TPO-26 - Integrated Writing Task 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 b

The passage and lecture both discuss a kind of shellfish, which is dubbed zebra mussel, and its impact in North America. The reading claims that the invasion of this creature cannot be stopped and it would be a prominent dangerous. In contrast, the professor explains that there are some effective ways to control zebra’s spread nowadays.

Firstly, the text indicates the past experience of spreading the zebra mussel by ships is a significant evidence to confirm that possibly this invasion is without cease. The professor refutes this and says that now there are an effective ways to stop ships to transport mussels to the new location. For instance, the ships should be required to empty out the fresh water and use ocean water as ballast when they are in the oceans. This salt water can kill all of the mussels.

Secondly, the passage puts out when the mussels reach to a new area they have a great chance to dominate it. However, the speaker mentions that mussels can dominate the new environment only at the beginning. According to the professor, in the Europe, local birds found mussels as new food and switch to eat them. The birds eat a lot of mussels, and hence they not dominate new habitat anymore.

Thirdly, the reading points the zebra mussel’s competition for food in the new environment can cause a reduction in the other fish population. The lecture denies this and talks that it is true that mussels have some negative impacts on the fish that eat planktons. But they also have positive benefits for other fish. For example, the mussels produce the nutrients that are eaten by fish that feed near the bottom of the river.