Hieroglyphs on the Beach

Hieroglyphs on the Beach
Ashby Gale

Charleton Fossil Adventures

Photography by Ashby Gale

 

 

Believe it or not, there are hieroglyphs hidden all across Edisto Beach. Thousands, possibly millions, of people walk along the quiet shores of Edisto every year, unsuspectingly passing over these incredible works of art. They’re not hidden at all. In fact, they’re hiding in plain sight.

 

If you listen closely on the beach, you can hear the scritch-scritch-scritch of such ancient hieroglyphs being etched slowly into the various detritus strewn along the shoreline. If you look even closer, your eyes may catch a glimpse of these ancient traces. Signs of life on an otherwise “lifeless” tide line. What are these strange glyphs you might ask? Trade that fedora and bullwhip for a magnifying glass and you’ll begin to uncover the storied past, present, and future of the mollusks and other crustaceans that call our quaint island shores home.

 

Life in the Slow Lane: Sure to Make You Take Your Time

It’s a little pondered notion: what animals create all of these shells? To many, the answer comes easy. “Oh, they’re from conchs and hermit crabs!” However, as with all things in life, the answer is much more complicated and fascinating. Beachcombers find two main types of mollusk shells on the beach: those from bivalves (clams), and those from gastropods (snails). Bivalves are made of two hard shells connected by an umbo (hinge) and one squishy body, while gastropods only possess one hard shell on their squishy body, which serves as their foot.

 

To start this journey, we’ll track the growth cycle for one of Edisto’s renowned knobbed whelk shells, Busycon carica, whom we’ll affectionately dub “BC.” Contrary to popular belief, knobbed whelks are not conchs. Whelks are carnivorous snails that inhabit temperate waters, while true conchs are herbivorous and favor the warmer, tropical waters of the Florida Keys and Caribbean.

 

Egg case - The papery string of egg cases laid by the knobbed whelk,  Busycon carica .

Egg case - The papery string of egg cases laid by the knobbed whelk, Busycon carica.

Egg case - Exit holes left by hatchling knobbed whelk snails.

Egg case - Exit holes left by hatchling knobbed whelk snails.

 

Life for BC begins inside the crowded confines of a two foot long “120-story high rise” with around 35 of his brothers and sisters on each story. Indeed! A single knobbed whelk female can lay on average 4000 eggs, twice a year in the fall and spring months. Seen as common tide line artifacts, these egg cases are collected by eager beachcombers as “mermaid necklaces,” and have a beautiful chain-like appearance. After 3-13 months, the eggs inside each case hatch, and the baby whelks -- no larger than a grain of rice -- drill their way out of a weak spot in the capsules, leaving behind only a single hole to indicate their exit.

 

Once out of the egg case, life for baby BC is perilous, and fraught with many predators and obstacles. For now, we’ll focus on a successful life, from maturation to reproduction. Such a life can last comfortably for up to 18 years of age, and even longer if successful at avoiding hungry predators. Whelks primarily spend their lives in nearshore and estuarine waters, ranging offshore up to 150 ft (45 m). Mature whelks can easily attain lengths of 9 inches...a favored discovery by many a beachcomber!

 

If BC were able to tune into the news channels of our fellow Homo sapiens, he may chuckle at our debates and discussions on gender identity. That’s so, because he is now a she! Knobbed whelks -- in fact, many snail species -- are hermaphrodites, changing reproductive strategies based on the percentage of males and females in the local population. Numerous snail species, both terrestrial and marine, can gauge hormone levels in the surrounding area and assist in furthering the reproductive and genetic success of the species. (Knobbed whelks were recently analyzed to exhibit slight pseudohermaphroditism, and are not true hermaphrodites, but we’ll not get too technical here…)

 

Whelks - The left-handed and right-handed lightning and knobbed whelks; left and right, respectively. Note the squishy foot and bony operculum of the live lightning whelk.

Whelks - The left-handed and right-handed lightning and knobbed whelks; left and right, respectively. Note the squishy foot and bony operculum of the live lightning whelk.

