Island Migration Research Articles

Phylogenomics and phylogeographic model testing using convolutional neural networks reveal a history of recent admixture in the Canarian Kleinia neriifolia.

Multiple-island endemics (MIE) are considered ideal natural subjects to study patterns of island colonization that involve recent population-level genetic processes. Kleinia neriifolia is a Canarian MIE widespread across the archipelago, which exhibits a close phylogenetic relationship with species in northwest Africa and at the other side of the Sahara Desert. Here, we used target sequencing with plastid skimming (Hyb-Seq), a dense population-level sampling of K. neriifolia, and representatives of its African-southern Arabian relatives to infer phylogenetic relationships and divergence times at the species and population levels. Using population genetic techniques and machine learning (convolutional neural networks [CNNs]), we reconstructed phylogeographic relationships and patterns of genetic admixture based on a multilocus SNP nuclear dataset. Phylogenomic analysis based on the nuclear dataset identifies the northwestern African Kleinia anteuphorbium as the sister species of K. neriifolia, with divergence starting in the early Pliocene. Divergence from its sister clade, comprising species from the Horn of Africa and southern Arabia, is dated to the arid Messinian period, lending support to the climatic vicariance origin of the Rand Flora. Phylogeographic model testing with CNNs supports an initial colonization of the central island of Tenerife followed by eastward and westward migration across the archipelago, which resulted in the observed east/west phylogeographic split. Subsequent population extinctions linked to aridification events, and recolonization from Tenerife, are proposed to explain the patterns of genetic admixture in the eastern Canary Islands. We demonstrate that CNNs based on SNPs can be used to discriminate among complex scenarios of island migration and colonization.

Modeling the interaction of vegetation and sea level rise on barrier island evolution.

Barrier islands provide a first line of defense against ocean flooding and storm surge. Biogeomorphic interactions are recognized as important in coastal system processes, but current barrier island models are primarily dominated by physical processes. Recent research has demonstrated different biogeomorphic states that influence response to sea level rise and other disturbance. Building on this understanding, we present a cellular model utilizing biotic and abiotic processes and their interactions for barrier island evolution. Using the literature and field derived parameters, we model barrier island evolution and compare to three decades of change for Smith Island, a Virginia Coast Reserve barrier island. We conduct simulations that show the impact of biogeomorphic states on island migration under different sea level rise scenarios. We find that migration is highest in areas with low topography and light vegetation cover (i.e. disturbance reinforcing) compared to areas with greater topographic complexity and high cover of woody vegetation i.e. disturbance resisting). This study demonstrates the importance of biogeomorphic interactions for barrier island evolution with sea level rise and will aid future predictions for these important ecosystems with climate change.

Predicting Barrier Island Shrub Presence Using Remote Sensing Products and Machine Learning Techniques

AbstractBarrier islands are highly dynamic coastal landforms that are economically, ecologically, and societally important. Woody vegetation located within barrier island interiors can alter patterns of overwash, leading to periods of periodic‐barrier island retreat. Due to the interplay between island interior vegetation and patterns of barrier island migration, it is critical to better understand the factors controlling the presence of woody vegetation on barrier islands. To provide new insight into this topic, we use remote sensing data collected by LiDAR, LANDSAT, and aerial photography to measure shrub presence, coastal dune metrics, and island characteristics (e.g., beach width, island width) for an undeveloped mixed‐energy barrier island system in Virginia along the US mid‐Atlantic coast. We apply decision tree and random forest machine learning methods to identify new empirical relationships between island geomorphology and shrub presence. We find that shrubs are highly likely (90% likelihood) to be present in areas where dune elevations are above ∼1.9 m and island interior widths are greater than ∼160 m and that shrubs are unlikely (10% likelihood) to be present in areas where island interior widths are less than ∼160 m regardless of dune elevation. Our machine learning predictions are 90% accurate for the Virginia Barrier Islands, with almost half of our incorrect predictions (5% of total transects) being attributable to system hysteresis; shrubs require time to adapt to changing conditions and therefore their growth and removal lags changes in island geomorphology, which can occur more rapidly.

