ABSTRACT
A growing body of evidence shows that the behavior of metamorphosed zebra mussels is important for their survival and distribution. After settlement, mussels live in dense aggregations, byssally attached to substrate. Their attachment strength depends mainly on substrate quality. However, attachment strength is also negatively affected by multiple factors, such as hypoxia, light, and efuents from crushed conspecics. On the other hand, temperature, water movements, healthy conspecics, and predator kairomones stimulate adhesion. Zebra mussels often leave their attachment sites, either by choice or because of substrate loss, and crawl in search for another attachment location at a rate of up to 48 cm/h. Mussels avoid light and reduce activity when illumination is unavoidable. They are also less mobile in the presence of crushed conspecics. Small individuals tend to climb upward, but light and predator kairomones inhibit this behavior. Zebra mussels are able to sense conspecics and actively seek other individuals, which leads to colony formation. Clumping
is further increased by the presence of predators. In general, danger cues (predators, crushed conspecics, light) seem to affect zebra mussel behavior. When these cues are absent, mussels are active, often relocate, move upward, and keep shell valves open to access suitable conditions of habitat and food. When danger is detected, mussels stop moving, stay near the bottom, aggregate, and close shell valves to increase safety at a cost of increased exposure to less favorable environmental conditions.
