Provide an example of an invasive species and explain its potential impact on ecosystem dynamics.

• A. Zebra mussels in North America alter food webs, clog water systems, and outcompete native species, changing energy flow and nutrient cycling.
• B. Zebra mussels in North America are beneficial and improve energy flow.
• C. Zebra mussels only affect terrestrial ecosystems.
• D. Zebra mussels have no impact on their new environment.

Answer: (B)

An invasive species can drastically alter energy flow and nutrient cycling in an ecosystem by changing which organisms are present and how they interact. Zebra mussels introduced to North American waters are a clear example. They attach in huge numbers to boat hulls, pipes, and native mussels, and they are powerful filter feeders. By removing large amounts of phytoplankton from the water, they reduce the food available to other plankton feeders and to species that rely on plankton as a primary food source, which shifts the way energy moves through the food web. Their intense competition for space also allows them to outcompete native mussels, lowering biodiversity and reshaping predator–prey relationships.

Their activity changes nutrient cycling as well. By filtering vast amounts of water, they alter the form and distribution of nutrients, and those nutrients can end up stored in the mussels themselves or released in different forms as waste, affecting plant growth and overall ecosystem productivity. The sheer abundance of these mollusks can also affect sediment characteristics and water clarity, further influencing habitat structure and energy transfer up the chain. In short, invasive species like zebra mussels tend to disrupt ecosystem dynamics, not improve them, illustrating how introductions can rewire energy pathways and nutrient flows in ecosystems.