Oh! Snap!: "Have You Heard Those Snapping Shrimp?" Redux : A Lowcountry Tail

Latest update: 2 June 2022 

This post is based on an oldie-but-goodie website article originally authored by Dennis Adams, Information Services Coordinator (Retired) for the Library's previous website. My husband and I live along a tidal creek and during the COVID-19 shutdown, we spent more time than usual enjoying the fragrances of the lowcountry while sitting on the porches in the early morning or early evening hours. Less traffic on the roads meant less traffic noise wafting over the salt marshes and more sounds of nature coming from the tidal creeks, including pops that we hadn't noticed in a long time. Perhaps you heard some too. 

You may have wondered what causes those popping noises coming from the marshes and pluff mud at low tide.

Is it the mud popping? Or maybe a creature like an oyster or a clam?

The answer is: "None of the above."

You've heard of snapping turtles, but how about "snapping shrimp"? In an e-mail [to Adams in or before 2007], Amber Von Harten, [then Fisheries Specialist at the SC Sea Grant Extension Program explained] that the marsh popping sound "is made by a small crustacean that makes its home in the salt marsh, called the Bigclaw Snapping Shrimp, Alpheus heterochaelis.  The shrimp grows up to two inches in length and is characterized by its single, large, modified claw used to generate the loud popping sound many residents hear emanating from the marsh at low tide."

She continued: "Basically the fingers of the claw have two opposing smooth disks with a thin layer of water in between the disks. When the disks separate due to increased pressure, the claw forcibly opens and makes the loud popping sound. This concussion, produced by the claws separating, stuns small animals and is a manner in which to capture prey. The sound is also a defense mechanism to ward off larger predators."

Von Harten found her information in Seashore Animals of the Southeast: A Guide to Common Shallow-Water Invertebrates of the Southeastern Atlantic Coast by Edward E. Ruppert and Richard S. Fox (Columbia, SC: University of South Carolina Press, 1988). She highly recommends this book to local residents as "one of the best for our region of the coast."

Bigclaw Snapping Shrimp are also known as "pistol shrimp." According to Seashore Animals of the Southeast, their sound "can be heard clearly across a large room" in aquariums and "reportedly can break glass." (Some members of the saltwater aquarium community affirm that this is possible while others believe this statement to be more along the lines of an urban legend.) The shrimp's larger claw has a notch "in both the upper and lower margins at the base of the fingers."

Figure 5.1: (A) Alpheus heterochaelis - one of  the largest snapping shrimp. The large snapper claw may be either on the right or the left in both sexes. Modified after Brooks & Herrick [8]. (B) Close-up of the snapper claw in its cocked position. The claw is made transparent by the use of methyl salicylate. The claw has a protruding plunger (labeled pl ) on the dactyl ( d ) and a matching socket ( s ) in the immobile propus ( p ) (Photograph by B. Seibel). During the extremely rapid closure of the snapper claw a high-velocity water jet is formed when the plunger displaces the water from the propus socket. 

Though the web article "Snapping Shrimp Make a Flash with Bubbles" (October 10, 2001) from the California Academy of Sciences' "This Week in the Wild" website is no longer active, the three videos below confirm the statements: "The water jets out of the claws at a speed of up to 62 miles per hours, producing the "low pressure bubble(s) that collapse with a telltale crack." If enough shrimp are snapping their claws at a given moment, they can interfere with sonar tracking of submarines in their immediate area!

"Amazing Pistol Shrimp Stun 'Gun'" from Nat Geo Wild's "World's Deadliest" series:

"Listen to the Crackling of Snapping Shrimp" from Woods Hole Oceanographic Institution: 

Among the comments was this one : "It sounds like they are being fried" with which I concur. This is closer to the sound that I hear behind my home.

"Pistol Shrimp Sonic Weapon" from BBC Weird Science:

I'm a little skeptical about whether the pistol shrimp sounds as much like a pistol firing as the video seems to indicate - but this video does not give the species name of the shrimp being recorded. It may be that the cavitation bubble imploding sound recorded here is not one made by Alpheus heterochaelis that lives in our local salt marshes. 

When the shrimp snap their claws, they also produce a visible but extremely brief (10 nanoseconds or less) burst of light. Nobody knows whether the light serves any purpose for the shrimp. Heat inside the tiny bubbles after a snap can reach 8,500 degrees Fahrenheit. 

Alpheus heterochaelis  Photo by Robert Aguilar, Smithsonian Environmental Research Center. 

The Smithsonian Marine Station at Fort Pierce, Florida website says that these living noisemakers range from the southern Chesapeake Bay to Florida, extending further south to the Gulf of Mexico, Cuba, and Brazil. It is a colorful creature: the body color of the Bigclaw Snapping Shrimp is translucent green, and its walking legs are pale red. Often there are bright red or orange tones on the tips of the claws and a blue or purple edge along the uropods (fantail) and body. 

Sources:

"What is a Salt Marsh?" in Guide to the Salt Marshes and Tidal Creeks of the Southeastern United States by the SC Sea Grant Consortium  

Seashore Animals of the Southeast: A Guide to Common Shallow-Water Invertebrates of the Southeastern Atlantic Coast by Edward E. Ruppert and Richard S. Fox (Columbia, SC: University of South Carolina Press, 1988).

Nonideal Turbulence - Scientific Figure 5.1(A) and (B) on ResearchGate 

Amazing Pistol Shrimp Stun 'Gun'" from Nat Geo Wild's "World's Deadliest" series, 11 April 2013 (01:12)

"Listen to the Crackling of Snapping Shrimp" from Woods Hole Oceanographic Institution, 17 February 2020 (01:13) 

"Pistol Shrimp Sonic Weapon" from BBC Weird Science, 16 January 2009 (01:36) 

Wikipedia contributors, "Cavitation," Wikipedia,  

Alpheus heterochaelis, photo by Robert Aguilar, Smithsonian Environmental Research Center, 13 April 2006 posted to Wikipedia Commons on 25 February 2019 

"Alpheus Heterochaelis" by J. Masterson, last updated 1 September 2008, Smithsonian Marine Station at Fort Pierce website