Jellyfish is invisible to prey

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It's not just hi-tech jets and submarines that can move without detection; Swedish scientists have shown that a species of jellyfish can sneak up on prey as though it is invisible.

An international team of researchers has shown that the North American comb jellyfish uses microscopic hairs to create a gentle current of water around its body which essentially makes it invisible to its prey.

The comb jelly fish Mnemiopsis leidyi, which is now found throughout Northern Europe as well as its native American waters, has a large gelatinous body. The large size increases its chances of encountering prey, but also means that it should in theory become more visible to prey organisms which are often highly sensitive to movements in the water.

Nevertheless, the comb jellyfish manages to catch large amounts of copepod plankton, which are known for their excellent escape response.

Co-author Lars Johan Hansson, a researcher at the Department of Marine Ecology at the University of Gothenburg said: "Copepods have a well developed ability to detect even the slightest water disturbance.They can swim well clear of the source of water deformation in just a split second. How the comb jellyfish is able to approach and catch some of the animal world's most vigilant plankton has up until now been unknown."

The team used advanced video technology to study the way water flows around and within the comb jellyfish. These measurements were then used to calculate the amount of water deformation generated by the jellyfish and compare this with the levels that trigger an escape response in copepods.

Hansson said: "It emerged that the comb jellyfish uses microscopic, hair-like cilia inside its oral lobes to generate a feeding current that carefully transports water between the lobes. As the water accelerates slowly and is transported undisturbed into the jellyfish together with the prey, there is nothing that alarms the prey until it is next to the capture site inside the lobes, by which time it's too late to escape. This makes the jellyfish a hydrodynamically silent predator!"