How do zebra mussels cause ecological harm in the Great Lakes?

Zebra mussels cause significant ecological harm in the Great Lakes primarily by filtering plankton from the water. This process drastically reduces the availability of food resources for native species, such as juvenile fish and other aquatic organisms that rely on plankton as a critical part of their diet. As zebra mussels multiply, they can filter large volumes of water—potentially up to a liter per mussel per day—which can lead to a severe decline in the phytoplankton and zooplankton populations. This decline disrupts the entire food web, negatively impacting not only the species that directly consume plankton but also those that rely on them, ultimately altering the dynamics of the entire aquatic ecosystem.

In contrast, the other options do not accurately reflect how zebra mussels impact the environment. While they can affect habitat availability through colonization, they do not compete with native fish for habitat directly. Zebra mussels are also not known to release toxins into the water, which eliminates option C. Lastly, while their presence may influence sediment dynamics, they do not primarily cause increased sediment levels in the water, which makes option D less relevant to their ecological impact.