The passage and the lecture discuss about whether Zebra Mussel- a fresh water shellfish has spread serious treats to other fish population or not in North America. The passage states that this population is dangerous for other fresh water fish population. The lecture, however, refutes and cites variety of ways to control the population of zebra mussels.
First, The passage mentions that population of Zebra Mussel is out of control and reasons for it is transportation through ballot water. In contrast, the lecture argues that people do not have enough knowledge to control it. There are effective ways to control them. For instance, The ballot water, which they carry in ship, is generally fresh water that is suitable for Mussels. If they will use ocean water, that will kill the mussels. In this way, they can control the transportation of Zebra mussels from Europe to North America.
Second, the passage claims that Zebra mussels dominate a new habitat due to absence of predators at a new location. ON the other hand, the lecture disclaims it by adding that it was scenario in the beginning. After that, aquatic birds exploited Zebra Mussels, and preyed on them by switching their food to those fishes. Thus, the lecture contradicts the point that lack of predators made in the passage.
Lastly, the passage asserts that the dominant Zebra Mussel species lead to declination in overall fish population by eating plankton –food for many fishes. The lecture agrees on that negative impact of the Zebra Mussel. Conversely, the lecture points out the favorable outcomes of the Mussels’ population. They provide nutrition to bottom feeding species of fish resulting in to increase in population of bottom feeding fishes. Hence, this point made by the professor also dismisses the author’s argument.
TOEFL listening lectures: A university lecture by a professor of Natural History