In the moment of our birth, we are dragged across four hundred million years of evolutionary time. We turn from aquatic creatures to dwellers of air and land. We gasp, sucking the alien gas into lungs previously filled with warm, salty ocean. Our eyes are pulled from the dim, reddish glow of the deep into jabbing brightness. The chill of evaporation slaps our drying skin.

No wonder we wail. No wonder we forget, burying the memory in the soil of the subconscious.

Our earliest and only experience of sound before birth was the hum and throb of an aquatic cocoon. Our mother’s voice found us, as did the sounds of her surging blood, breath flowing in lungs, and churning digestion. Fainter were the sounds of the world beyond our mother, from places then unimaginable to our mostly unformed brains. High tones were attenuated by the enclosing walls of flesh and fluid, and so our first sonic experiences were low and often rhythmic as her body pulsed and moved.

In the womb, hearing develops gradually. Before twenty weeks, our world is silent. At about twenty-four weeks, hair cells start to signal through nerves running to rudimentary auditory centers in the partly developed brain stem. Cells tuned to low-frequency tones mature first, and so our hearing starts with bass throbs and murmurs. Six weeks later, furious growth and differentiation of tissues result in a frequency range of hearing similar to that of an adult. Sound flows from mother’s fluids into ours, directly stimulating the nerve cells in the innermost part of our ears, unmediated by ear canals, drums, or middle ear bones.

All of this gone, in a moment.

Birth removes us from our watery surrounds, but our final aural transition to air happens hours later. The fatty vernix that swaddles us at birth lingers in the ear canal, muffling airborne sound for a few minutes or, for some, days. Soft tissues and fluid likewise recede over hours from the bones of the middle ear. When these vestiges of our fetal selves finally dissolve, our ear canals and middle ears are filled with the dry air that is our inheritance as terrestrial mammals.

Yet even in adulthood the hair cells of our inner ears are bathed with fluid. We keep a memory of the primal ocean and womb inside the coils of our inner ear. The rest of the ear’s apparatus–pinnae, middle ear chamber, and bones—delivers sound to this watery core. There, deep inside, we listen as aquatic beings.

I lie belly-down on the wooden dock. The splintery boards toast me with the stored heat of the summertime Georgia sun. In my nose, the sulfurous, ripe aroma of salt marsh. The flowing water under the dock is turbid, a mud soup sweeping past on a falling tide. I’m on Saint Catherines Island, a barrier island whose eastern shores face the Atlantic. Here, on the western side of the island, ten kilometers of salt marsh separate me from the flood-prone piney woods of the mainland. In the humid air, these woods are mere haze on the horizon. Salt marsh grasses, interrupted by narrow, twisting tidal creeks, cover the intervening distance. These grasses grow knee or waist high on all the mudflats, as thickly packed and as deep green as lush fields of young wheat.

The marshes seem monotone, their uniform verdure spiced only by snowy egrets stalking the creek edges and the pumping wing beats of glossy ibises passing overhead. But these are the most productive habitats known on Earth, capturing and turning into plant material more sunlight per hectare than the lushest of forests. Marsh grasses, algae, and plankton thrive in the happy confluence of fertile mud and strong sun. Such abundance supports a diverse animal community, especially of fish. More than seventy fish species live in these tidal marshes. Ocean-dwelling fish also swim here to spawn. Their larvae grow in the protection and plenty of the marshes, then catch a ride to adulthood on an outbound tide.

For all terrestrial vertebrate animals, rich salt water such as this was our original home, first as single-celled creatures, then as fish. About 90 percent of our ancestry was underwater. I clamp headphones over my ears and drop a hydrophone from the dock. I’m taking my ears back to where they came from.

The heavy capsule, a waterproof rubber and metal ball containing a microphone, sinks quickly, pulling the cable after it. I wedge a cable loop under my knee, holding the hydrophone above the creek bottom’s mud and debris, about three meters down in the opaque water.

