If you were to stare down into one of a few dozen intertidal pools at low tide, as waves glide in and out, you might have a hard time spotting the robots.

That’s because they look just like the real mussels that surround them. (If you want to see how hard it is, try clicking on the robotic mussel in the photo above.)

“It’s a problem finding them again,” said Brian Helmuth, a professor of marine science and public policy at Northeastern University, “because they do look so much like mussels.”