July storms may have taken some of the sting out of sea nettle levels

Last month’s rain storms washed unsightly trash, logs and debris into the region’s waterways, complicating life for anglers and boaters.

Swimmers, however, might have picked up a win.

Using a formula that depends on salinity levels and water temperatures, a National Oceanographic and Atmospheric Administration buoy in Annapolis has estimated a major decrease in sea nettles, a member of the jellyfish family.

Using data collected by a buoy stationed at the mouth of the Severn River, NOAA predicted a 2 percent chance of spotting nettles, down from between 10 and 20 percent just before last month’s recordsetting storms.

At that level, it’s unlikely that anyone on the water would encounter a nettle, said Allen Collins, an NOAA researcher who studies invertebrates.

The nettles prefer to live in water within a specific temperature and salinity range, and the storms — especially the freshwater runoff that flowed into waterways — ruined nettles’ preferred conditions, he said.

“All the increased rain is keeping all the salinity low,” Collins said.

Data from the buoy shows that temperatures dropped to 76.7 degrees on July 22 from 82.6 degrees when the rain began on July 20. Salinity levels dropped to 1.6 practical salinity units on July 28 from 8 units on July 25.

Opening the Conowingo Dam gates on July 26 on the Susquehanna River created a rush of freshwater downstream, carrying logs, debris, trash and sediment into waterways. Marinas were clogged with navigational hazards while beaches were temporarily closed for cleanup operations and high bacteria and pollution levels.

It was the wettest July in the region since data was first collected in 1870, with a total for the month of 16.67 inches of rain measured at Baltimore-Washington International Thurgood Marshall Airport, well above the 4-inch average for July.

Allison Colden, a Maryland fisheries scientist with the Chesapeake Bay Foundation, said some adult nettles were likely washed downstream. Juveniles, meanwhile, probably stayed put near the seabed.

“They do have the ability to swim a little bit, but when it comes to fighting back against these raging river flows, they’re not really a match for that,” Colden said. “They are being physically flushed out of the system, but in their early life stages, they have the abilities if the water gets too fresh or too cold, they go sort of into a dormant stage and sort of hang out at the bottom.”

Bill Smith, coordinator of the Chesapeake Paddlers Association, a kayakers club, said he hasn’t noticed jellyfish in his most recent excursions on the water.

“So far as sea nettles go, I hardly see any,” he said.

They are usually pretty common this time of the year, but he said he expected the rain to wash them away.

“It’s pretty normal for them to vacate once the rain hits, and it’s been a pretty wet summer,” Smith said. “We’ve had a tremendous amount of rain, so the fact that they’re not here is not surprising.”

Nettles help protect the oyster population from some predators, and they are also a source of food for some turtles and fish. The full impact of last month’s rainstorms on their population won’t be clear for some time, Colden said.

“Having an event and having the rainstorms and having as much freshwater as we have, there’s likely to be significant impact and we won’t know for a while,” she said.

But the nettle population, Collins said, likely will rebound. The young “polyps” are pretty hearty and the adult “medusae” tend to not stick around very long even without a storm.

“My expectation is that they’ll be just fine,” he said.