TPO26-integ

Both the reading and lecture discuss possible theories behind the widespread distribution of zebra mussels which are freshwater shellfishes in North America. The reading claims that they cause serious problems for native habitat since their invasion cannot be stopped. However, the lecturer finds all the ideas dubious and presents some evidence to refute them all.

First, the reading holds the view that the mussel transfers to new areas by sticking on bottom of the ships. Also, it mentions that they can survive in freshwater names "ballast water". In contrast, the professor brings up the idea that although the ships take some freshwater which consists of zebra mussel, they were refilled by ocean water that kill the mussel.

Furthermore, the author argues that new habitats of the mussels give them the opportunity to grow dramatically. In fact, there are not any predators in the new region to eat them, and consequently they thrive rapidly. On the contrary, the lecturer dismisses the issue due to the fact that the mentioned reason seems be true at first glance. But after a while, other animals particularly the birds find them and eat them. In addition, he mentions that the birds can eat a lot of zebra mussels which confirms that they cannot be increased enormously.

Last but not least, the passage asserts that fish population will be decreased since they compete with zebra mussels on a mutual food named "plankton". Conversely, the professor contrasts that zebra mussels provide other nutrients that are useful for other fishes in the bottom of river and lakes. As a result, they do not seem useless to their environments.