Jellyfish Gone Wild — Text-only | Flash Special Report
A VORACIOUS PREDATOR TIGHTENS ITS TENTACLED GRIP ON THE EASTERN SEABOARD OF THE U.S.
Populations of the gluttonous, rapidly producing comb jelly called Mnemiopsis are increasing throughout the eastern seaboard. In addition, the northern border of this creature’s range recently advanced from Cape Cod to Boston Harbor. These changes are probably at least partly caused by rising temperatures.
Increases in Mnemiopsis populations are disturbing because the belly of this jelly, which feeds continuously, is virtually bottomless. Driven by an insatiable appetite, large swarms of fist-sized Mnemiopsis jellies can almost literally eat a whole in the ocean.
Among the waters that are supporting increasing populations of Mnemiopsis are:
Since 1971, Narragansett’s population of comb jellies has at least doubled; during their annual peaks, comb jellies are now a dominating force on Narragansett’s ecology.
Narragansett’s comb jelly explosion correlates with an increase of almost two degrees centigrade in average winter temperatures since 1950. This warming enables some comb jelly clusters to, as never before, survive the winter and start breeding and accumulating large populations in the spring. By contrast, comb jellies used to take until mid-summer to do so. A longer comb jelly season means more comb jellies.
In addition, Narragansett’s comb jellies used to bloom too late in the summer to exploit blooms of small crustaceans, called copepods, which bloom in the spring; but now that comb jellies also bloom in the spring, they can consume large volumes of copepods. Because copepods are also eaten by fish, whales and sea birds, the impacts of their increased consumption by comb jellies may cascade throughout the food chain.
The Chesapeake Bay:
No one knows how abundant gelatinous creatures were in the Chesapeake Bay before humans began impacting this heavily polluted water body. But the Chesapeake currently harbors large populations of many types of gelatinous creatures, including comb jellies, that are locked in a perpetual power struggle with large populations of comb jelly-eating sea nettles. Ecological dominance in the Chesapeake frequently swings back and forth between these two types of gelatinous creatures.
Currently, comb jellies wield the upper hand (or upper tentacle) in their power struggle with sea nettles. Why? One theory is that ongoing climate change produces conditions that are more favorable to highly adaptable comb jellies than to sea nettles, which have more rigid environmental requirements. Another theory is that the harvesting of the Chesapeake’s oysters by the fishing industry has reduced habitat for juvenile sea nettles, which cling to hard surfaces --including oyster shells--and thereby helped reduce the Chesapeake’s population of sea nettles. (By contrast, young comb jellies swim freely without clinging to hard surfaces.)
Continued dominance of the Chesapeake by comb jellies may damage its fish populations. Why? Because comb jellies eat more of the same foods that are eaten by fish and eat more fish eggs than do sea nettles.
Invasive comb jellies, which originated on the East Coast of the United States, are now proliferating in European seas. (See “The Black Sea.”)
A JELLIFIED WATER BODY
About 500,000 people are stung by jellyfish annually in the Chesapeake Bay, a degraded water body. Credit: Scott Bauer, USDA
A HEARTLESS PREDATOR
Though humble in appearance, the fist-sized comb jelly (Mnemiopsis)--which is heartless, spineless and brainless --is a various predator that dominates many ecosystems during the summer. Credit: Laurence Madin, Woods Hole Oceanographic Institution