When Injured, the Moon Jellyfish Doesn’t Repair. It Recycles!

moon jellyfish

Moon jellyfish possess a unique mechanism for self-repair. (Photo credit: Byba Sepit/Moment/Getty Images)

The moon jellyfish is a tough creature to figure out. For one, while experts argue that the species consists of numerous subspecies, it is nearly impossible to distinguish one from another without DNA testing, which leads other scientists to propose the distinction is meaningless. This is why you’ll often see conflicting names and population estimates for them.

Generally speaking, however, the defining characteristic of the moon jellyfish (Aurelia aurita) is its four horseshoe-shaped gonads located at the center of a round, white, body. This jellyfish gets its name from its translucent body. When caught by light, it looks a lot like the moon when lit by the sun. Although moon jellyfish have inhabited the seas for millions of years, scientists just recently found out something new and exciting about them. Moon jellyfish possess a unique mechanism for self-repair, one never before witnessed in nature. While scientists have seen creatures such as seastars regrow limbs when one gets injured, moon jellyfish instead redistribute their limbs to replace one that is lost. They basically rearrange their bodies to maintain symmetrical in order to keep swimming.

The discovery happened quite serendipitously. Michael Abrams, a graduate student at the California Institute of Technology (Caltech) in Professor Lea Goentoro’s lab, wanted to study the repair mechanisms in the immortal jellyfish (Turritopsis dohrnii). The interesting thing about this species is that it can, at any time during adulthood, revert back to its immature polyp state, meaning that it essentially lives forever. The specimens Abrams needed, however, were taking a long time to arrive from Japan. He decided to start some preliminary experiments on the more common moon jellyfish, doing amputations just to get experience. It was then when he realized the phenomenon.

Young moon jellyfish start out with eight legs situated radially about their bodies, making them resemble small snowflakes. Abrams observed that, if he cut one of the legs off, the others would rearrange to give the jellyfish radial symmetry once again. Cutting off two, three, or four had the same result. In fact, if left with only two legs, each would move to opposite sides of the jellyfish’s body. The adaptation was clearly necessary for survival. And while the odds of successful adaptation decreased according to the number of limbs removed (96 to 72%), those that did adapt grew to “normal” adulthood. They may have had fewer limbs and stomachs (they usually have four stomachs), but they matured normally. Those that failed to adapt would grow oversized mouths and undersized bellies and languish at the bottom of the tank. The big questions for Abrams, of course, were how the jellyfish accomplished this, and what was the advantage of this adaptation?

Logically, one would think this repair requires that the jellyfish produce new cells, ones that could push the remaining limbs apart. Another idea might be that they instead kill off cells to accomplish the same task. However, when Abrams stopped all cell activity, the jellyfish continued to adapt. And they would continue to adapt until the he paralyzed them to stop all movement. No movement resulted in no adaptation and no regain of symmetry. The only conclusion is that it’s the pulsations of their bodies that push the limbs apart.

“It’s kind of beautiful that their normal swimming and feeding process leads to this self-repair,” Abrams told a reporter from Livescience. In a way, nature is showing that you don’t need to replace missing parts, you just need to rearrange what you already have.

The implications of this discovery are still not clear. It could result in new ways of thinking about how to design self-repairing materials. In other words, the design principle would focus not on replacement but compensation. Perhaps more importantly, the idea would entail making repair not a distinct response, but rather a function of the material.

More to Explore
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Mix-n-Match Arms: Jellyfish Rearrange Limbs After Injury
Instead Of Replacing Missing Body Parts, Moon Jellies Recycle
National Aquarium: Moon Jellyfish

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