Environment-Plant-Consumer Interactions
Resource availability, periwinkle herbivory,
and plant age
Salt marshes are nutrient-limited ecosystems threatened by anthropogenic nutrient loading. Yet, we know little about how excess nutrient availability can shape herbivory and saltmarsh plant traits. In this mesocosm study, we tested the framework provided by the resource availability hypothesis (RAH) to assess how eutrophication influenced herbivory and the defenses of Spartina alterniflora. We then built upon this framework by measuring each plant trait in both originally planted stems and clonally-grown new stems, finding that new stems were more palatable than older stems. (Wittyngham, Carey, & Johnson, 2023)
Mesocosms growing Spartina alterniflora under varying nutrient conditions using a mechanically-tidal system.
A marsh periwinkle (Littoraria irrorata) crawling on Spartina alterniflora in a mesocosm.
Consumer fronts shape saltmarsh sediment and plant traits
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 focused on fronts created by the purple marsh crab, Sesarma reticulatum, as it consumed the smooth cordgrass, Spartina alterniflora. We found that Sesarma fronts altered vertical accretion capacity and reduced soil organic matter and sediment shear strength. Further, direct grazing by Sesarma reduced Spartina growth traits and defensive ability, presenting an additional pathway in which these fronts shape ecosystem function. (Wittyngham & Johnson, in review)
A purple marsh crab (Sesarma reticulatum).
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A consumer front created by Sesarma with experimental cages.
(Photo credit: Aileen Devlin | Virginia Sea Grant)
Salinity and simulated herbivory
Sea-level rise is expected to drive saline waters into previously fresher regions of estuaries. This saltwater intrusion may bring with it several species of herbivores who were previously physiologically constrained by salinity. In this mesocosm study, I tested how various salinities and simulated herbivory (using garden shears) influenced the growth of the smooth cordgrass, Spartina alterniflora, collected from oligohaline and mesohaline marshes. I found that plants from the mesohaline marsh were better defended than those from the oligohaline marsh, and that increased salinity and simulated herbivory decreased new stem and belowground biomass production. (Wittyngham 2021)
A particularly muddy day collecting from a freshwater marsh.
Measuring Spartina and counting new stems.