But a mathematical model suggested salps somehow might be capturing food particles smaller than that, said Kelly Sutherland, who co-authored the PNAS paper after her PhD research at MIT and WHOI.
In the laboratory at WHOI, Sutherland and her colleagues offered salps food particles of three sizes: smaller, around the same size as, and larger than the mesh openings.
"We found that more small particles were captured than expected," said Sutherland, now a post-doctoral researcher at Caltech. "When exposed to ocean-like particle concentrations, 80 percent of the particles that were captured were the smallest particles offered in the experiment."
The finding helps explain how salps--which can exist either singly or in "chains" that may contain a hundred or more--are able to survive in the open ocean where the supply of larger food particles is low.
"Their ability to filter the smallest particles may allow them to survive where other grazers can't," said Madin.
Perhaps most significantly, the result enhances the importance of the salps' role in carbon cycling. As they eat small, as well as large, particles, "they consume the entire 'microbial loop' and pack it into large, dense fecal pellets," Madin says.
The larger and denser the carbon-containing pellets, the sooner they sink to the ocean bottom. "This removes carbon from the surface waters," said Sutherland, "and brings it to a depth where you won't see it again for years to centuries."
And the more carbon that sinks to the bottom, the more space there is for the upper ocean to accumulate carbon, hence limiting the amount that rises into the atmosphere as CO2, said paper co-author Roman Stocker of MIT.
"The most important aspect of this work is the very effective shortcut that salps introduce in the process of particle aggregation," Stocker said. "Typically, aggregation of particles proceeds slowly, by steps, from tiny particles coa
|Contact: Cheryl Dybas|
National Science Foundation