1. How many zebra mussels were there in the Hudson River within a year of their first appearance? A. 500 billion B. 500 million C. 500 thousand D. 500
2. This text explains a cause-and-effect pattern in the Hudson River ecosystem that began with the zebra mussel invasion. What effect did the zebra mussels have on the phytoplankton in the Hudson River? A. The number of phytoplankton in the river rose by a little. B. The number of phytoplankton in the river fell by a little. C. The number of phytoplankton in the river rose by a lot. D. The number of phytoplankton in the river fell by a lot.
3. Phytoplankton are one of the most important parts of the food web in the Hudson River. What evidence supports this conclusion? A. The population of phytoplankton dropped sharply soon after zebra mussels invaded the river. B. The decrease in phytoplankton caused a decrease in the river's zooplankton, fish, and native mussel populations. C. The decrease in phytoplankton meant that the river's turbidity, or cloudiness, decreased. D. Zebra mussels caused oxygen levels in the river to drop, partly by removing the phytoplankton that produce oxygen.
4. Which population was helped by the invasion of the zebra mussels? A. phytoplankton B. zooplankton C. water celery D. native mussels
5. What is the main idea of this text? A. In the years right after the invasion, zebra mussels evolved and adapted to the Hudson River ecosystem. B. In the years right after the invasion, zebra mussels caused a number of changes in the Hudson River ecosystem and food web. C. In the years right after the invasion, zebra mussels did not have a major impact on the Hudson River ecosystem or food web. D. At first, zebra mussels did not have any impact on the Hudson River ecosystem, but their impact increased over time.
6. Read these sentences from the text. "In the years right after the invasion, phytoplankton fell by 80 percent. Zooplankton (which eat phytoplankton) declined by half. And the smallest zooplankton (called microzooplankton), fell by about 90 percent." Based on these sentences, what does the word "decline" most nearly mean? A. to drop in number B. to fall over C. to increase D. to stay the same
7. Choose the answer that best completes the sentence. With far less phytoplankton, the water got clearer. ______, rooted aquatic plants such as water celery increased by up to 40 percent. A. In contrast B. However C. As a result D. Similarly
8. What are two populations that decreased as an immediate result of the zebra mussel invasion?
9. One direct effect of the zebra mussel invasion was a decrease in the cloudiness of the water. How did this affect species in the Hudson River ecosystem?
10. Once scientists understood the short-term impact of the zebra mussel invasion, they started to wonder about the invasion's long-term impact on the ecosystem. Why might the Hudson River ecosystem look different many years after the zebra mussel invasion than it did just a few years after the invasion? Use evidence from the text to support your answer.