Oysters, soft-bodied animals without skeletons, are important for the underwater community they share with plants, fish, and other life. They are food     1     crabs and other animals. As new oysters grow, they attach their shells to older ones,     2     (form) bigger reefs with many small spaces     3     other animals live. Oysters eat algae (藻类). If algae grow too fast, they can exhaust oxygen from the water—and even fish need oxygen     4     (breath)!

Because so many animals depend on them, oysters are called a keystone species. If a keystone species     5    (disappear), other plants and animals may die off and not grow back.

That’s     6     (exact) what happened 100 years ago in New York Harbor—a group of rivers and bays around New York City. Before then, lots of oysters lived in these waters. The oysters were famous! They     7     (ship) to restaurants around the world. The oysters were delicious—maybe too delicious. By the early 1900s, people were eating them faster than they could grow.

The oysters were in trouble for     8     reason. Pollution was pouring into the waters of the growing city. The harbor became so     9     (pollute) that few types of animals could live in it. Since the 1970s, new laws     10     (help) reduce toxic waste. Some fish started to swim through again. But oysters were still missing—until recently.