The transition from youth to adult is awkward for everyone, but some species have particularly odd or arduous transformations when navigating into a new stage of life. The sea urchin falls into this latter category.
We're used to seeing this creature in tidal zones or coral reefs, a spine-covered ball wandering around feasting on seaweed. But before it becomes this familiar adult, it goes through a very strange adolescence.
When larvae hatch from an egg, they are the shape of a lunar lander. They swim through the open ocean looking very much like a space ship traveling across the universe. Inside that space ship, a juvenile sea urchin body — a mini version of an adult — is growing. When the larvae travels closer to shore and feels the turbulence of crashing waves, it knows it's time to break out.
KQED Science reports:
When it reaches the rocky shore, the juvenile urchin bursts out.“It sticks its little tube feet out of the side of the little pluteus larva swimming around, and it grabs hold of the rocks or the bottom of the seafloor,” says Nat Clarke, a graduate student in Chris Lowe’s Laboratory at Stanford’s Hopkins Marine Station in Pacific Grove.
KQED crafted a fantastic short video explaining this fascinating transition:
Why exactly does it matter how a sea urchin is born? Unraveling the mystery of how tidal zone animals reproduce and how they survive their open-ocean youth is critical to understanding aspects of ocean ecology that affect humans here on shore.
“These sorts of studies are absolutely crucial if we want to not only maintain healthy fisheries but indeed a healthy ocean,” Jason Hodin, a research scientist at the University of Washington’s Friday Harbor Laboratories, tells KQED. “Research lately has been very, very strongly suggesting that most larvae come back to somewhere near the same shoreline that their parents came from,” Hodin says. “It’s something that people didn’t realize 15 to 20 years ago. There’s a lot more connectivity between the shoreline and the waters offshore where the babies are.”
It may seem like impossible odds for sea urchins to even make it to adulthood. But when they do, it's worth the effort. They're capable of lifespans that last well over 100 years. In fact, the red sea urchin can live to be more than 200 years old. These long-lived spiny seaweed-eaters still hold many secrets that scientists hope to uncover.