DIVE DRY WITH DR. BILL #809: THE PURPLE-STRIPED SEA JELLY
Recently Grace Lim, a dive friend, took a break from her work at the Jet Propulsion Lab and came out to Catalina with Craig Yeaton and two of her friends who wanted to learn how to dive. I drove the Dr. Bill Mobile down to say hi. After Grace finished her first dive of the day, she asked me if we ever get jellyfish in the dive park. I answered "Yes, but not frequently." When I returned home, I checked all my images of sea jellies (the PC term for them... grrr) and discovered it had been years since I'd written about any of our local species.
So I'm dedicating this column to a species that is probably one of the more common ones I've filmed in the dive park... the purple-striped jellyfish (OK, sea jelly). To us well-educated scientists, its name is Chrysaora colorata although when I first learned it back in the dark ages it was Pelagia colorata. When intact specimens drift into our waters, they are really photogenic... even when I'm taking the pictures! The geographic range of this sea jelly is mostly along the California coast, especially the Monterey Bay area, down to southern California. However they may occasionally be seen as far north as Washington state. They generally are found out in open water but may drift in towards shore as well.
The bell of the purple-striped jelly may exceed two feet in diameter. There are eight long arms, sometimes referred to as tentacles extending from the margin of the bell. The number may vary with the age of the individual. Very young ones are pinkish in color with dark maroon marginal arms.There are also four thicker oral arms extending from the underside of the bell that are coiled and frilly.
As they age the purple stripes appear and the tentacles get thicker and more pale. The Aquarium of the Pacific stated that there are 16 stripes, which seems consistent with the ones I've observed. Often times the oral arms will slough off and disappear. They may also lose the purple coloration and be totally white. Like most cnidarians (critters with stinging cells known as nematocysts), the sea jelly has an oral opening on the underside that is also used to expel wastes.
Like most sea jellies, this species chows down on zooplankton such as copepods and other crustaceans, comb jellies, salps, other jellies and fish. According to the Monterey Bay Aquarium, ocean sunfish (Mola mola) have been observed munching on these beauties. Of course that is no surprise since molas frequently dine on sea jellies. Hopefully they don't mistake plastic bags or mylar balloons as appropriate fare. Some sources stated sea turtles also feed on them, but the reptiles are largely absent from much of their range. There are also parasitic amphipods (a form of crustacean) that feed on this sea jelly.
Prey is detected by the marginal tentacles on contact. These then discharge the stinging cells which serve to immobilize the prey. The marginal tentacle moves inward, carrying its tasty hors d'oeuvre towards the frilly oral tentacles. It is then transported up to the oral opening and digested in the gastrovascular cavity. The sting of this species can be pretty painful for humans, but at least they are too big to be ingested!
Technically most marine biologists consider sea jellies as part of the plankton community. They drift in the currents with all the tiny plant and animal plankters. However, sea jellies are also capable of propelling themselves... albeit well below the posted speed limit. You can observe their bells pulsing... expanding and contracting... to push them forward at slightly more than a snail's pace.
Now I'm well aware that my readers often want the prurient details of an organism's sex life. Well, you may be half disappointed with this species since it reproduces both sexually and asexually. Adults in what is referred to as the medusa stage are either male or female. The male release mucus strands with sperm from the oral arms. The female then captures these strands and moves them into her gastrovascular cavity where fertilization occurs. I guess humans may do something similar since adults often tell kids that mommy has a baby in her "tummy." The fertilized eggs are brooded and hatch into larvae that drift for a while before settling down.
The bottom dwelling post-larval stage is known as a planocyst. It transforms into as polyp and initially reproduces by budding. Then when conditions are right it changes to a different form of asexual reproduction known as strobiliation. In this processs the young medusae are formed, resulting in what is known as the alternation of generations. This species is fairly fragile and has a fairly short lifespan, believed to be as little as a year but possibly up to 2-3 years.
© 2019 Dr. Bill Bushing. For the entire archived set of over 800 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: A purple-striped sea jelly in the dive park and garibaldi snacking on a spicy treat.
