People aren’t the only ones flooding the beaches along the coast of Northern California this month.

In recent weeks, seemingly alien creatures have been found washed up in Monterey Bay, according to SF Gate. The animals look harmless, but they have caused issues within the fishing communities and may also be a sign of a more ominous issue. So what are these mysterious sea dwellers and what does their appearance mean?

Pyrosomes, also referred to as “sea pickles” or “fire bodies,” are made up of multicellular creatures called zooids. National Geographic reported that the fire bodies can be recognized by their cucumber shape and transparent, Jell-O like exterior. Researchers have also noted that the organisms are asexual, as stated in The Guardian.

They are more commonly found in tropical waters but have been spotted since 2015 in increasing numbers along the Northern California Current, which spans Northern California to Oregon and Washington, according to the National Oceanic and Atmospheric Administration. Researchers from NOAA Fisheries’ Northwest Fisheries Science Center have partnered with universities in Oregon to explore why the creatures have surged off that state's coastline after having rarely been seen there before. Some pyrosomes — which can glow in the dark — have even been spotted as north as Alaska, according to Reuters.

The Guardian reported that NOAA research biologist Rick Brodeur, along with marine biologist expert Dr. Lisa-ann Gershwin, suspect increasing water temperatures may be related. Further studies would need to be conducted though to discover if there is a definite link between climate change and the pyrosome’s appearance.

The influx of the creatures has already had a pronounced impact in some areas.

National Geographic stated that one research net pulled up around 60,000 of the pyrosomes within a five minute window. A crew of Alaskan fishermen also had to give up after being unable to remove all the sea cucumbers from their hooks, the site said.

Those who were able to catch anything noticed some fish were regurgitating sea cucumbers. National Geographic said it was unknown whether the creatures had been intentionally eaten or consumed because the fish were unable navigate through the masses of pyrosomes.

Natural predators have been bony fish, dolphins and whales, according to NOAA.