Marine animals living in the cold, dark depths of the ocean are interconnected across the world by a hidden “superhighway”, a groundbreaking new study suggests.
The research, published in the journal Nature, provides a detailed global map of marine creatures closely related to starfish called brittle stars.
Researchers at Australia’s Museums Victoria Research Institute assessed how these spiny creatures occupied every ocean, from tropical shallows to icy depths stretching from the equator to the polar regions.
They analysed DNA from nearly 2,700 brittle star specimens taken during hundreds of research expeditions and housed in 48 natural history museums worldwide and found that these creatures had crossed entire oceans over millions of years.
The gradual migration of these deep-sea creatures led to invisible links forming between ecosystems as far apart as Iceland and Tasmania, they found.
Brittle stars have lived for over 480 million years and come to occupy all ocean floors, including at depths of over 3,500 meters.
“You might think of the deep sea as remote and isolated, but for many animals on the seafloor, it is actually a connected superhighway,” Tim O’Hara, lead author of the study, said. “Over long timescales, deep-sea species have expanded their ranges by thousands of kilometres. This connectivity is a global phenomenon that’s gone unnoticed, until now.”
The study also examines the critical role played by these creatures in marine ecosystems across all the oceans. While life forms in shallow waters are restricted by temperature boundaries, the deep-sea environments are more stable, allowing species to disperse over vast distances.
In such environments, brittle stars produce yolk-rich larvae that drift on 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. The secret lies in their biology,” according to Dr O’Hara, “their larvae can survive for a long time in cold water, hitching a ride on slow-moving deep-sea currents.”
Deep-sea ecosystems are more closely related across regions than their shallow-water counterparts. Marine animals off southern Australia, for instance, share close evolutionary links with species in the North Atlantic, on the other side of the planet.
“A close relationship exists between deep-sea faunas of the northern Atlantic and, on the opposite side of the globe, southern Australia,” researchers said.
But extinction events, environmental change and geography have over the millennia created a patchwork of biodiversity across the seafloor.
“It’s a paradox,” Dr O’Hara explained. “The deep sea is highly connected, but also incredibly fragile. 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.”
