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ABSTRACT Herbivore fronts can alter plant traits (chemical and/or morphological features) and performance via grazing. Yet, herbivore‐driven trait alterations are rarely considered when assessing how these fronts shape ecosystems, despite the critical role that plant performance plays in ecosystem functioning. We evaluated herbivore fronts created by the purple marsh crab,Sesarma reticulatum, as it consumes the cordgrass,Spartina alterniflora, in Virginian salt marshes.Sesarmafronts form at the head of tidal creeks and move inland, creating a denuded mudflat between the tall‐formSpartinalow marsh (trailing edge) and the short‐formSpartinahigh marsh (leading edge). We quantifiedSesarmafront migration rate, tested ifSesarmaherbivory altered geomorphic processes andSpartinatraits at the trailing and leading edges, and examined how these trait changes persisted through the final 8 weeks of the growing season.Sesarmafront migration in our region is two times slower than fronts in the Southeast United States, andSpartinaretreat rate at the leading edge is greater than the revegetation rate at the trailing edge.Sesarmafronts lowered elevation and decreased sediment shear strength at the trailing edge while having no impact on soil organic matter and bulk density at either edge. At the leading edge,Sesarmagrazing reducedSpartinagrowth traits and defensive ability, and trait changes persisted through the remaining growing season. At the trailing edge, however,Sesarmagrazing promoted belowground biomass production and had limited to no effect on growth or defensive traits. We show that herbivore fronts negatively impact saltmarsh plant traits at their leading edge, potentially contributing to front propagation. In contrast, plants at the trailing edge were more resistant to herbivore grazing and may enhance resilience through elevated belowground biomass production. Future work should consider herbivore‐driven plant trait alterations in the context of herbivore fronts to better predict ecosystem response and recovery.
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Role of ecological interactions in saltmarsh geomorphic processes
Accelerated sea-level rise poses a significant threat to coastal habitats, such as salt marshes, which provide critical ecosystem services. Persistence of salt marshes with rising sea levels relies, in part, on vertical accretion. Ecogeomorphic models emphasize the role of plant production in vertical accretion via sediment trapping and belowground organic matter contribution. Thus, changes in plant production can influence saltmarsh persistence with sea-level rise. However, models of marsh accretion do not consider animal-mediated changes in plant production. We tested how 2 marsh crabs, Minuca pugnax and Sesarma reticulatum , which have contrasting effects (facilitation vs. herbivory) on Spartina alterniflora production, may indirectly influence sediment deposition and belowground production, through observational surveys and field manipulation. Minuca facilitated Spartina biomass in some marshes, but not sediment deposition, and had no effect on belowground organic matter contribution, suggesting that in isolation, Minuca has little indirect impact on saltmarsh geomorphic processes. Sesarma reduced Spartina biomass; however, sediment deposition increased, contrary to ecogeomorphic models, likely due to sediment resuspension by Minuca . When Minuca and Sesarma co-occur, the effect on Spartina production and sediment deposition depended on the amount of grazing. When Sesarma grazing is low, Minuca facilitates Spartina growth and mitigates the effect of grazing. However, when Sesarma grazing is high and vegetation is removed, Minuca can resuspend sediment through bioturbation, suggesting the net effect of these species may depend on their relative abundance. This study demonstrates that the effects of plant-animal interactions on marsh resilience against sea-level rise are context dependent.
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- Award ID(s):
- 1832221
- PAR ID:
- 10296988
- Date Published:
- Journal Name:
- Marine Ecology Progress Series
- Volume:
- 658
- ISSN:
- 0171-8630
- Page Range / eLocation ID:
- 149 to 161
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3354/meps13554
