skip to main content


Title: Plasticity drives the trait variation of a foundation marsh species migrating into coastal forests with sea‐level rise
Abstract

Climate‐driven ecosystem shifts occur through turnover in the foundation species which structure the landscape. Therefore, to predict the fate of areas undergoing climate‐driven ecosystem shifts, one approach is to characterize ecological and evolutionary responses of foundation species along dynamic environmental gradients. One such gradient is the ecotone between tidal marshes and maritime forests in coastal areas of the US Mid‐Atlantic region where accelerated sea‐level rise and coastal storms of increased frequency and intensity are driving forest dieback and inland marsh migration. Mid‐Atlantic tidal marshes are structured by marsh grasses which act as foundation species, and these grasses exhibit trait variation across their distribution from established marsh interior to their inland migration front. We conducted a reciprocal transplant experiment withSpartina patens, a dominant high marsh grass and foundation species, between established populations in the high marsh and range edge populations in the forest understory at three Mid‐Atlantic sites. We monitored environmental conditions in marsh and forest understory habitats, measured plant traits (above‐ and belowground biomass, specific leaf area, leaf N and C concentrations) in transplanted and reference non‐transplanted individuals, and used microsatellite markers to determine the genetic identity of transplants to quantify clonality between habitats and sites. Individuals transplanted into the forest understory exhibited a plastic shift in resource allocation to aboveground structures associated with light acquisition, with shifts in transplants making them more morphologically similar to reference individuals sampled from the forest habitat. Clonal diversity and genetic distance among transplants were relatively high at two of three sites, but individuals at all sites exhibited trans‐habitat plasticity regardless of clonal diversity or a lack thereof. Individuals grown in the forest understory showed lower vegetative and reproductive fitness. Nevertheless, the trait plasticity exhibited by this species allowed individuals from the forest that were transplanted into the marsh to recoup significant biomass in only a single growing season. We predict high plasticity will facilitate the persistence of colonizingS. patensindividuals under suboptimal forest shade conditions until forest dieback increases light availability, ultimately promoting continued inland migration of this foundation species under sea‐level rise.

 
more » « less
Award ID(s):
1832221
NSF-PAR ID:
10537641
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Ecosphere
Volume:
15
Issue:
8
ISSN:
2150-8925
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    As sea‐level rise converts coastal forest to salt marsh, marsh arthropods may migrate inland; however, the resulting changes in arthropod communities, including the stage of forest retreat that first supports saltmarsh species, remain unknown. Furthermore, the ghost forest that forms in the wake of rapid forest retreat offers an unknown quality of habitat to marsh arthropods. In a migrating marsh in Virginia, USA, ground‐dwelling arthropod communities were assessed across the forest‐to‐marsh gradient, and functional use of ghost forest and high marsh habitats was evaluated to determine whether marsh arthropods utilized expanded marsh in the same way as existing marsh. Diet and body condition were compared for two marsh species found in both high marsh and ghost forest (the detritivore amphipod,Orchestia grillus, and the hunting spider,Pardosa littoralis). Community composition differed among zones along the gradient, driven largely by retreating forest taxa (e.g., Collembola), marsh taxa migrating into the forest (e.g.,O. grillus), and unique taxa (e.g., Hydrophilinae beetles) at the ecotone. The low forest was the most inland zone to accommodate the saltmarsh speciesO. grillus, suggesting that inland migration of certain saltmarsh arthropods may co‐occur with early saltmarsh plant migration and precede complete tree canopy die‐off. Functionally,O. grillusoccupied a larger trophic niche in the ghost forest than the high marsh, likely by consuming both marsh and terrestrial material. Despite this, both observed marsh species primarily consumed from the marsh grass food web in both habitats, and no lasting differences in body condition were observed. For the species and functional traits assessed, the ghost forest and high marsh did not show major differences at this site. Forest retreat and marsh migration may thus provide an important opportunity for generalist saltmarsh arthropods to maintain their habitat extent in the face of marsh loss due to sea‐level rise.

