Global warming lends power to jellyfish
In Narragansett Bay and Long Island Sound, nonnative species are taking over
The Boston Globe,July 2, 2002
The teachers had expected to catch an array of marine life in their nets. They got jellyfish, nothing but jellyfish; jellyfish so plentiful that the gelatinous organisms came up dangling through the net like slimy icicles. And with each haul came more.
''Eventually it seemed that our deck was coated with vaseline,'' said Captain Eric Pfirrmann, who works for Save The Bay, an advocate for Narraganset Bay in Rhode Island. He drives a research vessel that had taken some high school teachers on a marine field trip. ''I've seen blooms like this before,'' Pfirrmann said, ''but never so early in the summer.''
The culprit is a nonstinging invertebrate about the size and shape of a tulip blossom and commonly known as the combjelly. These blobs of summer, combined with sea squirts, an entirely different organism taking over Long Island Sound, are thriving in large part because water temperatures have risen about 3 degrees in the past two decades, according to scientists. This environmental shift favors them - and not others.
While the jellyfish invasion has helped decimate the winter flounder population in Narragansett Bay, the nonnative sea squirt may overrun the local oyster and blue mussel communities. They have cute names, sea squirts and combjellies, but they may be harbingers of economic trouble to come aboard a warming planet where just a few degrees in an environment out of sight can make such a difference.
''There is evidence of jellyfish explosions around the world that appear related to the adverse impact of human activities, and those include global warming,'' said Sarah Chasis, the senior attorney for the New York City-based Natural Resources Defense Council.
Historically, Narraganset Bay was the northern limit of the combjelly, whose domain extends as far south as Argentina. Last November, combjellies were documented for the first time in Boston Harbor, although in numbers as yet too sparse to affect the harbor's ecology. But this is not the case in Narragansett Bay, according to Barbara Sullivan, an oceanographer from the University of Rhode Island who has been studying the organism for the last two years with a grant from the National Science Foundation. In Rhode Island, warmer water is changing the rules of who eats whom.
The combjelly's ability to reproduce is temperature related, and traditionally the animal's population exploded during the warmth of late summer and early autumn. But because the bay has warmed an average of 3.4 degrees during the past 20 years, the combjelly is now reproducing and ''blooming'' four months earlier, which enables the organism to gobble up the eggs and larvae deposited in the spring by spawning fish as never before.
''We have seen areas of the bay where these things have cleaned out everything edible floating in the water column,'' she said. One consquence has been the demise of the winter flounder population, although no one is ready to place the blame squarely on the combjelly. In 1982, approximately 4,200 metric tons of the flounder were landed in Rhode Island. In 2000, the most recent year for which state statistics are available, approximately 600 tons of the flounder were caught.
''Combjellies do indeed eat many winter flounder larvae,'' said Tim Lynch, the principle marine biologist for the state Division of Fish and Wildlife, ''but I do not believe they are the sole cause of the population decline in Narragansett Bay.'' Factors such as overfishing and water quality probably also play a role, Lynch said.
While the combjelly raises havoc by gorge feeding, a nonnative sea squirt is hording all the living space - perhaps to the detriment of commercially valuable mussels and oysters, according to Robert Whitlatch, a marine scientist at the University of Connecticut.
''Space is the limiting factor in this scenario, and we are discovering that whoever gets there first has a tremendous advantage,'' Whitlatch said.
Sea squirts are filter-feeding animals an inch to 3 inches long that attach themselves to hard substrates such as pilings, rocks, or the underside of bouys. Once they get a foothold, they spread out in colonies that dominate like an unrolling carpet. In the past 15 years, Whitlatch has documented in the sound the doubling of aliens, which probably arrived on the hulls of ships, while the local populations have diminished by half. While he doesn't fully understand why, winter water temperature is an important factor, he said. From the late 1970s to 2001, the average temperature of Long Island Sound, monitored for the first three months of each year, increased about 8 percent, from 37.4 degrees to 40.2 degrees. The alien sea squirts have been able to capitalize on the warming and get the jump on accommodations.
''There's a potential here to crowd out other animals [such as oysters and mussels] that need hard substrates to grow,'' Whitlatch said. ''We don't know where this is all going. We're just in the initial phases of exploration in the laboratory.''
This story ran on page C1 of the Boston Globe on 7/2/2002.