Abiotic & Biotic Control on PFTs
Resource availability, periwinkle herbivory,
and plant age
Salt marshes are nutrient-limited ecosystems threatened by anthropogenic nutrient loading and runaway consumption by herbivores. Yet, we know little about how these stressors shape saltmarsh plant traits and antiherbivore defenses, which influence trophic interactions and ecosystem resilience. In this mesocosm study, we tested the framework provided by the resource availability hypothesis (RAH) to assess how these stressors, eutrophication and herbivory, influence the defenses of Spartina alterniflora. We then built upon this framework by measuring each trait in both originally planted stems and clonally-grown new stems. Stay tuned for results! (Wittyngham, Carey, & Johnson, in revision)
Mesocosms growing Spartina alterniflora using a mechanically-tidal system.
A marsh periwinkle (Littoraria irrorata) crawling on Spartina alterniflora in a mesocosm.
Predation pressure and plant forage quality as drivers of consumer fronts in salt marshes
Consumer-driven disturbance plagues ecosystems worldwide, and when high densities of consumers aggregate at the edge of a resource, they form consumer fronts. Our study tests four potential drivers of consumer fronts created by the purple marsh crab, Sesarma reticulatum, as it consumes Spartina alterniflora. Sesarma consumer fronts form at the heads of tidal creeks and create distinct zonation between the short-form Spartina high marsh and the tall-form Spartina low marsh as they move landward. This directional propagation inland allows tall-form Spartina to revegetate, enhancing ecosystem resilience and preventing marsh loss. We used a series of surveys and experiments to test how sediment characteristics, environmental conditions, predation pressure, and plant forage quality influenced Sesarma consumer front movement. (Wittyngham & Johnson, in review)
A purple marsh crab (Sesarma reticulatum).
A consumer front created by Sesarma with experimental cages.
(Photo credit: Aileen Devlin | Virginia Sea Grant)