They may look like rather unexciting little bags of jelly, but salps may be the most efficient filter feeders in the ocean, according to a study just out in the journal PNAS. And this could make them important players in the draw down of carbon from surface waters into the deep sea.
Salps are a variety of tunicate, a group of animals that also includes sea squirts and are, surprisingly, evolutionarily related to vertebrates. They are filter feeders a few centimetres long that are either solitary or live in chains that can be hundreds of salps long.
Until now, scientists thought that although they were very efficient at filter feeding using a mucous ‘net’ type structure, they could only catch food that was larger than the holes of the net – a fairly sensible assumption to make if you think about things like fishing nets and sieves. But Kelly Sutherland and her colleagues used lab experiments where they offered salps specifically sized polystyrene balls of 0.5 to 3 micrometers in diameter and showed that even the smallest particles were picked up at a higher rate than expected.
So it turns out that salps can eat food in a huge range of sizes – in the words of one of the paper’s authors, ‘like being able to eat everything from the size of a mouse to a horse!’. And this is extremely beneficial as it allows salps to thrive on a wide range of different phytoplankton, zooplankton and other particles.
Another really interesting suggestion made by the authors is that the salps could be contributing more than expected to take down of carbon into the deep ocean. Because they consume tiny, tiny particles and then combine them into much larger faecal pellets, that allows carbon to be taken out of the top layer of the seawater and sink down to the ocean floor.
So, efficient and important for the environment – again proof that you shouldn’t judge an animal by its looks!