TPO 26 Integrated TOEFL Writing

The reading and the lecture are about zebra mussel, which is freshwater shellfish native to Eastern Europe, but now they are spread worldwide. The author of the reading feels that the zebra mussel invasion brings many challenges to the freshwater fish population in North America, and they could not be stopped from spreading more. The lecturer disputes the claims made in the article. His position is that there are ways to control their population and that mussels are not a threat to some freshwater fishes.

According to the reading, zebra mussels were brought into American waters by human ships. The article mentions that mussels can attach themselves to a ship's bottom specific area called ''ballast water'', and upon arrival to North America, they colonize there. The lecturer challenges this specific argument. He claims that the earlier ship crew did not know about these creatures and that mussels are attached to their ship, and upon arrival, they emptied their ballast water. Additionally, he points out that now they could be prevented by not emptying their ballast water in the seas but to let them die by removing their ballast water into the ocean; hence, saltwater will kill the mussels.

Secondly, the author suggests that mussels once dominate a new environment they would produce a higher reproduction and would add to their population. In the article, it is said that once they grew in large number and without any natural predators, it would be a severe threat. The lecturer, however, asserts that in the beginning, there were no predations of the zebra mussels, but they do have one predation that decreases their population. He goes on to say that birds prey on mussels and often eats mussels as their primary food.

Finally, the author posits that zebra mussels might have been the declining cause of the fish population. The author contends that mussels eat plankton, which is also a crucial food element of fish, so they may compete with the fish population. In contrast, the lecturer's stance is that the fact they decline overall fish population is true, but some other fishes may take advantage of mussels. He notes that mussels generate nutrients that are eaten by bottom fish species, so bottom-feeding fish populations may increase.