I was surfacing after my first dive a while back and looked up to see if any divers were above me. This behavior is instilled in divers due to the possibility of boats and other obstacles being overhead. Since the dive park is off limits to boats, I was safe there (unless an errant kayak was approaching). Instead I saw the large bell of a purple jellyfish with its tentacles dangling down towards me. Since divers are supposed to rise to the surface slowly, I had plenty of time to adjust course and start videotaping this critter.
I learned something new when I returned to the office and pulled out my field guidesto research this column. What I've always known as the "purple jellyfish" (Pelagia noctiluca) turns out to have been separated from that species (which has a near-global distribution) as a different species (Pelagia colorata). This one is larger than the other "purple jellyfish" and is only found on our West Coast. Researching even further, I found its name had again been changed to Chrysaora colorata. See how difficult it is to be a biologist? What if you were a librarian and your books kept changing titles, or authors! My readers can just call it by its common name, the purple-striped "jellyfish."
I've placed the word "jellyfish" in quotes because it is now more accepted to call them "sea jellies." Likewise the old term "starfish" has been replaced by "sea stars." It seems scientists think the public can't distinguish between these two groups and real fish. I know Tony Baloney can do it when he asks everyone to "count the fish" as he sings his rendition of Pinkard and Bowden's "I Lobster, And Never Flounder" on Antonio's Cabaret patio each afternoon. He doesn't count star "fish," jelly "fish" or whales ("they're mammals"). As a well-trained marine biologist, I too know the difference... but "jellyfish" and "starfish" are fine with me.
These sea jellies can reach up to 2-3 feet in diameter. They have a series of purple stripes or streaks radiating from the center of the bell to its margins. Younger members of this species tend to be a more solid pinkish color with long (12-16 feet) dark maroon tentacles that fade as they age. The tentacles in older individuals are usually shorter, thicker and pale in color. The tentacles are covered with stinging nematocysts, like other members of its phylum (including corals and anemones), which can give a person a good zap. Normally they use them to capture dinner- usually zooplankton including copepods, larval fish, ctenophores, salps, other jellies, and fish eggs. However, it is reported this species can effect a powerful "sting." I didn't care to test that theory.
Fertilized eggs from these sea jellies develop into larvae and then miniatures of the adults. Both these stages are free swimming. Most other sea jellies have a bottom-dwelling stage known as a polyp. This stage is similar to a sea anemone with the body attached to the substrate and the tentacles extending above rather than downward. The purple-striped "jellyfish" lives as a large member of the plankton community throughout its life.
For some reason young crabs are particularly attracted to this species after they leave the plankton. It is not uncommon to see many crabs living on an old purple-striped sea jelly. Here they feed on food gathered by the jelly, and may even take bites of the jelly itself. It is reported the crabs can even enter the jelly's stomach without being digested! When they grow large enough, these hitchhikers drop off the jelly and begin their bottom-dwelling phase. These jellies are eaten by the ocean sunfish and by blue rockfish, which are not present in the dive park but may be seen at colder locations around the island and further north.
It is believed that these jellies live in calmer offshore waters, but enter nearshore regions when ocean currents or other conditions change. Because they are fairly fragile, jellies are often torn apart by rocks on the shore in surf, or boat propellers and other contact. It is not unusual to find shreds of these jellies in the water or on the beach where they can sting bathers or beach goers. No one seems certain how long individuals who don't meet such a fate can live.
While conducting my research, I learned that this species may have been involved in a lawsuit in 2003. A California artist named Richard Satava started creating glass sculptures using these sea jellies as a model. He was quite successful at it, developing a profitable business. Later a Hawaiian glass artist named Christopher Lowry started making very similar sculptures and was sued for "copyright" infringement. Satava lost the suit because no artist can copyright an image based on a naturally occuring organism unless it contains creative elements that are truly original. So the "law of the land" applies to the ocean as well.
© 2004 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.
Images of the purple-striped jellyfish near the surface in the Dive Park.
This document maintained by
Dr. Bill Bushing.
Material © 2004 Star Thrower Educational Multimedia