Though the sea nettle hogs the press, egg-yolk jellies are the real honchos because, in these parts, they are the apex predator of the gelatinous food chain. Aquarists at the Monterey Bay Aquarium who culture jellies observe that their egg-yolk beasts outcompete and consume the purple-striped quarry, even when a tank’s purple population is much greater, and has bell diameters that are considerably larger than those of the introduced egg yolks.
Once the two species make bodily contact, the purple-striped jelly displays an obvious flight response: tentacles and oral arms (long, frilly appendages that transfer food on the tentacles to the mouth) retract, and the bell’s pulse rate rapidly increases, not unlike a racing heartbeat. Eventually, the egg yolk grabs on and engulfs its victim. Egg-yolk jellies aren’t light eaters. In the wild, they overstuff their gut pouches with as much of the jelly as can be packed in. Visualize a squirrel with cheek pouches bulging with nuts, and you get the idea. The scenario sounds gory but the graceful, noiseless, bloodless drama looks more like the forging of a close friendship. Et tu Brute?
Don’t assume it’s all gloom and doom for any jelly bungling into a voracious egg yolk, because some jellies can escape if they are physically fit and pulsing strongly. And extra-large jellies find success by breaking away from the egg yolk’s attempts at imprisonment. Overall, jellies as a group are formidable to most species but some critters have discovered loopholes. Alepas pacifica, a species of gooseneck barnacle, lives life on the go unlike others of its ilk that remain cemented for life to a pier piling or other static substrate. Freewheeling A. pacific larvae instead settle onto the cushy “pillow top” of a jelly’s bell and travel with its jelly host. While a jelly derives no benefit from the hitchhikers, it is powerless to sever ties.
Like all barnacles, A. pacifica filter feeds by thrusting out a fan of multiple hairy legs, which it uses like a comb to strain microscopic bits from the water. Did you notice in the attached picture that the barnacles look to be consuming jelly tentacles? Since this is impossible, something else must be going on. Turns out that, in another instance of evolutionary ingenuity, the barnacle is only passing the jelly tentacle over its leg hairs to scrape off edibles. The jelly, though unharmed, ends up fishing for two. If the jelly is oriented such that the barnacle can’t reach a tentacle, the bell rider twirls around at its point of attachment, then reaches as far as the stalk allows to presumably feed on jelly mucus.
The barnacles may segue from being a nusience to causing injury or death to their host. Overweighting the bell (dependent on jelly size versus collective weight of the hangers-on) will sink the jelly. In another twist of fate, barnacles centrally attached atop the bell of a vigorously pulsing jelly may be helplessly whipped around in circles, thus behaving like a screw drilling into Jell-O. I see the resulting damage more often than not but the barnacles responsible I see not at all.
I suppose this article wouldn’t be complete without my somehow linking jellies to humans. When stung by an egg-yolk’s tentacles, I barely notice, whereas the sting of a purple striped gets my instant attention. Alternatively, I don’t want to tangle with the oral arms of the egg yolk but those of the purple-striped jelly are of little consequence. Since sensitivity is subjective, you may react differently. Personally, I’m open to the risks inherant in any jelly interaction because I want to admire their beauty up close and study their pulsating motion. These benefits definitely take some of the, um, sting out of inadvertent impact.
— Judith Lea Garfield, naturalist and underwater photographer, has authored two natural history books about the underwater park off La Jolla Cove and La Jolla Shores. Send comments to firstname.lastname@example.org.