Scientists are concerned about a growing population of sea nettles in Barnegat Bay
In all his years sailing New Jersey’s Barnegat Bay, scientist Kent Mountford never saw mobs of stinging jellyfish. But he came to know the sea nettles all too well during his career studying Chesapeake Bay, where the jellyfish make some waters unswimmable all summer.
So when Mountford took a boat north through his old Barnegat cruising grounds in late June, he was astonished to see dozens of baby sea nettles ghosting alongside, in sizes from a few millimeters to just less than an inch wide. The sign of a breeding population, he thought.
“I never saw one in my life [in Barnegat Bay]. The first one I’d seen was when I went to the Chesapeake in ’63 or ’64,” says Mountford, formerly the senior scientist with the Environmental Protection Agency’s Chesapeake Bay program.
With full-grown mantles 4 inches wide and stinging tentacles trailing 4 or 5 feet below, sea nettles make water-contact sports almost impossible in parts of the Chesapeake. If a large, permanent sea nettle population is established at the Jersey Shore — vacation spot for millions of people in the New York-Philadelphia corridor — “It will kill Barnegat Bay,” Mountford says.
Other scientists and longtime Barnegat boaters agree sea nettles are showing up in large numbers in the bay’s northern coves, where lower salinity levels and a plentiful food supply of smaller jellyfish provide favorable habitat for the nettles.
Chesapeake Bay research has shown peak sea nettle populations come at low salinities centered around 13.5 parts per thousand — almost a third of the salt content at ocean inlets — and warm water temperatures from the upper 70s into the mid-80s.
Some popular Barnegat Bay anchorages and gunkholes, like Tices Shoal just north of Barnegat Inlet, should stay nettle-free when they have higher salinity levels. But locations along the Intracoastal Waterway in the bay from Toms River northward almost to the Point Pleasant Canal, such as Silver Bay and coves near Mantoloking, have seen significant numbers of jellyfish. Some boaters say sea nettles suddenly became a problem just a few years ago in lagoons off the west side of the northern bay, where salinity is even lower.
Art Darton of Brick, N.J., says he’s been on the water for 40 years and never saw sea nettles until a neighbor was painfully stung while swimming in their lagoon three years ago.
“There were all kinds of jellyfish in the lagoon,” says Darton. “I got my crab net and pulled some out. I couldn’t believe it.”
Darton says he called government environment and health offices about his find, but no one was interested enough to come out and look. “I think there’s going to be a tremendous problem unless they make a frontal attack on these things,” he says.
Michael Kennish, a longtime Barnegat Bay researcher with the Institute of
Marine and Coastal Studies at Rutgers University, agrees. “There could be real problems ahead,” says Kennish. He says sea nettles have been showing up in greater numbers in the Toms River and northern Barnegat Bay than seen previously.
The question is whether this is a temporary condition or a sign that Barnegat Bay’s ecosystem is dramatically tipping under the weight of storm water runoff pollution from suburban growth on land. Around the world, scientists are looking at jellyfish swarms as a result of runaway growth of microscopic aquatic plants, called phytoplankton, that’s fueled by nitrogen and phosphorus compounds washing into coastal waters from rapid urban and agricultural development.
Work by such researchers as John F. Caddy of the United Nations Food and Agriculture Organization and Robert Ulanowicz at the University of Maryland points to a similar worldwide coastal pollution syndrome called eutrophication. It’s a chemical and biological trend marked by big phytoplankton blooms and low dissolved oxygen levels in the water, which can kill or drive away native fish. Eutrophication may be causing jellyfish eruptions and a biological “short circuit,” says Ulanowicz.
According to this theory, increasing soil erosion and runoff pollution from shoreside development increases plant nutrients in coastal waters, favoring smaller phytoplankton organisms over the slightly larger microscopic animals called zooplankton, which used to dominate, Ulanowicz says. The tiny plants are easily eaten by small jellyfish called ctenophores, which in turn are the favored prey of sea nettles, according to Ulanowicz.
In the open sea, jellyfish are eaten by sea turtles, but in brackish back bay waters they have no predators. Biologically, jellyfish are sucking up energy from the system that used to go to fin fish and shellfish, and the food chain becomes “a dead end,” he says.
Experts also say there’s a chance the sea nettles are exploiting a chance combination of favorable conditions — lucky for them, bad for swimmers — that could change in time. Spring rainfall seems to be a strong determining factor in the Chesapeake, with a dry April favoring more sea nettles as summer approaches, Ulanowicz says.
The sea nettles could just be exploiting big ctenophore populations under good conditions, says Jennifer Purcell, who studied Chesapeake Bay sea nettles for years and is a resident scientist at Western Washington University’s Shannon Point Marine Center in Anacortes, Wash.
Scientists associated with Rutgers University and the EPA-funded Barnegat Bay Estuary Program are determining how to track and monitor sea nettle swarms. But local naturalists and boaters already are alarmed by reports because they are coming from areas of the bay where scientists have already seen that eutrophication is a serious threat.
Sen. Frank Lautenberg, a Democrat from New Jersey, requested that the National Oceanic and Atmospheric Administration open an investigation into the Barnegat Bay sea nettle outbreaks.
“My fear is that Barnegat Bay will go the way of the Chesapeake Bay, where certain waters have become unswimmable due to swarms of sea nettles,” Lautenberg wrote in a July 23 letter to NOAA administrator Vice Adm. Conrad Lautenbacher.
Historic accounts of Chesapeake sea nettles date to at least the 1700s, and the jellyfish were such a serious deterrent to swimmers by the late 1800s that they were a major factor in the Bay shore’s decades of rural isolation, Mountford says. But the big shift in the Chesapeake’s ecosystem probably occurred in the 1950s, according to Ulanowicz, and there is a danger Barnegat Bay could be following that path.