Meanwhile, as BC grows inside of his (or “her”) small shell, so does the shell. Snails and clams never leave their shell to find a larger one as hermit crabs do, but make their shells larger as they age and grow. Shell growth is formed by the mantle, an organ that covers the soft body of the whelk and processes dissolved calcium carbonate into a solid form. The mantle is able to convert sea water and the bodies of bivalves the whelk eats into shell-building material. Bit by bit, the mantle adds layer after layer of calcium carbonate to the edge of the whelk’s shell, spiraling around and growing ever larger for most of the snail’s life. Thus, as the snail grows, so does its shell. BC is able to use this hard shell, and a bony flap made of keratin as the walls and door of his home to protect himself and grow to a ripe old age.

 

Whelks- Knobbed whelk (left) displaying more prominent knobs than the lightning whelk at right.

Whelks- Knobbed whelk (left) displaying more prominent knobs than the lightning whelk at right.

In the ideal fairy tale ocean world, BC could live well past the age of 18, possibly on to 45, eventually slipping away into a gentle watery slumber, yielding the home he worked so hard to build, to some future occupant.

 

The Battlegrounds: Only One “Shell” Claim Victory

We all desire a peaceful, conflict-free life, but it’s a snail eat snail world out there, and the time has come for BC to fight for his life and fight others for theirs.

 

Of all the feeding strategies in the animal kingdom, BC has one of the most terrifyingly unique. As a gastropod (which translates to “stomach foot”), whelks slide around the ground on their slimy foot, and use various parts of their body to hunt down prey. Once a tasty morsel is in their sights -- usually a mussel, oyster, or other clam -- the whelk moves in for the kill. Securing the bivalve with its foot, the whelk uses suction to slowly pull against the clam’s umbo, and work open a gap in the edge of the shell. As soon as the clam opens, the whelk quickly (for a snail) slides the edge of his shell between the two of the clam and twists, forcing the clam open even wider. What follows is best described as the scene out of a classic James Bond film. A long, thin tube-like proboscis extends from the whelk. At the end of the tube is a radula, equipped with 100,000 teeth, swirling deep into the clam. Once the entrapped clam turns into a pulpy mass, the whelk slurps up the remnants like a gas station slushie and discards the now empty shell.

 

Moon snail- The Atlantic moon snail,  Neverita duplicata .

Moon snail- The Atlantic moon snail, Neverita duplicata.

Yet, whelks are only one player in the watery arena. Enter the Atlantic moon snail. Also known as shark eyes, Neverita duplicata are carnivorous snails similar to whelks, but their feeding strategy is much more precise and indiscriminate. The observant beachcomber may note the presence of a singular hole on the raised portion of a clam shell, often in perfect placement for a seaside necklace. Such marks are indications of a moon snail’s handiwork. Moon snails utilize their toothy radulas and a secreted acid to target their prey in “sniper fashion” with one quick blow.

 

The cunning moon snail must decide between two strategies in hunting down its prey. 1) The snail can aim for the thinnest part of the shell which would result in the quickest drill time. However, the thinnest section of a clam shell is adjacent to the valve edges where our sniper risks harm from quickly-shutting valves, pinching and potentially harming or deterring the predator. 2) Alternatively, the snail may opt for the safer route of drilling at the umbo, far from the snapping valve edges. However, this section of shell is much thicker and takes longer to drill through. More time means more exposure of the moon snail to its own predators, and potential competition for the same food source. More often than not, the snail opts for its own safety, and takes the time to drill away at the thick umbo. However, moon snails aren’t picky with their prey, and often resort to cannibalism and consuming their own kind!

 

Successful - A successful predation attempt by the Atlantic moon snail on an incongruous ark shell.

Successful - A successful predation attempt by the Atlantic moon snail on an incongruous ark shell.

Unsuccessful- Not every attempt is successful! This moon snail gave up or was eaten during the attempt to eat this ponderous ark.

Unsuccessful- Not every attempt is successful! This moon snail gave up or was eaten during the attempt to eat this ponderous ark.

 

Our embattled mollusks must be ever vigilant in avoiding predation by other mollusks. But, they must also watch out for predators from outside their own Phylum; two such predators from other animals groups include the shell-peeling crabs and loggerhead sea turtles.

