Case Study: American Atlantic Coast Comb Jelly

The American Atlantic coast comb, Mnemiopsis leidyi, is a seemingly harmless jellyfish, small and without stingers. This appearance is deceptive, however, as the comb jelly has proven to be a very dangerous biological invader of the Black and Azov Seas. In 1982, ships carrying ballast water from the American coast transported this jellyfish to a port in the Black Sea.

With few enemies in its new habitat, the comb jelly propagated at an alarming rate, quickly spreading into the Azov Sea as well. The Black Sea is naturally anoxic (suffering from oxygen deficiency) and has had extensive problems with algae, which covers the surface, using up oxygen and suffocating the upper layer of sea life. Algae also shades the shallow-water sea grass beds that produce necessary oxygen and prime habitat to fish, crustaceans, and sponges. Zooplankton eat algae, thus providing an important service to the plants and animals of the Black Sea. Comb jellies, however, eat zooplankton, and have done so with such voracity as to virtually eliminate zooplankton populations in both the Black and Azov Seas. In this manner, the comb jelly has successfully outcompeted other species by increasing alga concentrations and lowering the oxygen level in these environments. It now makes up more than 90% of all biomass present in the Black Sea. The seafood industry of the Black Sea has suffered incredible economic setbacks due to the comb jelly invasion, losing over $350 million dollars in the past 18 years. The anchovy fisheries of the Azov Sea, already under stress by overfishing and pollution, simply folded.

Eradication of this invader is almost impossible, given its widespread establishment. Focus has now moved to controlling the growth and success of the comb jelly in attempts to reverse the fisheries decline in the Black and Azov Seas. The best option for control involves deliberate introduction of a parasite or predator to keep the jellyfish in check, but introductions of this type hold the potential to cause other ecosystem changes. The invasion of the American Atlantic coast comb jelly serves as yet another warning of the dangers of the international transport of ballast water.

^{-- Bright, C., Life Out of Bounds: Bioinvasion in a Borderless World , Worldwatch Environmental Alert Series (New York, NY: Norton, 1998). pp. 89-92, 182}

^{Related Link:
-- Academy of Natural Sciences}