The zebra mussel, a freshwater shellfish native to Eastern Europe, has long been spreading out from its original habitats and has now reached parts of North America. There are reasons to believe that this invasion cannot be stopped and that it poses a ser

Both the reading and lecture discuss zebra mussel. The reading implies that the intrusion of zebra mussel is unstoppable and it threatens the fresh water fish populations which habitat in North America. However, the professor strongly disagrees with the reading passage. Accordingly, he presents three refutations.

First of all, the reading passage mentions that invasion cannot be stopped. Yet, the lecturer severely challenges the theory by arguing that people have limited knowledge. Furthermore, he states that there are ways to prevent ship spreading this creature to new locations. Therefore, the invasion of zebra mussels can be successfully avoided actually.

Secondly, the passage suggests that as long as zebra mussels arrive at new habitat, they will be able to dominate the environment. Nevertheless, the scholar seriously contradicts the hypothesis by calling into question predator of mussels. In fact, natural predators would switch their food sources and eat zebra mussels a lot. As a result, it is unlikely for mussels to dominate their habitat.

Last but not least, the reading indicates that zebra mussels might bring about the decline of overall fish population in habitat. Once again, the speaker opposes the evidence revealed in the article. In addition, he points out that even though the fish which is plankton eater would be affected negatively by mussels, another species of fish which live in bottom layer would reverse effect because of the nutrition from zebra mussels. Apparently, the third explanation is unconvincing.

In conclusion, the professor argues against each theory in the reading. That is to say, he maintains that it is not clear that zebra mussels have great impact on fish population and habitat.