California's Monterey Bay has been covered as of late with tiny blue sails -- but not because of a miniature boat festival or anything like that.

The area's pristine, federally-protected waters, where visitors typically spot miles of kelp beds, beaches sprinkled with sand dollars and groups of yelping sea lions parked atop piles of ocean rocks, are currently being navigated by thousands of velella velellas -- small blue marine invertebrates that grow to about the size of an adult's hand and sport a curved, cellophane-like appendage that acts like a sail and leaves the aquatic critters gliding in the whatever direction marine winds blow.

Oftentimes, like what's taking place in the Monterey region, a mass of the vulnerable velella velellas end up stranded onshore.

"I've seen them in years past up on Bonny Doon, Davenport Beach, but I've never seen them alive before. They're really cute, they just kind of sail out there," local photographer Jodi Frediani told the San Jose Mercury News.

Known as "by-the-wind-sailors," velella velellas, which were previously categorized as a kind of jellyfish, were relatively common along the Golden State's Central Coast, then all but disappearing for the better part of a decade.

Nancy Black, a marine biologist and owner of Monterey Bay Whale Watch, said in the Mercury News story that for a long time the velella velellas began to show up every spring, so their arrival in the dogfish days of summer is a little unusual.

"It's been eight years, plus or minus, that we've seen them," Black said. "Why they've come now, it's hard to say."

Kate Cummings, a naturalist and co-owner of Blue Ocean Whale Watch in Moss Landing, speculated warmer ocean temperatures -- nearing 65 degrees locally -- are the reason for the creatures' return.

"By Sunday afternoon we were seeing hundreds of them grouped together," Cummings said.

The warmer tides are bringing other unusual sights too, including more sightings of long-beaked dolphins, Risso's dolphins, and the bay's resident Pacific white-sided dolphin.

Black said she has also been witnessing something else: sunfish, or mola molas, eating velella velellas (that's right, we said it).

"I've never seen a sunfish eating a by-the-wind-sailor in all my 28 years," Black said.