Investigating the Role of Dune Grasses, Carbon Storage, and Marine Nutrient Subsidies to the Functions and Services of U.S. Central Atlantic Coastal Dune Ecosystems

Sandy beaches and dunes cover approximately one-third of the world’s ice-free coastlines and provide ecosystem services including coastal protection, recreation, wildlife habitat, and carbon sequestration. These dynamic interface habitats are variably shaped by wind, waves, sedimentary processes, and vegetation feedbacks. Positive biophysical feedbacks lead to the formation of vegetated coastal dunes when wind-blown sand is captured by burial-tolerant vegetation such as dune grasses. By promoting sand capture and stabilization over time, dune grasses help shape foredunes and protect coastlines from wave overtopping and inundation. Moreover, foredunes store carbon both in the vegetation and in the foredune sand itself, serving as a potentially important ecosystem in mitigating rising levels of greenhouse gases. Thus, it is integral to understand the contribution of dunes to important coastal ecosystem functions and services. In this dissertation, I investigate the role of dune grasses in shaping barrier island foredunes and their ecosystem services along the U.S. Atlantic Coast. The North Carolina Outer Banks is a sandy barrier island system with alongshore variability in its beach and foredune geomorphology, vegetation composition and density, sand supply, and oceanographic conditions. These barrier islands are also particularly vulnerable to coastal erosion due to their low elevation and exposure to sea level rise and extreme storm events. Furthermore, the ranges of two native dune grass species, Uniola paniculata and Ammophila breviligulata, overlap in this region. Due to differences in their functional morphology, growth density, physiology, and sand accretion properties, these grasses are thought to have species-specific effects on foredune morphology. Although studies have documented the importance of dune grasses to dune building processes in this region, less is known about the factors that control dune grass productivity and the role of dune grasses in shaping foredune morphology and ecosystem services including carbon storage. Here I use a combination of observational surveys, laboratory analyses, and statistical models to examine the physical and ecological feedbacks in foredunes to better understand the factors important to foredune morphology, carbon storage, and dune grass productivity along the North Carolina Outer Banks. In Chapter 2, I explore the interactive effects of sand supply, beach geomorphology, and vegetation on foredune morphology. Specifically, I ask: 1) What is the relative contribution of shoreline change rate, beach morphology, and dune grass density and species identity in shaping foredune morphology over space and time? and 2) Do the dune grass species A. breviligulata and U. paniculata affect foredune morphology in species-specific ways, and if so, how? I found that beach morphometrics and sand supply to the beach (i.e., shoreline change rate, beach width, and backshore slope) were the most important factors (72-90% of explained variance) influencing foredune morphology, particularly height and width, while grass density explained a smaller proportion of the variance (10-28%). However, grass density metrics were more important when changes in foredune morphology were considered (36-50% of explained variance). In particular, I found that an increase in A. breviligulata density was associated with an increase in foredune width and a decrease in foredune height, corroborating previous findings that the more lateral growth form of A. breviligulata, compared to that of U. paniculata, has species-specific effects on foredune morphology. In Chapter 3, I measure carbon storage in dune grasses and sand in North Carolina Outer Banks foredune ecosystems and examine the role of beach geomorphology and sand deposition in shaping variability in carbon stocks. In doing so, I ask: 1) How much carbon is stored in Outer Banks foredunes and how does carbon storage vary by carbon stock type, island, foredune profile location, and dominant dune grass species? 2) Does carbon storage in these foredunes decrease with depth, and are changes in sand carbon with depth related to changes in dune grass carbon? and 3) If carbon storage varies spatially, what geomorphological and ecological factors best explain this variability across the study region? I found that aboveground grass carbon stocks (0.004-0.19 kg C/m2) were comparable to those in eelgrass beds and salt marshes (0.03-2.30 kg C/m2) on a per area basis, while sediment organic carbon values in our study system (0.9 0.6 kg C/m3) were significantly lower compared to previous measurements in other dunes (2.2 kg C/m3 in Italian dunes and up to 4.7 kg C/m3 in U.K. dunes) and other coastal ecosystems (averaging 10 and 28 kg C/m3 in salt marshes and mangroves, respectively). Carbon storage in Outer Banks foredunes varied between aboveground grass (0.1 0.1 kg C/m2), belowground grass (1.1 1.6 kg C/m3), and sand (0.9 0.6 kg C/m3) carbon stocks, with the largest proportion contained in the belowground grass. Belowground and aboveground carbon stocks varied at both regional (island) and local (foredune profile locations) scales, with values generally increasing from north to south along the Outer Banks coast and in the landward direction along the foredune profile. I found that variability in sand carbon density was related to patterns in dune sand deposition, beach slope, and grass density, with the relative importance of these factors varying between islands and dune profile locations. Islands with high sand deposition and high grass density tended to have low sand carbon density, while profile locations with lower sand deposition and higher grass density tended to have high sand carbon density, suggesting that self-reinforcing feedbacks between vegetation and sediment determine sand carbon values in these foredunes. In Chapter 4, I examine whether dune grass production and foliar nitrogen content vary at regional and local scales as a result of marine subsidies, sand nitrate concentrations, and proxies for sand supply to the foredune (i.e., beach and foredune morphology). Specifically, I ask: 1) Do macrophyte wrack biomass and composition, sand nitrate concentration, and dune grass production vary at local and regional scales? Do dune grasses utilize marine derived nitrogen (δ15N) and, if so, how does δ15N and %N vary across species, foredune profile locations, and islands? and 3) What factors, including macrophyte wrack biomass, sand nitrate, and sand supply metrics, are important to dune grass production and foliar nitrogen metrics? I found that proxies for sand supply and marine subsidies both influence dune grass production and that dune grasses growing on the seaward portion of foredunes utilize marine nutrients. Specifically, dune grass production and foliar %N were higher in areas with greater sand nitrate concentration, taller foredunes, and eroding beaches. Dune grasses growing at the foredune toe had greater δ15N in their tissues compared to those growing at the foredune crest and heel, and δ15N levels increased with foredune height and sand supply. Taken together, these findings suggest that differences in sand nitrate concentrations with latitude, along with beach and foredune sand supply metrics, mediate the delivery of marine subsidies to foredune vegetation and thus dune grass production. The results of this dissertation provide insights into the complex dynamics that shape coastal barrier island foredunes and their ecosystem services. By quantifying the role of dune grasses, carbon storage, and marine nutrient subsidies to the ecosystem functions and services of U.S. Central Atlantic coastal dunes, we can better manage this vulnerable ecosystem given anticipated shifts in dune grass distributions, sea level rise, and extreme storms as a result of climate change

