title: Crab: snail size-structured interactions and salt marsh predation gradients.
abstract: We studied size-structured predator-prey interactions between blue crabs (Callinectes sapidus) and marsh periwinkles (Littoraria irrorata) with a combination of field studies, laboratory experiments and individual-based modeling. Size distributions of Littoraria differed among years at the same sites in a salt marsh and could largely be explained by dominance of strong cohorts in the population. At a given site, abundance increased with elevation above tidal datum. Size-selective predation by blue crabs does not appear to be an important regulator of snail size distributions but may have a major effect on local abundance. Laboratory studies indicated that predator-prey interactions between Callinectes and Littoraria are strongly size-dependent. Crabs were generally effective at feeding on periwinkles at size ratios greater than approximately 6 (crab width: snail length). At lower size ratios crabs were far less effective at manipulating the snails, which often survived but with damaged shells. An individual-based model which incorporated information about incidence of snail shell scarring (resulting from non-lethal interactions) and snail density, predicted reduced predation rates and smaller average crab size with distance from the low tide refugium for crabs.
authors.affiliation: Center for Limnology, University of Wisconsin, 680 North Park Street, 53706, Madison, WI, USA.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Schindler
authors.affiliation: Center for Limnology, University of Wisconsin, 680 North Park Street, 53706, Madison, WI, USA.
authors.forename: Brett M
authors.initials: BM
authors.lastname: Johnson
authors.affiliation: Center for Limnology, University of Wisconsin, 680 North Park Street, 53706, Madison, WI, USA.
authors.forename: Neil A
authors.initials: NA
authors.lastname: MacKay
authors.affiliation: Center for Limnology, University of Wisconsin, 680 North Park Street, 53706, Madison, WI, USA.
authors.forename: Nicolaas
authors.initials: N
authors.lastname: Bouwes
authors.affiliation: Center for Limnology, University of Wisconsin, 680 North Park Street, 53706, Madison, WI, USA.
authors.forename: James F
authors.initials: JF
authors.lastname: Kitchell
keywords: Callinectes; Littoraria; Predation; Salt marsh; Size-structure