The restaurant delivery problem with uncertain cooking time and travel time

Eliminating delays under uncertain delivery conditions presents a formidable challenge for meal delivery platforms. Nevertheless, by implementing effective measures, these platforms can successfully mitigate the impacts of uncertainties on delays. This paper introduces a scenario-based chance-constrained programming model tailored for meal delivery services with uncertain cooking time and travel time, ensuring a more accurate representation of real-world scenarios. The objective is to minimize the delivery cost while considering the decision preferences of a platform. To generate high-quality solutions, this work proposes a novel island harmony search algorithm that incorporates several key components, including greedy search, harmony selection, neighborhood reduction, island migration, and scenario-based simulation. Additionally, a matheuristic is introduced for the purpose of comparison. Comparative evaluation against a set of adopted benchmarks reveals the superior performance of both algorithms. A series of sensitivity analyses are conducted to explore the advantages of considering uncertainty, and investigate how decision preference values influence the feasibility of solutions for meal delivery platforms. The proposed formulation and algorithm yield high-quality solutions for delivery platforms with various preferences, facilitating decision-making that aligns with their operational context.

On the verge of misplacement: Pacific Island and climate-induced migration

The Pacific Island nations are severely impacted by climate change due to their comparatively miniscule geography, dense population concentration, and reliance on ecological systems for longevity. Pacific Islanders are compelled to leave their homes and migrate due to dwindling resources for their subsistence, freshwater, and nutrition, which leads to climate-persuaded migration. Such migration is likely to obliterate the indigenous perspectives and sense of national identity. Considering it, there is a good chance that the international reaction to global changing climate will result in a reduction in migration. The international accords are falling short of attaining their climate change objectives through the use of qualitative evaluation of secondary data gathered primarily from online sites, as well as scholarly articles. As a result, minimizing the effects of climate change is of prime significance & this global risk necessitates worldwide dedication to identify & address the terrible ramifications in order to lessen the increase in migration. The research comprehends migration & climate change’s linkage. The recent growing tendencies in migration would be illustrated by the study of Kiribati. The case study would also demonstrate how important it is to put existing international conventions into practice in order to protect Pacific Island communities and their right of statehood.

Contrasting genetic diversity between Planchonella obovata sensu lato (Sapotaceae) on old continental and young oceanic island populations in Japan.

Genetic diversity of plant populations on islands is likely to be influenced by characteristics such as island origin (oceanic or continental) and their age, size, and distance to continental landmasses. In Japan, Planchonella obovata sensu lato which is found on both continental and oceanic islands of varying age, size, and distance to East Asian continental areas-is an ideal system in which to investigate the factors influencing genetic diversity of island plant species. In this study, we examined the genetic diversity of P. obovata s.l. populations, in the context of the species population genetic structure, demography, and between island migration, from 668 individuals, 28 populations and 14 islands including both continental (the Yaeyama Islands) and oceanic islands (the Daito, Bonin, and Volcano Islands) using 11 microsatellite markers. The Yaeyama and Volcano Islands respectively had the highest and lowest genetic diversity, and island origin and age significantly affected genetic diversity. Clustering analysis revealed that populations were grouped into Bonin, Volcano, and Yaeyama + Daito groups. However, Bonin and Volcano groups were distinct despite the relatively short geographical distance between them. Approximate Bayesian Computation analysis suggested that the population size was stable in Bonin and Yaeyama + Daito groups, whereas population reduction occurred in Volcano group, and migration between groups were very limited. Younger oceanic islands showed lower genetic diversity, probably due to limited gene flow and a lack of time to accumulate unique alleles. Genetic structure was generally consistent with the geographic pattern of the islands, but in Volcano, a limited number of founders and limited gene flow among islands are likely to have caused the large genetic divergence observed.

