integrated topic.

In this set of material, the reading passage mainly discussed that the zebra mussels continue to grow in North America and accounts as a threat to freshwater fish population. While the professor casts doubt on what is stated in the reading and provides some reasons to repudiate the claim.

First of all, based on the reading, zebra mussels' spread is continuing by human's activities through the water ways. Whereas the professor believes that now people have enough knowledge about it and the zebra mussel's population would not increase like the past. Since when ships received to North America and made their ballast water containers, which had zebra mussels, empty. Then, the ships crew can do not empty their containers and inhibit of their spread.

Although the reading states that this species has ability to adapt to the new environment easily and have no predators, the professor refutes this point by saying that it is true that they do not have predator at first but local birds change their habitat for catching them after a while. They feed on zebra mussels and can eat a lot of them. Thus, zebra mussels cannot dominate to the habitat.

At last, the author of the reading claims that competition for plankton among the zebra mussels and other plankton eaters causes a decrease in the fish population. On the contrast, the professor states that even though the zebra mussels have negative impact on plankton eaters, they have positive effect on other species which feed on under water species.