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Abstract Mangrove trees are invading saltmarshes at subtropical ecotones globally, but the consequences of this vegetation shift for ecosystem sustainability remain unknown. Using the Coastal Wetland Equilibrium Model (CWEM) to simulate vegetation survival and sediment accretion, we predict that black mangroves,Avicennia germinans, can build soil elevation by 8 mm yr−1, four times greater than saltmarshes at the same site, a finding that is broadly consistent with field measurements of elevation change. Mangroves build elevation more rapidly than saltmarshes by producing much greater live and labile belowground biomass, but when mangroves drown, they abruptly lose elevation due to the large volume of quickly decomposing necromass following flood‐induced mortality. Under certain conditions, young mangroves can accumulate root mass faster than mature trees and, therefore, gain elevation more rapidly, but neither saltmarshes nor mangroves of any age survived a centenary sea‐level increase of 100 cm. The acceleration of sea‐level rise that coastal marshes are encountering raises the question of how coastal wetlands should be optimally managed and these results provide managers with predictive information on wetland building capacity of mangroves versus marshes.
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Using vulnerability assessment to characterize coastal protection benefits provided by estuarine habitats of a dynamic intracoastal waterway
The existence of coastal ecosystems depends on their ability to gain sediment and keep pace with sea level rise. Similar to other coastal areas, Northeast Florida (United States) is experiencing rapid population growth, climate change, and shifting wetland communities. Rising seas and more severe storms, coupled with the intensification of human activities, can modify the biophysical environment, thereby increasing coastal exposure to storm-induced erosion and inundation. Using the Guana Tolomato Matanzas National Estuarine Research Reserve as a case study, we analyzed the distribution of coastal protection services–expressly, wave attenuation and sediment control–provided by estuarine habitats inside a dynamic Intracoastal waterway. We explored six coastal variables that contribute to coastal flooding and erosion–(a) relief, (b) geomorphology, (c) estuarine habitats, (d) wind exposure, (e) boat wake energy, and (f) storm surge potential–to assess physical exposure to coastal hazards. The highest levels of coastal exposure were found in the north and south sections of the Reserve (9% and 14%, respectively) compared to only 4% in the central, with exposure in the south driven by low wetland elevation, high surge potential, and shorelines composed of less stable sandy and muddy substrate. The most vulnerable areas of the central Reserve and main channel of the Intracoastal waterway were exposed to boat wakes from larger vessels frequently traveling at medium speeds (10–20 knots) and had shoreline segments oriented towards the prevailing winds (north-northeast). To guide management for the recently expanded Reserve into vulnerable areas near the City of Saint Augustine, we evaluated six sites of concern where the current distribution of estuarine habitats (mangroves, salt marshes, and oyster beds) likely play the greatest role in natural protection. Spatially explicit outputs also identified potential elevation maintenance strategies such as living shorelines, landform modification, and mangrove establishment for providing coastal risk-reduction and other ecosystem-service co-benefits. Salt marshes and mangroves in two sites of the central section (N-312 and S-312) were found to protect more than a one-quarter of their cross-shore length (27% and 73%, respectively) from transitioning to the highest exposure category. Proposed interventions for mangrove establishment and living shorelines could help maintain elevation in these sites of concern. This work sets the stage for additional research, education, and outreach about where mangroves, salt marshes, and oyster beds are most likely to reduce risk to wetland communities in the region.