When I first release the hydrophone, all I hear is the high gurgle of streaming water. As it descends, the swirling sounds fall away. Suddenly I’m plunged into a pan of sizzling bacon fat. Sparkles surround me, a sonic shimmer. Every glistening fragment is a fleck of sunlit copper, warm and flashing. I’ve arrived in the acoustic domain of snapping shrimp.

This crackling is common in tropical and subtropical salt waters worldwide. Its sources are the hundreds of species of snapping shrimp that live in seagrass, mud, and reefs. Most of these animals are half the length of my finger or smaller, equipped with one hefty claw for snapping and a lighter one for grasping. I’m hearing a chorus of claws.

As the claw snaps shut, a plunger slams into a socket, shooting forward a jet of water. In the wake of this jet, water pressure drops, causing an air bubble to pop into existence, then collapse. This implosion sends a shockwave through the water, the snap that I’m hearing. The sound pulse lasts less than a tenth of a millisecond, but it is strong enough to kill any small crustacean, worm, or fish larva within three millimeters of the claw tip. Shrimp use the sound as a territorial signal and jousting weapon. As long as they keep a centimeter away from their neighbors, they can spar unharmed.

The combined racket of snapping shrimp is, in some tropical waters, loud enough to befuddle military sonar. In World War II, US submarines hid among the snapping shrimp beds off Japan. To this day, navy spies deploying hydrophones must work around the sonic haze of shrimp claws.

My first lesson in this sonic immersion is that the underwater world can be a boisterous place. Before I donned the headphones, airborne sound came to me in bursts: squalls of whistles from boat-tailed grackles, pulses of cricket and cicada sound, occasional nasal caws from fish crows, and the melodies of distant songbirds. Underwater, the shrimp innervate their surroundings with unflagging sonic energy. There are no silent spaces between song phrases or cries. Sound travels more than four times faster in salt water than in air, adding to the sense of brightness. This is especially true at close range, between the reflective surfaces of the muddy bottom and the upper water boundaries, where sounds have not been attenuated by the viscosity of water.

Into the cloud of shrimp sound come stammering bursts of knocks. Each batch lasts a second or two, a cluster of ten or more taps. Then a pause of five or so seconds, more regular taps, interrupted by occasional hesitations. The taps sound like an impatient fingernail drumming on a hard‑cover book, sharp and low, with a touch of resonance. The sounds come from silver perch close by. These finger-length fish come to the salt marsh to spawn before returning in late summer to the deeper waters of the estuary and offshore. Alongside these knocks come faster bursts of tapping, almost purrs, the calls of the Atlantic croaker, a bottom-feeding fish that grows as long as my forearm.

Waa! The bleat of a lamb, but quieter. These complaints occasionally poke into the background of shrimp, perch, and croaker, and come from an oyster toadfish, probably hiding in its lair on the bottom of the tidal creek. Like their namesake, toadfish are scaleless and warty, with huge gulping mouths. Their fist-sized heads and tapered bodies are also well endowed with spines. Males call to attract females to shallow burrows. After mating, males stay with the fertilized eggs for weeks, defending them and cleaning the nest. The one I hear now is muffled and soft. He must be at some distance from the hydrophone, perhaps burrowed into debris around the dock’s pilings.

All three of the fish that I hear through my hydrophone make sound by vibrating their swim bladders. Each bladder is an air-filled sac running inside the fish, stretching for about one-third of the body length below the spine. Muscles pressed against the thin walls of these bladders shiver, and these motions evoke squeaking or grunting sounds from the air within. The muscles are among the fastest known in any animal, contracting hundreds of times per second. Sound waves from the swim bladder flow into the fish’s tissues and then into the water. For these fish, the whole body is an underwater loudspeaker.

The acoustic realm of these shrimp and fish seems alien to me. I’m used to the melodies, timbres, and rhythms of humans, birds, and insects. Here, though, percussive sounds dominate: the sparkle of thousands of hammer blows by shrimp claws, the knocks of perch and croaker, and the unmodulated burr of the toadfish.

But unity undergirds these differences.

The shrimps’ stony, articulated exoskeleton bristles with fine sensory hairs. Sound also stimulates clusters of stretch receptors in...