The Phases of the Moon Jelly
By Ethan Dewald
Moon Jelly (Aurelia aurita)
Drifting. Pulsing. At the whim of the waves. The currents push, and it is fruitless to resist the flow. This is the life of the moon jelly, one of the more common species of jellyfish found around the Florida Keys. These spineless blobs are plankton, which means they are unable to swim against a current. They drift along through the ocean eating whatever gets caught in their tentacles. Jellyfish are one of the most feared organisms that students encounter during their time at MarineLab. Often the first question I hear when we are going to the reef is, “Are there jellyfish there today?” to which my response is always, “Not sure, I forgot to call ahead!”
The moon jelly is completely clear, but can appear bubblegum pink from the surface!
Jellyfish are invertebrates, lacking a backbone. They appear translucent and light in color with only four horseshoe-shaped reproductive organs showing through their otherwise clear bodies. Moon jellies lack the long tentacles of other jellyfish species, and instead have several shorter tentacles along the circumference of their bells, which flap and flutter in the current when they pulse. When moon jellies are born, they are white, but they take on shades of blue, pink, or purple as they mature. They can live around ten to twelve months, and live close to shore or inside sheltered waterways where the water is usually warmer and plankton, the favored food source, is more plentiful.
Moon jellies are plankton, organisms that are unable to fight the current
Have you ever wondered how a jellyfish sting works? Inside the tentacles of a jellyfish lie the cnidocytes, or stinging cells. Each of these cells is equipped with a stinging apparatus, the nematocyst, which consists of a tiny harpoon with a hair-sensitive trigger. When this trigger is impacted by contact, the harpoon is released, which is the sting that is felt upon contact with a tentacle. These cells can react to stimuli even when the jellyfish is dead, such as when they wash up on the beach! For moon jellies the sting is relatively harmless. Those of us who have accidentally bumped these alien critters describe the feeling as something between a mosquito bite and a bee sting. Like most boats in the Keys, MarineLab vessels all carry vinegar; this might sound strange but it helps to stop any active cnidocytes left behind, not just make you into a human pickle!
Jellyfish are an important food source for our favorite animals like sea turtle! Photo credit Maria Laukaitis
Jellyfish are not an irritant to be avoided on a snorkel. Eaten by sea turtles, seabirds, ocean sunfish, and other large plankton-feeding animals, jellyfish are an important component to the marine ecosystem. On reef trips where moon jellies are particularly prevalent, sea turtles can be seen munching on these gelatinous creatures, making for a memorable experience for snorkelers fortunate enough to observe this behavior. An abundance of jellyfish can be seen as a good thing; the more food available for a sea turtle, the higher likelihood that a turtle will make an appearance and hang around! Jellyfish have no brain, and also cannot swim against a current, so the best method to avoid a jellyfish is to simply swim around- but as you do, don't forget to look closely at these beautiful animals (and the fish that live in their tentacles). The moon jellyfish is not something to fear, and in fact, is just another cool critter you could potentially see on your MarineLab snorkel!