Comb jellies (phylum Ctenophora) are exclusively marine invertebrates found throughout the world’s oceans. They are often mistaken for true jellyfish (phylum Cnidaria), but comb jellies are genetically distinct and lack the stinging cells characteristic of their cnidarian counterparts. Characterized by gelatinous, often transparent bodies and eight rows of fused cilia—the “combs”—they are active predators in the water column. Their unique anatomy and feeding strategies allow them to efficiently capture prey, making them significant components of marine food webs.
Primary Prey Items
Comb jellies are voracious carnivores whose diet consists primarily of small planktonic organisms, known collectively as zooplankton. A large part of their caloric intake comes from micro-invertebrates such as copepods, which are tiny crustaceans abundant in marine waters. Certain species, like the sea walnut (Mnemiopsis leidyi), can consume nearly 500 copepods in a single hour, demonstrating their capacity for intense predation. The diet often includes the early life stages of other marine organisms, such as pelagic fish eggs and newly hatched larvae. This consumption of ichthyoplankton establishes the comb jelly as a direct competitor and predator of developing fish stocks. Comb jellies are also opportunistic feeders and will consume other gelatinous animals, including smaller zooplankton and even other ctenophores. The tentacle-less, sac-shaped comb jellies in the genus Beroe are specialized predators that consume other, often larger, comb jellies, swallowing them whole.
Specialized Feeding Apparatus
The mechanism a comb jelly uses to capture prey depends heavily on its species and body form, which broadly fall into two main groups: tentaculate and lobate forms. Tentaculate ctenophores, such as the rounded cydippids, possess a pair of long, retractable tentacles that they deploy like fishing lines. These tentacles are armed with specialized adhesive structures called colloblasts, which are sticky cells unique to ctenophores. When prey brushes against the tentacles, the colloblasts rupture and release a sticky, glue-like substance that traps the organism without using the venomous stingers found in true jellyfish.
Lobate ctenophores, like the Mnemiopsis species, employ a different strategy using large oral lobes that extend beneath their mouths. These lobes contain specialized, beating cilia that generate a strong, continuous current of water, sweeping planktonic prey directly toward the mouth. This movement allows the ctenophore to filter-feed continuously, capturing a wide range of small particles and organisms. In a third group, the beroid ctenophores, the mouth is large and muscular, allowing them to engulf and consume entire organisms, often other comb jellies, without the aid of tentacles or colloblasts.
Diet Variation and Ecological Impact
Comb jelly diet is not static, varying significantly based on the species, the size of the individual, and the local availability of prey. The high feeding rates of these animals mean they play a substantial role in regulating zooplankton populations in marine ecosystems. When environmental conditions are favorable, comb jellies can quickly form massive population blooms that drastically alter the local food web structure. This ecological impact is best illustrated by the invasive sea walnut, Mnemiopsis leidyi, which was accidentally introduced into the Black Sea in the 1980s via ship ballast water. The intense, unchecked predation by M. leidyi on zooplankton, fish eggs, and fish larvae led to a sharp decline in the populations of commercially fished species, such as anchovy and sprat. The resulting collapse of the fishery severely degraded the entire pelagic ecosystem, showcasing how the feeding habits of a single comb jelly species can cause profound ecological and economic disruption.