 

Crabs within the Calappidae Family include the box crabs and shame-faced crabs. Members of this family are often called shell-peeling/breaking crabs due to their propensity for smashing open shells with their hooked right claw, while delicately removing the snail’s body with a surgically-precise left claw. Look for signs of unsuccessful shell-peeling crab predation on whelks and other mollusks by noting ragged scars along the shell’s exterior, and a step down in shell thickness. Repaired shell margins are often much thinner as the mollusks resume growth of their shells following the peeling and cracking actions of the crab.

 

Sand Collar- Egg case of the Atlantic moon snail. Called a “sand collar,” these cases are made from sand glued together by a secretion from the snail. Note the hundreds of eggs laid on the underside of this large collar!

Sand Collar- Egg case of the Atlantic moon snail. Called a “sand collar,” these cases are made from sand glued together by a secretion from the snail. Note the hundreds of eggs laid on the underside of this large collar!

Sand Collar

Sand Collar

 

While it may be easy for a snail to avoid a walking crab, not all predation comes on foot. Knobbed whelks and other large mollusks are at risk from above, should a hungry loggerhead sea turtle spy the slow moving snails trudging along the seafloor. These poor snails don’t stand a chance to the bite force of a loggerhead. Wide, powerful jaws easily chomp through any shell the large turtle can fit its mouth around. Any whelk a beachcomber finds along Edisto that is missing a significant portion might have fallen victim to these durophagous (shell-eating) turtles!

 

Hieroglyphs and Shell Graffiti: Such a Boring Topic

Snails. Why’d it have to be snails?” might be what Indiana Jones would say when analyzing shells along our shoreline. But fear not, Indy! The markings on these mollusks came from many different creatures.

 

Snails, sponges, clams, bryozoan, and acid-spewing worms are all culprits of marking up mollusks and befuddling many a beachcomber. The designs left by these organisms are truly close encounters of the third kind, and ones that turn that “broken, boring shell fragment” into a storytelling apparatus to transfix even the most aloof teenager.

 

Cliona Whelk- Numerous holes left by the boring sponge,  Cliona celata , on a knobbed whelk shell.

Cliona Whelk- Numerous holes left by the boring sponge, Cliona celata, on a knobbed whelk shell.

One such storyteller is the boring sponge. (Apologies on not discussing the exciting sponges!) All joking aside, the sulphur boring sponge (Cliona celata) is a rarely seen organism along the tide line, but whose handiwork is readily apparent on easily half of all shells strewn along the beach. Employing the use of acid, Cliona etches its way into the shells of deceased and living mollusks; for those that are still living, the sponge can weaken the shell so much that it ends up killing the mollusk! After the sponge completely colonizes the host mollusk and dies, massive voids within the walls of the shell are visible, and often confuse beachcombers, who think they’ve collected coral. These sponges are important players in the beach environment, however, as their process of breaking down shells contributes to the volume of sand present along our shores.

 

Boring Clams- Three holes left by pholad boring clams in a fossilized bone fragment. Note the clam still inside the middle hole.

Boring Clams- Three holes left by pholad boring clams in a fossilized bone fragment. Note the clam still inside the middle hole.

As if boring sponges weren’t enough, now we have boring clams. Call in the next five minutes and we’ll triple your offer, with species such as the oyster piddock, shipworm clam, and wedge piddock! On Edisto, the oyster piddock (Diplothyra smithii) is the main culprit of holes drilled into rock and shell material. These marks are usually congregated together in a relatively tight cluster, and on some thicker rocks, the clam itself may still be lodged inside. The pholad boring clams and Teredinidae shipworms use these burrowing practices for protection from predators who are unable to pluck the prey from their stony homes.

 

Moving into far more “exciting” animals, it’s time to talk about your friendly neighborhood bryozoan. Everyone has that one neighbor that decorates with lace and doilies; well, bryozoan is that resident along our shoreline. Bryozoan, also known as “moss animals,” are a diverse group of invertebrates, with over 4,000 species. These humble animals are often overlooked on beach detritus as a “crust” or “crud” that must be removed to make a shell prettier, when in fact, with the right magnification these critters make the shells far more intricate than any human touch.

 

Bryozoan- The lacy patterns of a bryozoan colony on an oyster shell.

