Last week my younger daughter’s birthday coincided with spring break so we all took a little time off and spent it having fun. One of our outings was to the Anchorage Museum to see the new Mammoths and Mastodons exhibit (find information here). While we were at the museum we had to pop in at the Imaginarium and that meant I could visit one of my favorite exhibits: the tank full of moon jellies. There in that dark water, lit from above, the translucent, floating orbs appear to glow from within. They undulate slowly and move even more so, bringing to mind a ghostly apparition. They are spellbinding.
In fact moon jellyfish are a pretty simple organism whose scientific name is Aurelia aurita. Most average about six inches across, although they can be as large as ten. They, like all other forms of medusae including the Portuguese man-of-war which we have discussed before, are not technically one living organism but a set of groups of cells that manage to work together. They have no respiratory, excretory or circulatory systems, although they are equipped with a neural net and gonads. There are, surprisingly, male and female moon jellies but only they know how to tell each other apart. It’s sort of mind boggling if you think about it too long.
These interesting critters are mostly found in tropical and subtropical waters with the Aurelia aurita being common to the Atlantic, Caribbean and Gulf of Mexico. There are other species of Aurelia – which are impossible to tell visually from the aurita type – that inhabit the Pacific and Indian Oceans. They consume a surprisingly varied diet of mollusks and other crustaceans, larvae, protozoa, fish eggs and even smaller medusae. The food is basically wrapped up in mucus and then directed via a tentacle to the gastro-cavity where it is dissolved by enzymes amoeba-style. Moon jellies can live over a year in good conditions. They live only about five to six months in the wild where, if they are not consumed by the many predators that find them tasty, they generally die from the effort of daily reproduction. That’s right; these guys reproduce themselves on a daily basis so after a few months they are so worn out that they are completely susceptible to infections and cellular degradation.
The thing that makes me particularly fond of moon jellies – aside from how darn cool they look – is their historical ties to seafaring in general and the old school buccaneers in particular. Moon jellies aren’t really capable of swimming per ce and have to rely on the tide to keep them moving. Because of this, and doubtless as a form of protection, they congregate together in groups that reflect moon and starlight at night. Frequent notations in logs and journals about great shoals of jellyfish glowing offshore are probably references to moon jellies. And they would have been a happy sight, not only as an extra source of light on a very dark sea but as an indication of something even more valuable: fresh food.
One of the moon jelly’s most common predators is the sea turtle, particularly the leatherback sea turtle that was a favorite delicacy of boucaniers and buccaneers. Considered healthier than pork, the turtles were savored boiled in stews, fried, roasted and smoked over a boucan to make a form of jerky. They were an all purpose food, and since they were large a few turtles could feed a whole ship’s crew. In the Great Age of Sail, turtles were caught whenever possible by both freebooters and navy ships as a welcome fresh meal. It may be as much an influence of seafarers as location that New Orleans in particular is fond of turtle soup to this day. More on ways to prepare turtle will be forthcoming on Friday.
Moon jellyfish are, thankfully, still relatively numerous all over the world. I’ve yet to see a large group at sea at night, but I hope to. Just another thing on the bucket list, but I’d count such an experience as a little gift from the gods of the sea. Until then, there’s always the museum.
Header: Moon jellies at the Anchorage Museum, Anchorage, Alaska