Deep-sea brittle stars are always on the move. That’s what a new study seems to suggest, anyway, after analyzing thousands of brittle star specimens and finding that the spiky, star-shaped creatures are much more closely related across the deep sea than across the shallows.
The study, which was published in Nature, turned to the DNA of brittle stars to capture a clearer picture of their movement and connectivity worldwide. The results reveal that deep-sea brittle stars have spread around the world’s oceans throughout the past 100 million years, connecting regions as far-flung as Tasmania and Iceland.
“You might think of the deep sea as remote and isolated,” said Tim O’Hara, a study author and a curator of marine invertebrates at the Museums Victoria Research Institute, in a press release. “But for many animals on the seafloor, it’s actually a connected superhighway.”
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Deep-Sea Species Migration
Brittle stars, or Ophiuroidea, are ancient animals with small bodies and spindly, sometimes spiny, arms. At around 480 million years old, they appear at almost any ocean depth, from the shallows to the deep, including as deep as 11,500 feet below the water’s surface.
But how mobile are these brittle stars, and how does their depth affect their movement over time? To find out, researchers analyzed the DNA from 2,699 brittle star specimens. Taken from different depths, the specimens were collected on 332 research voyages and acquired from 48 natural history museums, making the study the most comprehensive assessment of brittle star DNA to date.
The researchers’ analysis showed that the brittle stars that were collected from the deep sea shared more DNA across regions than the brittle stars that were collected from the shallows. In fact, deep-sea brittle stars from Australia were surprisingly similar to brittle stars from the Atlantic Ocean, suggesting that the creatures spread across whole oceans over millions and millions of years.
“Over long timescales, deep-sea species have expanded their ranges,” O’Hara said in the release. “These animals don’t have fins or wings, but they’ve still managed to span entire oceans.”
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Making Moves Without Fins or Wings
According to the researchers, the trick to these massive migrations is found in the brittle star’s larval stage. Indeed, in the colder depths, baby brittle star larvae survive for long stretches of time, but in the warmer shallows, their lifespans are significantly shorter.
“The secret lies in their biology,” O’Hara said in the release. “Their larvae can survive for a long time in cold water, hitching a ride on slow-moving deep-sea currents.”
The mobility of deep-sea brittle stars is also boosted by the conditions of their surroundings. While a single species of brittle star may survive in a number of deep-sea regions, which are relatively steady and similar in temperature around the world, an individual brittle star might struggle to live in many shallow sea areas, which differ dramatically in terms of their temperature, from the cool waters of the Arctic Ocean to the temperate waves of the Pacific and Atlantic.
Of course, the deep sea isn’t completely consistent. Though it’s much more stable, the depths still feature fluctuations in temperature and other conditions, and can still suffer from environmental change and extinction, creating some areas where brittle stars thrive and some areas where brittle stars suffer.
“It’s a paradox. The deep sea is highly connected, but also incredibly fragile,” O’Hara added in the release. “Understanding how life is distributed and moves through this vast environment is essential if we want to protect it, especially as threats from deep-sea mining and climate change increase.”
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Article Sources
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Sam Walters is a journalist covering archaeology, paleontology, ecology, and evolution for Discover, along with an assortment of other topics. Before joining the Discover team as an assistant editor in 2022, Sam studied journalism at Northwestern University in Evanston, Illinois.