Couple simulations with CFD and ladybug + honeybee tools for green façade optimizing the thermal comfort in a transitional space in hot-humid climate

ABSTRACT Vertical gardens have become important strategies for urban heat island migration in recent years. However, the simulation tools for green façade (GF) with climbing plants coupling the shading and wind-induced effects are still lacked. This study focused on GF effects on human thermal comfort (HTC) optimization in a transitional space. The main purpose was to develop a couple method on HTC simulations. Field measurements in a hot-humid climate area were conducted to obtain the parameters of GF foliage layers. A couple simulation method with Ansys Fluent, Ladybug, and Honeybee tools was developed. Seven GFs layouts on a standard balcony model were simulated. In field measurements, the Ave. global irradiation was reduced by 73.29%, leaf area index was measured at 1.56–3.61, and foliage cover ratio was measured at 49.74–92.88%. In the simulations, the results of the Ave. wind velocity were reduced by 0.20–0.77 m s−1, the Ave. air temperature was reduced by 0.2°C, the Ave. mean radiant temperature was reduced by 0.5–7°C, and the Ave. physiological equivalent temperature was reduced by 0.3–3.2°C. The couple method could support the architectural and landscape design integrating with the GFs in future.

A unique form of collective epithelial migration is crucial for tissue fusion in the secondary palate and can overcome loss of epithelial apoptosis.

ABSTRACTTissue fusion frequently requires the removal of an epithelium that intervenes distinct primordia to form one continuous structure. In the mammalian secondary palate, a midline epithelial seam (MES) forms between two palatal shelves and must be removed to allow mesenchymal confluence. Abundant apoptosis and cell extrusion support their importance in MES removal. However, genetically disrupting the intrinsic apoptotic regulators BAX and BAK within the MES results in complete loss of cell death and cell extrusion, but successful removal of the MES. Novel static- and live-imaging approaches reveal that the MES is removed through streaming migration of epithelial trails and islands to reach the oral and nasal epithelial surfaces. Epithelial trail cells that express the basal epithelial marker ΔNp63 begin to express periderm markers, suggesting that migration is concomitant with differentiation. Live imaging reveals anisotropic actomyosin contractility within epithelial trails, and genetic ablation of actomyosin contractility results in dispersion of epithelial collectives and failure of normal MES migration. These findings demonstrate redundancy between cellular mechanisms of morphogenesis, and reveal a crucial and unique form of collective epithelial migration during tissue fusion.

Nearshore bathymetric changes along the Alaska Beaufort Sea coast and possible physical drivers

Erosion rates along Alaska's Beaufort Sea coast, among the highest in the world, are negatively impacting communities, industrial and military infrastructure, and wildlife habitat. Decreasing maximal winter ice extent and increasing summer open water duration and extent in the Beaufort Sea may be making the coast more vulnerable to destructive storm waves than during recent, colder, icier decades. Previous studies of Beaufort Sea coastal change have been limited to subaerial analyses of the shoreline. Here we describe nearshore seafloor change by comparing post-World War II (WWII) (1945-53) bathymetry data to recently acquired (1985–2018) bathymetry data and relate the observed seafloor change to adjacent shoreline change near Utqiagvik, within Stefansson Sound, and immediately west of Barter Island and Kaktovik. Within the Utqiagvik region, seabed erosion was generally highest (>1.0 m of loss) offshore of Point Barrow and along the eastern end of the Tapkaluk Islands, while there were lesser amounts of deposition (<0.5 m of gain) within the protected waters of Elson Lagoon. Sedimentation was generally highest offshore of Point Barrow, in a region of converging currents, and on the landward side of the barrier islands and spits fronting Elson Lagoon, which is likely related to a regional trend of westerly sediment transport and landward migration of the barrier islands. Within Stefansson Sound, perhaps the most notable changes from post-WWII bathymetry data compared to recent data are a switch from mixed, low erosion and deposition in 1997 to low deposition (<0.5 m) in 2018 east of the Boulder Patch, a switch from low erosion in 1997 to neutral depth change in 2018 in the channel between the north and south Boulder Patch areas, and higher deposition from 1997 to 2018 landward of the rapidly retreating barrier islands along the Sound's northern border. At Barter Island, high erosion near north-facing shorelines and high deposition near west-facing shorelines generally matched shoreline changes. One of our goals is to identify possible processes responsible for the depth changes we quantified. Using simple metrics that relate sediment characteristics with modeled waves and non-wave induced currents, we show that sediment resuspension and transport by both wave and non-wave driven currents likely contribute to the overall patterns of change within the ∼13 m isobath along the open coast, and that the influence of wave action affecting sediment transport is expanding seaward.

