"Not so much as you might think. I don't suppose that the oysters will invade dry land and chase the natives from one rain puddle to another, but they'll grow without check, build oyster reefs that'll menace navigation, change the chemical composition of Niobe's oceans, pollute the water with organic debris of their rotting bodies, and so change the ecological environment of this world that only the hardiest and most adaptable life forms will be able to survive this!" "But they'll be self-limiting," I protested. "Sure. But by the time they limit themselves, they will eliminate about everything else." "If you're right, then, there's only one thing to do. We'll have to let the natives know what the score is and start taking steps to get rid of them." "Oh, I'm right. I don't think you'll find anyone who'll disagree with me. We kicked this around at the Lab for quite a spell before I came up here with it." "Then you've undoubtedly thought of some way to get rid of them." "Of course. That was one of the first things we did. The answer's obvious." "Not to me." "Sure. Starfish. They'll swamp up the extra oysters in jig time." "But won't the starfish get too numerous?" "No. They die off pretty fast without a source of food supply. From what we can find out about Niobe's oceans, there is virtually no acceptable food for starfish other than oysters and some microscopic animal life that wouldn't sustain an adult." "Okay, I believe you. But you still leave me cold. I can't remember anything about a starfish that would help him break an oyster shell." Bergdorf grinned. "I see you need a course in marine biology. Here's a thumbnail sketch. First, let's take the oyster. He has a big muscle called an adductor that closes his shell. For a while he can exert a terrific pull, but a steady tension of about nine hundred grams tires him out after an hour or so. Then the muscle relaxes and the shell gapes open. Now the starfish can exert about thirteen hundred grams of tension with his sucker-like tube feet, and since he has so many of them he doesn't have to use them all at one time. So, by shifting feet as they get tired, he can exert this pull indefinitely. "The starfish climbs up on the oyster shell, attaches a few dozen tube feet to the outside of each valve and starts to pull. After a while the oyster gets tired, the shell opens up, and the starfish pushes its stomach out through its mouth opening, wraps the stomach around the soft parts of the oyster and digests it right in the shell!" I shuddered. "Gruesome, isn't it?" Bergdorf asked happily. "But it's nothing to worry about. Starfish have been eating oysters on the half shell for millions of years. In fact I'll bet that a starfish eats more oysters in its lifetime than does the most confirmed oyster-addict." "It's not the fact that they eat them," I said feebly. "It's the way they do it. It makes me ill!"