In 2006, biologists sounded the alarm farther north when American comb jellies were first discovered in Dutch, Danish and Swedish waters. The species went on to invade nearby waters-including the eastern Mediterranean and the Caspian Sea, which borders Russia to the east and Iran to the south-with similar environmental and economic damage as in the Black Sea. To add insult to injury, the jellies were devouring not just the fish’s food, but their eggs and young as well. This caused a total collapse of local fisheries specializing in anchovies and sardines-fish that feed on the same plankton the jellies eat. By 1989, when the Black Sea’s population of the invasive species peaked, some areas held more than 14 jellies per square foot. A gallon may not sound like a lot, until you consider the sheer number of individuals eating their way through the food supply. In their constant search for grub, small species like American comb jellies sift through approximately a gallon of seawater every day, says Keith Bayha, a marine biologist at the University of California at Merced.
Jellies eat by filtering food from water. Altogether, true jellyfish and their cousins account for up to a third of the world’s marine biomass, according to some experts. Other cousins, like comb jellies, lack stinging needle cells-one reason why they’re classified separately from Cnidarians. It’s also a Cnidarian, but it belongs to a different class than true jellies like mauve stingers and moon jellyfish ( Aurelia aurita), a common species found on the eastern and western coasts of the U.S. Other gelatinous cousins are often also referred to as “jellies” or “sea jellies.” The Portuguese man-of-war ( Physalia physalis), a strikingly beautiful creature with an agonizing sting, is one such cousin. True jellyfish (which aren’t fish at all) fall under the class Scyphozoa. Jellyfish belong to the invertebrate phylum Cnidaria. They probably smell chemicals in the water. “Jellyfish aren’t just blobs,” says Jennifer Purcell, a marine scientist at Western Washington University who studies the creatures. Although jellies appear extremely simple, scientists believe that there’s a lot more going on than meets the eye.
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