Box 183 Comb Jellies Alien Invaders

Comb jellies are well known as invaders. For example, Mnemiopsis leidyi, a lobate cteno-phore in the Class Tentaculata were inadvertently carried in ships' ballast water from the Chesapeake to the Black Sea in the early 1980's. Without natural predators, by 1990 they had bloomed so much that surveys estimated that Mnemiopsis now comprised one billion tons of biomass in the Black Sea. This one species single-handedly caused the collapse of an ecosystem and the fisheries that went with it. This case has been well studied, and it is believed that the jellyfish ate the larvae of other species including sardines, as well as the food sources that the larvae would eat; this combination of direct and indirect effects prevented other species from regaining viable populations.

Elsewhere in the world, other ctenophore and medusa species have been considered pests, either through exotic species introductions, or through local perturbations that allowed the jellyfishes to alter existing ecosystems; perturbations include overfishing, pollution, and changes in water temperature. Jellyfish can bloom rapidly when conditions are ideal or go for long periods of time without food if necessary. Their potential to quickly change pelagic assemblages, therefore, is great.

Cydippida, Fig. 18.8A) have a small spherical body with two tentacles. Bolinopsis-type comb jellies (Order Lobata, Fig. 18.8C) have an egg-shaped body with two large lobes. Beroe-type comb jellies (Order Beroida, Fig. 18.8B) have a flattened palm-of-the-hand-shaped body without tentacles. (Box 18.3.)

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