Marine protected areas are a key strategy for conserving marine biodiversity. However, their design and implementation often emphasize surface and shallow-water ecosystems, overlooking the structural and ecological complexity of deeper ocean layers.
This is particularly critical in the deep sea, where protections are limited despite these habitats being highly vulnerable to climate change. Improving our understanding of the connectivity among deep-sea biomes is essential for developing more effective and comprehensive ocean conservation strategies.
O’Hara, T.D., Hugall, A.F., Haines, M.L., Weber, A.A.T., Eichsteller, A., Brogger, M.I., Eléaume, M., Fujita, T., Kongsrud, J.A., Martinez Arbizu, P. and Mills, S. 2025. Spatiotemporal faunal connectivity across global sea floors. Nature. DOI: 10.1038/s41586-025-09307-1.
A new global study uses brittle stars (invertebrates in the class Ophiuroidea) to explore connectivity across ocean depths and regions. Researchers compiled nearly 2,700 DNA samples, primarily from museum specimens gathered across 332 research expeditions, covering the world’s oceans from shallow continental shelves to the abyssal plains. By applying a phylogenetic approach, they examined how biodiversity has diverged and spread over evolutionary timescales, providing one of the most comprehensive looks at deep-sea connectivity to date.
The results reveal striking contrasts between shallow and deep marine environments. Continental shelf communities, especially in tropical and temperate zones, are highly divergent, shaped by geographic barriers such as the closure of ancient seaways and shifts in ocean circulation.
In contrast, assemblages in the deep sea are far more connected than previously realized. Many deep-sea lineages have achieved global ranges, with evidence of dispersal across ocean basins over millions of years. For example, researchers found close evolutionary links between deep-sea faunas in the North Atlantic and southern Australia. These patterns suggest that deep-sea species are capable of both vertical and horizontal dispersal, aided by relatively stable temperature layers, seafloor topography, and ocean currents.
While the deep sea shows higher levels of connectivity, it is not uniform. Regional differences still arise from varying rates of species formation, movement, and extinction. Importantly, the study highlights that deeper parts of the ocean are not just species-rich but also under significant threat, from climate-driven changes in temperature and oxygen levels to growing interest in resource extraction such as deep-sea mining.
These findings underscore the need to move beyond surface-focused conservation protections. Efforts to safeguard marine connectivity have traditionally emphasized shallow waters and coastal regions, but mounting evidence shows that deeper ecosystems contain unique biodiversity and play an essential role in global ecological processes. Protecting connectivity across depth layers will be critical to sustaining the resilience of marine life in a rapidly changing ocean.
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