Paper: Kamio, Michiya, et al. “Phyllosomas of smooth fan lobsters (Ibacus novemdentatus) encase jellyfish cnidae in peritrophic membranes in their feces.” Plankton and Benthos Research 11.3 (2016): 100-104.
Approximately 99% of people in the world have never thought about lobster poop. Most people are way more interested in how lobsters taste to them, not how lobsters are tasting and processing their own food. But, a team of researchers at Hiroshima University decided to look deeply into lobster poop to answer one stinging question: how do lobsters protect their intestines from the stings of their main food source, jellyfish?
Let’s back up a little bit. Lobsters eat jellyfish? As a matter of fact, some of them do. The smooth fan family of larval lobsters eat jellyfish almost exclusively during the lobsters’ stage of life called phyllosoma. As another oceanbites writer posted last year, they’ve developed a good strategy: they “ride” on top of the jellyfish to help protect themselves from predators seeking a snack-sized lobster (Figure 1). They don’t get stung by the jellyfish when they ride on top because the stinging cells of the jelly, called the nematocysts, can’t penetrate the lobster’s hard shell.
While the lobsters are hitching a ride, they also help themselves to a snack. The phyllosoma stage lobsters have been observed eating the jellyfish tentacles as they float around. When they do that, they allow the stinging cells of the jellyfish to come into their bodies, where they’re not as well-protected as they are on the outside. In theory, the jellyfish stinging cells are still active as they go through the lobster’s digestive tract, which is as soft and squishy and vulnerable as our own digestive tracts. These venomous stinging cells should be killing the lobster from within, but they don’t.
That fact intrigued our researchers. They wanted to figure out why the lobsters are not dying from ingesting the nematocysts. There are two major ways the lobsters could be protecting themselves: they could be genetically immune to the venom – like clownfish are immune to sea anemone stings – or they could have specialized structures in their digestive tracts that act as a physical barrier to the stingers – like chain mail protected knights from swords. It was the goal of the researchers to figure out which.
They first tested whether or not the lobsters were immune to the stinging cells by injecting lobsters with jellyfish venom extracted from one of the species they ride on. The experimental lobsters were injected with the venom and the control lobsters were injected with a neutral buffer, just to make sure the injection itself wasn’t the cause of death. 90% of the lobsters injected with the venom died, compared to 0% of the lobsters injected with the neutral buffer. Clearly, the lobsters were vulnerable to the venom, so they have to have some protective barrier to the stingers in their digestive tract. It was just a matter of figuring out what.
The researchers had a pretty glamorous task ahead of them to answer that question. They fed the larval lobsters a diet of jellyfish tentacles and watched them for a few hours until they pooped. The researchers then collected the waste and put it under the microscope to see what is going on in the lobster gut that protects it. They found that the jellyfish stinging cells had been active – that is, they had discharged their venom – but they were covered by a sheath-like material. They found that this protective membrane neutralizes the stinging cells by preventing the stingers from penetrating into the lining of the gut (Figure 2).
This study shows that interesting questions can be raised and answered from unlikely places – and that these lobsters have a pretty cool adaption helping them in their early stages of life.
Engage: Even though it can be gross, why is it important to look at the feces of different animals?