It was hot and sunny Thursday afternoon on Windward Beach Park in Brick Township, N.J.

A dozen or so families hung out on the beach, but no one was swimming.

"It's because of the jellyfish," said Susan Hess, who sat in a lawn chair watching her grandchildren play in the sand.

"I've been coming to the beach here for about 10 years with different grandchildren and they always were able to use the beach," Hess said of her grandchildren.

No more.

The beach is on the Metedeconk River, just upstream from Barnegat Bay. A few feet off the shoreline, the knee-deep water is teeming with white blobs. The blobs float lazily in the waves, six inches to a foot apart.

These small jellyfish, known as sea nettles, have exploded in the northern part of the bay over the past 10 years. But no one has a reliable count to document how the population has grown. This summer, researchers are trying to change that.

Related: What you can do to reduce the jellyfish explosion

Setting a baseline

Nina Sassano and Jen Barny, two field technicians with the Barnegat Bay Partnership, waded into the water Thursday, wearing tights to protect themselves from sea nettle stings. Once they reached chest-deep water, they unfurled a 50-foot wide net between them and start walking toward the shore, capturing any jellyfish floating in the water as they went.

When Sassano and Barny lay the net flat on the beach, they revealed their catch: crabs, small silver fish, and a mass of jellyfish in a strip about six inches thick running the length of the net.

"It kind of just (looks like) a big goo pile," Barny said. "Once the nettles are out of the water, they look like circles with kind of little straight pieces hanging off."

Along with informal counts by lifeguards at area beaches and research conducted by scientists in the area, the partnership's netting project is an attempt to establish a baseline on jellyfish populations and learn more about the water conditions they like.

"Once we pull in the net, we measure each fish or nettle or crab or whatever we get, and record it, and we send them swimming, because we don't want to kill them," Barny said.

Earlier in the week, the team had collected about 1,400 jellyfish in their 50-foot net, the most to date. Jim Vasslides, the Barnegat Bay Partnership's scientist, said the numbers are worrisome.

"It tells us that things have changed, that something's out of balance, something is out of whack," Vasslides said.

Vasslides said a handful of factors are likely contributing: rising water temperatures – measured as high as 91 degrees in the bay this summer -- changes in water salinity, and fewer predators.

Nitrogen runoff in the most densely populated areas of the watershed causes low dissolved oxygen levels in the bay and surrounding waterways, which kills off many types of fish but leave jellyfish thriving.

Finally, an increase in man-made structures in the bay, including docks and bulkheads, gives jellyfish polyps an ideal place to attach, overwinter and multiply. Ironically, the jellyfish seem to do better on plastic surfaces that started replacing pressurized wood when concerns were raised about harmful chemicals leeching into the bay.

Vasslides said the sea nettles are not just an annoyance, but can alter the makeup of the water and the bay's ecosystem.

"Sea nettles are very voracious eaters. They do a really good job at collecting a lot of the small little baby fish that are important to the commercial and recreational species," Vasslides said. "They'll also eat a lot of the smaller prey...that are food for bigger fish, so they could really wipe out some of these smaller fish populations."

Boom points to a larger problem

Scientists have not noticed a parallel to the sea nettle explosion on the ocean side of the shore. They have seen changes in when one variety, called lion's mane jellyfish, begin to appear in the winter, but nothing as dramatic as the influx in Barnegat Bay. Still, the natural boom and bust cycles of jellies and salp, a jellyfish-like creature, have garnered the attention of residents and visitors alike this week.

About 40 miles south of Brick Township, on the beach at Long Beach Island, Jennifer Scala flew kites on the windswept beach with her two kids Thursday.

"We noticed them coming up on the beach about two days ago, and there was just so many of them that my children were collecting them and wanting to keep them as pets in buckets of water," said Scala, who is visiting with her family from New York State. She said they used the jellyfish as windows in their sandcastles.

Her 8-year-old daughter Isabella Scala-Palladino also had a less charming interaction.

"I was boogie boarding in the water and I felt this shock on my lip," Scala-Palladino said. "It felt like electrocution... it felt like BZZZZZZ."

Experts recommend applying vinegar to stings to relieve burning after removing any tentacles.

While unhappy surprises like Isabella's are nothing new, a global explosion in the jellyfish population is causing bigger problems. Jellies threatened to shut down a power plants in Israel last month and have tripped up commercial fishing operations in Japan. Their proliferation is raising alarm in the scientific community around the world, who point to climate change, over-fishing and pollution as likely factors in the rise of the jellyfish.

In Barnegat Bay, Jim Vasslides said the first steps are finding out how much the sea nettle population has grown, how they can protect swimmers, and why, exactly the meddlesome nettles are doing so well.



Have you had any run-ins with jellyfish at the beach this summer? How do you deal with them? Share you experiences with readers in the comment below.