Sea stars are not often synonymous with parental care. But when research zoologist Christopher Mah carefully cracked open a deep-sea starfish specimen to examine its stomach contents, he was intrigued to find a bellyful of babies. Like a star-shaped nesting doll, the sea creature’s body cavity was stuffed with nearly a dozen miniature sea stars.Mah, who specializes in studying sea stars and other echinoderms, was examining several undescribed specimens deposited in a drawer in the National Museum of Natural History’s Invertebrate Zoology collection. The specimens hailed from the icy Southern Ocean around Antarctica and had not been studied in several decades, if ever. Here he came across the expectant sea star, which was still swaddled in toilet paper from its journey from Antarctica to Washington by way of a prolonged pitstop in New Zealand. In a paper published last month in the journal Zootaxa, Mah named several of these deep-sea starfish. Some of the specimens he described were teeming with offspring. Known as brooding in sea stars, this reproductive behavior allows starfish to retain their eggs within their bodies as they develop into embryos and eventually juveniles.
The specimens were collected during the 1960s by scientists aboard the USNS Eltanin, an Antarctic research vessel that had previously been an ice-breaking naval ship. For a decade, the Eltanin (which is named after a star in the northern Draco constellation) was crucial to the National Science Foundation’s United States Antarctic Program (USAP). The ship crisscrossed the Southern Ocean, mapping remote stretches of seafloor around Antarctica and collecting all manner of sea creatures from the icy depths.
To help sift through this bounty, USAP researchers sent specimens to experts around the world. A trove of deep-sea starfish were initially sent to an echinoderm expert in New Zealand.
Around 2010, the sea stars were shipped to the museum (a repository of many USAP specimens) where Mah first came across them. He’s been painstakingly unpacking them ever since. In the process, Mah has described several new species, including the first sea star discovered at a deep-sea hydrothermal vent.
But the new paper represents Mah’s most fruitful endeavor yet with the USAP specimens. “When the museum was still quiet coming back from the pandemic, I discovered six species in the collection in one week,” he recalled. In the new paper, Mah named a total of 11 new species and one new genus (the taxonomic category above species and below family. It is denoted by a capitalized Latin name that comes before the species name like Homo or Tyrannosaurus). He named one of the brooding sea star species Paralophaster ferax after the Latin word for fruitful or fertile.
The research highlights just how common brooding is amongst Antarctic sea stars. Whereas the reproductive strategy is relatively rare across all sea stars, Mah estimates around 40% of all known Antarctic starfish brood their young.
And each group of sea stars has put their own spin on the odd behavior — some keep their young right by their mouths while others keep their offspring tucked inside baskets of interlocking spines. Paralophaster ferax, which can live more than 14,500 feet below the surface, stash their litter in their internal body cavity (called the coelom) before presumably giving birth through their mouth. No other Antarctic starfish is known to brood juveniles in this cavity. This species is also one of the deepest known species to brood offspring.
Why sea stars in the Southern Ocean’s frigid waters have developed all these complex strategies for raising their young remains a mystery (one guess is to keep their offspring snug in the frigid conditions). However, researchers like Mah are running out of time to solve this evolutionary puzzle.
Like the rest of Antarctica’s wildlife, these sea stars are threatened by warming ocean waters. As water temperatures rise, environmental conditions like currents change and marine ecosystems are thrown into disarray as warm-water species descend from the north.
Because of how difficult it is to conduct field work in the remote seafloors fringing Antarctica, it is difficult to determine how these sea stars will handle the heat. This makes studying specimens of sea stars in museum collections even more valuable. The information gleaned from preserved individuals could offer crucial clues to the future of their living brethren in the wild.
“Collections like these really are a treasure trove,” Mah said. “Even if the specimens are quite old, they can still yield a ton of new information.”
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