Science News

Lobsters eat jellyfish without injury

Thu, 25th Aug 2016

Chris Smith

Eating is a matter of life and death, but for some baby lobsters every meal could be fatal, because they dine on venomous jellyfish tentacles. Sea Nettle Jellyfish

Now, by following a meal on its journey through a juvenile lobster's innards, Japanese researchers have solved the mystery of why they don't get stung inside!

Hatchling lobsters exist initially as tiny larvae called phyllosomas. They float through the water until they settle on a jellyfish, which is literally eaten alive as the developing lobster grows.

But many jellyfish are endowed with stinging tentacles which are used to immobilise prey. The stinging structures on the tentacles are called nematocysts and they are the equivalent of a spring-loaded hypodermic. Contact, or a certain set of chemical conditions, causes them to discharge and inject their deadly cargo, which can include paralysing neurotoxins.

Most people had assumed that lobsters are naturally immune to the poison, but injecting jellyfish venom brings about a speedy demise, proving this isn't true.

To solve the mystery of how these crustaceans dine so dangerously but with apparent impunity, a team from Tokyo University of Marine Science and Technology led by Michiya Kamio visited the local fish market and bought a freshly-landed fertile female lobster.

Young from the female were reared in tanks and fed exclusively on a diet of Japanese sea nettle (a type of jellyfish) tentacles.

After their meals had made their way through the lobsters, the researchers collected the faeces with a pipette and looked at them under the microscope.

The faecal material, they saw, had been wrapped up inside a membrane, almost like it had been packed in a bag.

Many nematocysts were visible, locked up inside. This, the scientists explain in their paper in the journal Plankton & Benthos Research, is a structure called a peritrophic membrane. It gets secreted around the intestinal contents by the gut lining.

Intriguingly, insects also use a similar system to protect their digestive tracts from a range of nasties. The peritrophic membrane is like a string bag, which holds things in and stops the jellyfish nematocysts delivering a deadly dose of venom into the animals' guts, but it doesn't interfere with the process of digestion or nutrient absorption.

Most importantly, from the lobster's perspective, bowel contents can be safely discharged afterwards without being a pain in the backside!

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