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Stings or seafood? The dilemma of the sea nettle
Uncomfortable hazard of the bay and local rivers also eats the predators of oyster spat, crabs
Friday, Aug. 14, 2009
 Click here to enlarge this photo Image courtesy of Michael Durham
Mason Warburton, 3, and his older brother, Owen, 7, of upstate New York gaze at the comb jellies floating in the display tank at the Calvert Marine Museum.
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It's that season again. Time to stock up on vinegar and meat tenderizer while watching the waters nervously.
The sea nettles have returned.
It's safe to say that sea nettles, also known as jellyfish or Chrysaora auinquecirrha (if you're a scientist), don't have a lot of human friends on the Patuxent and Potomac rivers. The wispy, translucent animals are known for inflicting painful stings on boaters, swimmers and fishermen, and they are bountiful this time of year.
Pests they may be, but sea nettles aren't all bad.
The animals have a strange, ghostly beauty, a fascinating life cycle and a particular taste for the types of jellyfish that prey on increasingly rare oyster larvae.
So, as we celebrate the summer sun, it wouldn't hurt to give a grudging moment of respect to the simple sea nettle.
The jellyfish farm
Kenny Kaumeyer, biological curator at the Calvert Marine Museum in Solomons, is spending his workdays raising sea nettles. On purpose.
Tanks line the shelves and walls of Kaumeyer's laboratory just a doorway away from the museum's visitor floor. Each tank houses nettles in various phases of their life cycle. In the smaller tanks are oyster shells, suspended in the water with what looks like tiny sea anemones attached to them.
"That's a jellyfish polyp," Kaumeyer notes, pointing to a "big one" less than half an inch long. This is where nettles begin life each spring, popping off a multi-tiered polyp like tiny paper cups coming off a stack. Each polyp can last several seasons and produce scores of little "ephyra," tiny domed jellies. The name, ephyra, references the sea nymphs of Greek mythology.
Kaumeyer and his team collect the ephyra with eyedroppers and move them to another tank to mature. Here, the ephyra bop around in the artificial current, looking like animated bits of bubble wrap.
The ephyra don't stay small for long. Soon, they begin to grow tentacles and ravenously filter the water for their food, tiny organisms called plankton. Once an ephyra grows its stinging tentacles, it is called a "medusa," another Greek mythological reference to the monster woman with snakes for hair and the power to turn people to stone with one look.
So why would anyone purposely cultivate these creatures?
Kaumeyer likes to tease visitors, saying that the museum is breeding this "endangered" species and plans to release them into the wild. But he always 'fesses up, explaining that the museum is just growing its own stock of nettles to display in an exhibit.
The museum would like to display nettle medusae in its jellyfish tank over the winter, except that the nettles all get old and die off by December, no matter how much you baby them. So, last winter, Kaumeyer and his team started an in-house breeding program.
The museum team must also raise food for the nettles, such as algae, plankton, brine shrimp and comb jellies. It has also had to custom-build most of its jellyfish tanks. "You can't go to the store and buy a jellyfish tank," Kaumeyer observed.
The delicate balance
Fortunately, sea nettle medusae aren't as dangerous as their namesake. Medusae can grow 4- to 5-foot-long tentacles with thousands of nematocysts, microscopic, spring-loaded barbs full of fiery neurotoxin that can make victims wish for death. But they can only cause death in humans in cases of allergic reaction.
Still, most people associate the nettle with that painful childhood experience of accidentally finding one on the wrong side of their bathing suit. In the 1960s, scientists tried (unsuccessfully) to cull the nettle population in the Chesapeake and its tidal tributaries with poisonous chemicals and nets. However, the poisons also killed off other bay life.
Kaumeyer said that we should be glad the sea nettle survived these assaults. "If it were not for jellyfish, we would not have oysters," Kaumeyer said. He admitted he exaggerates a bit, but not much. If there were no nettles, Kaumeyer said, "You could probably walk across the bay on [comb jellies]."
Most people know comb jellies as the eerie green light that churns in the prop wash of a motorboat on a summer night. Comb jellies are bioluminescent, like lightning bugs, but they are also one of the main predators of oyster larvae and small crabs.
