Beneath the cold, dark, and highly pressurised world of the deep sea, marine life has been found to be far more globally connected than previously imagined – a finding made by researchers at Museums Victoria which could prove transformational of our understanding of life at the furthest depths of the ocean.

Published this week in Nature, this landmark study maps the global distribution and evolutionary relationships of brittle stars (Ophiuroidea), the ancient, spiny animals found within both shallow coastal waters and the deepest abyssal plains, from the equators to the poles.

By analysing the DNA of thousands of specimens collected on hundreds of research voyages and preserved in natural history museums around the world, scientists have uncovered how these deep-sea invertebrates have ‘quietly migrated across entire oceans’ over millions of years, linking ecosystems from Iceland to Tasmania.

A dataset labelled ‘unprecedented’ by those working with it, the study offers new insights into how marine life has evolved and dispersed across the ocean over the past 100 million years.

“You might think of the deep sea as remote and isolated, but for many animals on the seafloor, it’s actually a connected superhighway,” said Dr Tim O’Hara, senior curator of Marine Invertebrates at Museums Victoria Research Institute and lead author on the study. “Over long time scales, deep-sea species have expanded their ranges by thousands of kilometres. This connectivity is a global phenomenon that’s gone unnoticed, until now.”

Using DNA from 2,699 brittle star specimens housed in 48 natural history museums across the globe, this is the most comprehensive study of its kind. Brittle stars have lived on Earth for over 480 million years and can be found at depths of more than 3,500 metres.

Unlike marine life in shallow waters – which is restricted by temperature boundaries – deep-sea environments are more stable and allow species to disperse over vast distances. Many brittle stars produce yolk-rich larvae that can drift on deep ocean currents for extended periods, giving them the ability to colonise far-flung regions.

“These animals don’t have fins or wings, but they’ve still managed to span entire oceans,” said Dr O’Hara. “The secret lies in their biology – their larvae can survive for a long time in cold water, hitching a ride on slow-moving deep-sea currents.”

The research has gone lengths to show that deep-sea communities – particularly those at temperate latitudes – are more closely related across regions than their shallow-water counterparts. For example, marine animals found off southern Australia share close evolutionary links with those in the North Atlantic, on the other side of the planet.

At the same time, it highlights that the deep sea is not uniform and while species can spread widely, factors such as extinction events, environmental change, and geography have created a patchwork of biodiversity across the seafloor.

“It’s a paradox. The deep sea is highly connected, but also incredibly fragile,” said Dr O’Hara. “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.”

The Museum believes that not only does this research ‘transform our understanding’ of deep-sea evolution, but it highlights the ‘enduring scientific value of museum collections’ themselves. The DNA analysed in this study came from specimens collected during 332 research voyages – many of those undertaken decades ago. 

“This is science on a global scale,” said Lynley Crosswell, CEO and director of Museums Victoria. “It demonstrates how museums, through international collaboration and the preservation of biodiversity specimens, can unlock new knowledge about our planet’s past and help shape its future.”

The paper – titled ‘Spatiotemporal faunal connectivity across global sea floors’ – is now published in Nature.

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