Listen: underwater crackly, groany kōans

Drop a hydrophone into shallow salt water at latitudes less than 40° and you’re likely to hear a crackling sound, sometimes so loud that it drowns out almost all other underwater sounds. This din is created by snapping shrimp, tiny crustaceans that click one of their front claws so fast that the motion creates a bubble of air, a cavitation in the water. The rapid opening and closing of the bubble generates sounds as loud as 200 dB (as loud or louder than dolphins and whales) and very briefly heats the bubble to a temperature just shy of that on the surface of the sun. Understandably, nearby prey are stunned, as was I when I read these figures. The shrimp also use their loud, hot snaps to wrangle over territories and to attract mates.

Here are the sounds of these creatures recorded from the dock at St Catherine’s Island (if you’re an email subscriber or viewing on a phone, you might need to click on the header link to go to the website to get sounds…):

 

In some tropical sponge-dwelling snapping shrimp “a sentinel shrimp reacts to danger by recruiting other colony members to snap in concert for several to tens of seconds” (Tóth and Duffy 2005). So these shrimp are somewhat like crows, honeybees, and other social creatures: networking information through their societies.

Another sound from the dock, heard amid the shrimp (I filtered out many of the high frequencies to make the sound a little easier to hear):

 

This is the territorial call and the mating cry of a toadfish. These ogre-like creatures sit under rocks or in crevices the bottom of the seafloor, waiting to ambush smaller fish and other morsels. The Billy Goat Gruff of the seas. Their mouths are liked toothed baseball mitts.

Despite its unappealing visage, the toadfish has much to recommend it to the curious naturalist. The call is produced by vibratory muscles attached to the swim-bladder (bagpipes?). These muscles are the fastest known among all vertebrates. Once mating is done, the male toadfish defends the eggs, then guards the hatchlings until they find their own bridge to hide under.

NASA once sent toadfish into space. According to Wikipedia, they found that toadfish inner ear bones developed in the same way in orbit as back here on planet Earth. Good to know. This study also answers the kōan,

Can a toadfish in space orbit be said to be under his rock?

But poses a new one,

If a toadfish vibrates his swim bladder in the vacuum of space, is he singing? And, for extra kōa-credit, who might answer his airless call?

For now, toadfish are hiding under their rocks with even greater diligence, fearing capture for space experiments, waiting for Homo sapiens to pass on by. Here is the sound of our departure from the dock, heard from the toadfish’s watery home:

 

Many thanks to Dr John Schacke from UGA and the Georgia Dolphin Ecology Program who helped me to understand what I was hearing.

4 thoughts on “Listen: underwater crackly, groany kōans

  1. Michael Wall

    Are these snapping shrimp commonly found around Caribbean corral reefs? If so, that’s what that noise was! Always wondered.

    Reply

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