JUNEAU, Alaska -- Strange sea creatures that resemble large pink thimbles are showing up on the coast of southeast Alaska for the first time after making their way north along the West Coast for the last few years.

Scientists say the creatures are pyrosomes, which are tropical, filter-feeding spineless creatures usually found along the equator. They appear to be one long pink tube, but in reality, they're thousands of multi-celled creatures mushed together, generally about 6 inches long.

Pyrosomes have been working their way north, Ric Brodeur, a researcher with the U.S. National Oceanic and Atmospheric Administration, told the Associated Press on Monday.

Brodeur, who is based at the agency's Northwest Fisheries Science Center in Newport, Oregon, said pyrosomes were first seen on the Oregon coast in 2014 and every year since. More recently, the animals have made their way up farther north on the Washington state coast, Canada's British Columbia and Alaska.

Jim Murphy, a biologist with the U.S. National Oceanic and Atmospheric Administration, said pyrosomes spotted near Alaska this year marked the first documented presence of the animals that far north, and their appearance is cause for concern.

"It means that we are clearly seeing really big changes in the marine ecosystem," he told The Juneau Empire.

Researchers have speculated that the bloom is tied to warmer ocean temperatures in the Pacific Ocean in recent years. But temperatures have nearly cooled back to normal this year, Murphy said, and these pyrosomes started showed up in the middle of winter.

Leon Shaul, a biologist with Fish and Game, has been tracking the appearance of pyrosomes in southeast Alaska. He said he's "emailed the whole world" about the issue, but hasn't heard much back.

Brodeur told the AP that it's also unusual how close to shore the pyrosomes have come, although they are now being found farther offshore again.

He said the creatures have a low nutritional value, and that raises concerns on how they will affect the fish that eat them.

"They're not the greatest food for the animals out there, compared to the things they normally have," he said.

Pyrosomes aren't harmful to humans, but they have puzzled those who've encountered them.

Angler Don Jeske was fishing for king salmon in February when he said he found himself surrounded by "millions" of the tube-shaped creatures and he'd never seen anything like it in his 50 years of trolling around Sitka, a fishing town about 90 miles southwest of Juneau.

"They were all over out there, they were everywhere. . I would say millions, not hundreds of thousands," he said. "This is a weird organism, man."