In the tightly knit ecosystem of the Chesapeake Bay and its tributaries, oysters depend on sea nettles to keep the comb jelly population under control. It's a quirk of nature that nettles can eat comb jellies, but they can't sting or digest oyster larvae. So, the more nettles that are in the water, the better chance oyster larvae have to survive long enough to attach to a hard surface and make it to maturity.
Dumb as a brick
Jellyfish are composed of 98 percent water. This doesn't leave much room for brains.
Both Kaumeyer and Maggie Sexton, a University of Maryland graduate student from Cambridge who is completing her doctorate on nettles, made it clear that nettles are pretty much mindless.
"They have this nerve net," Kaumeyer said, making a sort of dome with his hands. This neural net stimulates the bell of a medusa to contract, propelling it through the water.
According to Sexton, the nettle can sense light, gravity and the chemical smells of food, but not much else.
"I really like the simplicity of them," Sexton said.
According to these scientists, nettles are basically overgrown plankton. They drift on the current, passively combing tiny food from the water, but they are basically simple life support systems servicing their main function — sexual reproduction.
There are male and female nettles, producing either sperm or eggs that are spewed into the water to find each other. Males are purer white, while females can have a reddish-brown coloring. If a nettle egg becomes fertilized, it will form a larva and, like an oyster, seek out a hard surface on which to anchor and form a polyp.
Jellyfish can also sense how much salt is in the water. They tend to prefer it brackish. When this area and points north of Maryland experience heavy rains in the spring, jellyfish numbers tend to drop, since the nettle polyps hunker down and form a cyst to protect themselves if the water gets too fresh. They can stay like this for a year if necessary.
"Basically, they make a little tent," Kaumeyer explained.
Forearmed is forewarned
For all the studying by scientists like Kaumeyer and Sexton, much of jellyfish behavior and biology remains unknown. The bay's and the rivers' murky waters make it hard to even theorize about where nettles largely originate or why they sometimes suddenly disappear at the end of August instead of drifting around in the creeks until the first September chills.
Sexton's big project these days is working with the National Oceanographic and Atmospheric Administration on a mathematical model to predict where jellyfish are concentrated in real time by measuring temperature and salinity around the bay and its tributaries.
The project is still experimental, but citizens can make use of the research map already at NOAA's Web site.
The state of the science of jellyfish stings is beginning to come out of the realm of old wives' tales. Science has confirmed that treating nettle stings with vinegar or meat tenderizer can shorten the duration of a sting by disarming any unfired nematocysts. However, urine, an expedient folk remedy, can actually trigger dormant nematocysts and make the sting last longer.
Disabling unfired nematocysts is important, Kaumeyer, said, since the stinging cells are resilient and can still be active in dried-up nettles.
Swimmers can protect their exposed skin by covering it with petroleum jelly. The protective layer of jelly is intended to prevent the nematocyst barbs from reaching the skin surface.
Sexton said that the petroleum jelly trick does work, but noted, "Of course, the problem is then that you're covered in Vaseline."
One Maryland company has developed a less messy solution to prevent nettle stings. Nettle Net, based in Severna Park, produces a fine mesh net which is suspended from a floating ring and can be deployed from a boat. The net enclosure isn't cheap, but the company's owner said it allows boaters to escape the hot summer sun without risking nettle welts.
"It was the first thing I bought when I bought a boat," said David Nolte. Nolte liked the product so much he bought the company.
Nolte said that his product avoids the two problems that have plagued the jellyfish nets deployed at public beaches — it uses a finer mesh so nettle parts can't fit through, and it doesn't stay in the water long enough to turn into a synthetic reef and grow its own ecosystem.
"It's a pretty effective barrier," said Nolte, who counts himself as one of the few Marylanders hoping for high nettle populations, since it's good for sales. Still, Nolte said everyone should welcome the nettles. "If you like crabs and oysters, root for the sea nettles."
For more about jellyfish, see the National Oceanographic and Atmospheric Administration's NOAA's experimental sea nettle site at http://155.206.18.162/seanettles/.
