integrated

The reading claims that the zebra mussel, a fresh water shellfish, has long been spreading and this invasion cannot be stopped and it poses a serious threat to freshwater fish populations in all of North America, and provides three reasons of support. In contrast, the professor states that there are ways to control of spreading the mussel and it is not clear that it have a serious threat. He refutes each of the author's reasons.

First, the article avers that the history of the zebra mussel's spread suggests that the invasion might be unstoppable. However, the lecturer opposes this point by stating that it is true that it speards quickly in the past because there was no enough knowledge to stop it. In fact, he provides an example that the way zebra mussel travels through ballast water in Europe and it could be empty in the North of America, but ships can required refill the water with ocean water. He mentions that mussels will be killed by salt water and it will not be spread.

Second, the reading posits that once zebra mussels are carried to a new habitat, they can dominate it. On the other hand, the professor counters this point by saying that there are no predators only in the begning. Actually, he argues that in Europe when zebra mussels dominate there, birds noticed that there is a new kind of food and they changed their habitat. Surprisingly, birds switched to eat mussels because there were abundant for them to eat.

Third, the passage asserts that zebra mussels are likely to cause a decline in the overall fish population in habitats where they become dominant. Conversely, the professor casts doubt on this point by explaining that the overall fish population will not decrease, but it is true that mussels have a negative effect on fish population. In addition, mussels have a positive effect on another fish because they will create general nutrients for fish and fish may increased significantly.