Stubborn Sea Stars Thwart Student Scientists by Expelling Microchip Implants

Sea stars are much stranger than we imagined. Biology students at the University of Southern Denmark implanted a group of the animals with microchips and went about their business. When they checked in days later, the chips were lying on the floor of the sea stars’ tank.

The students realized that the sea stars had spit the trackers out—not through the original implantation sites in their skin, but through the tips of their arms. As Mary Beth Griggs notes in Popular Science, “That would be like a human getting shot in the leg and then ejecting the bullet from their fingers without any internal injuries.”

Rather than getting frustrated, the young biologists put their scientific curiosity to work and decided to conduct formal experiments to better understand the animals' behavior. The researchers microchipped another 53 sea stars and monitored them using ultrasound scanners, watching the animals’ bodies to see where the chips were going.

What they saw was strange. The chips moved through the sea stars’ bodies at a rate of about 10 percent of the distance from entry to exit point per day, but the route they took was far from direct. First, they were sucked into the sea stars’ body cavities. From there, they took what the researchers call “a somewhat haphazard wander” through the body, down the arm, and out the tip. It’s hardly an efficient process, and it took about 10 days, but it did work—and the sea stars didn’t appear to be hurt or distressed as they did it.

Like so many discoveries about the natural world, these findings raise more questions than they answer. Why would an animal need to do this? Why don’t they just spit out foreign objects from the same holes they came in? How are they even doing this?

One question, at least, has a very clear answer. Are sea stars bizarre, wonderful, alien monsters? Yes. Yes, they are.