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- Award ID(s):
- 2224999
- PAR ID:
- 10563248
- Publisher / Repository:
- Taylor and Francis
- Date Published:
- Journal Name:
- PeerJ
- Volume:
- 12
- ISSN:
- 2167-8359
- Page Range / eLocation ID:
- e16738
- Subject(s) / Keyword(s):
- Coastal vulnerability natural capital ecosystem services NERRS Florida
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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ABSTRACT Climate‐induced range shifts may displace species into novel habitats where their life history characteristics may differ in response to new physiological conditions. One such species is the mangrove tree crab,Aratus pisonii, that has expanded beyond mangrove habitats into salt marshes, with the help of anthropogenic structures such as boat docks that mimic its natural habitat in many ways. Individuals in the salt marsh grow to smaller sizes and have different reproductive patterns than individuals in the native mangrove or in boat dock habitats. We examined the metabolic rates of crabs associated with each of these three habitats to determine whether changes in energy expenditure could account for the life history changes that have been documented. We found that the metabolic patterns were similar in the three habitats, with metabolic rate increasing with body size and with temperature, being higher for females than for males and increasing during reproduction. However, once these factors were accounted for, there was no additional difference in metabolic patterns between habitats. Combining these patterns with known patterns of temperature differences and differences in food intake between the mangrove, salt marsh, and boat docks provides mechanistic insight into the energy mismatch that has been created by this range expansion from mangroves to salt marshes. The energy dynamics in these different habitats are consistent with and are capable of explaining the observed patterns of life history variation that accompany this range expansion. Our study provides an example of a mechanistic approach to understanding the influence of climate change and associated range shifts on life history variation across habitat types.more » « less
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High-magnitude storm events such as Hurricane Sandy are powerful agents of geomorphic change in coastal marshes, potentially altering their surface elevation trajectories. But how do a storm’s impacts vary across a large region spanning a variety of wetland settings and storm exposures and intensities.We determined the short-term impacts of Hurricane Sandy at 223 surface elevation table–marker horizon stations in estuarine marshes located across the northeast region of the United States by comparing poststorm surface elevation change with pre-storm elevation trends.We hypothesized that the storm’s effect on marsh elevation trends would be influenced by position relative to landfall (right or left) and distance from landfall. The structural equation model presented predicts that marshes located to the left of landfall were more likely to experience an elevation gain greater than expected, and this positive deviation from pre-storm elevation trends tended to have a greater magnitude than those experiencing negative deviations (elevation loss), potentially due to greater sediment deposition. The magnitude of negative deviations from elevation change in marshes to the right of landfall was greater than for positive deviations, with a greater effect in marshes within 200 km of landfall, potentially from the extent and magnitude of storm surge. Overall, results provide an integrated picture of how storm characteristics combined with the local wetland setting are important to a storm’s impact on surface elevation, and that the surface elevation response can vary widely among sites across a region impacted by the same storm.more » « less
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Abstract Mangroves buffer inland ecosystems from hurricane winds and storm surge. However, their ability to withstand harsh cyclone conditions depends on plant resilience traits and geomorphology. Using airborne lidar and satellite imagery collected before and after Hurricane Irma, we estimated that 62% of mangroves in southwest Florida suffered canopy damage, with largest impacts in tall forests (>10 m). Mangroves on well-drained sites (83%) resprouted new leaves within one year after the storm. By contrast, in poorly-drained inland sites, we detected one of the largest mangrove diebacks on record (10,760 ha), triggered by Irma. We found evidence that the combination of low elevation (median = 9.4 cm asl), storm surge water levels (>1.4 m above the ground surface), and hydrologic isolation drove coastal forest vulnerability and were independent of tree height or wind exposure. Our results indicated that storm surge and ponding caused dieback, not wind. Tidal restoration and hydrologic management in these vulnerable, low-lying coastal areas can reduce mangrove mortality and improve resilience to future cyclones.more » « less
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The capacity of coastal wetlands to stabilize shorelines and reduce erosion is a critical ecosystem service, and it is uncertain how changes in dominant vegetation may affect coastal protection. As part of a long-term study (2012–present) comparing ecosystem functions of marsh and black mangrove vegetation, we have experimentally maintained marsh and black mangrove patches (3 m × 3 m) along a plot-level (24 m × 42 m) gradient of marsh and mangrove cover in coastal wetlands near Port Aransas, TX. In August 2017, this experiment was directly in the path of Hurricane Harvey, a category 4 storm. This extreme disturbance event provided an opportunity to quantify differences in resistance between mangrove and marsh vegetation and to assess which vegetation type provided better shoreline protection against storm-driven erosion. We compared changes in plant cover, shoreline erosion, and accreted soil depth to values measured prior to storm landfall. Relative mangrove cover decreased 25–40% after the storm, regardless of initial cover, largely due to damage on taller mangroves (> 2.5 m height) that were not fully inundated by storm surge and were therefore exposed to strong winds. Evidence of regrowth on damaged mangrove branches was apparent within 2 months of landfall. Hurricane-induced decreases in mangrove cover were partially ameliorated by the presence of neighboring mangroves, particularly closer to the shoreline. Marsh plants were generally resistant to hurricane effects. Shoreline erosion exceeded 5 m where mangroves were absent (100% marsh cover) but was relatively modest (< 0.5 m) in plots with mangroves present (11–100% mangrove cover). Storm-driven accreted soil depth was variable but more than 2× higher in marsh patches than in mangrove patches. In general, mangroves provided shoreline protection from erosion but were also more damaged by wind and surge, which may reduce their shoreline protection capacity over longer time scales.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.7717/peerj.16738