Bryozoan- The lacy patterns of a bryozoan colony on an oyster shell.

Bryoliths- Two bryolith colonies mimicking a snail shell.

Bryoliths- Two bryolith colonies mimicking a snail shell.

 

Bryozoan colonize hard substrate such as shells, rocks, corals, and even the carapaces of our beloved loggerhead sea turtles and horseshoe crabs! Whether in an encrusting colony or an erect, branching colony, bryozoan feed by extending miniscule tentacles outward to cage, flick, and filter phyto- and zooplankton into their mouths. One particularly fascinating colony, called a bryolith, colonizes on a snail shell, and continues growing in the shape of the shell, to allow further inhabitation by hermit crabs seeking a new home.

 

Our shoreline search for hieroglyphs wouldn’t be complete without a look at the many shapes etched away by the polydorid polychaete worms. If you’re bristling with excitement about this category, it’s to be expected! The bristle worms are a fascinating group of hairy, acid-spewing worms that rule the seas with over 10,000 species worldwide. Also known as the polychaete worms, these organisms have a successful body-design that’s lasted over 500 million years and survived multiple mass extinction events in the fossil record. Polychaete morphology generally follows a segmented design, with stiff bristles projecting off of the body at regular intervals. Fittingly, the name polychaete means “many bristles.” In some species these bristles are venomous, and for the ones found on Edisto, can secrete acid that weakens the calcium carbonate in mollusk shells. As the bristle worm dissolves the shell, its stiff bristles file away at the surface, creating intricate tunnels and designs.

 

Bristle- Puzzling patterns left by acid-secreting bristle worms.

Bristle- Puzzling patterns left by acid-secreting bristle worms.

Other Fascinating Beach Features

While Atlantic beachcombers may not be able to find the abalone that’s iconic to the California coast and other parts of the world, Edisto does have a mollusk known for producing similar hues. Atrina rigida, or the stiff penshell, creates a beautiful iridescent nacre on the inside of its shell. The rainbow hues that are so iconic of abalone and penshell nacre come from light refracting off microscopic layers of calcite. Touching these parts of a penshell it becomes readily apparent why these layers are important: the nacre smooths the surface of the shell, protecting the soft body of the penshell from any irritants that may enter. Should a grain of sand or shell fragment make its way past the valve of the penshell, it is possible that a pearl may even be formed!

 

Nacre - A stiff penshell,  Atrina rigida , showing off the iridescent nacre inside the shell.

Nacre - A stiff penshell, Atrina rigida, showing off the iridescent nacre inside the shell.

As if hieroglyphs on Edisto weren’t alien enough, it’s worth covering perhaps the most alien-looking creature found crawling on the beach: the horseshoe crab. Straight out of any science fiction film, the horseshoe crab (Limulus polyphemus) is a decapod with ten legs and ten eyes! As close relatives of the scorpions, spiders, and ticks, such a body design makes sense. Two compound eyes sit on top of the carapace, and four sets of light sensors are spread across other parts of the body. A set of “book gills” are located within the abdomen; appropriately named, as they spread apart to reveal multiple “pages” of gills for breathing. In the center of a horseshoe crab’s legs sits a bristly mouth, with multiple moving parts to effectively shred apart worms, mollusks, shrimp, and other small crustaceans. This body design hasn’t changed much since the horseshoe crab’s earliest ancestors evolved out, over 445 million years ago, and it’s safe to say these aliens on the beach will continue to crawl around for many years to come.

 

Horseshoe- A female horseshoe crab,  Limulus polyphemus , displaying all ten legs and bristly mouth parts.

Horseshoe- A female horseshoe crab, Limulus polyphemus, displaying all ten legs and bristly mouth parts.

The ancient Egyptians once said: a house has the character of the person who lives in it. The same applies to the myriad shells adorning Edisto Island. Whether a bivalve or a gastropod, broken or whole, there remains a beauty in the creation of a shell. Mathematically intricate spirals, arcs, rays, and spines reveal a level of precision thought only to be possible at the hands of a human. So maybe, these homes and their adornments capture something spiritual, and deserving of reverence. Shapes and designs that are truly hieroglyphikos: sacred carvings.