Why are zebra mussels classified as an invasive species?

Zebra mussels are classified as an invasive species primarily because they negatively affect native species. Invasive species are typically defined as non-native organisms that, when introduced to a new environment, cause harm to the ecosystem, economy, or human health. Zebra mussels can outcompete native mussel species for resources like food and space, leading to a decline in these native populations. They also filter large amounts of water, which can alter the availability of nutrients essential to local aquatic plants and disrupt the entire food web.

This impact on native species is substantial because a drop in species diversity can lead to ecosystem imbalances, affecting everything from predator-prey relationships to the health of the overall habitat. Their aggressive colonization can also lead to economic issues, such as damaging boats and clogging water intake systems for power plants and municipal water treatment facilities.

The other choices do not accurately reflect the reasons behind zebra mussels being classified as invasive. For example, natural processes do not account for their introduction, as zebra mussels were introduced through human activities, particularly shipping practices. While they do disrupt local habitats and can block waterways, the most critical factor leading to their classification involves their negative impact on native species and communities, which is the primary concern with invasive species.