moon jellies

Drifting aimlessly across the ocean, Moon Jellies are some of the most recognizable and common jellyfish in our bay. Floating just under the waves, these delicate beauties thoughtlessly pulse their bell, and, pushed around by the currents, they’re just along for the ride. Especially abundant during summer bloom months and lacking a brain, bones, or heart, these feats of nature are wonderful indicators of environmental change in the chesapeake.

 

Moon jellies are more than 90% water. They can reach up to 12 inches in diameter, and have a simple net of nerves instead of a brain, allowing them to pulse their bell to have some control of their movement. They absorb oxygen from the water around them, and only live for a year or two. If you look closely, you can see branching vein-like structures around their bell. These are their gastrovascular canals, which transport nutrients from food around the jelly. They don’t need a lot to survive, so they are adaptable to a large range of environments, including different salinity levels, temperatures, and low dissolved oxygen levels. In late summer, jellyfish spawn. Fertilized eggs develop into larvae, which float around until finding a hard surface to latch to. Here, they stay as polyps through the winter, until waters warm enough for them to break off and develop into full grown jellies, causing the jelly blooms you might see in early summer.

 

Somehow, entering high school, jellyfish became my personality. You will always see me wearing my classic jellyfish necklace, and don't get me started with questions, because I could talk your ears off with all of my useless facts. I have been absolutely captivated by the slow, pulsing movements and frilly, colorful tentacles. Moon Jellies are especially important to me because they are a good ‘starter’ jellyfish, as you can see straight through them and they are harmless to humans, making them perfect for education. If you take a visit to the National Aquarium in Baltimore, make sure to stop by the touch tanks on level 3. Here, they keep a well-filtered tank of moon jellyfish. If you reach in gently, you can brush a few fingers along the top of their bell. It feels like a soggy gummy bear, squishy but slightly firm, with a thin layer of slimy mucus to protect it. You have to be careful, though, not to touch the underside- they can’t hurt you, but you can certainly hurt them! Their undersides, full of intricate tentacles and ruffles, are their exposed organs. The clover shape underneath, visible through their translucent bell, contains their reproductive systems and stomachs. After a yummy meal of brine shrimp at the aquarium, you might see these clovers with a pink tint, as you see their food moving through their bodies.

 

Jellyfish have two kinds of tentacles- oral arms and stinging tentacles. It can be hard to see the different kinds on longer nettles, but because moon jellies have short tentacles, it's pretty clear to see. The thick, wide tentacles coming from the center are the jelly’s oral arms, where food moves up towards their mouth. The thin, longer tentacles around the edge of their bell are for stinging prey. Jelly tentacles have special stinging cells called nematocysts, which inject venom upon contact. Since moon jellies only prey on very small organisms like zooplankton, their sting is very mild and harmless to humans, allowing them to be the most heavily researched jellyfish.