The mysterious Black Jellies are back in the news. These large maroon colored jellies are turning up every Summer on Southern California beaches in recent years. Before 1989 they were rarely seen and were not scientifically described until 1997! This is amazing considering they reach three feet across with arms as long as twenty feet and tentacles recorded as much as 30 feet. In fact Black Jellies are the largest invertebrate to be described in the 20th century!
I have lived in San Diego for eleven years and when I first came these jellies were thought to bloom (reproduce in large numbers) infrequently off the coast of California when warm currents swept them North and the plankton they feed on became plentiful. When the jellies are too close to shore they break up and are often washed onto the beach. One year a large number came right into Mission Bay and floated in the calm water like dark purple trash can lids!
The Birch Aquarium at Scripps in La Jolla bred these jellies in 1999 working out the complex life cycle, and you can see them on display now. Here are a few photos I took recently.