this project built upon existing programs within the NERRS to support transitioning the initiative to a national level, with the hope that research and data can become more accessible and relatable to communities throughout the nation. The information included in this report and the client deliverable sought to answer four research questions: 1) what are the benefits and challenges of using art to communicate science?, 2) can art help different learning styles comprehend and retain scientific data and concepts?, 3) what practices have been used to successfully complete art and science collaboratives?, and 4) where and why has the NERRS used art to communicate science in the past? We found that funding does not have strong institutional support, and further research and assessment is needed in order to further art-science collaborations’ impact. However, art-science collaborations can play an important role in increasing stewardship. Therefore, expanding upon art-science collaborations in the NERRS to nationally leverage art could help increase stewardship and engagement among communities. Reserve scientists are extremely interested in participating in art-science collaborations, and in creating an artist-in-residence program at Research Reserves. With increased national support, art-science collaborations could make a significant impact on stewardship and engagement within reserve communities.Item Open Access Climate drives the geography of marine consumption by changing predator communities.(Proceedings of the National Academy of Sciences of the United States of America, 2020-11) Whalen, Matthew A; Whippo, Ross DB; Stachowicz, John J; York, Paul H; Aiello, Erin; Alcoverro, Teresa; Altieri, Andrew H; Benedetti-Cecchi, Lisandro; Bertolini, Camilla; Bresch, Midoli; Bulleri, Fabio; Carnell, Paul E; Cimon, Stéphanie; Connolly, Rod M; Cusson, Mathieu; Diskin, Meredith S; D’Souza, Elrika; Flores, Augusto AV; Fodrie, F Joel; Galloway, Aaron WE; Gaskins, Leo C; Graham, Olivia J; Hanley, Torrance C; Henderson, Christopher J; Hereu, Clara M; Hessing-Lewis, Margot; Hovel, Kevin A; Hughes, Brent B; Hughes, A Randall; Hultgren, Kristin M; Jänes, Holger; Janiak, Dean S; Johnston, Lane N; Jorgensen, Pablo; Kelaher, Brendan P; Kruschel, Claudia; Lanham, Brendan S; Lee, Kun-Seop; Lefcheck, Jonathan S; Lozano-Álvarez, Enrique; Macreadie, Peter I; Monteith, Zachary L; O’Connor, Nessa E; Olds, Andrew D; O’Leary, Jennifer K; Patrick, Christopher J; Pino, Oscar; Poore, Alistair GB; Rasheed, Michael A; Raymond, Wendel W; Reiss, Katrin; Rhoades, O Kennedy; Robinson, Max T; Ross, Paige G; Rossi, Francesca; Schlacher, Thomas A; Seemann, Janina; Silliman, Brian R; Smee, Delbert L; Thiel, Martin; Unsworth, Richard KF; van Tussenbroek, Brigitta I; Vergés, Adriana; Yeager, Mallarie E; Yednock, Bree K; Ziegler, Shelby L; Duffy, J EmmettThe global distribution of primary production and consumption by humans (fisheries) is well-documented, but we have no map linking the central ecological process of consumption within food webs to temperature and other ecological drivers. Using standardized assays that span 105° of latitude on four continents, we show that rates of bait consumption by generalist predators in shallow marine ecosystems are tightly linked to both temperature and the composition of consumer assemblages. Unexpectedly, rates of consumption peaked at midlatitudes (25 to 35°) in both Northern and Southern Hemispheres across both seagrass and unvegetated sediment habitats. This pattern contrasts with terrestrial systems, where biotic interactions reportedly weaken away from the equator, but it parallels an emerging pattern of a subtropical peak in marine biodiversity. The higher consumption at midlatitudes was closely related to the type of consumers present, which explained rates of consumption better than consumer density, biomass, species diversity, or habitat. Indeed, the apparent effect of temperature on consumption was mostly driven by temperature-associated turnover in consumer community composition. Our findings reinforce the key influence of climate warming on altered species composition and highlight its implications for the functioning of Earth's ecosystems.Item Open Access Coral-associated Crabs and Macroalgae Alter Disease Spread in Branching Corals on the Great Barrier Reef(2020) Renzi, Julianna JollyDisease is an important driver of coral loss regionally and is projected to become more severe as temperatures increase around the world. Although there has been substantial research into the abiotic factors (e.g. temperature, nutrients) controlling coral diseases, we know significantly less about the biotic factors (i.e. species interactions) influencing disease dynamics. We examined how the species living on and within corals affect coral tissue loss from a white syndrome-like condition on Heron Island in the southern section of the Great Barrier Reef. We exposed Acropora aspera fragments