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

Transport and mortality of newly settled post larvae potentially have a lar ge influence on the population dynamics and adult distributions of coastal benthic species, including the soft-shell clam Mya arenaria. Post-settlemen t transport typically occurs when boundary shear stresses are high enough t o resuspend the surface sediments in which the small clams reside. The obje ctive of the present study was to examine the effect of disturbance by the mud snail Ilyanassa obsoleta on the hydrodynamic transport of recently sett led M. arenaria. Laboratory flume experiments showed that disturbance by ac tivities of I. obsoleta caused suspension of small clams (1.8 and 2.3 mm) a t boundary shear velocities (1.0 and 1.3 cm s(-1)) that were too slow to su spend undisturbed clams. In shear velocities high enough to cause bulk sedi ment transport (1.4 and 2.0 cm s(-1)), more clams were suspended in the pre sence of snails than in their absence. Manipulative field experiments using cages to exclude snails demonstrated that abundances of juvenile M. arenar ia (year-1 recruits) were lower in sediments where snails were present than where snails were absent. These results suggest that biological disturbanc e, such as that imposed by activities of mobile, benthic deposit feeders, m ay play an important role in postlarval transport and, eventually, in the a dult distributions of infaunal bivalves.