Although there are many places where, on quieter shores and protected shoals, such richness of life may be found, certain ones live most clearly in my memories. On one of the sea islands of Georgia is a great beach that is visited only by the most gentle surf, although it looks straight across to Africa. Storms usually pass it by, for it lies well inside the long, incurving arc of coast that swings between the Capes of Fear and Canaveral, and the prevailing winds are such that no heavy swells roll in upon it. The texture of the beach itself is unusually firm because of a mixture of mud and clay with the sand; permanent holes and burrows can be dug in it, and the streaming tidal currents carve little ripple marks that remain after the tide goes out, looking like a miniature model of the sea’s waves. These sand ripples hold small food particles dropped by the currents, providing a store to be drawn on by detritus feeders. The slope of the beach is so gentle that, when the tide falls to its lowest ebb, a quarter of a mile of sand is exposed between the high-tide line and the low. But this broad sand flat is not a perfectly even plain, for winding gullies wander across it, like creeks across the land, holding a remnant of water from the last high tide and providing a living place for animals that cannot endure even a temporary withdrawal of the water.
It was in this place that I once found a large “bed” of sea pansies at the very edge of the tide. The day was heavily overcast, a fact that accounted for their being exposed. On sunny days I never saw them there, although undoubtedly they were just under the sand, protecting themselves from the drying rays of the sun.
But the day I saw them the pink and lavender flower faces were lifted so that they were exposed at the surface of the sand, though so slightly that one could easily pass them by unnoticed. Seeing them—even recognizing them for what they were—there was a sense of incongruity in finding what looked so definitely flowerlike here at the edge of the sea.
These flattened, heart-shaped sea pansies, raised on short stems above the sand, are not plants but animals. They belong to the same general group of simple beings as the jellyfish, sea anemones, and corals, but to find their nearest relatives one would have to desert the shore and go down to some deeplying offshore bottom where, as fernlike growths in a strange animal forest, the sea pens thrust long stalks into the soft ooze.
Each sea pansy growing here at the edge of the tide is the product of a minute larva that once dropped from the currents to this shore. But through the extraordinary course of its development it has ceased to be that single being of its origin and has become instead a group or colony of many individuals, bound together into a whole of flowerlike form. The various individuals or polyps all have the shape of little tubes embedded in the fleshy substance of the colony. But some of the tubes bear tentacles and look like very small sea anemones; these capture food for the colony, and in the proper season form reproductive cells. Other tubes lack tentacles; these are the engineers of the colony, attending to the functions of water-intake and control. A hydraulic system of changing water pressure controls the movements of the colony; as the stem is made turgid it may be thrust down into the sand, drawing the main body after it.
As the rising tide streams over the flattened shapes of the sea pansies, all the tentacles of the feeding polyps are thrust up, reaching for the living motes that dance in the water—the copepods, the diatoms, the fish larvae small and tenuous as threads.
And at night the shallow water, rippling gently over these flats, must glow softly with hundreds of little lights marking out the zone where the sea pansies live, in a serpentine line of gleaming points, just as lights seen from an airplane at night wander across the dark landscape and show the path of settlement along a highway. For the sea pansies, like their deep-sea relatives, are beautifully luminescent.
In season, the tide sweeping over these flats carries many small, pear-shaped, swimming larvae from which new colonies of pansies will develop. In past ages, the currents that traversed the open water then separating North and South America carried such larvae, which established themselves on the Pacific coast, north to Mexico and south to Chile. Then a bridge of land rose between the American continents, closing the water highway. Today the presence of sea pansies on both Atlantic and Pacific coasts is one of the living reminders of that past geologic time when North and South America were separated, and sea creatures passed freely from one ocean to the other.
In that liquescent sand at the edge of the low tide, I often saw small bubblings and boilings under the surface as one or another of the sand dwellers slipped in or out of its hidden world.
There were sand dollars, or keyhole urchins, thin as wafers. As one of them buried itself the forward edge slipped obliquely into the sand, passing with effortless ease from the world of sunlight and water into those dim regions of which my senses knew nothing. Internally, the shells are strengthened for burrowing, and against the force of surf, by supporting pillars that occupy most of the region between upper and lower shells except in the center of the disc. The surface of the animal is covered with minute spines, soft as felt. The spines shimmered in the sunlight as their waving movements set up currents that kept the sand grains in motion and eased the passage of the creature from water into earth. On the back of the disc was dimly marked out a design like a five-petaled flower. Repeating the meaning and the symbolism of the number five—the sign of the echinoderms—were five holes perforating the flat disc. As the animal progressed just under the shifting film of surface sand, grains moved up from the under side through the holes, aiding its forward movement and spreading a concealing veil of sand over its body.
The sand dollars shared their dark world with other echinoderms. Down in the wet sand lived heart urchins, which one never sees at the surface until the thin little boxes that once contained them are found by the tide and carried in to the beach, to be blown about by the wind and left at last in the litter of the high-tide line. The oddly shaped heart urchins lay in chambers six inches or more below the surface of the sand, keeping open for themselves channels lined with sticky mucus; through these they reached up to the floor of the shallow sea, finding diatoms and other particles of food among the sand grains.
And sometimes a starlike pattern twinkled in that firmament of sand, proclaiming that one of the sand-dwelling starfishes lay below, marking out its image by the flow of water currents, as the animal drew sea water through its body for respiration, expelling it through many pores on its upper surface. If the sand was disturbed, the astral image trembled and faded, like a star disappearing in mist, as the animal glided away rapidly, paddling through the sand with flattened tube feet.
Walking back across the flats of that Georgia beach, I was always aware that I was treading on the thin rooftops of an underground city. Of the inhabitants themselves little or nothing was visible. There were the chimneys and stacks and ventilating pipes of underground dwellings, and various passages and runways leading down into darkness. There were little heaps of refuse that had been brought up to the surface as though in an attempt at some sort of civic sanitation. But the inhabitants remained hidden, dwelling silently in their dark, incomprehensible world.
The most numerous inhabitants of this city of burrowers were the ghost shrimps. Their holes were everywhere over the tidal flat, in diameter considerably smaller than a lead pencil, and surrounded by a little pile of fecal pellets. The pellets accumulate in great quantity because of the shrimp’s way of life; it must eat an enormous amount of sand and mud to obtain the food that is mixed with this indigestible material. The holes are the visible entrances to burrows that extend down several feet into the sand—long, nearly vertical passageways from which other tunnels lead off, some continuing down into the dark, damp basement of this shrimp city, others leading up to the surface as though to provide emergency exit doors.