Wet Beast Wednesday: pistol shrimp
Oh snap, it's the snapping shrimp post for Wet Beast Wednesday! Snapping shrimp or pistol shrimp are loud little critters that have evolves a very useful and fascinating tool in their pincers. Let's not waste time and shoot off to learn about these little gunslingers.
(Image: a pistol shrimp. It is a mostly white shrimp with red stripes. One of its claws is considerably larger than the other. It is standing on gravel and next to some seaweed. End ID)
Pistol shrimp are over 1,000 members of the family Alpheidae, which is part of the infraorder Caridea. This means they are true shrimp, not to be confused with superficially similar animals like brine shrimp, mantis shrimp, tadpole shrimp, and prawns. Yeah, I only recently learned that prawns and shrimp aren't a language difference between British English and American English like chips vs fries. They're not even that closely related. As true shrimp, pistol shrimp have two main body parts: the cephalothorax and abdomen, which are composed of 19 body segments. The abdomen forms a flexible tail with a fin on the end. When startled, the fin can rapidly curl under the body, propelling the shrimp backwards. Like other decapods, there are 10 limbs. The front pair of limbs have evolved into claws used to manipulate objects. The claws are the most distinguishing feature of pistol shrimp. They are asymmetrical, with one growing extremely large, over half the size of the body. The big claw has a modified version of the typical pincer. This pincer has an upper claw that can open up at a right angle. Under the claw is a pocket in the lower pincer, into which water flows. The upper pincer then slams down into this pocket, forcing the water out. The pressure of the pincer closing water in the pocket creates a cavitation bubble that is forced away from the claw at up to 26.8 meters per second. This is enough force to seriously wound small animals and hurt larger ones into leaving the shrimp alone. The cavitation bubbles can reach up to 4,427 degrees C (8,000 F) . For comparison, the surface of the sun is about 1,000 decrees (C) hotter. When the bubble pops, it creates a snapping sound that can reach 218 decibels. For comparison, most gunshots max out at around 170 db. This puts pistol shrimp is the running for the loudest ocean animals, with whales being the other main competitors. If that all sounds like a lot, the whole event happens so fast that the heat doesn't have time to affect much and the noise sounds like a moderately loud snap to us. Adults can snap their claws shut with an acceleration of up to 30 meters per second squared and juveniles can do it up to 20 times faster. The whole process takes less than a millisecond. When the cavitation bubble collapses, it can produce light. This is called sonoluminescence and nobody knows how it happens. If a pistol shrimp loses its large claw, the small claw will grow into a new large one while the missing limb will regenerate into a small claw. Adult pistol shrimp average between 3 and 5 cm long.
(Image: a drawing showing the process of a pistol shrimp snapping its claw. In the first panel, the claw is closed. In the second, the upper claw opens at a 90 degree angle, revealing a cavity. In the third panel, the cavity fills with water. In the final panel, the claw is closed again and a jet of water is ejected from the claw. End ID. Source: Wikipedia user Carermyers)
(Gif: black and white, slow-motion video of a pistol shrimp's claw snapping shut and creating a cavitation bubble. End ID. Source)
Pistol shrimp live worldwide, though most species live in tropical or temperate water. There are some cold water species and even freshwater species. Most prefer habitats where they can make burrows and where there are plenty of other animals. Coral reefs, oyster reefs, seagrass beds, mangrove groves are common habitats. Snapping is used for hunting and communication. They typically hide in burrows, waiting for fish or other small animals to pass by. When prey passes, the shrimp will snap to stun or seriously wound the prey, then drag it into the burrow. Some social species actually form eusocial hives with a single queen who produces all offspring. These shrimp are the only known marine eusocial species and all occur within the same genus (Synalpheus), though not every member of that genus is eusocial and eusociality appears to have evolved at least 3 times within that genus. It appears that a reason why only this genus developed eusociality is their larvae do not disperse, instead staying in the same area as the parents. The hives are usually located within sponges. Other social species are not eusocial, but still live together in colonies. Many less social species have formed a symbiotic relationship with gobies. Both species live in burrows, but gobies are bad at digging while the shrimp have poor eyesight. The goby will protect the shrimp while it digs a burrow, then the two live together. They will forage together, with the goby using its superior eyesight to watch for predators and warn the shrimp to get back to the burrow. Pistol shrimp are monogamous, the same pair coming back to mate over and over again (this does not apply to the eusocial species in which only the colony's queen is permitted to mate). The female is only fertile during a short period after molting. The male will stay with the female and protect her during the vulnerable period after mating and some species will remain with each other until the eggs hatch or permanently.
(Image: a eusocial pistol shrimp queen with eggs. Her body is translucent and multiple eggs are attached to her abdomen. The eggs look like translucent balls. The is inside of an orange sponge. End ID)
(Image: a pistol shrimp and goby emerging from a burrow in the sand. The shrimp is a mottled green and white. The body is a bright yellow fish covered with blue spots. End ID)
Pistol shrimp are a major source of noise in the places where they live. If you've ever been swimming and can hear repeated cracking noises, that may have been a bunch of pistol shrimp. Some scientists monitor the level of pistol shrimp noises as a method of monitoring the ecosystem. If the noise level drops, that is an indicator that the local ecosystem is suffering. The noise of the shrimps can get so loud that it actually interferes with sonar and forms of underwater communication. During World War II, members of the navy realized that the shrimp disrupted sonar enough to hide submarines, so they started hiding submarines near reefs with lots of the shrimp to keep them from being found by enemy subs. Weirdly not the only small marine animals to mess with submarines. I'll get the the other major one soon. The largest threats to pistol shrimp come from habitat destruction. Some species of pistol shrimp have entered the pet trade. As coral reefs, seagrass beds, and other habitats are destroyed, the shrimp that rely on them will suffer as well.
Yet another time I get to use one of these cards in a post
(Image: the Weird n' Wild Creatures card featuring pistol shrimp. End ID)