Recently Grace Lim, a dive friend, took a break from her work at the Jet Propulsion Lab and came out to Catalina with Craig Yeaton and two of her friends who wanted to learn how to dive. I drove the Dr. Bill Mobile down to say hi. After Grace finished her first dive of the day, she asked me if we ever get jellyfish in the dive park. I answered "Yes, but not frequently." When I returned home, I checked all my images of sea jellies (the PC term for them... grrr) and discovered it had been years since I'd written about any of our local species.
So I'm dedicating this column to a species that is probably one of the more common ones I've filmed in the dive park... the purple-striped jellyfish (OK, sea jelly). To us well-educated scientists, its name is Chrysaora colorata although when I first learned it back in the dark ages it was Pelagia colorata. When intact specimens drift into our waters, they are really photogenic... even when I'm taking the pictures! The geographic range of this sea jelly is mostly along the California coast, especially the Monterey Bay area, down to southern California. However they may occasionally be seen as far north as Washington state. They generally are found out in open water but may drift in towards shore as well.
The bell of the purple-striped jelly may exceed two feet in diameter. There are eight long arms, sometimes referred to as tentacles extending from the margin of the bell. The number may vary with the age of the individual. Very young ones are pinkish in color with dark maroon marginal arms.There are also four thicker oral arms extending from the underside of the bell that are coiled and frilly.
As they age the purple stripes appear and the tentacles get thicker and more pale. The Aquarium of the Pacific stated that there are 16 stripes, which seems consistent with the ones I've observed. Often times the oral arms will slough off and disappear. They may also lose the purple coloration and be totally white. Like most cnidarians (critters with stinging cells known as nematocysts), the sea jelly has an oral opening on the underside that is also used to expel wastes.
Like most sea jellies, this species chows down on zooplankton such as copepods and other crustaceans, comb jellies, salps, other jellies and fish. According to the Monterey Bay Aquarium, ocean sunfish (Mola mola) have been observed munching on these beauties. Of course that is no surprise since molas frequently dine on sea jellies. Hopefully they don't mistake plastic bags or mylar balloons as appropriate fare. Some sources stated sea turtles also feed on them, but the reptiles are largely absent from much of their range. There are also parasitic amphipods (a form of crustacean) that feed on this sea jelly.
Prey is detected by the marginal tentacles on contact. These then discharge the stinging cells which serve to immobilize the prey. The marginal tentacle moves inward, carrying its tasty hors d'oeuvre towards the frilly oral tentacles. It is then transported up to the oral opening and digested in the gastrovascular cavity. The sting of this species can be pretty painful for humans, but at least they are too big to be ingested!
Technically most marine biologists consider sea jellies as part of the plankton community. They drift in the currents with all the tiny plant and animal plankters. However, sea jellies are also capable of propelling themselves... albeit well below the posted speed limit. You can observe their bells pulsing... expanding and contracting... to push them forward at slightly more than a snail's pace.
Now I'm well aware that my readers often want the prurient details of an organism's sex life. Well, you may be half disappointed with this species since it reproduces both sexually and asexually. Adults in what is referred to as the medusa stage are either male or female. The male release mucus strands with sperm from the oral arms. The female then captures these strands and moves them into her gastrovascular cavity where fertilization occurs. I guess humans may do something similar since adults often tell kids that mommy has a baby in her "tummy." The fertilized eggs are brooded and hatch into larvae that drift for a while before settling down.
The bottom dwelling post-larval stage is known as a planocyst. It transforms into as polyp and initially reproduces by budding. Then when conditions are right it changes to a different form of asexual reproduction known as strobiliation. In this processs the young medusae are formed, resulting in what is known as the alternation of generations. This species is fairly fragile and has a fairly short lifespan, believed to be as little as a year but possibly up to 2-3 years.
© 2019 Dr. Bill Bushing. For the entire archived set of over 800 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: A purple-striped sea jelly in the dive park and garibaldi snacking on a spicy treat.