in flow-through tanks to a fully crossed factorial experiment with three factors: the presence of a common symbiotic crab (Cyclodius ungulatus), contact with a common macroalgal complex, and simulated wounding mimicking fish predation. We found that crab presence increased coral survival from a white syndrome-type disease by over 25%, likely by removing macroalgae if present and by cleaning infected tissue. Conversely, contact with macroalgae dramatically increased coral mortality, with the chance of survival dropping to nearly 0 by the end of 25 days for corals that were in contact with algae. Wounding had no direct effect on coral health, but wounded corals with crabs did significantly better than corals with no wounding and crabs, which may be the result of coral-crab signaling. We suggest that A. aspera may produce nutrient-rich mucus when wounded, which attracts crab symbionts that help slow disease progression. These results suggest that incorporating biotic interactions into restoration designs may dramatically improve restoration outcomes and that adding beneficial symbionts may improve disease resilience at a local level.
Item Open Access Creating a Toolkit for Implementing Blue Carbon Projects(2016-04-28) He, Xie; Hernandez, Connie; Lamb, Emily; Gutierrez Sepulveda, Tatiana; Schwaner, CarolineBlue Carbon is a relatively new term, used to refer to the biological processes by which carbon is stored in coastal ecosystems. There has been a rapid expansion of the literature about blue carbon, particularly as it relates to climate change mitigation activities. The experience of initial blue carbon projects highlighted the need for a centralized source of information. In response our client, LabEX Mer, asked our group to create a toolkit that would be readily accessible to project managers with a broad array of institutional capacities. The toolkit aims to help project managers sort through the available information quickly and effectively. We chose to use an open-source Google Drive as the platform for our toolkit. Our decisions were informed by the work of two of our team members who travelled to Ecuador to conduct fieldwork and input from our client. Summary analyses about blue carbon policy and markets were also created.Item Open Access Determining Living Shoreline Distribution in North Carolina: A Mixed Methods Study(2023-04-28) Lienhard, Kathryn; Fairbairn, NicholasCoastal landowners in North Carolina have traditionally deployed hardened structures like seawalls and bulkheads to protect coastal development from erosion and inundation. However, living shorelines have emerged in recent decades as a more ecologically integrated solution, incorporating natural and human-made components to address erosion. To date, few studies have used geospatial tools to understand the deterministic factors driving the distribution of living shorelines in North Carolina. We consider how the distribution of living shorelines varies with a community’s socioeconomic demographics, proximity to enabling institutions, and vulnerability to coastal inundation. We explore the barriers that homeowners face in acquiring a living shoreline and the perceptions that inform their decisions. Using a mixed methods approach, our study uses geospatial tools, decision-tree analysis, and semi-structured interviews with coastal landowners to distill the primary determinants governing the distribution of living shorelines across North Carolina’s coast. We find that among coastal census tracts in North Carolina, the distribution of living shorelines has a significant negative correlation with the percent of the population living in poverty, suggesting that income constrains implementation of these projects. In contrast, vulnerability to coastal inundation and proximity to enabling institutions are not predictive of living shoreline distribution. Interviews elucidate that access to information and relevant networks, capacity to navigate the installation process, and ability to pay informed many homeowners’ decisions to install a living shoreline. Taken together, our findings shed light on the need to consider equity and vulnerability in shoreline protection and coastal restoration.Item Unknown Development and Land Use Impacts on Marine Ecosystems in the United States Virgin Islands (USVI)(2017-04-25) Rohrs, SuzanneAnthropogenic and natural stressors have long been a source of concern as they relate to water quality and marine ecosystem health, particularly in the United States Virgin Islands (USVI). Although many studies have been conducted in the USVI on factors influencing near-shore ecosystems, most are concentrated on just one or two inputs leaving data gaps. By conducting a meta-analysis of available long-term data produced by different organizations in ArcGIS, correlations between the following factors were observed: 1) land use 2) development 3) water quality and 4) coral health. In areas with a high