The effect of crab cues and clam density on Mya arenaria : burrowing depth and resource allocation

by Elizabeth Bryson

Previous research has shown that Mya arenaria (soft-shell clam) responds to chemical cues from Carcinus maenas (green crab) by burrowing deeper into the mud, and this can have a cost in terms of lower feeding rate. This study sought to examine the roles of crab predation cues and intraspecific competition on M. arenaria behavior and growth. A theoretical model is outlined as a basis for predictions that (1) without crab cues, there will be no effect of growth, and (2) in the presence of crab cues, competition will affect burrowing depth and clams will make trade-offs between maximal net energy gain and maximal survival. The results of this study confirm that M. arenaria respond to predation cues by burrowing more deeply, but they do not indicate that this deep burrowing is costly in terms of growth. In addition, this study does not indicate that clams respond to intraspecific competition by changing burrowing depth or total growth rate. Instead, M. arenaria responds to intraspecific competition by allocating resources to shell and soft tissue growth rather than siphon growth. Based upon the nature of the resounces allocation, it is likely that the primary competitive interaction is through interference rather than exploitation.