Leveraging the Interdependencies Between Barrier Islands and Backbarrier Saltmarshes to Enhance Resilience to Sea-Level Rise

Barrier islands and their backbarrier saltmarshes have a reciprocal relationship: aeolian and storm processes transport sediment from the beaches and dunes to create and build marshes along the landward fringe of the island. In turn, these marshes exert a stabilizing influence on the barrier by widening the barrier system and forming a platform onto which the island migrates, consequently slowing landward barrier migration and inhibiting storm breaching. Here, we present a novel framework for applying these natural interdependencies to managing coastal systems and enhancing barrier-island resilience. Further, we detail application of these principles through a case study of the design of a marsh creation project that showcases the interdisciplinary engagement of scientists, engineers, stakeholders, and policymakers. Specifically, we describe: (1) the ecologic, sedimentologic, stratigraphic, and morphologic data obtained from the southern 4 km of Cedar Island (Virginia, United States) and nearby backbarrier tidal channels, tidal flats, and flood-tidal deltas, and (2) the use of those data to develop an engineering and design plan for the construction of a high (46 ha) and low (42 ha) fringing marsh platform located behind the island, proximal to a former ephemeral inlet. Additionally, we chronicle the process used to narrow five initial alternative designs to the optimal final plan. This process involved balancing best-available existing science and models, considering design and financial constraints, identifying stakeholder preferences, and maximizing restoration benefits of habitat provision and shoreline protection. Construction of this marsh would: (1) provide additional habitat and ecosystem benefits, (2) slow the rapid migration (up to 15 m/yr at present) of the barrier island, and (3) hinder island breaching. Ultimately, this project – presently at the final design and permitting stage – may enhance the storm and sea-level rise resilience of the island, backbarrier marshes and lagoons, and the mainland town community; and provide an example of a novel science-based approach to coastal resilience that could be applied to other global barrier settings.

Islander migrations and the oceans: From hopes to fears?

This paper explores islanders’ hopes and fears for migration and non-migration, highlighting the role of the ocean. Migration, non-migration, hope, and fear are human conditions. To examine these conditions for islanders and oceans, this paper uses a qualitative evidence synthesis for collating and interpreting themes on the topic. Some types of hopes and fears, and a few reasons why they might emerge, are covered for islanders and ocean-related migration. Then, different ocean representations which islander migration and non-migration produces and portrays are presented. The conclusions question dichotomies and norms in the context of islander fears and hopes, as well as threats and opportunities, regarding ocean migrations.

Fifty-year dynamics of the Lena River islands (Russia): Spatio-temporal pattern of large periglacial anabranching river and influence of climate change

The Lena, a large river that drains the northern coldest region of the Northern Hemisphere, is deeply influenced by the continuous permafrost and degradation of the frozen ground has been shown to be the main cause of the marked increase in water discharge. The first objective of this study conducted on the middle Lena was to analyze the island dynamics for the last 50 years (1967 to 2017). Several morphological parameters were surveyed using a GIS on seven series of aerial photographs and satellite images of a 100 km-long reach: island size, eroded and deposited areas, position and morphology of the islands. This approach enabled the identification of evolutionary models. Our second objective was to evaluate the potential impact of ongoing climate change. We analyzed morphological parameters with respect to two main factors: efficient discharge (bar-full, bankfull and flood discharges) and water temperature. A potential erosion index (PEI) was calculated by coupling the duration of discharge exceeding the bar-full level and water temperature.The results identified several morphological changes that occurred at the end of the 20th century: an increase in the number of islands, greater eroded surfaces and accelerated migration of islands. Comparing the dynamics of islands with and without permafrost is a good indicator of their sensitivity to climate change. A major change was observed concerning the erosion and migration of islands with and without permafrost. This evolution seems to be linked both with the duration of the discharge that exceeds the bar-full level and with the number of flood peaks. The water temperature in May and August have a major influence on permafrost islands that become increasingly destabilized. Thus, as large rivers are assumed to slowly react to climate change, the recent changes in the Lena River prove that the global change deeply impacts periglacial rivers.