percentage of land development, lower water quality and reduced live coral cover were observed at corresponding time scales. The results indicate the importance of linking multiple parameters to overall ecosystem health in order to develop focused management strategies to protect fragile near-shore environments.Item Unknown Early recovery of river herring spawning habitat use in response to a large-scale dam removal(2022-04-22) Huang, ClaireHistorical loss of river and stream habitats due to impassable dams has contributed to the severe decline of many fish species. Anadromous fishes that migrate from the sea to freshwater streams to spawn have been especially impacted as dams restrict these fish from accessing essential spawning habitats. In 2018, Bloede Dam was removed from the Patapsco River near Baltimore, Maryland, restoring approximately 100 km (60 mi) of potential river and tributary habitat for migratory fish. This study assessed the response of anadromous river herring, alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis), to this dam removal by monitoring environmental DNA (eDNA), ichthyoplankton, and passive integrated transponder (PIT) tags from 2015 to 2021 at locations upstream and downstream of the dam site during the river herring spawning migrations. Findings show early recovery of habitat use by river herring beyond the dam site within 3 years of the removal, including species-specific differences in relative abundance and upstream migration. No adult river herring, eDNA, or eggs were detected upstream of Bloede Dam prior to its removal. Post-removal, blueback herring exhibited the strongest response with DNA detected at two sites upstream of Daniels Dam, a remaining manmade waterfall. Although eDNA presence in restored habitat increased, there was no evidence of increased egg abundance upstream or downstream of the former dam site and no tagged fish were detected upstream of the dam site post-removal. While further monitoring is needed to determine a population-level response to the removal of the Bloede Dam, applying multiple monitoring methods provided a comprehensive picture of habitat use recovery by spawning river herring. These results will be key in informing future dam removal priorities for anadromous fish conservation in the Chesapeake Bay.Item Unknown Effects of Oyster Castle reefs on shoreline erosion and sediment composition(2022-04-20) Rebellon, JuanDeclines in wild oyster populations and the growing need to protect coastal communities have led to the creation of novel reef substrates for use in oyster reef restoration. However, innovations in alternative substrates have outpaced scientific research quantifying their efficacy, leaving managers without the information needed for widespread adoption. To assess the effects of Oyster Castles, a concrete-based oyster restoration structure, on rates of horizontal and vertical shoreline erosion and sediment composition, we constructed replicate reefs just offshore of a medium-energy eroding salt marsh shoreline in North Carolina. We monitored vertical accretion of sediments and sediment composition behind reefs versus control shorelines and also measured rates of horizontal shoreline change over a two-year period. Our results show that reef and control sites did not differ significantly in terms of vertical sediment accretion, horizontal shoreline change, or sediment composition. The lack of differences between our reef and control sites may be due to our reef design choices or to the short study period. To fill the data-gap marine managers face when choosing reef designs, we recommend monitoring restoration sites over longer timeframes (> 5 years) and assessing efficacy differences between reef designs and spatial scales.Item Unknown Evidence Mapping: Investigating the Social and Ecological Impacts of Conservation in Mangrove Ecosystems(2019-04-26) Brooks, Willa; Manz, Amy; Woolston, ColyerThe global extent of mangrove forests has been rapidly declining in recent decades, raising concerns about the loss of the ecological and social services they provide. There is an increasing urgency to understand best approaches to conserve mangrove forests given their decline. This project seeks to identify literature that addresses the question: What is the extent and occurrence of evidence for ecological and social impacts of conservation interventions within mangrove ecosystems? Following systematic mapping standards, we develop and apply a search strategy to identify relevant literature that evaluates the impacts of conservation in mangrove forests. Our research culminates in a structured matrix, organizing our findings by interventions and outcomes of interest. We find that of the 39 included studies, the majority of the evidence base examined linkages between conservation interventions and ecological outcomes, with a noticeable dearth in studies evaluating social outcomes; specifically, awareness