In terms whether the zebra mussel will exert negative influence on North American, the passage and lecture are contradictory to each other. The author believes that zebra mussel might do harm the local species as they arrived while the lecturer holds a different opinion.
First of all, the author makes a point that the history events suggest the zebra mussel's invasion is unstoppable. In the past, human transportation makes it possible for zebra mussel spread around the whole Europe and it is likely to happen again in North American. However, the lecturer demonstrates a different idea that a change made in the "ballast water" will prevent the invasion of zebra mussel from continuing. He says that if we refill the "ballast water" with ocean water, the mussel will no longer survive because the saline water might probably kill them all.
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