It’s easy to think of sounds when you think about many animals. Singing birds. Whining cicadas. Roaring lions. Vibrating lobsters.
Okay, maybe that last one was not so familiar.
There’s a series of quite elegant papers on sound in spiny lobsters, mainly coming from Sheila Patek’s lab. They make squeaking sorts of sounds in a way like running your finger over a wet plate.
Clawed lobsters are different line of crustaceans from spiny lobsters, and they make sound in a different way. What is clear is that clawed lobsters make the sound by vibrating their exoskeleton. It’s a very different way of making sounds than spiny lobsters and most other arthropods, most of which rub two limbs together. The sound made by clawed lobsters was first described 45 years ago, but there hasn't been a lot of research on it since.
Ward and colleagues took up the challenge to answer what the function of the sound is. And I say “challenge,” because while clawed lobsters can make sound, they are reluctant to. It’s rare for lobsters to vibrate; only about 7% did so in a previous study.
For these experiments, the authors went through 1,000 lobsters and picked out those that vibrated when tested twice, ending up with just 47 out of that thousand.
Ward and colleagues placed their young lobsters in tanks alone (control), with other lobsters, with one of two species of live fish, and fake fish.
The lobsters would make sounds in all conditions. But the two conditions where the lobsters made sound the most often, by a long shot, was when they were with the fish. And the lobsters didn’t sound off just any old time when the fish were in the tank, but were much more likely to do it when the fish approached the lobster.
Then, the lobster would “buzz.” The sound is loud, too – 118 decibels sound pressure level, which is around pneumatic drill volumes. The lobster would do this without typical “claws up” aggro behaviour that lobsters make.
And the fish would back off. For striped bass, the few fish they tested (a grand total of three) would stay away from the lobster for half an hour.
The lobster would do the same thing to fake fish, too. This strongly suggests that the main function of this sound is predator deterrence.
Why this sound is effective is mysterious, as is why the lobster seem to make it so rarely. I would like to have seen recordings of the buzz played back to the fish to ensure that the sound alone ward off the fish. Here, all the sounds were made by the lobsters as far. The fishes used were pretty small, too, so the fish might not have been much of a real threat to the lobsters. Would the sound would be enough to deter a bigger fish? Would the lobster be more likely to “buzz” when confronted with a bigger fish?
Why the lobsters made sounds to each other is also not at all clear. Lobsters seemed not to do anything in response to the sound, though they can probably here it.
Even more mysterious are those rare times that the lobsters were alone. What would lobster be doing that for?
Maybe just because it felt gooooooooooood.
Ward D, Morison F, Morrissey E, Jenks K, Watson W. 2011. Evidence that potential fish predators elicit the production of carapace vibrations by the American lobster. The Journal of Experimental Biology 214(15): 2641-2648. DOI: 10.1242/jeb.057976
Photo by BrentMWilson on Flickr; used under a Creative Commons license.