Comparative Dynamics of Retrograde Actin Flow and Focal Adhesions: Formation of Nascent Adhesions Triggers Transition from Fast to Slow Flow

Dynamic actin network at the leading edge of the cell is linked to the extracellular matrix through focal adhesions (FAs), and at the same time it undergoes retrograde flow with different dynamics in two distinct zones: the lamellipodium (peripheral zone of fast flow), and the lamellum (zone of slow flow located between the lamellipodium and the cell body). Cell migration involves expansion of both the lamellipodium and the lamellum, as well as formation of new FAs, but it is largely unknown how the position of the boundary between the two flow zones is defined, and how FAs and actin flow mutually influence each other. We investigated dynamic relationship between focal adhesions and the boundary between the two flow zones in spreading cells. Nascent FAs first appeared in the lamellipodium. Within seconds after the formation of new FAs, the rate of actin flow decreased locally, and the lamellipodium/lamellum boundary advanced towards the new FAs. Blocking fast actin flow with cytochalasin D resulted in rapid dissolution of nascent FAs. In the absence of FAs (spreading on poly-L-lysine-coated surfaces) retrograde flow was uniform and the velocity transition was not observed. We conclude that formation of FAs depends on actin dynamics, and in its turn, affects the dynamics of actin flow by triggering transition from fast to slow flow. Extension of the cell edge thus proceeds through a cycle of lamellipodium protrusion, formation of new FAs, advance of the lamellum, and protrusion of the lamellipodium from the new base

A dated molecular phylogeny of mite harvestmen (Arachnida: Opiliones: Cyphophthalmi) elucidates ancient diversification dynamics in the Australian Wet Tropics

