The scientists are studying eight species of feather stars in shallow and deeper reef depths, tracking their relationships with the tiny shrimps, crabs, and snails that live on them as well as how quickly feather stars can regrow their limbs when they get lopped off.
That’s right: Feather stars can regenerate their limbs, seemingly indefinitely if they’re left in the water. Some species of crinoid can grow up to 150 arms; sever one and back it grows—slowly—at less than a millimeter per day at Stevenson’s research site.
Limb regeneration may be the reason why these animals have been, and continue to be, so successful after 200 million years of existence, Stevenson says.
“We’re unsure about their lifespan, but I'm starting to think these animals are immortal. They can pretty much grow back to their full size as long as part of their centradorsal (the central disk where all arms radiate from) is intact,” she says.
Others aren't so sure about that. Tomasz Baumiller, a crinoid expert at the University of Michigan, says he doesn't know of a limit on how many times a feather star can regrow its arms. But that doesn't mean it's immortal.
"Some feather star body parts cannot be regrown—the centrodorsal disk that holds some of the nervous and other systems must be retained. So that body part can age," Baumiller says. His work hints at long lifespans in these creatures, but he doesn't yet know if they die of old age.
These incredible regenerating creatures also seem to be coping well with warming seas. (Related: "Window to Save World's Coral Reefs Closing Rapidly.")
“We know some species seem to do quite well in warming temperatures,” Stevenson says. “They regenerate arms faster when we elevate temperature,” she says, referring to experiments warming waters by two degrees Celsius in the lab. Stevenson says she suspects that warming might be harming predators that would normally eat baby feather stars, allowing more stars to reach adulthood.
Meanwhile, ocean temperatures are rising: NOAA’s quarterly “State of the Climate: Global Climate Report” for January through March stated that the global ocean heat content during that time was the highest in their records, which go back to 1955. That’s a trend not expected to reverse.
“I doubt the demise of coral will affect feather star populations,” she says. “All they need, really, are currents to bring food to them, and a substrate—any substrate—to perch on.”
Baumiller says there's not enough data on feather star populations around the world to draw that conclusion, and that the failure of coral reefs would certainly affect the feather stars that live on them. "The greatest diversity of feather stars is on coral reefs. So if the reefs are gone, so are most feather stars," he says.
Source: National Geographic | 23 August 2018