raising, and education and training outcomes. We conclude with recommendations for how to use our systematic map geared towards conservation researchers, policy makers, and practitioners.Item Unknown From Wastelands to Wetlands: The Story of Coastal Wetlands in the United States(2023-04-26) Kendall, MarianaCovering about 40 million acres of the United States, coastal wetlands are incredibly important ecosystems for humans and non-humans alike. Each year, coastal wetlands provide significant benefits due to their ability to protect coastlines from storm damage, sequester large amounts of carbon, and provide habitat for ecologically and economically valuable wildlife. Unfortunately, coastal wetlands are being lost at a rate of 80,000 acres per year, equivalent to 7 football fields lost per hour. This loss is largely driven by human development and related activities, as well as the effects of climate change and sea level rise. This project seeks to answer the question of how we got to this point of loss by discussing the ways humans have used coastal wetlands in the Eastern and Gulf Coasts of the United States throughout history, as well as analyzing the way entertainment media’s negative portrayal of wetlands has helped to form a negative association with wetlands in the eyes of the public.Item Unknown Incorporation of Species Interactions in Seagrass Conservation and Restoration(2019) Zhang, Yin San StacyCoastal ecosystems and the valuable services they provide have and continue to be degraded by anthropogenic stressors across the globe. Conservation efforts to mitigate deleterious impacts have largely failed at aiding ecosystem recovery such that restoration has become a predominant method of stemming the loss of critical habitats and the communities they support. Globally, it is estimated that 29% of seagrass beds have been lost or converted, and this translates to trillions of dollars lost in ecosystem services as well as commercial and recreational prospects. In this dissertation, I evaluate how ecological interactions can alter restoration trajectories and shift community dynamics. Namely, I focus on facilitative and trophic interactions among seagrasses, bivalves, and the associated nekton and mesograzer communities propagate through seagrass ecosystems. To do this, I use a combination of scientific literature review, surveys, and manipulative field experiments to apply ecological theories of species interactions in seagrass restoration and conservation. Reviews of the coastal restoration research reveal a paucity of studies that consider biological interactions as important factors that may determine restoration success (Chapter 1). Because foundation species, such as seagrasses, can promote the success and survival of numerous other organisms through facilitation, I further tested if and how a facilitation cascade among seagrass beds and pen clams, Atrina rigida, may affect local diversity and ecosystem functions (Chapter 2). Since studies have, in fact, shown that positive interactions can also enhance restoration of coastal foundation species, I investigated in how the inclusion of intra- and interspecific interactions can affect seagrass restoration from seed and adult shoots. Finally, given that top-down influences can also affect bivalve abundances and seagrass productivity, I explored how large predator removals (via exclusion stockades) may shift seagrass community structure and propagate onto primary producers.
In these studies, I find that facilitative interactions can promote not only the success and yield of bivalve populations, but that in some instances, bivalves can also, in turn, facilitate the growth of seagrasses. Similarly, alteration to diversity at higher trophic levels can have positive top-down impacts on bivalve abundances despite alterations to mesopredator abundances. Whereas biological interactions have historically been ignored in the restoration literature, my dissertation research makes the argument that consideration and incorporation of species interactions is necessary for understanding the ecology that underlies the stability, recovery, and resilience of coastal ecosystems.
Item Unknown Megafauna Utilization of and Impact on Salt Marshes(2024) Gaskins, Leo ChanMegafauna (>45kg) are known to inhabit and reshape freshwater, terrestrial, and marine systems throughout the globe through consumptive and engineering pathways. Following long-term conservation, large consumers have expanded and recolonized regions thought to be beyond their niche space. By re-entering these systems, these large consumers may restructure these new habitats. The goal of this dissertation research was to document what megafauna use salt marshes and examine the effects of megafauna recolonization of salt marshes. We first conducted a literature review and found that a variety of megafauna utilize salt marshes, a total of 34 species including sharks, manatees, pinnipeds, crocodilians, sea