Austropurcellia, a genus of dispersal-limited arachnids endemic to isolated patches of coastal rainforest in Queensland, Australia, has a remarkable biogeographic history. The genus is a member of the family Pettalidae, which has a classical temperate Gondwanan distribution; previous work has suggested that Austropurcellia is an ancient lineage, with an origin that predates Gondwanan rifting. Subsequently, this lineage has persisted through major climatic fluctuations, such as major aridification during the Miocene and contraction and fragmentation of forest habitats during the Last Glacial Maximum (LGM). In order to understand Austropurcellia's evolutionary and biogeographic history, we generated DNA sequences from both mitochondrial and nuclear loci and combined this information with previously published datasets for the globally-distributed suborder Cyphophthalmi (i.e., all mite harvestmen). We generated phylogenetic trees using maximum likelihood and Bayesian approaches to date divergences using a relaxed molecular clock. According to our estimates, the family Pettalidae diversified in the late Jurassic, in accordance with Gondwanan vicariance. Within Pettalidae, Austropurcellia split from its sister group in the early Cretaceous and began to diversify some 15 Ma later. Therefore, its presence in Australia predates continental rifting-making it one of very few hypothesized examples of Gondwanan vicariance that have withstood rigorous testing. We found a steady rate of diversification within the genus, with no evidence for a shift in rate associated with Miocene aridification. Ages of splits between species predate the Pleistocene, consistent with a "museum" model in which forest refugia acted to preserve existing lineages rather than drive speciation within the group

Species-Specific Functional Morphology of Four US Atlantic Coast Dune Grasses: Biogeographic Implications for Dune Shape and Coastal Protection

Coastal dunes arise from feedbacks between vegetation and sediment supply. Species-specific differences in plant functional morphology affect sand capture and dune shape. In this study, we build on research showing a relationship between dune grass species and dune geomorphology on the US central Atlantic Coast. This study seeks to determine the ways in which four co-occurring dune grass species (Ammophila breviligulata, Panicum amarum, Spartina patens, Uniola paniculata) differ in their functional morphology and sand accretion. We surveyed the biogeography, functional morphology, and associated change in sand elevation of the four dune grass species along a 320-kilometer distance across the Outer Banks. We found that A. breviligulata had dense and clumped shoots, which correlated with the greatest sand accretion. Coupled with fast lateral spread, it tends to build tall and wide foredunes. Uniola paniculata had fewer but taller shoots and was associated with ~42% lower sand accretion. Coupled with slow lateral spread, it tends to build steeper and narrower dunes. Panicum amarum had similar shoot densities and associated sand accretion to U. paniculata despite its shorter shoots, suggesting that shoot density is more important than morphology. Finally, we hypothesize, given the distributions of the grass species, that foredunes may be taller and wider and have better coastal protection properties in the north where A. breviligulata is dominant. If under a warming climate A. breviligulata experiences a range shift to the north, as appears to be occurring with U. paniculata, changes in grass dominance and foredune morphology could make for more vulnerable coastlines

Literature-based latitudinal distribution and possible range shifts of two US east coast dune grass species (Uniola paniculata and Ammophila breviligulata)

Previous work on the US Atlantic coast has generally shown that coastal foredunes are dominated by two dune grass species, Ammophila breviligulata (American beachgrass) and Uniola paniculata (sea oats). From Virginia northward, A. breviligulata dominates, while U. paniculata is the dominant grass south of Virginia. Previous work suggests that these grasses influence the shape of coastal foredunes in species-specific ways, and that they respond differently to environmental stressors; thus, it is important to know which species dominates a given dune system. The range boundaries of these two species remains unclear given the lack of comprehensive surveys. In an attempt to determine these boundaries, we conducted a literature survey of 98 studies that either stated the range limits and/or included field-based studies/observations of the two grass species. We then produced an interactive map that summarizes the locations of the surveyed papers and books. The literature review suggests that the current southern range limit for A. breviligulata is Cape Fear, NC, and the northern range limit for U. paniculata is Assateague Island, on the Maryland and Virginia border. Our data suggest a northward expansion of U. paniculata, possibly associated with warming trends observed near the northern range limit in Painter, VA. In contrast, the data regarding a range shift for A. breviligulata remain inconclusive. We also compare our literature-based map with geolocated records from the Global Biodiversity Information Facility and iNaturalist research grade crowd-sourced observations. We intend for our literature-based map to aid coastal researchers who are interested in the dynamics of these two species and the potential for their ranges to shift as a result of climate change

Alirocumab and cardiovascular outcomes after acute coronary syndrome

BACKGROUN