Published in the Ocean Watch column, Honolulu Star-Advertiser © Susan Scott
October 25, 2002
Sometimes, when my phones won’t stop ringing, the leaf blowers are roaring and practically everyone I know needs a ride to the airport, I pack up my laptop and go hide on my sailboat in the Ala Wai Boat Harbor.
Below deck is another world. The boat rocks gently in its slip like a cradle, the water laps the hull — and the shrimp wage war.
Well, that’s what it sounds like some days. What the heck is going on down there, I sometimes wonder, to get those little guys so excited?
The underwater snap, crackle and pop sounds we commonly hear throughout the tropics are made by little shrimp bearing one enlarged front claw, which the shrimp can cock open. When the creature snaps the claw shut, it makes a loud popping noise and creates a little shock wave in the water.
Members of this large family are known as snapping shrimp or pistol shrimp. They grow from 1 to 2 inches long and snap for several reasons.
One is for food. In some species, the shock wave produced by the fast claw closure stuns plankton and passing fish. Other types of snapping shrimp crack small clams with their big claw.
Another reason shrimp snap is the same reason we humans sometimes snap: It’s a warning to others to back off. Snapping both defines and maintains a shrimp’s territory.
Snapping shrimp live in a wide variety of habitats in Hawaii and throughout the tropics.
Some live under rocks and rubble from the shoreline to about 40 feet deep. Another type, bright orange, lives in the spaces between the branches of cauliflower coral.
One species, called the petroglyph shrimp, makes branched channels up to 10 inches long on the surfaces of coral heads. These dark fissures resemble ancient Hawaiian petroglyphs and are easy to spot in places with large growths of encrusting corals.
A good place to see petroglyph shrimp homes is outside the reef at Hanauma Bay. Look carefully in the fissures and you will see clusters of tiny hydroids (jellyfish relatives) lining the edges of the burrows like armed guards. You will not, however, see the shrimp. Besides being almost colorless, they stay deep within the burrows where they farm and eat algae.
Pairs of male and female petroglyph shrimp excavate their burrows together but don’t live together. The male has his own home, the female hers.
No one knows how these shrimp create furrows in coral, but some researchers believe it may be a chemical process.
Another interesting snapping shrimp shares a burrow with a small fish called a shrimp goby. The nearly blind shrimp excavates and expands passages in the burrow while the keen-sighted goby keeps watch.
You can see these busy shrimp pushing sand out of their tunnels like bulldozers while their gobies stands guard. The shrimp keeps tabs on outside happenings by holding one antenna in contact with its sentry’s tail fin. When danger draws near, the fish twitches its tail and both creatures dart into the hole.
I don’t know why snapping shrimp are sometimes subdued and other times go off like a popcorn factory. But I don’t mind their noise. That kind of commotion, I enjoy.