Swimming sea cucumbers intercept sinking carbon near the Galápagos
Observations from 23 submersible dives reveal how an unusual sea cucumber catches organic particles in midwater. Its effect on long-term carbon storage remains unmeasured.
Swimming sea cucumbers intercept carbon-bearing particles before they reach the deep seafloor near the Galápagos Islands, according to research announced by the Monterey Bay Aquarium Research Institute (MBARI) on October 8. The findings about Pelagothuria natatrix identify a participant in the ocean’s carbon cycle, although they do not establish how much it changes long-term carbon storage.
MBARI senior scientist Bruce H. Robison analysed observations from 23 submersible dives. The institute reports that the animals were abundant between 250 and 650 metres deep, placing them in the path of organic material descending through the water. The study’s abstract describes direct observations of the animals intercepting those settling particles.
The study appears in the September 2026 issue of Ecology under the title ‘Pelagic sea cucumbers in the Galapagos: Midwater grazers that short-circuit deep-sea carbon flux’. Phys.org republished MBARI’s account on October 9. Those announcement dates do not identify when the dives took place.
How Pelagothuria catches marine snow
Among more than 1,700 species of sea cucumbers, MBARI describes Pelagothuria natatrix as the only one known to live in the water column rather than in close association with the seabed. That unusual habitat gives it access to food before the material reaches the bottom.
Its specialised tube feet form a webbed veil that serves both swimming and feeding. The animal typically holds this veil open toward the surface, creating a funnel that catches sinking organic particles, often called marine snow. A ring of feeding tentacles surrounds the mouth at the centre.
Most sea cucumbers scavenge organic material after its journey to the seafloor. Pelagothuria feeds earlier along that route. The distinction matters to the finding: the observed animals are consuming particles in midwater, where carbon can enter different biological pathways before any remaining material continues downward.
In its announcement, MBARI says the relatively high densities observed suggest the species ‘may have an important role in ocean carbon cycles in tropical waters’. That is a proposed wider significance of the Galápagos observations, rather than a measurement of its contribution throughout tropical oceans.
Where sinking ocean carbon goes
Woods Hole Oceanographic Institution’s explanation of the biological carbon pump provides context for that distinction. Microscopic phytoplankton take up carbon dioxide in surface waters, incorporating carbon into organic material. Feeding, waste and sinking remains then help transfer some of that carbon into deeper water.
The downward journey includes recycling. WHOI explains that animals and bacteria consume material within the ocean’s twilight zone. Uneaten dead animals, discarded tissues and faecal matter can continue sinking, carrying carbon farther down. Interception by an animal therefore describes one stage in the journey, without establishing the carbon’s ultimate destination.
Carbon transported into the deep ocean can remain isolated for hundreds to thousands of years, according to WHOI. That general storage timescale helps explain interest in the pathways linking surface life to deep water. It is not a measured storage duration for carbon consumed by Pelagothuria.
The properties of sinking particles also matter. WHOI describes gelatinous animals called salps producing dense faecal pellets that can reach the seabed within days. This separate example shows how feeding can generate material that continues downward; it does not establish the speed or fate of waste produced by the sea cucumbers.
What the Galápagos observations leave unresolved
MBARI’s announcement and the study abstract establish particle interception, but provide no numerical estimate of how much carbon Pelagothuria consumes or how much its feeding changes deep-sea sequestration. They do not demonstrate a reduction in global carbon storage or a resulting warming effect.
The unresolved questions include how much intercepted carbon the animals respire, how much leaves as sinking waste, and where that material ultimately goes. Those quantities would be needed to connect the observed feeding behaviour to an estimate of its net effect on carbon transport.
The reported abundance is also tied to the observed Galápagos community. MBARI’s announcement does not give dive dates, detailed survey effort or numerical density estimates. Its suggestion of broader importance in tropical waters should therefore remain attributed to the institute, with the scale of that role still uncertain.
Sources and context
- New research reveals surprising link in ocean carbon cycle: Swimming sea cucumbersPhys.org; supplied by Monterey Bay Aquarium Research Institute
- New research reveals surprising link in ocean carbon cycle: swimming sea cucumbersMonterey Bay Aquarium Research Institute
- Pelagic sea cucumbers in the Galapagos: Midwater grazers that short-circuit deep-sea carbon fluxEcology / Wiley for the Ecological Society of America; abstract and bibliographic record hosted by PubMed
- Biological Carbon Pump: How the Ocean Stores CO2Woods Hole Oceanographic Institution
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