PARENT SESSION
Contributed Oral Session 9: Marine Ecology: Disturbance; Dispersal; Recruitment
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 519 A, Level 5, Palais des congrès de Montréal
Consumer fronts, drought stress, and community collapse in southern salt marshes.
Silliman, Brian*,1, van de Koppel, Johan 2, Bertness, Mark 3, Stanton , Lee 4, Mendelssohn, Irv 4, 1 Department of Zoology, Gainesville, FL, United States2 Spatial Ecology Department, Yerseke, The Netherlands3 Department of Ecology and Evolutionary Biology, Providence, RI, United States4 Department of Oceanography and Coastal Sciences, Baton Rouge, LA, United States
ABSTRACT- Degradation of marine ecosystems is intense and occurring worldwide. In the Southeast U. S., salt marshes have recently experienced unprecedented dieback. Physical forces have been hypothesized to be primary causal factors. However, survey of many affected marshes revealed high-density (600-2300 ind./ m2) fronts of plant-grazing snails. Exclusion experiments demonstrate snail fronts convert plant-dominated marshes to barren mudflats, increasing dieback area 15-160%. Reconstruction of conditions prior to die-off implicates drought stress and intense grazing pressure as interacting, contributing factors. Analysis of a spatially-explicit, plant-herbivore model suggests that if both grazer pressure and drought stress are high, small localized disturbances may lead to cascading vegetation collapse, spreading over large spatial scales by means of traveling front of snails. Vegetation loss remains local when grazer densities are low, and localized die-off did occur in the absence of snails. Our results provide the first experimental demonstration of a factor contributing to massive marsh die-off. Moreover, model analysis predicts that future increases in consumer pressure, potentially related to anthropogenic influences (e.g. over-fishing of snail predators, eutrophication), could invoke a runaway response, and lead to widespread degradation of salt marshes.
Key words: Trophic Cascade, Herbivory, Modeling, Salt Marshes