Predator and flow influence on bivalve clam excurrent jet characteristics

Abstract

Predator–prey interactions, and subsequently, marine communities, may be controlled by the hydrodynamics of the fluid flow in which the organisms live. This study looked at the pumping behavior of the bivalve clam, Mercenaria mercenaria, and how clams may use ambient and jet hydrodynamics to control the information available to their tracking predators. Specifically, this study quantified the velocity of the excurrent jet of actively pumping clams in the presence and absence of predator chemical cues under several ambient crossflow velocities using particle image velocimetry (PIV). Clams were found to increase the standard deviation values of the jet velocity fluctuations and to increase the randomness (as measured by fractal dimension) of the velocity values when predator chemical cues were present in the flow. The increased standard deviation of the jet velocity fluctuations, when a predator was present upstream, corresponded to increasing the energetic cost of pumping by approximately five times. However, increasing the randomness of the velocity values (as measured by the fractal dimension) did not appear to be more energetically costly. The changes seen here in the fluctuating characteristics of the clam excurrent jet are likely to promote the mixing of clam chemical metabolites by controlling the chemical source characteristics, which suggests that the behavior may be a means of predator avoidance.