Einstein Science Reporting for Kids
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American Association for the Advancement of Science

Mussels grow a thick skin against a crab bully

The invading Asian crab Hemigrapsus sanguineus.

"Grow thicker skin" is what people tell us when a bully bothers us. Atlantic mussels are even taking the advice and doing so quickly.

About 15 years ago an Asian shore crab named Hemigrapsus sanguineus moved in to the Atlantic mussels' Atlantic Ocean neighborhood around New Jersey and found the mussels very tasty. These Asian crabs are called an "invaders" because they don't belong in the Atlantic Ocean. They have made themselves at home and moved as far south as North Carolina and as far north as Maine. And, they still enjoy eating the mussels.

But the mussels are giving the crabs a hard time. They grew thicker shells to make it tougher for the crabs to eat them. Animals are known to eventually evolve, or change, to handle different situations including predators. That usually takes a very long time, but these mussels have evolved very quickly.

The scientists -- Aaren Freeman and James Byers -- believe this is the first example of an invader triggering such a fast change in a native species. Freeman and Byers found that these mussels sense something the Asian crabs put out in the water and that triggers the mussels to grow thicker shells.

Invaders like the crab come into new areas and create trouble for the animals that are already there, so it is important to learn more about how some smart animals work to survive.