Teacher Resources

"Aliens. Invaders. Creatures from a distant shore, they are taking over Rhode Island's coast," I say. "Want to see?"

"Yes," says the girl.

We walk down to the line where the water meets land. It is low tide. It is muddy and wet. "Flip over that rock," I say.

She bends over and lifts a stone the size of a dinner plate. "Crabs. Crabs," she screams.
A dozen banded, brownish crabs scurry for cover. They'd been hiding under the rock, waiting for high tide. Now they scamper for their life.

I pick one up and show the girl the bands on the legs. We lift another rock and there are at least a dozen more, about the size of a watch, crawling madly for safety.

I explain to the girl that these Asian shore crabs, which look very much like the well-known green crabs, are invaders because they came by boat from Japan about 12 years ago.

"I didn't know crabs took boats," she said.

Big cargo ships travel the world and the often take on large amounts of seawater for balance and stability. This is called ballast water. Since the water comes directly from the sea, the water is filled with sea life. Some of it lives and some of it dies. One day Asian shore crabs and their eggs were sucked into the boat's ballast water. The crabs and the eggs took a free ride to the United States and were pumped off the ship near the coast of New Jersey.

The crabs liked their new country. There was plenty to eat. Many places to hide and not many animals were interested in eating them.

Life is so good for the Asian shore crabs that they now dominate the crab world along our shores. They are the easiest crabs to find in Rhode Island. Find a beach at low tide with rocks you can flip over and I guarantee you will find an invader that scurries off.