Sea pickles, scientifically known as Pyrosomes, glow through a natural process called bioluminescence. The genus name Pyrosoma translates from the Greek as “fire body,” referring to the animal’s ability to produce its own light. Their bright blue-green light display makes them one of the most visually striking organisms in the world’s open oceans.
What Exactly is a Sea Pickle?
The common name “sea pickle” refers to a free-floating, colonial organism that is scientifically classified as a pyrosome, a type of pelagic tunicate. Pyrosomes are chordates, placing them in the same phylum as vertebrates, though they lack a backbone and are not jellyfish. The entire structure is a single, hollow, cone-shaped tube comprised of thousands of tiny, individual organisms called zooids.
Each zooid is only a few millimeters long, but they are all embedded in a shared, gelatinous matrix that forms the wall of the colony. This colonial structure can vary dramatically in size, with some pyrosomes measuring just a few centimeters, while others can extend to lengths of several meters. The zooids work in concert to filter feed on microscopic plankton, drawing water in and expelling it into the colony’s interior.
The Chemical Mechanism of Pyrosome Light
The glow is produced by the thousands of individual zooids that make up the colony wall. Bioluminescence is a chemical reaction involving the light-emitting molecule luciferin and the enzyme catalyst luciferase. The enzyme speeds up the oxidation of luciferin, and the resulting energy release generates a “cold light” with almost no heat.
Pyrosomes exhibit stimulated bioluminescence, meaning the light is typically triggered by external movement, such as a physical disturbance or a nearby current. In some species, this light is produced by symbiotic bacteria, such as Photobacterium species, that reside within specialized light organs of the zooids. When a stimulus excites a single zooid, the light it emits can act as a trigger, causing its adjacent neighbors to also flash.
This chain reaction results in a ripple or wave of light that appears to travel down the length of the entire colony. The overall effect is a prolonged blue-green light, which is the color that travels most effectively through ocean water. This coordinated, sequential flashing is what makes the pyrosome a highly effective light producer in the deep sea.
Ecological Role of Bioluminescence
The light production is an adaptive trait, but its exact function is thought to be multifaceted. One primary hypothesis is that the bright flash serves as a defense mechanism, startling or momentarily blinding a potential predator. The sudden burst of light may also serve as a “burglar alarm,” attracting a larger predator that may target the animal attempting to eat the pyrosome.
The ability to communicate is another proposed function, allowing zooids to coordinate their actions or possibly signal danger to other pyrosome colonies nearby. Light may also play a role in attracting prey or in reproductive signaling among colonies for mating. The production of this bright, long-lasting light is an integral adaptation for survival in the pelagic environment.