otters, hippos, and large terrestrial animals, such as lions, bears and water buffalo. Next, we examined the impacts of 2 species of megafauna that recolonized salt marshes in Elkhorn Slough using observational and experimental studies. We conducted a control-impact study to understand the potential effects of harbor seals (Phoca vitulina) hauling out of the water on the structure of salt marsh edges. We found that sites with harbor seal haul outs had significantly more compressed soil, that the foundation plant species were heavily denuded, and that animal diversity shifted strongly - burrowing crabs were almost eliminated entirely from the edges of marshes, while birds congregated in high number. Erosion is a pressing issue in Elkhorn Slough at 0.5 m/yr, and despite the vast differences in regions with seal haul outs and denuded surface, we found no increase in erosion rate, likely due to compensatory effects of an intact root system, lack of crab burrows, and highly compressed sediment. These findings suggest that harbor seals act as ecosystem engineers in salt marshes by hauling out onto marsh platforms and generating large disturbances. Though megafauna can reshape systems and potentially drive erosion, they are not the only major drivers within estuarine systems – eutrophication is another major factor that reshapes salt marshes and is known to cause erosion. Recent studies showed that sea otters (Enhydra lutris) consume root-eating marsh crabs and through this trophic cascade, lower edge erosion rates. Using a factorial experimental design (sea otter presence x nutrient addition) at the edge of the creek banks, we examined the relative impact of otters and fertilization on erosion rates. We did not detect differences in marsh erosion rates or crab burrows or activity from otters or fertilization but did find effects of both main factors on plant communities. These findings do not match previous studies that show significant effects of both otters and eutrophication on erosion rates, but this mismatch likely stems from the interaction of differences in duration, scale, and erosion rates that vary greatly along creek banks. Taken together, this work highlights the importance of studying the impacts of megafauna on salt marshes, and variability in their effects.
Item Open Access Non-Genetic Littoraria Fitness: How Size, Environment, and Health Affect Survivorship of Predator Interactions(2022-05) Murphy, ThomasMarsh periwinkles (Littoraria irrorata) have many predators. When they encounter one, traits of both the periwinkle and its environment should contribute to whether or not it escapes. A better understanding of how these interactions are affected could provide greater insight into how changing habitats will affect ecosystem dynamics in Atlantic salt marshes. By counting the scars from such interactions on periwinkles hand-collected from several sites in salt marshes near Beaufort, NC, the effect of the environment (i.e. density and height of vegetation, distance from ocean access) and the periwinkle’s own non-genetic characteristics (i.e. size/age) on survivorship were determined. Using Single and Multiple Linear Regression analyses, no correlation between these features and the rate of scarring was determined.Item Open Access Northward Expansion of Bopyrid Isopod Parasites in Daggerblade Grass Shrimp in Cape Cod, MA(2022-04-21) Wilczek, ElizaThe daggerblade grass shrimp, Palaemonetes pugio, is among the most abundant species of shrimp inhabiting estuaries along the East Coast and the Gulf of Mexico. They play an important trophic role as epiphyte grazers, detritivores, and prey for many commercially and ecologically important species. Due to the vital role they play in these estuarine environments, any change in their population has the potential to alter community composition and disrupt ecosystem functioning. Grass shrimp are also the definitive host of bopyrid isopod Probopyrus pandalicola, an ectoparasite that decreases energy availability and prevents reproduction by sexually sterilizing its female host, potentially decreasing shrimp populations. The bopyrid isopod has been reported in grass shrimp in the Southeastern U.S at rates ranging from .001% to 5.7% but has not been documented north of Maryland. This project documents the prevalence of P. pandalicola parasitized P. pugio in Cape Cod, Massachusetts after receiving personal observations of bopyrid isopods parasitizing grass shrimp at Long Pasture Wildlife Sanctuary in 2019. Findings in this study indicate a northward expansion of P. pandalicola in a novel host population of P. pugio at rates higher than previously reported in the literature. Based on this research, we are working on establishing a long-term monitoring program with Long Pasture Wildlife Pasture to manage this population of bopyrid isopods.Item Open Access Operationalizing the Duke Restore Seagrass Farm(2023-04-25) Domeyer, DevinI