Boaters and swimmers encountering masses of gelatinous nubs in local marine waters need not worry that some new creepy invasive species is taking over Long Island Sound.

The small, clear blobs, sometimes called "sea snot," are a type of native open sea plankton that periodically gets blown in by offshore storms, according to two local marine biologists who saw a photo of the creatures taken near the northeast side of Fishers Island this weekend.

James Carlton, professor of marine sciences at the Williams College-Mystic Seaport Maritime Studies program, on Monday identified them as salps, a benign creature that usually lives in deeper offshore waters, forming long chains.

"They don't sting," he said. "They can be annoying, because they can clog engine intakes. But they're harmless."

Colonial species that resemble glass marbles, Carlton said they typically don't survive long in the shallower waters where local residents have been seeing them. As they die, the long chains break apart.

John Swenarton, a biologist at the environmental lab at the Millstone Power Station in Waterford, also identified the animal as salps, a type of tunicate. Many have been reported recently in the waters off Block Island, he said in an email message, and he's been hearing chatter on marine radio from boaters saying their strainers are getting clogged with fish eggs that he surmises are probably chains of salps.

The upshot, said Carlton, is that these strange drifters are native pelagic plankton - those that normally live far from shore - that are not a threat to shellfish beds or humans.

"It's not a major concern, unless we get huge numbers of them," he said.

j.benson@theday.com

Twitter: @bensonjudy