Which of the following is a natural behavior that contributes to zebra mussel spread?

The natural behavior that significantly contributes to the spread of zebra mussels is their ability to attach to boats and equipment. This behavior allows them to travel between different water bodies, making it easier for them to infest new areas. Once they latch onto a surface, such as the hull of a boat or fishing gear, they can be transported without the need for direct water connectivity between habitats. This mode of transport is particularly concerning because it often goes unnoticed; individuals using recreational boats or equipment may not realize they are facilitating the spread of this invasive species.

The other options play different roles in the ecology of aquatic systems but are not primary factors in the spread of zebra mussels. Zebra mussels do not migrate through waterways in a way that contributes significantly to their colonization of new areas. They reproduce primarily in freshwater environments, making reproduction in saltwater irrelevant. Additionally, while larger fish might consume zebra mussels, this predation does not enhance their spread; in fact, it can potentially limit their population in certain areas. Thus, the behavior of attaching to vessels and gear is the key natural factor that leads to their widespread dissemination.