Science

Mysterious seadragon finally spotted alive – and caught on video

Scientists discovered a new species, but had never actually seen the animal alive. Now they have, and it's full of surprises.

This composite image shows all three species of seadragon. From top to bottom: Common Seadragon (Phyllopteryx taeniolatus), Original photograph of the (dead) Ruby Seadragon (Phyllopteryx dewysea), shortly after being trawled in 2007, Leafy Seadragon (Phycodurus eques).
Images courtesy of Greg Rouse/Nerida Wilson/Western Australian Museum
|
Caption

Seadragons, with strange appendages protruding from their bodies and long, straw-like snouts, seem like mythical creatures. But marine biologists have known for more than 150 years that there are at least two distinct species that actually exist. 

So imagine how surprised marine biologists Greg Rouse and Josefin Stiller were when they discovered a third species of seadragon, which they named the ruby seadragon.

But part of what makes their finding remarkable is the journey that led them to this new species. The researchers didn't discover the the critter swimming around in the ocean. That surprise came later. The team was analyzing dead, decades-old tissue from museum collections when they made a startling realization: a few of the ancient specimens had been incorrectly classified as the common seadragon.

When they reported their discovery in 2015 they still had yet to see one of the creatures alive, but this kicked off a hunt for the ruby seadragon in the wild.

It has been a long journey from tiny tissue samples to a whole, living creature, but in April 2016, the marine biologists finally spotted the enigmatic and elusive fish in its Southern Ocean habitat – and captured the event on video.

Seeing the ruby seadragon in real life revealed some surprises, like the hint that it has a curled, prehensile tail like its cousin, the seahorse, and has helped resolve many of the mysteries enshrouding the fish, according to a paper published Friday in the journal Marine Biodiversity Records. 

Dr. Rouse and Ms. Stiller didn't set out to discover a new species when they were analyzing those tissue samples from old museum specimens. They were looking at the genetic material of the other seadragon species, the leafy seadragon (Phycodurus eques) and the common seadragon (Phyllopteryx taeniolatus), as part of a broader population genetics project.  It was during that project that they stumbled upon the ruby seadragon, or Phyllopteryx dewysea. 

"Our approach was to go and find them in the wild by scuba diving. We had permission to take a small tissue sample from them and then release the fish," Rouse, a professor at the Scripps Institution of Oceanography at the University of California San Diego, recalls in a phone interview with The Christian Science Monitor. "So over lots of trips we accumulated lots of samples, but we wanted more."

So Stiller, Rouse's PhD student, reached out to museums in Australia in a quest for more tissue samples. The specimens they received were not whole fish, just small tissue samples. So when the pair saw that the DNA they had sequenced from one sample sent from the Western Australian Museum in Perth didn't look like any of the other common seadragon genetic material they had, they asked for the whole fish carcass to be sent. 

"They sent us the fish and also they had a photograph of the fish before it was frozen and put into ethanol. And that's why we knew it was red," Rouse says. 

After scouring collections, the team was able to obtain four specimens of this new seadragon in total. Based on those specimens and their genetic analysis, Rouse, Stiller, and their colleague Nerida Wilson, of the Western Australian Museum, published the first description of the species in 2015. 

The two other species are known to live in shallow, seagrass-filled kelp beds, but the researchers had an idea that they might be able to find the ruby seadragon in deeper water.

They had a few reasons for that hunch. First, they had data for where some of the specimens had been trawled, even though they had been collected in the early 1900s, mid-century, and 2007. And those were collected from deeper waters than scientists would have previously expected to find seadragons.

The animals' distinctive color also gave the researchers a clue to their habitat. While the common and leafy seadragons are patterned in yellows and browns to match the kelp beds, the bright red color of the ruby seadragons stood out to the scientists.

"We figured the red color was associated with living deep, because red light is the first light that gets taken out when light is going through water," Rouse explains. "If you're a red fish, you're effectively black, so you're camouflaged. So many fish are red, in fact, that live in deeper water."

And, unlike their relatives, these animals had no strange protrusions, just stubs where they might have been on a common seadragon to blend into their seagrass, kelp-bed surroundings. So the researchers suspected that the ruby seadragon would be found in a very different habitat than its relatives.

