Rates of consumption of marsh periwinkles (Littoraria irrorata) by mud crabs (Eurytium limosum and Panopeus obesus) between August and December in a Georgia salt marsh

Predatory mud crabs (Panopeus obesus and Eurytium limosum) are two of the main resident infaunal predators in southeastern US salt marshes.The relative importance of the two species in the trophic control of marsh periwinkles (snails; Littoraria irrorata) is likley to change across seasons. We therefore manipulated the these predator species (Panopeus obesus and Eurytium limosum) in experimental cages in the field (at Dean Creek, Sapelo Island, GA) and assessed monthly predation rates over four months, between 15th August to 15th December. We included 3 treatments, consisting of two treatments containing each species alone, and one containing both species together; all treatments had the same density. Specifically, 1) 4 x Panopeus individuals; 2) 4 x Eurytium individuals; 3) 2 x Panopeus individuals + 2 Eurytium individuals. Only adult crabs (33-40mm carapace diameter) were used. We maintained the treatments over 4 months (15th Aug - 15th Dec 2009), replacing any missing crabs every two weeks and counting the number of snails killed by predators each month.