Invasion of the Blobs

Although the moon jellyfish is currently widely distributed throughout the world, scientists believe that this jellyfish was probably transported and introduced to many of its current habitats by ships.

How do ships introduce non-native species of jellyfish to new habitats? For one thing, young jellyfish, known as polyps, travel with ships after clinging to their hulls. In addition, ships take on ballast water needed for stability in originating harbors, and then dump this water along with accompanying organisms, including jellyfish, into destination harbors.

Ships currently transport millions of gallons of ballast water around the world annually. Largely because of this phenomenon, 15 to 25 percent of all marine species that are currently found in global sea ports are non native.

Once non-native jellyfish are released from ships into new habitats where conditions suit them, they may colonize these habitats. And if these invasive jellyfish face few or no predators to control their numbers, their populations may explode into large swarms. Large jellyfish swarms may consume large numbers of commercial fish and thereby damage the fishing industry.

Invasions of non-native species of jellyfish have wreaked havoc on many ecosystems, including the Gulf of Mexico, the Sea of Japan, the Black Sea, the Caspian Sea and the Mediterranean. The costs of resulting ecological problems to the tourism and fishing industries have been staggering.

How do scientists distinguish native from invasive species of jellyfish? By using DNA analyses. Native species that have had a long history in a particular ecosystem have had time to diversify, while specimens taken from recently introduced species show more similarity with each other.

In addition, scientists are currently poring over records of worldwide marine life that were fastidiously maintained by some early explorers. Such analyses will help scientists map the natural distributions of jellyfish species before large-scale shipping introduced non-native species to new habitats.

— Lily Whiteman, National Science Foundation. Photo Credit: NOAA

Editor's Note: For more eye-popping photos, videos and facts about jellyfish, see the National Science Foundation's special report on jellyfish: Jellyfish Gone Wild: Environmental Change and Jellyfish Blooms.