Salps are gelatinous marine organisms, distributed worldwide, except the Arctic. They are typically swim upwards during the night to feed out of plankton and goes back to the deep water during the day to protect from predators. However, sometimes they can be seen washed out the ocean laying in the beach or forming long chains in superficial waters during the day.

Most of people do not know what salps are, so here are some common question and misconceptions about salps:

Are they Jellyfish?

The answer to this question is no. Salps are from the class Thaliacea of the phylum Tunicata, while jellyfish are cnidarians. They can look like jellyfish at simple sight, due to their gelatinous body with high amount of water. However, salps and jellyfish have plenty of differences In different topics, such like body morphology and composition, life cycle, ecology, evolutionary story. The main differences between salps and it’s lookalike relatives are that salps have complex nerves and a proper digestive system.

How can they form such long chains?

Salps are able to form long and dense swarms, mainly when food availability is high. This can last for several weeks moving around waters with high nutrient richness, and this is the usual way how these organisms are seen. When the conditions are right, salps start forming swarms, what they usually do is they start asexual reproduction and start creating clones of themselves, one next to the other.

How can they glow in the dark?

Some species of salps can produce light, visible during the night time, this is it call bioluminescence. This it is not a phenomenon in marine organism, there are plenty of marine animals able to produce light, for example some jellyfish, dinoflagellates, ctenophores, etc. Bioluminescence is the result of chemical reactions in the organism that is possible only with the presence of a molecule called luciferin in

Bioluminescent salp By Nick Hobgood (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons
the organism. However, not all the organisms that show bioluminescence have this molecule in their system, usually they cope with bacteria and therefore they are able to “glow in the dark”.

This technique is used for many different organisms and for many different reasons, can be for attract prey, as a defense method against predators, to attract mates using specific signals, as a method of camouflage, among others.

How do they swim?

Salps use jet propulsion to swim, moving water in and out of their bodies  (see picture on the side) by compressing muscle bands located around their bodies. The process stars by making the fluid enter into the

Classic body plan of a salp species (The Natural History of Bodega Head)

oral siphon, filling their body with water. Afterwards, the decrease of the jet chamber volume it is needed, this is achieved by the closing of oral lips and the contraction of the circular muscle bands, leading to the expulsion of liquid and triggers jet propulsion.

What is the role of Salps in the ecosystem?

The role of Salps in the ecosystem it is not 100% clear. There are not many research done in this specific topic. However, it is known that salps are included in the diet of some fish, corals, mollusc, crustaceans and marine turtles.

The most studied and clear role of salps in the ecosystem is controlling phytoplankton blooms. Salps are known for being fast eaters, they have been called “ the vacuum cleaners of the sea” because they feed by suction and its ravenous way of feeding while forming swarms.

Salps also produce large fecal pellets, with a high concentration of carbon as well as their carcasses. Hence, contributing to the carbon flux and impacting the concentration of particulate organic matter in the sediments. However, the knowledge in this topic is incomplete, mainly due to the exclusion of salps per se in ecosystem and biogeochemical models. Salps are hard to include in these studies because of their biological characteristics, when they are included, is within a different category, such as “gelatinous zooplankton”, and without specific studies, it is hard to identify the main role of salps in the carbon cycle.

 

Check some videos to see how salps swim and how long the chains can be.

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