     
    more » « less
  2. Abstract

    Determining factors that shape a species’ population genetic structure is beneficial for identifying effective conservation practices. We assessed population structure and genetic diversity for Saltmarsh Sparrow (Ammospiza caudacuta), an imperiled tidal marsh specialist, using 13 microsatellite markers and 964 individuals sampled from 24 marshes across the breeding range. We show that Saltmarsh Sparrow populations are structured regionally by isolation-by-distance, with gene flow occurring among marshes within ~110 to 135 km of one another. Isolation-by-resistance and isolation-by-environment also shape genetic variation; several habitat and landscape features are associated with genetic diversity and genetic divergence among populations. Human development in the surrounding landscape isolates breeding marshes, reducing genetic diversity, and increasing population genetic divergence, while surrounding marshland and patch habitat quality (proportion high marsh and sea-level-rise trend) have the opposite effect. The distance of the breeding marsh to the Atlantic Ocean also influences genetic variation, with marshes farther inland being more divergent than coastal marshes. In northern marshes, hybridization with Nelson’s Sparrow (A. nelsoni) strongly influences Saltmarsh Sparrow genetic variation, by increasing genetic diversity in the population; this has a concomitant effect of increasing genetic differentiation of marshes with high levels of introgression. From a conservation perspective, we found that the majority of population clusters have low effective population sizes, suggesting a lack of resiliency. To conserve the representative breadth of genetic and ecological diversity and to ensure redundancy of populations, it will be important to protect a diversity of marsh types across the latitudinal gradient of the species range, including multiple inland, coastal, and urban populations, which we have shown to exhibit signals of genetic differentiation. It will also require maintaining connectivity at a regional level, by promoting high marsh habitat at the scale of gene flow (~130 km), while also ensuring “stepping stone” populations across the range.

     
    more » « less
  3. Abstract

    The lateral extent and vertical stability of salt marshes experiencing rising sea levels depend on interacting drivers and feedbacks with potential for nonlinear behaviors. A two‐dimensional transect model was developed to examine changes in marsh and upland forest lateral extent and to explore controls on marsh inland transgression. Model behavior demonstrates limited and abrupt forest retreat with long‐term upland boundary migration rates controlled by slope, sea‐level rise (SLR), high water events, and biotic‐abiotic interactions. For low to moderate upland slopes the landward marsh edge is controlled by the interaction of these inundation events and forest recovery resulting in punctuated transgressive events. As SLR rates increase, the importance of the timing and frequency of water‐level deviations diminishes, and migration rates revert back to a slope‐SLR‐dominated process.

     
    more » « less
  4. Abstract

    Tidal marshes in the Chesapeake Bay are vulnerable to the accelerating rate of sea-level rise (SLR) and subsidence. Restored and created marshes face the same risks as natural marshes, and their resilience to SLR may depend upon appropriate design and implementation. Here, the Coastal Wetland Equilibrium Model (CWEM) was used to assess the resilience of tidal marshes at the Paul S. Sarbanes Ecosystem Restoration Project at Poplar Island (PI) in mid-Chesapeake Bay, MD, where dredged material from navigation channels is being used to create new tidal marshes planted withSpartina alterniflorain the low marsh andS. patensin the high marsh. The site is microtidal with low inorganic sediment inputs, where the rate of marsh elevation change is dominated by the production of organic matter and, therefore, is proportional to net ecosystem production (NEP). The model demonstrated the importance of marsh development for surface elevation gain. In created marshes, the buildout of belowground biomass adds volume and results in faster growth of marsh elevation, but the gains slow as the marsh matures. Elevation gain is the lessor of the recalcitrant fraction of NEP sequestered in sediment or the rate of increase in accommodation space. Marshes can keep up with and fill accommodation space with sequestered NEP up to a tipping point determined by the rate of SLR. The PI low marsh platform was forecasted to drown in about 43 years after construction at the current rate of SLR. Marsh loss can be mitigated by periodic thin layer placement (TLP) of sediment. CWEM was used to simulate PI marsh responses to different TLP strategies and showed that there is an optimal design that will maximize carbon sequestration and resilience depending on the trajectory of mean sea level.

     
    more » « less
  5. null (Ed.)
    Complexities of terrestrial boundaries with salt marshes in coastal lagoons affect salt marsh exposure to waves and sediments creating different potentials for marsh migration inland and seaward-edge erosion, and consequently, for marsh persistence. Between 2002 and 2017, migration and edge erosion were measured in three mainland geomorphic marsh types (headland, valley, hammock) and were used to assess the rate and spatial extent of marsh change for a Virginia coastal lagoon system. Treelines, shorelines, and marsh perimeters were delineated in ArcGIS at 1:600 resolution. All marsh types increased in spatial extent; increases were greatest for the valley type (0.58 ha ± 0.31 ha or + 0.32% per annum). Measured rates of migration (headland > valley > hammock) and erosion (headland > hammock > valley) for each geomorphic type were averaged and applied to obtain changes in these same marsh types at the regional scale. At this scale, valley marsh area increased (82.5 ha or 5.5 ha a−1) more than the other two marsh types combined. This analysis demonstrates the critical influence that geomorphic type has on lateral marsh responses to sea-level rise and that efforts to conserve or restore salt marshes are most likely to be successful when focused on valley marshes. 
    more » « less