Sea Nettles: A Closer Look At a Painful Visitor

Swimming in the bay this summer may seem to be an enticing offer, but I wouldn’t do that if I were you.

The are here. Just in time for the summer rush, Mother Nature throws us a curve ball in the midst of a heat wave. It would be such a relief to take a cool dip in the bay, but stinging jellyfish are a big deterrant.

What is a sea nettle, you ask? In a word, Ouch. This gelatinous sea can cause a nasty welt if you are stung. Each summer, tides of jellyfish float in, causing havoc among swimmers and boaters.

A Complex Organism

James Vasslides of the Barnegat Bay Partnership said in an email that sea nettles are complex organisms that have a place in our watershed.

He said sea nettles have several life stages that are worth identifying if you want to avoid the sting.

"Sea nettles (Chrysaora quinquecirrha) are true jellyfish in the class Scyphozoa.  This means that they have two distinct body forms, medusae and polyp, reproduce both sexually and asexually, and may go through five life stages: egg, planula, polyp, ephyra and medusa," said Vasslides.

"The medusa is the floating adult stage that comes to mind when people think of jellyfish, while the polyp stage is sessile (doesn’t move) and attaches to the substrate or other structure in the water."

The floating forms of sea nettles are almost invisible in the water. You can only spot them in the water if you look hard enough. Otherwise they simply blend in with the darker water color.

The Right Conditions

Vasslides said that these jellyfish happen at certain times and under certain water conditions. "When the water temperature and salinity are suitable, the polyps undergo a process called strobilization, during which they form a stack of discs (think pancakes) that then pop off and become free swimming immature medusa known as ephyra," said Vasslides.

Many readers may confuse these jellyfish with the more eye appealing glowing jellies called comb jellyfish. Images a thousand light green blobs floating on a dark summer night are a sight to see on a cool summer night.

But sea nettles are not those kind of jellyfish.

"Sea nettle medusa are typically found in Barnegat Bay from late spring through early fall, and have been reported throughout the bay, though they appear to be most abundant north of the Toms River.  The medusa are killed off by water temperatures below 50F, but the polyps are able to form cysts and can overwinter, 'waking up' the following spring and producing ephyra when water temperatures get above 65F… So really they are here with us year round— we just don’t always see them," said Vasslides.

Tidal Ecosystem

As with all jellyfish, sea nettles are at the mercy of the tide. They come in with the waves and hang around for as long as they can. Finding a part of the bay not choked with these stinging sea nettles can be almost impossible if the conditions are right. Vasslides said that sea nettles are here to stay for the time being.

"It is worth pointing out that sea nettles have always been a part of the Barnegat Bay’s ecosystem; their apparent increase in abundance is a relatively recent phenomenon. A number of potential causes for this increase have been suggested by scientists.  Increased development around the bay, including bulkheads, pilings, and floating docks, may be providing more places for the polyps to attach. A single floating dock can hold thousands of polyps, which asexually produce millions of medusa.  Changes in the bay’s salinity may also have an effect."

 Some species of fish and sea turtles eat jellies on a regular basis. Unfortunately for us, sea nettles are not on the menu for our bay inhabitants. "The removal of predators and potential competitors for food through increased fishing pressure may also affect sea nettle abundance. However, we do not know which species of fish or other animal, if any, prey on sea nettles in Barnegat Bay," said Vasslides.

The Sting and Welt

A sea nettle sting happens so quickly and without warning. In fact, most people don’t even know they have been stung until they come out of the water.

Vasslides said that sea nettlers are not unlike other species that sting, however.

"Like most members of the phylum Cnidaria (corals, sea anemones, jellyfish), sea nettles have specialized stinging cells, in this case nematocysts.  These little harpoons line the tentacles of the sea nettle and fire when a potential prey item brushes against them," he said.

The sea nettles do this automatically, whether we intended it harm or not.

"Unfortunately for us, the trigger mechanism cannot be turned off, so when a tentacle brushes against us, it automatically fires.  Bumping into a small sea nettle can cause an itching sensation, while the larger nettles will pack a bit of a wallop, causing welts or a rash and a painful sensation.  The nematocysts are fairly small and fragile, so a light protective layer (a wetsuit, lycra rashguard, pantyhose) will prevent stings."

It is important to note that not all jellyfish sting. Sea nettles are a unique species of jellies that can sting and can cause more discomfort than anything.

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