Sea pickles, also known as pyrosomes, are marine organisms that often drift in the open ocean. These creatures sometimes wash ashore in large numbers, sparking curiosity about their nature and ecological role.
Defining Sea Pickles
Sea pickles are colonial tunicates, specifically belonging to the class Thaliacea and the family Pyrosomatidae. Their genus name, Pyrosoma, means “fire body” in Greek, referring to their bioluminescence. They are not a single organism but a colony composed of hundreds to hundreds of thousands of tiny individual animals called zooids. These zooids are linked together by shared tissue to form a larger, unified structure.
The overall colony typically forms a hollow, cylindrical, or conical tube, which can range significantly in size from a few inches to over 60 feet in length. The outer surface is gelatinous, semi-translucent, and often described as bumpy. Their coloration can vary, appearing pale pink, yellow, or blue in sunlight. The common name “sea pickle” arises from their resemblance to a cucumber.
Biology and Unique Features
The colonial nature of sea pickles is a defining characteristic, where countless zooids are embedded within a common gelatinous tunic. Each zooid within the colony contributes to its overall functions, including feeding, protection, and reproduction. Sea pickles are efficient filter feeders, drawing water through siphons to capture microscopic plankton. As individual zooids filter water from the outside and expel it into the colony’s central cavity, this coordinated process generates a slow form of jet propulsion, allowing the colony to move through the water column.
A prominent feature of sea pickles is their bioluminescence, the ability to produce their own light. This light is typically a bright blue-green, though it can also appear pink or yellow, and can be remarkably brilliant, visible for many meters in dark waters. Each zooid contains a pair of luminescent organs, and when one zooid is stimulated, it can trigger a wave of light that passes through the entire colony, suggesting a form of communication between individuals without a neural pathway. The purpose of this light production is thought to play roles in attracting prey, deterring predators, or even signaling danger to other colonies.
Sea pickles employ both sexual and asexual methods of reproduction, contributing to their ability to form massive population blooms. Each zooid is hermaphroditic. Sexually reproduced embryos develop into a small, four-zooid stage that then buds asexually to form a new colony. This combination of reproductive strategies allows for rapid growth and regeneration of colonies.
Their Ocean Home and Ecological Role
Sea pickles are pelagic organisms. While most commonly found in tropical and subtropical waters, their distribution is global, extending into temperate and even colder regions, including the Antarctic. They can be found at various depths, from surface waters down to over 2,300 feet (700 meters), and some species undertake daily vertical migrations, rising towards the surface at night to feed and descending to deeper waters during the day.
Within the marine food web, sea pickles serve as primary grazers of plankton. They also become a food source for a variety of larger marine animals, including fish, sea turtles, seabirds, and even marine mammals like dolphins and whales. Beyond their direct role as food, pyrosomes can provide shelter for other deep-sea organisms.
Sea pickles contribute to ocean nutrient cycling, particularly in the marine carbon cycle. Their rapid growth during blooms allows them to consume significant amounts of phytoplankton, which are carbon-rich. When sea pickles die, their gelatinous bodies can sink to the seafloor, transporting carbon from the surface waters to the deep ocean, where it becomes available as food for benthic organisms. This process helps sequester carbon from the atmosphere.
Common Inquiries About Sea Pickles
The name “sea pickle” is a common nickname given to these creatures primarily because of their cylindrical, translucent shape and gelatinous texture, which can resemble a pickled cucumber. This informal name helps distinguish them, though their scientific classification is pyrosomes.
Despite their name, sea pickles are not considered edible for humans. Their gelatinous consistency and bland taste make them unpalatable. They are not related to sea cucumbers.
Sea pickles are often mistaken for jellyfish due to their translucent, gelatinous appearance and their free-floating nature. However, jellyfish belong to the phylum Cnidaria, while sea pickles are tunicates, placing them in a group more closely related to vertebrates than to jellyfish. Unlike jellyfish, which are individual animals, sea pickles are colonies of many smaller zooids working together.