Comb jellies, scientifically known as Ctenophora, are marine invertebrates. They are distinguished by eight rows of comb-like plates, which are fused cilia that beat in synchronized waves to propel them through water. These “combs” often create a shimmering, rainbow-like effect as they scatter light. Many comb jelly species produce their own light, a phenomenon known as bioluminescence, typically emitting a soft blue or green glow. Unlike jellyfish, comb jellies do not have stinging cells; instead, most use sticky cells called colloblasts on their tentacles to capture prey.
Global Oceanic Presence
Comb jellies exhibit a widespread distribution across all major ocean basins. They inhabit marine environments from the frigid Arctic and Antarctic polar regions to warm, temperate, and tropical waters, including the Atlantic, Pacific, Indian, and Southern Oceans. This broad geographical reach highlights their adaptability to various oceanic conditions. These gelatinous animals drift through the water column, making up a significant portion of planktonic biomass in many areas.
Diverse Marine Habitats
Comb jellies inhabit diverse marine environments, from the ocean’s surface to its deepest trenches. They are commonly found in surface waters, including coastal areas, open ocean regions, and estuaries. Some species, like the sea walnut (Mnemiopsis leidyi), are observed in bays and estuarine locations.
Some species thrive at extreme depths, in the lightless, or aphotic, zones of the deep sea at over 7,000 meters. These deep-sea inhabitants have evolved biochemical adaptations to cope with pressure and cold temperatures. Comb jellies tolerate a broad range of environmental conditions, including temperatures from -2°C to 30°C and varying salinities, from brackish estuarine waters to full marine salinity. This tolerance allows them to persist in areas with fluctuating water quality, including those with lower oxygen levels or pollution.
Invasive Species and Ecosystem Impacts
Certain comb jelly species have expanded their range beyond native habitats, becoming invasive in new ecosystems. A primary mechanism for this introduction is ballast water carried by ships, which can transport marine organisms across vast distances. Once introduced, their rapid reproduction and adaptability can lead to significant ecological shifts.
A prominent example is Mnemiopsis leidyi, the warty comb jelly or sea walnut, native to the western Atlantic coastal waters. This species was accidentally introduced into the Black Sea in the early 1980s via ship ballast water, and later into the Caspian Sea. Its rapid proliferation led to a decline in local fish populations, particularly commercially important species like anchovy, by preying on fish eggs, larvae, and zooplankton. This invasion resulted in substantial economic losses to the fishing industry, estimated at over $300 million in some regions.
Mnemiopsis leidyi has since spread to other European waters, including the Baltic and North Seas, establishing self-sustaining populations. Its ability to tolerate a wide range of temperatures and salinities, combined with its capacity for self-fertilization, contributes to its success as an invader.