Voracious comb jellyfish “invisible” to prey

The North American comb jellyfish Mnemiopsis leidyi has long been known to consume vast quantities of zooplankton. A few years ago the species became established in Northern Europe.

Like many other jellyfish, Mnemiopsis leidyi has a large gelatinous body. This large size increases a jellyfish’s chances to encounter prey, but can be a disadvantage because the prey organisms are often highly sensitive to movements in the water. Despite this, the comb jellyfish manages to catch large numbers of copepod plankton which are renown for their acute escape response.

Able to catch the world’s most vigilant plankton
“Copepods have a well developed ability to detect even the slightest water disturbance,” says Lars Johan Hansson, a researcher at the Department of Marine Ecology at the University of Gothenburg.

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

“It emerged that the comb jellyfish uses microscopic, hairlike 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.”

The research into the comb jellyfish’s ability to capture its prey was carried out jointly by researchers from the USA, Norway and the Department of Marine Ecology at the University of Gothenburg.

The study – Stealth predation and the predatory success of the invasive ctenophore Mnemiopsis leidyi – has been published in the scientific journal PNAS.
The study is also mentioned in this week’s issue of the scientific journal Nature.

CAPTION: The North American comb jellyfish Mnemiopsis leidyi has a simple structure with two large oral lobes for catching prey. Photo: Lars Johan Hansson