lent support for 18 months as a volunteer project manager to support the Duke Restore Seagrass Farm’s goal of operationalizing a hub for seagrass restoration. This work entailed geospatial analysis for potential farm sites, grant writing, permit acquisition, volunteer management, and relationship building with local community groups and landowners. Using my GIS site suitability analyses, we found fifteen potential locations for the Seagrass Farm in Carteret County, North Carolina and planted 0.3 acres for preliminary research.Item Open Access Relationships Between Vernal Pool Reptile and Amphibian Species Composition and Spotted Salamander (Ambystoma maculatum) Egg Mass Density in the North Carolina Piedmont(2023-04-25) Fajardo, MarisaSpotted salamanders (Ambystoma maculatum) are essential indicators of vernal pool health, yet little research has identified the effects of interspecies interactions on spotted salamander oviposition. In this study, I evaluated the relationships between vernal pool reptile and amphibian species composition and spotted salamander egg mass density within Durham and Orange County. I observed significantly higher egg mass densities in pools with more Salamandrid, Viperid, and Scincid species despite threats of predation. High egg mass densities were also correlated with the presence of early breeding spotted salamanders and more acidic pH levels. Results suggest that spotted salamanders select breeding sites based on environmental conditions, rather than in avoidance of predation or resource competition. These findings are likely influenced by scarcity of optimal breeding habitat within the study area due to history of urbanization and agricultural land use.Item Open Access The Effects of Parasites on Coastal Marsh Ecosystem Structure and Functioning(2021) Morton, Joseph PhilipRecent experiments and comparative surveys in Southern US salt marshes revealed that a common larval trematode parasite, Parorchis acanthus, generated a trophic cascade that protected foundational marsh plants (Spartina alterniflora) from drought-associated overgrazing by suppressing the per capita grazing impacts of its host, the marsh periwinkle (Littoraria irrorata). While it is clear that parasites can play a positive role in mediating marsh ecosystem response to disturbance, there is still little known about the context dependency of this interaction, the role of definitive avian hosts in regulating parasite prevalence, and whether other commonly-occurring parasites may also modify processes that underpin ecosystem stability. The purpose of this project was to extend the current understanding of the roles played by parasites and their hosts in mediating marsh ecosystem stability. A field manipulation of Littoraria density in which infection prevalence with Parorchis acanthus was held at a constant value revealed that these parasites yielded positive impacts on Spartina aboveground biomass at middling densities of snails, but the positive effects of parasites were negligible at both low, and high snail densities. Surveys of drought-impacted marshes revealed that birds – the definitive hosts for trematode that infect Littoraria – congregated within die-off areas and that increased bird usage of die-off areas was associated with increased trematode parasitism in snails within grazer fronts, decreased per capita grazing rates of snails, and proportionate decreases in ecosystem die-off rate. Multi-site bird exclusion and mechanistic field studies experimentally confirmed that birds increased ecosystem resistance to drought-driven die-off by acting as the dispersive vectors for parasites that suppress Littoraria grazing. Finally, we explored how the trematode Cercaria opaca in ribbed mussels (Geukensia demissa) influenced the facultative mutualism between Guekensia and Spartina – an interaction that underlies marsh ecosystem resilience to drought-associated die-off. A field manipulation using experimentally infected mussels revealed that mutualistic benefits to Spartina decreased with increasing infection intensity in mussels. Subsequent mechanistic experiments demonstrated that increasing infection with C. opaca decreased mussel biodeposit production, the functional trait underlying mutualistic benefits to Spartina. Additionally, increasing parasite load was associated with decreased strength of both shells and byssal attachments, potentially explaining the relatively higher predation on heavily infected mussels in our field study. A survey of five North Carolina salt marshes revealed that infection intensity in mussels increased with proximity to die-off areas, indicating that C. opaca could influence marsh recovery following die-off events. Taken together, these results underscore the importance of parasitism’s influence on Southern salt marsh ecosystem stability and more generally show that parasites can be major arbiters of community structure and functioning.