Every summer thousands flock to New Jersey bays and beaches to beat the heat. But they are not alone in finding our shores inviting.
“We’ve had significant blooms of stinging jellyfish periodically in the last decade,” said Mike Kennish, a research professor with Rutgers’ Institute of Marine and Coastal Sciences, School of Environmental and Biological Sciences. “When there is a bloom of sea nettles, if you look into some of the lagoon areas of the Barnegat Bay, the water looks almost like jelly on the surface.”
It’s too soon for an official tally – peak season for sea nettles is mid-July though August – but with this month’s high temperatures baking the bay, Kennish suspects the waters will be teeming with sea nettles, again.
“Global warming is causing jellyfish populations worldwide to reach higher abundance levels than we’ve seen in a long time,” Kennish said. “They’re expanding their latitudinal ranges as well in response to the warming ocean temperatures.”
In addition to being a scourge to swimmers, Kennish said the proliferation of sea nettles is a potential threat to the bay’s ecosystem.
“The stinging jellyfish consume a very large amount of zooplankton or early life stages of fish and invertebrates,” he said. “So the danger there is that they can have a dramatic effect on the food web of the bay, altering the energy flow in the system.”
Barnegat Bay has long been home to sea nettles, but the population began exploding around the turn of the millennium, with some years being worse than others over the past 13 years.
“It’s not necessarily consistent,” said Kennish, who added that the numbers were higher in 2011 and 2012. “We really don’t know why some years they are just unbelievably abundant and some years not. It’s difficult to determine their absolute abundance in the medusa stage because they are often so abundant as to clog sampling gear, and their soft tissues easily break apart in nets.”
The largely enclosed bay’s warm, brackish, nitrogen-enriched waters create an ideal habitat for sea nettles, said Kennish, whose research team conducts ecological studies in the bay from the Marine Field Station in Tuckerton. But it’s the bulkheads, he notes, that provide a perfect place for jellyfish to latch on during the polyp stage and ride out the winter.
“The northern part of Barnegat Bay, that area is almost completely bulkhead,” he said. “There’s so much development with hard structures right up to the shoreline; this gives the polyp stage ideal habitat to establish strong populations.”
That development, along with lower salinities than elsewhere in the bay that sea nettles prefer (about 15-17 parts per thousand) as well as the higher concentration of nitrogen flowing into the bay from the Toms and Metedeconk rivers, has enabled the sea nettle to attain highest numbers in the northern part of the bay in recent years, said Kennish.
But this year has been a different story – so far. “It’s just the opposite of what we normally see,” he said. “There are higher numbers reported in the Forked River area and farther south than in the northern part of the bay, which is very unusual.”
Why the reversal? Kennish suspects June’s record-breaking precipitation levels have a lot to do with it. The rains flushed massive amounts of fresh water into the northern bay from the larger Toms and Metedeconk rivers, lowering the salinity levels there. In the lower Metedeconk River, for example, recent salinity levels were only four to nine parts per thousand, very low for this time of year.
Now much higher numbers of sea nettles are being reported in the Forked River area across from Barnegat Inlet and waters south of there in Little Egg Harbor, where salinities are also higher said Matthew Csik, an environmental scientist specializing in water resources for the Ocean County Health Department. “Our southern beaches - Manahawkin and Barnegat - the guys have been coming back from sampling there and said you can barely wade out in the bay side without encountering an awful lot of sea nettles,” said Csik.
As the rain subsides and the salinity levels in the north increase, jellyfish blooms are likely to reappear there, Kennish said. Jellyfish generally create a strong concern for swimmers. While a sting from a sea nettle is not lethal, it is quite painful. “The problem is not one,” he said. “You can really be in trouble when you have a whole bunch around you and they’re stinging you all over the place. It’s no fun.” If a swimmer is stung multiple times, the pain could cause a victim to go into shock and perhaps drown.
The bay’s jellyfish infestation doesn’t seem to be impacting the ocean side of the barrier islands. While there are other species of jellyfish that have been observed in the nearshore ocean waters, they have been far less abundant than sea nettles in Barnegat Bay.
The jellyfish that do prefer ocean waters - lion’s mane and moon jellies - have not been reported in high numbers so far this season, said Bob Tormollan, a Lavallette life guard captain. That’s because lion’s mane are more prevalent in spring instead of summer, he said, and moon jellies require a consistent ocean temperature in the low to mid-70s. “We really don’t get too many of them,” Tormollan said. “Sometimes later toward the end of August, but not a lot.”