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Catching up to the Ruby Seadragon: new species raises new questions

  • The ruby seadragon (Phyllopteryx dewysea) avoided scientific detection for so long due to its deepwater habitat and the fact that bodies changed color after they perished.
  • The discovery has raised new questions about the evolution of seadragons.
  • Researchers don’t know how threatened the ruby seadragon is, but have petitioned the government for proactive protections.

In April 2016 at the Recherche Archipelago, just south of Western Australia’s coast, the ruby seadragon’s time as a science fugitive was about to end. There, Greg Rouse, a professor of marine biology at the Scripps Institution of Oceanography, his PhD Student Josefin Stiller, also conducting research at Scripps, and Nerida Wilson, a senior research scientist from the Western Australian Museum were taking a few days’ respite from scuba diving for their usual syngnathid subjects, the weedy seadragon (Phycodurus eques) and the leafy seadragon (Phyllopteryx taeniolatus). Instead, the trio was hoping the swell might subside enough for a remotely operated underwater vehicle, or ROV, to descend. And, if the place and time was right, to capture the first images of a species never before seen alive.

“It was a very exciting moment,” Stiller told Mongabay, describing the anticipation that day. “We were all very agitated. It had been over a year of imagining what the species may look like.”

The existence of this third seadragon species, Phyllopteryx dewysea, wasn’t known until 2014 when Stiller serendipitously discovered that the DNA from a tissue clipping she was analyzing didn’t match the profile of the two known seadragons.

In 2007, a biodiversity survey trawled a ruby seadragon with a brood of eggs attached to his tail. The Western Australian Museum sent Stiller a clipping of this male’s tail, which unexpectedly lead to the discovery of Phyllopteryx dewysea. Photo copyright: Western Australian Museum.

The DNA ended up belonging to a new seadragon species, a little thicker than the other two and colored a resplendent red, interrupted only by vertical bars of pink extending up its sides. But the ruby’s conspicuous color belies its furtive nature. Even in the rare instances where it was found dead – either washed up on an Australian beach or caught in a trawler – it was thought to be a common seadragon. These preserved specimens – one of which dates to 1919 – lost their color quickly after death allowing the species to avoid detection for nearly a century.

Part of the ruby seadragon’s elusiveness was due to the depths at which they live. Indeed, when the expedition’s camera-equipped ROV reached the vicinity of the ruby seadragon, it was 50 meters below the surface – well beyond the usual depths of the leafy and weedy seadragons and certainly below the range of most scuba divers. At these depths, the red renders a dull brown shade, allowing the animal to better hide in its sandy habitat.

On the fourth day of the expedition, the ROV finally came across their target. The ruby seadragon was due for its close up.

The 30-minute sighting revealed two ruby seadragons, “turning backwards and forwards to hold position in the surge,” hanging around sponges and similar “large objects,” according to a paper published in Marine Biodiversity Records by the researchers. The video also reveals surprising differences between this new species and the other two.

For example, the ROV camera captured a habitat very unlike the lush seagrass and kelp landscape that weedies and leafies love. In the video, the ruby seadragon floats just above a sandy ocean floor populated by sponges and other stationary animals. This vastness helps explain why the ruby seadragon lacks the flowing, leaf-like flourishes that the other seadragons rely on for camouflage.

“In the sparse habitat they occupy, appendages would serve little purpose as camouflaging agents and could add significant costs in drag or fluid resistance, particularly in strong surge,” the authors write in the paper.

Compare the weedy seadragon (left) and the leafy seadragon (right), who boast appendages that allow them to hide in dense vegetation. Conversely, the ruby seadragon has no such structures. Photo courtesy of: Greg Rouse, Josefin Stiller, and Nerida Wilson.

However, some of the ruby’s anatomical features elicit more questions than answers. The encounter shows the two seadragons curling their tails, which the study interprets as an ability to grab onto objects “to stop from being swept off” its deep reef habitat during ocean surges. Weedies and leafies don’t have this ability, but closely related pipefish genera, like Solegnathus and Syngnathoides, do. Before this finding, it was assumed that the seadragon’s ancestors had lost this characteristic, leaving all living seadragon species without a curling tail. But now, the ruby seadragon’s curling tail raises questions about their evolutionary history. Did all seadragons indeed lose the trait, only for it to evolve in the ruby seadragon later? Or is the ruby seadragon carrying the same prehensile ability that its ancestors had?

Perhaps the most vital question now concerns their protection. Reports from Dragon Search, a program that helped monitor seadragon sightings, call attention to “multiple contaminants” such as sewage, erosion, and stormwater runoff radiating into the ocean from South and Western Australia. Poor water quality is especially notable in marine habitats surrounding cities. Tracking the populations of seadragons themselves is no easy feat, so conservation groups can’t quite say how seadragon numbers have changed as a result of city-borne pollution.

“[Seadragons] often occur in rather remote parts of Australia where SCUBA diving takes a lot of effort,” Stiller said.

What scientists do know is that the seagrass meadows and kelp reefs where leafy and weedy seadragons live have been disappearing for at least two decades, putting the two species in the IUCN’s Near Threatened category.

“All three species are specialists in their habitats,” Stiller explained. “The common and leafy seadragons use kelp as shelter; the ruby lives among sponges. These habitats need to be healthy in order to have healthy populations of seadragons.”

The scientists are seeking government-enforced protections for the ruby seadragon. But, as a newly-identified species, relatively few things are known about it. The IUCN currently lists the species as Data Deficient, meaning conservationists don’t know enough yet to assess how threatened it is. Still, these initial revelations open the door for future study and conservation measures in its benthic habitat.

Though its penchant for mystery has allowed it to survive long enough for science to catch up to it, the ruby’s discovery may be what helps it continue to thrive.
Citations:

Baker, J.L. 2003. Dragon Search South Australia – Summary of South Australian Sighting Data to January 2003. Internal Report – Dragon Search Community-Based Monitoring Project.

Rouse, G. W., Stiller, J., & Wilson, N. G. (2002). First live records of the ruby seadragon (Phyllopteryx dewysea). Journal of Fish Biology, 61(3), 684–695. https://doi.org/10.1111/j.1095-8649.2002.tb00904.x

Stiller, J., Wilson, N. G., & Rouse, G. W. (2015). A spectacular new species of seadragon (Syngnathidae). Royal Society Open Science, 2(2), 140458–140458. https://doi.org/10.1098/rsos.140458

Stiller, J. (n.d.). Seadragon: Ruby Red with Pink Stripes | ESF Top 10 New Species. http://www.esf.edu/top10/2016/06.author.htm