title: Abiotic stress mediates top-down and bottom-up control in a Southwestern Atlantic salt marsh.
abstract: Increasing evidence has shown that nutrients and consumers interact to control primary productivity in natural systems, but how abiotic stress affects this interaction is unclear. Moreover, while herbivores can strongly impact zonation patterns in a variety of systems, there are few examples of this in salt marshes. We evaluated the effect of nutrients and herbivores on the productivity and distribution of the cordgrass Spartina densiflora along an intertidal stress gradient, in a Southwestern Atlantic salt marsh. We characterized abiotic stresses (salinity, ammonium concentration, and anoxia) and manipulated nutrients and the presence of the herbivorous crab Neohelice (Chasmagnathus) granulata, at different tidal heights with a factorial experiment. Abiotic stress increased at both ends of the tidal gradient. Salinity and anoxia were highest at the upper and lower edge of the intertidal, respectively. Nutrients and herbivory interacted to control cordgrass biomass, but their relative importance varied with environmental context. Herbivory increased at lower tidal heights to the point that cordgrass transplants onto bare mud substrate were entirely consumed unless crabs were excluded, while nutrients were most important where abiotic stress was reduced. Our results show how the impact of herbivores and nutrients on plant productivity can be dependent on environmental conditions and that the lower intertidal limits of marsh plants can be controlled by herbivory.
authors.affiliation: Laboratorio de Ecología, Departamento de Biología (FCEyN), Universidad Nacional de Mar del Plata, CC 573 Correo Central, B7600WAG Mar del Plata, Argentina. jalberti@mdp.edu.ar
authors.forename: Juan
authors.initials: J
authors.lastname: Alberti
authors.forename: Agustina
authors.initials: A
authors.lastname: Méndez Casariego
authors.forename: Pedro
authors.initials: P
authors.lastname: Daleo
authors.forename: Eugenia
authors.initials: E
authors.lastname: Fanjul
authors.forename: Brian R
authors.initials: BR
authors.lastname: Silliman
authors.forename: Brian
authors.initials: B
authors.lastname: Silliman
authors.forename: Mark
authors.initials: M
authors.lastname: Bertness
authors.forename: Oscar
authors.initials: O
authors.lastname: Iribarne
mesh_terms: D000818:Animals; D003445:Crustacea; D017753:Ecosystem; D010100:Oxygen / Q000032:analysis; D006109:Poaceae / Q000502:physiology; D012623:Seawater; D012965:Sodium Chloride / Q000032:analysis; D013312:Stress, Physiological; D014872:Water Movements
chemical_list: D012965:Sodium Chloride; D010100:Oxygen