They 0ften dig burrows, and many species live on coral reefs. The majority of species inhabit tropical and temperate seas, but a few can be found in colder waters.
The most noticeable feature of a Pistol Shrimp are its mismatched claws. One is very large, the other is comparatively small. The large claw is used for hunting. When a small fish comes by, the shrimp clicks its specialized claw with amazing force. This creates a bubble that generates acoustic (sound) pressure, and as the claw extends forward, the bubble reaches high speeds. The pressure becomes strong enough to kill the fish. That isn't the full story, though. The bubble then implodes and due to high temperatures inside it, produces a short burst of light. This is called sonoluminescence. The light is of low intensity and invisible to the naked eye. However, the temperature when the bubble implodes reaches 4,700 Celsius! It has been suggested that this may help kill the prey, but it is probably just a side effect and of no biological importance. And if the shrimp is attacked by a predator, and loses its large claw, no problem! Its small claw develops into a larger one, and the lost large claw regrows as a small one.
A Pistol Shrimp displays its fascinating mismatched claws
Quite a few species of these shrimps dig extensive burrow systems. The shrimps will spend a large amount of time caring for and extending their burrow.
Many species of Pistol Shrimps have a symbiotic relationship with gobies. Instead of killing and eating it, like it would with most small fish, the Pistol Shrimp welcomes it into its burrow. They will live there together, each having a different job. While the shrimp looks after its burrow, the fish keeps a watch out for predators. They have better eyesight than shrimps, and thus make a better lookout. If a predator does approach, the goby will warn the shrimp with a flick of its tail. This relationship benefits both individuals. The shrimp gets to have a lookout, and the goby gets to have a nice, clean burrow to hide in.
This image shows the symbiotic relationship, in this case between a Yasha Goby (Stonogobiops yasha) and a Candy Stripe Pistol Shrimp (Alpheus randalli)
Probably my favourite species of Pistol Shrimp is Synalpheus regalis. It is a small species, usually no more than just over 3cm in length. They do not have a symbiotic relationship with a goby. Something like a marine equivalent of ants, they live in large colonies in sponges, inhabiting burrows running through the sponge. Every individual in the colony are the offspring of the queen, a large female individual that rules the colony. She gives birth to tiny wriggling larvae, which develop into adults. It has also been suggested that there may be a ruling male that breeds with the queen. When the sponge comes under attack by predators, such as certain species of starfish, the shrimps will defend their home by snapping at the predator to ward it off. The sound of a colony of Pistol Shrimps snapping is so loud that it can interfere with sonar equipment.
The shrimps will scrape off the outer tissue of the sponge to feed on, which the sponge tolerates in return for protection from predators.
A pair of Synalpheus regalis on a sponge
A close-up of Synalpheus regalis
I hope that you've enjoyed this post. Look out for more Species of the Week!
Until next time, keep on the wild side!