Invasive Species: Warty Comb Jelly

A warty comb jelly (Mnemiopsis leidyi). The species has numerous other common names.

Comb jellies are often confused with the other soft-bodied transparent inhabitants of the world's ocean. However, unlike true jellyfish, box jellyfish, and other cnidarians, comb jellies cannot sting! They are also far more complex morphologically, including the presence of a complete digestive tract rather than the blind sack gut that Cnidarians use. Comb jellies are also classified on their own in the Phylum Ctenophora, with groups quite neatly and separately from Phylum Cnidaria. The origin of the common name "comb jelly" comes from the eight rows of cilia ("ctenes") that are arranged along the body of the organism. These cilia beat in unison and create the rainbow-like sheen that is so often seen when observing ctenophores. Compared to cnidarians, ctenophores are rather harmless. Some comb jellies are even bioluminescent.

M. leidyi in the Black Sea

When looking at the warty comb jelly, however, things are not all sunshine and roses. Ctenophores are all predators, but this particular species is a voracious predator of fish larvae and eggs. In fact, it can be directly linked to crashes of fisheries. Even worse was what happened when in the 1980's these creatures were accidentally introduced to the Black Sea via ballast water. Since the introduction, biodiversity has plummeted, as overall abundance of organisms and the biomass that is produced. The same has occurred in the Sea of Azov, Sea of Marmara, and Caspian sea, though the latter has been hit the hardest. Every part of the food web (or trophic level) has been affected, up to and including the endangered Caspian seal.

Management of the warty comb jelly is difficult, and may in fact prove to be impossible. However, there has been some success following the introduction of a biological control in the form of a natural predator: another ctenophore (Beroe ovata). Though the introduction was accidental (ironically, through ballast water as well), this new species is though to be the only viable way to control the warty comb jelly.

This is another organism from the 100 World's Worst Invasives list, where it sits at #57.


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