Sediment supply dampens the erosive effects of sea-level rise on reef islands

Large uncertainty surrounds the future physical stability of low-lying coral reef islands due to a limited understanding of the geomorphic response of islands to changing environmental conditions. Physical and numerical modelling efforts have improved understanding of the modes and styles of island change in response to increasing wave and water level conditions. However, the impact of sediment supply on island morphodynamics has not been addressed and remains poorly understood. Here we present evidence from the first physical modelling experiments to explore the effect of storm-derived sediment supply on the geomorphic response of islands to changes in sea level and energetic wave conditions. Results demonstrate that a sediment supply has a substantial influence on island adjustments in response to sea-level rise, promoting the increase of the elevation of the island while dampening island migration and subaerial volume reduction. The implications of sediment supply are significant as it improves the potential of islands to offset the impacts of future flood events, increasing the future physical persistence of reef islands. Results emphasize the urgent need to incorporate the physical response of islands to both physical and ecological processes in future flood risk models.

Shoreline changes in coral reef islands of the Federated States of Micronesia since the mid-20th century

With projections of accelerating sea-level rise, changing weather and wave regimes and increasing intensity of storm events associated with anthropogenic climate change, the physical persistence and consequently habitability of coral reef islands is a global concern. This study presents an analysis of shoreline changes on 104 coral reef islands from 16 atolls in the western equatorial Pacific nation of the Federated States of Micronesia across a period coincident with rising local sea level and a high frequency of storm events. Aerial photographs from the mid-1940s and 1970s were analysed alongside recent high-resolution satellite imagery to document shoreline changes and planform morphological adjustments in islands. Results revealed accretion has been the predominant mode of shoreline change, with 46% of the studied shorelines showing statistically significant accretion leading to a net increase of 64.37 ha (~3%) of planform land area across the archipelago. Three new islands were formed with a cumulative land area of 2.05 ha, conversely, three islands were completely eroded leading to a loss of net land area of 3.20 ha, providing a record of concurrent island formation and loss within a high storm frequency setting. Reef islands in the FSM demonstrated a range of styles of planform geomorphic adjustments including island rotation, expansion, contraction, spit extension, and migration of islands on the reef platform. Results provide empirical evidence of shoreline accretion despite local sea-level rise as well as of heterogeneity in magnitude and style of geomorphic responses of reef islands across FSM with considerable variability at inter and intra-atoll scales.

Silicene Growth through Island Migration and Coalescence

Silicene, the Si based counterpart to graphene is predicted to demonstrate similar desirable features to graphene, possessing a Dirac cone in the band-structure and Fermi velocities comparable to graphene. It has also been predicted to demonstrate several exotic properties such as the quantum spin Hall effect, chiral superconductivity and giant magnetoresistance. It has the added benefit of being easy to integrate into current industrial device engineering processes. Silicene monolayers have been grown on Ag (111) and Ir (111) substrates and recently a working field-effect transistor has been demonstrated at room temperature. While it is possible to characterize the final monolayer structure, it is impossible to probe experimentally the evolving atomic structure during growth.We perform massively-parallel molecular dynamics (MD) simulations to study long time monolayer silicene growth on an Ir (111) surface. We observe an intricate multi-stage growth process driven by atomic and cluster migration on the surface. Initial growth involves formation of sub-nanometer clusters via adatom surface diffusion. Subsequently, these clusters rearrange spontaneously with each additional Si atom, forming clusters containing 4–7 member rings. Growth of each cluster through adatom adhesion is accompanied by the formation of larger islands through cluster migration and coalescence. Coalescence of smaller, more mobile islands into larger clusters is aided by the internal rearrangement of rings within each cluster. This flexibility, both of clusters and their constituent atoms, allows the impinging clusters to reorient after first contact and form a more perfect union. We also report on the effect of temperature and flux on the growth process and the final nanostructure. Our study provides atomistic insights into the early stage growth mechanisms of silicene which can be significant for controlled synthesis of its 2D monolayers. Reference: Cherukara, M. J., Narayanan, B., Chan, H., & Sankaranarayanan, S. K. (2017). Silicene growth through island migration and coalescence. Nanoscale, 9(29), 10186-10192. Figure 1

