Why are the accidentally introduced zebra mussels referred to as an invasive species?

Zebra mussels are considered an invasive species because they are non-native organisms that have been introduced to new ecosystems, primarily through ballast water from ships. Once established, they reproduce rapidly and outcompete local species for resources, disrupting food webs and altering habitats. Their presence can also cause significant economic damage by clogging water intake systems and affecting industries such as fishing and tourism. This combination of ecological disruption and economic impact underscores their classification as an invasive species.