It’s Slow, It’s Brainless, It’s Ravenous…

And, no, it’s not a politician.

It’s the comb jelly:

THIS THING is NOT a jellyfish.

THIS THING is NOT a jellyfish.

Now, contrary to what the name might imply, the comb jelly is not actually a jelly fish. A jelly fish belongs to the phylum Cnidaria, while the comb jelly is of the phylum Ctenophora. But it’s a lot like a jellyfish (if you can’t see that). Most species of comb jelly are spherical in shape, and they have eight comb rows that extend from one end of their body (called the statocyst which is actually their sensory organ) opposite their mouth. These comb rows are where they derive their name. Well, actually, they derive their name from the Greek for “comb” and “bearer,” but I’ll let your biology teacher cover that. Comb jellies and others that share its phylum are usually colorless like the one above, but they have been known to occasionally have pigment, ranging from red or orange, to black or gold. 

The comb jelly, or Mnemiopsis leidyi, is sluggish and has no brain and therefore no cognitive ability. It’s basically a gelatinous blob that eats things. But it is surprisingly an extremely effective predator. Until recently, nobody knew why. The comb jelly is such an effective predator that it has recently become an invasive species in many parts of the world, taking out small animals at the base of the food chain. This throws off entire ecosystems. I mean, this thing eats a lotAccording to the Smithsonian, the comb jelly can eat ten times its body weight per day. And we think we’re fat. This little tiny thing wipes out entire ecosystems just because it eats so much.

Remind you of any other species?

Apparently, the comb jelly’s favorite food is this thing called a copepod. A copepod is a small crustacean that lives in pretty much every water-based habitat, even swamps. They are benthic, meaning that they are bottom-dwellers, and are used as bioindicators for aquatic ecosystems. A copepod is 100 times the size of a comb jelly, and can move up to 800 body lengths in a second as opposed to the comb jelly that basically just floats. Copepods have great sensory abilities, and they’re fast. So how does the slow, brainless comb jelly manage to eat so much without ever being spotted by the things it’s trying to eat?

Well, it turns out that the comb jelly is invisible to its prey. Yep, invisible. According to research by Sean Colin of Rhode Island’s Roger Williams University, the comb jelly is able to sneak up on the copepods because of the fluid dynamics of its feeding behavior. Basically, the jelly feeds by pulling water into its mouth using the cilia on all those combs all over its body, creating a current that draws things in.

So why can’t the copepod just sense that water current and get away? Because the current is such a minute change that the copepod can’t detect it, even with its super sensitive senosory gear (say that five times fast). The current is very wide and very slow, so not many animals can tell that they’re about to be lunch. This renders the comb jelly “hydrodynamically invisible,” in Colin’s words. He’s now wondering if turbulence affects the comb jellies’ feeding habits, so he’s comparing stomach contents of jellies from calm and turbulent waters by dragging a huge net around behind him in the ocean. If there’s a correlation, then we will be able to narrow down which places are monitored for this tiny, translucent predator.

This is all super useful information considering the comb jelly devastated the fishing industry in the Black Sea during the 1980’s. The comb jelly has been more recently discovered in the Bornholm Basin, which is where the Danes get their cod. They’re pretty crazy about cod, so when they heard that the comb jelly could potentially wipe out their precious fish, they flipped out. So it was a great relief when the Danes found out that salinity affects comb jellies’ breeding habits, and the Bornholm Basin has low salinity. However, countries surrounding the Baltic Sea are concerned about what this small animal could do to their own fish populations.

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