Resuspension of postlarval soft-shell clams Mya arenaria through disturbance by the mud snail Ilyanassa obsoleta

Abstract

Transport and mortality of newly settled post larvae potentially have a large influence on the population dynamics and adult distributions of coastal benthic species, including the soft-shell clam Mya arenaria. Post-settlement transport typically occurs when boundary shear stresses are high enough to resuspend the surface sediments in which the small clams reside. The objective of the present study was to examine the effect of disturbance by the mud snail Ilyanassa obsoleta on the hydrodynamic transport of recently settled M. arenaria. Laboratory flume experiments showed that disturbance by activities of I. obsoleta caused suspension of small dams [1.8 and 2.3 mm) at boundary shear velocities (1.0 and 1.3 cm s-1) that were too slow to suspend undisturbed clams. In shear velocities high enough to cause bulk sediment transport (1.4 and 2.0 cm s-1), more clams were suspended in the presence of snails than in their absence. Manipulative field experiments using cages to exclude snails demonstrated that abundances of juvenile M. arenaria (year-1 recruits) were lower in sediments where snails were present than where snails were absent. These results suggest that biological disturbance, such as that imposed by activities of mobile, benthic deposit feeders, may play an important role in postlarval transport and, eventually, in the adult distributions of infaunal bivalves.