Yes, “sea pickles” are real. These intriguing marine creatures, scientifically known as pyrosomes, are fascinating inhabitants of the ocean. They are not a single organism but rather a collection of many tiny individuals forming a larger structure.
Unveiling the Pyrosome
Pyrosomes are free-floating colonial tunicates belonging to the genus Pyrosoma, classified under the subphylum Tunicata within the phylum Chordata. The name “pyrosome” comes from the Greek words “pyro” (fire) and “soma” (body), referencing their ability to produce light.
A pyrosome colony forms a hollow, cylindrical or cone-shaped tube, composed of hundreds of thousands of individual animals called zooids. These zooids, each only a few millimeters long, are bound by shared tissue, creating a gelatinous, often bumpy outer surface. While many colonies range from an inch to two feet, some giant pyrosomes can reach up to 60 feet long, with internal openings wide enough for a human to swim through.
Each zooid possesses light-emitting organs, contributing to the colony’s bioluminescence. This light, a pale blue-green, is bright and sustained, visible for many meters underwater. Bioluminescence can spread in waves across the colony as zooids detect light and respond by emitting their own, or in response to mechanical stimulation.
Life in the Open Ocean
Pyrosomes are pelagic, inhabiting warm tropical and subtropical waters worldwide. They exist offshore and in deeper waters, capable of vertical migration. They move towards the surface at night to feed and descend to depths of up to 2,300 feet during the day. This daily migration helps them access productive feeding grounds.
Their movement is influenced by ocean currents and tides. However, a pyrosome colony can also achieve slow, coordinated movement through jet propulsion. This occurs as each zooid pumps water through its feeding filtration system, expelling filtered water into the colony’s central cavity and then out of one end of the tube.
Pyrosomes are filter feeders, consuming microscopic plankton. They draw in water through an incurrent opening, filter food particles using a mucus net, and expel the filtered water. Reproduction involves both sexual and asexual methods. Individual zooids are hermaphroditic, producing both eggs and sperm, and can self-fertilize. New colonies also form through budding, where a fertilized egg develops into a small group of zooids that then asexually reproduce to enlarge the colony.
The “Pickle” Name and Their Ecological Role
The common name “sea pickle” stems from their visual resemblance to a gherkin or cucumber, due to their tubular, gelatinous, and often translucent appearance. Other nicknames like “sea worms” or “fire bodies” also exist. Despite their appearance, pyrosomes play a role in marine ecosystems.
As filter feeders, they consume microscopic plankton, influencing energy transfer within the pelagic food web. Pyrosomes form large aggregations called “blooms,” which can impact food availability for other zooplankton, such as crustaceans, prey for fish and seabirds. Pyrosomes also contribute to the marine carbon cycle; through daily vertical migrations, they transport carbon to deeper waters by releasing feces, and when colonies die, their bodies sink to the seafloor, providing food for bottom-dwelling organisms and contributing to carbon sequestration. They also serve as a food source for various marine animals, including fish, sea turtles, and some marine mammals.