Relative influence of antecedent topography and sea‐level rise on barrier‐island migration

AbstractThe response of barrier islands to sea‐level rise is modulated by combinations of coastal processes, eco‐geomorphic feedbacks and structural controls, such as antecedent topography. Interactions among these drivers can lead to complex and non‐linear changes in island morphology and transitions between migrational, erosional or progradational states. This study seeks to constrain the morphological consequences of barrier islands migrating across complex antecedent topography in response to rising sea level. The stratigraphy of four barrier–backbarrier systems along the United States Mid‐Atlantic coast informs idealized geometries of diverse antecedent substrate. These outcomes are integrated into a cross‐shore morphodynamic model of barrier‐island migration to quantify the influence of this antecedent geology on barrier‐retreat behaviour. Additionally, this study explores the future response of specific barrier islands to various rates of sea‐level rise over multi‐decadal to millennial timescales. The results show that antecedent substrate slope plays a central role in barrier morphodynamic behaviour. In particular, migration across a subaqueous backbarrier ridge (for example, coastal barrier or dune deposits from earlier sea‐level highstands) can cause a succession of phase changes in a modern island. For example, the case studies illustrate that the steep slopes and decreased backbarrier accommodation associated with antecedent highs greater than 3 m in profile can greatly reduce island migration rates, effectively ‘pinning’ the island in place, even with sea‐level rise rates up to 6 mm yr−1. However, once the island migrates over the high, backbarrier accommodation increases, leading to enhanced overwash fluxes, more rapid landward migration, and possible drowning. Additionally, the results indicate that antecedent substrate may slow barrier‐island migration by providing sediment through both shoreface and inlet processes. The field and modelling insights from this study are presented as a conceptual model of the relative influence of various antecedent features on barrier‐island dynamics along sandy, siliciclastic coasts.

Modelling reef hydrodynamics and sediment mobility under sea level rise in atoll reef island systems

Abstract Low-lying coral reef islands will be significantly impacted by future sea-level rise (SLR). It is generally expected that SLR will destabilise reef islands because increasing reef submergence allows larger waves, and therefore greater energy transmission, across reef flats. However, the potential impacts of SLR on reef flat sediment transport and sediment delivery to island shorelines are poorly understood. Here, we use the currents of removal approach (coupling two-dimensional wave modelling with settling velocity data from 186 benthic sediment samples) to model shifts in both reef hydrodynamics and benthic sediment transport under different scenarios of mean reef submergence (MRS = +0 m, +0.5 m, +1 m) at two atoll rim reef sites in the Maldives. Under contemporary conditions (MRS = +0 m), we found that benthic sediment transport is likely occurring, consistent with active reef-to-island sediment connectivity. Under conditions of increased MRS, shifts in wave velocities, and in turn sediment potential mobility, were both non-linear and non-uniform. Significant between-site differences were found in the magnitude of projected shifts in sediment mobility under scenarios of increased MRS, which implies that morphological responses to increased MRS are likely to be diverse, even over local scales. Under increased MRS, the largest increases in sediment mobility were projected on the inner reef flat, whereas lagoonal zones remained as sinks for sediment deposition. We thus hypothesize that while reef islands will persist as sedimentary landforms under projected rates of MRS, lagoonward reef island migration is likely to occur. Findings have implications for predicting the future adaptive capacity of atoll nations. Our results highlight the need for national-scale vulnerability assessments to incorporate (1) potential increases in island mobility; (2) the importance of allowing natural sediment transport processes to occur (unhindered by human constructions); and (3) intra-regional diversity in reef system geomorphic responses to sea level rise.

