Factors affecting the movement of adult zebra mussels (Dreissena polymorpha)

Adult zebra mussels are generally thought of as sessile animals. However, when detached from their byssus, adult mussels exhibit creeping behavior similar to that of other bivalve species. Our study examined the effects of size, light, water hardness, temperature, and the presence of injured conspecifics on the movement of adult zebra mussels. Mussels were placed in aquaria and their movement was recorded after a 2-h interval. Mussels left visible trails in a thin layer of sand on the aquarium floor that allowed for accurate measurements of distance and direction of movement. The tendency to move and distance moved by the mussels was inversely proportional to size of the individual mussels. There was no significant effect of temperature on movement, though smaller mussels tended to move more at higher temperatures. Although distance traveled was not significantly different in light versus dark conditions, there was a significant effect of light on direction traveled. Zebra mussels were strongly negatively phototaxic. The presence of injured conspecifics decreased movement significantly, whereas water hardness did not have a significant effect on movement. The movement of adult zebra mussels is an under-appreciated phenomenon and deserves greater consideration for understanding dispersal vectors and development of antifouling methods to be used in the future.