Large dark jellyfish spotted by the hundreds in San Diego Bay

By KEN FIELDS

City News Service

Gray whales wandering San Diego Bay may be a bit old hat, but you can’t say the same for giant black jellies.

The large, dark-colored jellyfish have been appearing by the dozens or even hundreds in the harbor over the last several days, providing marine biologists and boaters alike with opportunities to glimpse a “rare and mysterious” sea creature, said Dr. Nigella Hillgarth, executive director of Scripps Institution of Oceanography’s Birch Aquarium.

Some have also been washing ashore on the county’s beaches.

“I think they’re beautiful,” said Hillgarth, whose staff has collected about a half-dozen of the gelatinous aquatic animals, officially known as Chrysaora achlyos.

Four have been put on public display at the bluff-top La Jolla aquarium.

While migrating whales have detoured into San Diego Harbor several times in recent years, hordes of black jellies drifting conspicuously through the bay is a new type of ocean-wildlife encounter — particularly such sizeable specimens.

“They’re bigger than we often see them,” Hillgarth said.

The elusive type of dark-brownish-purple jellyfish — whose dome-shaped upper bodies grow to three feet in diameter and their dangling tentacles up to 30 feet — was discovered in the 1920s. Subsequent sightings were documented only a handful of times until the 1990s, when they were finally recognized as a separate species.

Over the last 10 years, the jellies — also known as black sea nettles — have turned up in coastal waters more frequently. Their heightened presence may be due to warming ocean waters or habitat shifts on the part of the plankton they feed on, but scientists remain unsure of the reason for their periodic mass appearances.

Over the last eight decades, they mostly have arrived along the coasts of San Diego and Los Angeles counties, according to Hillgarth.

There have been no reports of people being stung by the wave of big, dark-colored jellyfish visiting San Diego-area waters this week. But beachgoers and harbor visitors encountering the creatures should be mindful of that possibility — which is a “not very nice’’ experience, Hillgarth noted.