Salp casts light on food chain and carbon cycle
By Lewis Smith
August 10 2010 Lewis Smith
A whorl of salps linked in a chain
Kelly Sutherland and Larry Madin, WHOI
The most efficient feeders in the seas have just been found to be even better at getting a meal than scientists dared believe.
But far from being a shark or one of the many other sharp-toothed killers of the deep the creature in question is the little-known salp, a creature that resembles a jellyfish.
Salps are filter feeders that eat mostly phytoplankton and it had been thought the smallest organism they could capture with their muscus mesh nets were 1.5 microns wide.
Researchers have now established that the tiniest particle the filters can trap can be 0.75 microns wide and perhaps even smaller.
The finding reveals that mid-ocean salps, which can join up to form chains of 100 or more individuals, can consume meals of sizes spanning four orders of magnitude. “This is like eating everything from a mouse to a horse,” said Larry Madin, director of research at the Woods Hole Oceanographic Institute (WHOI).
He said the discovery is important to the understanding of marine food chains and helps explain how salps are able to survive in regions of the open seas where larger food particles are in short supply: "Their ability to filter the smallest particles may allow them to survive where other grazers can't."
The discovery enhances the importance of the role salps have in the carbon cycle. They eat the “entire microbial loop and pack it into large, dense fecal pellets” which, being denser, sink to the ocean floor faster than the microbes would.
The effect is to take carbon away from the sea surface and out of circulation for centuries. Experiments suggested that 80 per cent of the salps’ food is made up of the particles that had previously been thought too small for them.
Salps swim and eat in rhythmic pulses, each of which draws seawater in through an opening at the front end of the animal. The mesh captures the food particles, then rolls into a strand and goes into the gut, where it is digested.
The research was carried out by scientists at WHOI and the Massachusetts Institute of Technology. The results are published in the journal "Proceedings of the National Academy of Sciences".
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