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Long stretches of mud and marsh grass on Beaufort Bay at low tide
Beaufort Bay at Low Tide
     
Cartoon drawing of shrimp with human hand snapping fingers  

Have you heard those
Snapping Shrimp?
by Dennis Adams, Information Services Coordinator

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

Is it is 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, Amber Von Harten, Fisheries Specialist at the S.C. Sea Grant Extension Program, told me 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. "

"Basically," she continued, "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 Southeast: A Guide to Common Shallow-Water Invertebrates of the Southeastern Atlantic Coast by Edward E. Ruppert and Richard S. Fox. She highly recommends this book ("one of the best for our region of the coast") to local residents. It is available at the Beaufort County Library, under call number 592.0975 (ask for the circulating and non-circulating copies at the Beaufort and Hilton Head Island branches, the circulating copy at our St. Helena Island branch, and the non-circulating copy at our Bluffton branch).

Bigclaw Snapping Shrimp are also known as "pistol shrimp." According to the book, their sound "can be heard clearly across a large room" in aquariums and "reportedly can break glass." The shrimp's larger claw has a notch "in both the upper and lower margins at the base of the fingers."

"Snapping Shrimp Make A Flash With Bubbles" (California Academy of Sciences' "This Week in the Wild" October 10, 2001 website, www.calacademy.org/thisweek) reported that the water jets out of the claws at a speed of up to 62 miles per hour, 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!

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.

The Smithsonian Marine Station at Fort Pierce, Florida website, (www.sms.si.edu/IRLFieldGuide/Alpheu_hetero.htm) said these living noisemakers range from the southern Chesapeake Bay to Florida, extending further south to the Gulf of Mexico, Cuba and Brazil.

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. Click here for pictures of the shrimp.

Volunteer application link   INFORMATION TIP:

Visit www.scseagrant.org to learn more about the offerings of the South Carolina Sea Grant Extension Program (a joint outreach program of the Clemson University Extension Service and the S.C. Sea Grant Consortium), or call (843) 470-3655 (extension 112) in Beaufort. You may also e-mail Amber Von Harten, Fisheries Extension Specialist at
ambervh@clemson.edu .

The program applies science-based information to educate individuals, businesses, local and state government, and other organizations on the wise use and conservation of coastal and ocean resources. The extension program focuses its efforts in six main areas: Aquaculture, Coastal Hazards, Coastal Business & Economics, Coastal Environmental Quality, Coastal Communities & Development, and Marine Fisheries & Living Marine Resources.

 
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