Tag Archives: snapping shrimp

Snapping shrimp pop to send alert and nab food

Published April 15, 2017 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2017 Susan Scott

Petroglyph shrimp channels are etched in lobe coral off Lanikai Beach. ©2017 Susan Scott

Decades ago, when Craig and I boarded a friend’s boat in the Ala Wai Boat Harbor, the crackling sound below deck made us wonder if the boat was falling apart. I later learned that the big noise comes from a small package: 1-inch-long snapping, or pistol, shrimp.

We oceangoers rarely see the little gunslingers because they live in burrows. But we hear them. The split-second closure of each shrimp’s single, oversize claw makes a popping sound. When the creatures pop by the thousands, as is often the case, it’s like snorkeling in a giant bowl of Rice Krispies.

The crackling is so loud that submarines can hide among shrimp colonies and go undetected by sonar.

The shrimp snaps for food, sending out a bubble bullet that stuns passing prey. The snaps can also be warning shots to trespassers, and perhaps a come-on to members of the opposite sex.

Most snapping shrimp dig, and live in, mud or sand burrows. We rarely see these basement apartments because they’re under rocks and rubble. One kind, though, lives in exposed sand burrows guarded by a pair of gobies. The shrimp digs while the fish keep watch. When a predator or curious snorkeler gets too close, the team dives into the hole together.

Other snappers, called petroglyph shrimp, set up housekeeping in living coral heads by making channels. No one knows how the shrimp creates the cracks. Either the animal is able to inhibit coral growth at the chosen site, or that big claw is an all-purpose tool that, in addition to firing lethal bubbles, can also dig.

Petroglyph shrimp (usually Alpheus deuteropus) create wavy, U-shaped crevices, the largest about a quarter-inch wide and 10 inches long. These are not the shrimps’ burrows, but rather boulevards lined with crops and cops.

The crops are seaweed, veggie meals for the shrimp. The cops are white hydroids, stinging jellyfish relatives that look like tiny trees. The hydroids protect the lane but might also eat the shrimps’ babies when they hatch. Security guards don’t come free. Gobies are carnivores, too.

The deepest parts of petroglyph channels bear cul-de-sacs that precisely fit each shrimp’s body. When it’s threatened, the shrimp retreats to its den, blocking the entrance with its large claw. Channels 2 inches or less usually house a single resident. Longer ones can accommodate two to four shrimp, each with its own separate burrow.

Hawaii’s petroglyph shrimp have pink eyes encircled by red dotted lines. The bodies are transparent with red surface dots.

So they say. I’ve not seen one. But I often see, and stop to admire, the shrimps’ plant-lined streets with twiggy sentries. The neighborhoods deserve a feature in Better Homes and Gardens.

Scientists learning more about snapping shrimp

Published June 24, 1996 in the “Ocean Watch” column, Honolulu Star-Advertiser ©1996 Susan Scott

FOR years, snapping shrimp have been an intriguing mystery to me.

First, I couldn’t figure out what was making that crackling noise I heard when I was swimming underwater or sitting below deck in my sailboat. The distinctive sound reminded me of bacon frying.

Eventually I learned that the noise came from the forceful clicking together of the giant claw of little creatures called snapping shrimp.

“How do they hang onto the boat?” a friend asked one day when I explained the sound.

“They don’t,” I said. “They live on the bottom.”

“What are they snapping about down there?” she asked. “They sure are making a commotion.”

I shrugged. I had never read an explanation of why these 1- to 2-inch shrimp sometimes go into such snapping frenzies.

This month, however, researchers shed some light on the subject in an article in Nature magazine.

After studying 30 groups of shrimp found in 30 Belize sponges, a marine biologist learned that these creatures live in colonies similar to those of bees, ants and termites.

Like those insects, snapping shrimp have a queen who bears all the young of a colony, one in each sponge. Older colonies have more that 300 members, all offspring of one queen and maybe a single male. Other colony members are workers who defend the sponge from intruders.

Sponge homes must have good defense systems because suitable housing for snapping shrimp is limited, making competition fierce.

IN one laboratory experiment, researchers implanted each of eight sponges with a female snapping shrimp, eight of her large male workers and eight of her juveniles.

When another member of the original family was introduced into the sponge, the residing shrimp welcomed it. However, it was a different story when another species of snapping shrimp was dropped in. The residents killed it, undoubtedly with their enormous clamping claws.

So, when we hear snapping shrimp clicking and clacking like crazy, they’re likely warring with invaders of their home territory.

Not all snapping shrimp prefer sponges. Some live in grooves in coral heads, obvious in places like Hanauma Bay. Look for wavy dark lines on the top of big heads of green lobe coral.

HOW do the shrimp make these burrows? I used to shrug at that question also, but now I have a new book that offers an explanation.

The authors speculate that the grooves are the result of coral not growing in the shrimps’ tracks, while the surrounding coral grows normally. Eventually, the grooves become deep, providing good shrimp shelter.

Some snapping shrimp living in coral heads poke their big claw into hungry starfish that try to eat the coral.

In this way, a coral colony has an advantage in being landlord to a snapping shrimp.

Researchers know little about the 100 or so species of snapping shrimp found throughout the world’s tropical marine waters. This discovery of bee-style shrimp colonies is likely just one of many more to come.

Marine biologist Susan Scott writes the newspaper column, “Ocean Watch”,
for the Honolulu Star-Bulletin, www.starbulletin.com