Herbivore Fronts Shape Saltmarsh Plant Traits and Performance.

Area of Science:

• Ecology
• Salt Marsh Ecosystems
• Plant-Herbivore Interactions

Background:

• Herbivore fronts significantly influence ecosystem structure and function through grazing.
• Plant trait alterations driven by herbivores are crucial but often overlooked in ecosystem assessments.
• The purple marsh crab (Sesarma reticulatum) creates distinct herbivore fronts in Virginian salt marshes by consuming cordgrass (Spartina alterniflora).

Purpose of the Study:

• To evaluate the impact of Sesarma reticulatum herbivore fronts on Spartina alterniflora traits and geomorphic processes.
• To quantify Sesarma front migration rates and Spartina retreat/re-vegetation dynamics.
• To assess the persistence of herbivore-induced trait changes in Spartina alterniflora.

Main Methods:

• Quantified Sesarma front migration rates in Virginian salt marshes.
• Assessed geomorphic changes (elevation, sediment shear strength, organic matter, bulk density) at leading and trailing edges.
• Analyzed Spartina alterniflora growth, defensive traits, and belowground biomass production.
• Monitored trait persistence over an 8-week period.

Main Results:

• Sesarma front migration was slower than in other regions, with Spartina retreat exceeding re-vegetation.
• Herbivory reduced elevation and sediment shear strength at the trailing edge but did not affect soil organic matter or bulk density.
• At the leading edge, grazing reduced Spartina growth and defensive traits, with effects persisting.
• At the trailing edge, grazing promoted belowground biomass production with minimal impact on other traits.

Conclusions:

• Herbivore fronts negatively impact saltmarsh plant traits at the leading edge, potentially driving front propagation.
• Plants at the trailing edge demonstrate greater resistance and resilience to herbivory, possibly due to increased belowground biomass.
• Incorporating herbivore-driven plant trait alterations is essential for predicting saltmarsh ecosystem responses and recovery.