Island migration and foraging behaviour by anatomically modern humans during the late Pleistocene to Holocene in Wallacea: New evidence from Central Sulawesi, Indonesia

Maritime migration and island adaptation by anatomically modern humans (AMH) are among the most significant issues in Southeast Asian anthropology and archaeology, and directly related to their behavioural and technological advancements. A major research hotspot is Wallacean Archipelago located between the past Sunda and Sahul continents during the late Pleistocene. The gaps between the Wallacean islands and both landmasses are very likely the major factor for the relative scarcity of animal species originating from Asia and Oceania and the high diversity of endemic species in Wallacea. They are also considered as a barrier for hominin migration into Wallacean islands and Sahul continent. We report about new archaeological research on the eastern coast of Sulawesi, which could have been the most potential location for the early AMH migration by sea crossings from the Maluku Islands along the northern routes towards Sahul. Based on the new findings, we discuss the evidence and timeline for migrations of early modern humans into the Wallacean islands. This includes an overview of the excavated stone and bone artefacts and faunal remains in the region in the context of changes in human foraging behaviour as well as the technological and cognitive aspects of human adaptation as a response to rapidly changing ecological conditions during the late Pleistocene to Holocene periods.

Impacts of Seagrass Dynamics on the Coupled Long‐Term Evolution of Barrier‐Marsh‐Bay Systems

AbstractSeagrass provides a wide range of economically and ecologically valuable ecosystem services, with shoreline erosion control often listed as a key service, but can also alter the sediment dynamics and waves within back‐barrier bays. Here we incorporate seagrass dynamics into an existing barrier‐marsh exploratory model, GEOMBEST++, to examine the coupled interactions of the back‐barrier bay with both adjacent (marsh) and nonadjacent (barrier island) subsystems. While seagrass reduces marsh edge erosion rates and increases progradation rates in many of our 288 model simulations, seagrass surprisingly increases marsh edge erosion rates when sediment export from the back‐barrier basin is negligible because the ability of seagrass to reduce the volume of marsh sediment eroded matters little for back‐barrier basins in which all sediment is conserved. Our model simulations also suggest that adding seagrass to the bay subsystem leads to increased deposition in the bay, reduced sediment available to the marsh, and enhanced marsh edge erosion until the bay reaches a new, shallower equilibrium depth. In contrast, removing seagrass liberates previously sequestered sediment that is then delivered to the marsh, leading to enhanced marsh progradation. Lastly, we find that seagrass reduces barrier island migration rates in the absence of back‐barrier marsh by filling accommodation space in the bay. These model observations suggest that seagrass meadows operate as dynamic sources and sinks of sediment that can influence the evolution of coupled marsh and barrier island landforms in unanticipated ways.

Connectivity in coastal systems: Barrier island vegetation influences upland migration in a changing climate.

Due to their position at the land-sea interface, barrier islands are vulnerable to both oceanic and atmospheric climate change-related drivers. In response to relative sea-level rise, barrier islands tend to migrate landward via overwash processes which deposit sediment onto the backbarrier marsh, thus maintaining elevation above sea level. In this paper, we assess the importance of interior upland vegetation and sediment transport (from upland to marsh) on the movement of the marsh-upland boundary in a transgressive barrier system along the mid-Atlantic Coast. We hypothesize that recent woody expansion is altering the rate of marsh to upland conversion. Using Landsat imagery over a 32year time period (1984-2016), we quantify transitions between land cover (bare, grassland, woody vegetation, and marsh) and the marsh-upland boundary. We find that the Virginia Barrier Islands have both gains and losses in backbarrier marsh and upland, with 19% net loss from the system during the timeframe of the study and increased variance in marsh to upland conversion. This is consistent with recent work indicating a shift toward increasing rates of landward barrier island migration. Despite a net loss of upland area, macroclimatic winter warming resulted in 41% increase in woody vegetation in protected, low-elevation areas, introducing new ecological scenarios that increase resistance to sediment movement from upland to marsh. Our analysis demonstrates how the interplay between elevation and interior island vegetative cover influences landward migration of the boundary between upland and marsh (a previously underappreciated indicator that an island is migrating), and thus, the importance of including ecological processes in the island interior into coastal modeling of barrier island migration and sediment movement across the barrier landscape.