But because the specimens were dead, the scientists couldn't be sure that the appendages hadn't just broken off in a net or when their carcasses had been rolled around in rough surf, Rouse says. So they had to see for themselves.

The marine biologists didn't actually end up seeing the ruby seadragons in person. "We're scuba divers, but that kind of depth is pretty challenging with scuba diving, so we figured using a little remote operated vehicle, a little robot, would be a fun thing to do" instead, Rouse says. So the team took a boat out to the location where one of their specimens had been trawled in 2007 and dropped a camera-equipped robot about 160 feet into the water below them.

"When it first loomed into view on the video, it was certainly a very exciting moment for everybody on board," Rouse recalls. "It was absolutely amazing."

The team only had time to watch two ruby seadragons swim around Bremer Bay, off Australia's southern coast, for about 30 minutes, but in that time they made several new observations about the animals. 

Not only did they confirm that the creatures live in this deep, sparse environment that the researchers call a "sponge garden habitat," they also saw that the ruby seadragons do indeed just have the stubs of appendages, but no appendages themselves. That makes sense, Rouse says, as they wouldn't need the leaf-like appendages among the fan-like sponges for camouflage as their relatives do among the seagrasses and kelp. 

The biggest surprise was the live animals' tails, Rouse says. "We couldn't tell this from the dead fish," he says, but "their tail curls dramatically like a seahorse."

The other two species lack curled tails, so the researchers think it might be prehensile and allow them to hold onto something in their surroundings when the waters get rough, which probably happens often in that environment.

"The first sighting of a vertebrate species is a rare event," David Booth, a marine ecologist at the University of Technology Sydney, who was not involved in the research, writes in an email to the Monitor. "It's a great result to be able to track down the live animal."

Although many questions remain about the new species, the researchers can look to the other two species for clues.

"Genetically, they're most closely related to the common seadragon," Rouse says. "They look a lot like the common seadragon, but they have a different number of vertebrae."

The fins near the fish's head, called pectoral fins, are also much more muscular, he says. "We think that because they live in this turbulent environment, they need to swim much more than the other seadragons."

And of course the ruby seadragon didn't have any appendages, while the common seadragon has a few and the leafy seadragon is covered in the protrusions.

That lack of appendages poses an evolutionary question for the scientists. Did the ruby seadragon lose its appendages or did the other two evolve them independently? Pipefish, the group of fish that include both seadragons and seahorses, tend to lack these long appendages. And, Rouse says, "we're inclined toward thinking that [the ruby seadragon] lost the appendages because they had the stumps of the appendages."

The researchers suspect the ruby seadragon's diet, unlike its appearance, is similar to its relatives, although it has a longer snout. The creatures use this long, straw-like snout to slurp up mysids, tiny, shrimp-like crustaceans, by the dozen. An animal will swim up to a cloud of these mysids, lower the bottom of the base of its snout to open the tip of its snout, which creates suction and allows the animal to slurp in a meal.

"We saw them feed ten times in the course of the 30 minutes" that the robot was recording the ruby seadragons, Rouse says. In the video, "you'll see it go up into the water column, and it snaps its jaw and snaps up something. And we think that they're probably hunting by silhouette because they're looking up."

The marine biologists still have many remaining questions about the evolution of seadragons, how the three species split apart, and the evolution of the whole group of popefish. But their ongoing population genetics research is focused on those questions, Rouse says. 

He adds that the museum specimens have been invaluable to the teams' research. "If we hadn't had those museum samples to look at, this discovery wouldn't have happened."

And the discovery of such an enigmatic new species is "a symbol of what remains to be found in the oceans," Rouse says. "The ocean is still a very poorly understood place in terms of biodiversity, and yet the oceans are warming, the oceans are becoming more acid, and we have a risk of losing things before we even discover them."

But because all pipefish are extended protection under the Australian government, the ruby seadragon already has a bit of protection. Still, as the other two species are very well protected, Rouse says, "We'd like it if [the ruby seadragon] were specially named for protection, too."

of 5 free articles this month > Get unlimited free articles
You've read 5 of 5 free articles

Sign up for a one month free trial.

Get unlimited access to CSMonitor.com for one month.

( No credit card required. )

( Or, learn about our Subscription options )