Trophic facilitation by the oystercatcher Haematopus palliatus Temminick on the scavenger snail Buccinanops globulosum Kiener in a Patagonian bay

This study investigated the role of the American oystercatcher (Haematopus palliatus) as a resource subsidizer for the scavenger snail Buccinanops globulosum in a northern Patagonian bay (40°45′S, 64°56′W, San Antonio Bay, Argentina). The most frequent food item for the snails was dead crabs Cyrtograpsus angulatus Dana, and the snails preferred this item. In the field, most dead crabs (78%) resulted from oystercatcher predation. Field densities of dead crabs were within the 95% confidence limits of the estimated densities produced by oystercatcher foraging activity, suggesting that a large proportion of carrion available for snails is a byproduct of oystercatcher predation. Dead crabs with injuries were more rapidly detected and consumed by snails, probably because injuries produced by oystercatchers increase leakage of body fluids and facilitate penetration of the proboscis of the snails. Our results suggest that oystercatcher predation subsidize this scavenger snail by increasing availability of food, decreasing variability in their provision and facilitating their consumption.