Salp (class Thaliacea)

InvertebrateTunicatePlankton

Overview

Salps are transparent, gelatinous, barrel-shaped animals that drift through the open ocean, often mistaken for jellyfish but in fact something far more surprising. They are tunicates — relatives of the sea squirts — and, like them, belong to the same broad group as the backboned animals, making these jelly-like drifters unexpected cousins of the vertebrates. A salp moves by pumping water through its hollow body, which both propels it along by jet and filters tiny plankton from the water to eat.

Salps are famous for their life cycle: they alternate between solitary individuals and long, connected chains of clones, so that under the right conditions they can multiply explosively and form spectacular ribbons and wheels of linked, glassy bodies stretching through the sea.

Note: “salp” covers several species in the class Thaliacea; details here describe them broadly. Treat general statements as approximate and verify against authoritative sources.

Habitat & Range

Salps live in the open ocean worldwide, drifting in the plankton from the surface down into deeper water, and they are especially abundant in cooler and productive seas, including around the Southern Ocean. They are creatures of open water rather than the seabed, carried by currents but able to swim by jet propulsion as they feed.

Diet

Salps are filter feeders that strain phytoplankton (tiny drifting algae) and other small particles from the water. As a salp pumps water through its body for propulsion, an internal mucus net captures the plankton, which is then passed to the gut. Because salps can feed and grow extremely fast and bloom in huge numbers, they consume vast quantities of plankton, and their dense, sinking droppings and dead bodies carry carbon down into the deep sea — giving these humble drifters a real role in the ocean's carbon cycle.

Behavior

The salp's signature is its alternation of generations. A single, solitary salp reproduces by budding off a long chain of genetically identical clones, which break free and swim and feed together before themselves reproducing sexually to start new solitary salps. This quick-cloning strategy lets salp populations explode when plankton is plentiful, forming the long chains, ribbons, and wheels for which they are famous — sometimes turning patches of sea into a soup of glassy bodies. Salps are among the fastest-growing of all animals, and many can glow with bioluminescence. They swim continuously by jet propulsion, pumping water through the body, so feeding and movement are one and the same action.

Human Interaction & Conservation

Salps are harmless to people — they have no sting — and they are increasingly recognised as important players in marine ecosystems and the ocean carbon cycle, even drawing scientific interest for how their blooms affect food webs and how carbon is transported to the deep. Their numbers swing dramatically with ocean conditions, and large blooms can sometimes clog fishing gear or intake screens. As open-ocean drifters, they are not exploited and are not of conservation concern, though they reflect the health of the plankton they depend on. Consult authoritative sources for details.

More photos of the salp