Meet the Amazing Salp
The first time I saw a photo of a colony of salp, I thought it was a picture of something from a science fiction movie:
As a science and nature writer, I’ve become familiar with many sea creatures over the years. But somehow, I had never come across the salp before. What in the heck was it? My first guess was some kind of jellyfish:
Salps are not Jellyfish!
Salps certainly look like jellies! But if you look closely at an individual salp, you’ll see that it is actually a complex organism compared to a jelly. The salp has internal organs and structures that jellies don’t have, such as a heart, vascular system, pharynx, and gonads.
Although salps may look like spineless jellyfish, biologists actually consider salps to part of the phylum of chordates—the group of vertebrate and invertebrate animals that at some point in their life cycle have at least rudimentary spinal cords or true backbones.
In their adult form, salps have lost almost all of the features that would classify them at chordates. They do indeed look like a kind of jellyfish. However, in their larval stage, salps have many of the anatomical features of true vertebrate animals such as fish, birds, reptiles, and mammals.
In fact, juvenile salps have tails, gills, a primitive eye and backbone (called a notocord), a slender nerve cord, and a hollow, enlarged brain.
If Salps aren’t Jellyfish, What Are They?
Salps belong to a group of undersea animals called tunicates. Tunicates are saclike filter-feeders that live on plankton and organic matter they strain from the water they pump through their bodies. Their more well-known relative is the sea squirt or sea pork.
Salps are the free-floating members of the tunicates. Individual salps range in size from 1 cm to 10 cm (4 inches.) They move their barrel-shaped bodies by contracting themselves. This pumps water through one end of the salp’s gelatinous body and expels it out the other.
As the salp moves through the water, it strains the pumped water through its internal feeding filters. The plankton it feeds on gets trapped in mucus and is passed through its pharynx to the stomach for digestion.
Solitary Phase and Colony Phase
Adult salps go through phases—in the first, they are solitary:
In the second phase, they join together in colonies—the long chains that look so eerie:
Salps are highly successful animals. They and their ancestors have been around for hundreds of millions of years. Salps can be found in every ocean, but are most abundant in the Southern Ocean near Antarctica, which is especially rich in the phytoplankton that salp feed on.
When salps find a bloom like this, it’s “nom, nom, nom” time! In fact, if the phytoplankton is too dense, the salps can actually clog up and sink to their death. Salps take advantage of the food bonanza by quickly budding off clones of themselves. These clones graze the phytoplankton and can grow at a rate that is believed to be faster than any other multicellular animal.
The salp population explodes into swarms of hundreds of millions of individuals, which can devour even huge phytoplankton blooms. Then the salps run out of food, millions of salps starve, and their population crashes back to normal levels.
The billions of bodies of salps and their fecal pellets carry enormous amounts of carbon to the sea floor. Scientists are trying to understand just how this affects the ocean’s carbon cycle and how this in turn could play a role in climate change.
One thing’s for sure: the more we learn about our “pale blue dot,” the more we see how interconnected and interrelated Earths’ ecosystems are and how important the oceans are to life on this planet. If we destroy our oceans, we will surely destroy ourselves.