What is a significant concern regarding zebra mussel populations in freshwater ecosystems?

The concern regarding zebra mussel populations in freshwater ecosystems primarily revolves around their ability to deplete oxygen levels for other organisms. Zebra mussels are filter feeders that consume a substantial amount of phytoplankton and zooplankton, which are critical components of the aquatic food web. By filtering out these organisms, zebra mussels can reduce the available food resources for other species, which can lead to a decline in the populations of fish and other aquatic life that depend on them. This over-filtering can also contribute to a decrease in dissolved oxygen levels, as less organic matter is available to support the respiration processes of aquatic organisms.

The other options do not accurately reflect the ecological impact of zebra mussels. They do not increase water acidity, nor do they serve as a food source for all fish species, as many fish cannot effectively consume them due to the hard shell of the mussels. While zebra mussels can enhance water clarity by filtering out suspended particles, this is not a universally positive effect, as it can disrupt the balance of the ecosystem and contribute to the original concern regarding decreased oxygen levels and overall biodiversity.