SHORE SCIENCE

THE H LE STORY

Critters large and small leave their marks all over the beach

BY TERRI KIRBY HATHAWAY

ICHNOLOGY IS A FUN, NEW WORD TO ADD TO YOUR VOCABULARY – and no, it’s not something you do when the mosquitos come out at dusk. Instead, ichnology is the study of footprints, tracks or other traces left behind by animals, both on land and sea.

So how many times have you walked on the beach and admired an array of different sized holes, whether in shells or in the sand? Keeping in mind that they’re all traces of the existence and behaviors of various animals, let’s put ichnology in action and start with holes in shells.

Shells with a great number of holes are common along Outer Banks beaches. These multiple holes are created by a sponge that chemically “drills” the holes for anchorage so it can stay in one place for its entire lifespan. And although the bright-yellow sponge is capable of smothering its host, it’s not a predator or a parasite. In fact, when the sponge drills into a shell, the bits of sediment it produces contributes to the beach in a small way.

If you find a differently marked shell with slender tubes etched into it, look closely until you locate a hole near one end of the tube. These calcareous tubes (which are made of calcium carbonate, just like the seashell) were once aquatic dwellings – and the builders and permanent residents of these small homes are called serpulid worms. These worms extend a fan of tentacles through the hole for feeding and respiration…though the fan can be quickly pulled back into the tube (where it’s protected by a golf-tee-shaped trap door known as an operculum) when a predator comes near.

Another often-coveted beach find is a shell with a single, perfect hole near its hinge. These treasures make perfect pendants or windchimes – but their origins may sound perhaps a bit more sinister. The handyman of these holes is a gastropod, a one-shelled snail-like mollusk such as a moon snail or an oyster drill, that uses its radula to A much smaller sandy hole between the low and high drill into two-shelled clam-like mollusks. The radula is a tide lines that’s surrounded by dark, chocolate-sprinkletooth-covered tongue that works much like a drill so the looking pellets is the home of an animal called a ghost gastropod can bore into the clam and eat it up. Gulp! shrimp – although they’re actually more closely related to

A piece of driftwood is a special beachcombing find, hermit crabs. These burrows can be up to six feet deep, too…but have you ever and they have multiple wondered what creates entrances complete all those intricate nooks and crannies? The answer is shipworms – although contrary to what their name implies, this species is more precisely described as a tubelike mollusk that feeds on wood with celluloseistock.com/MBCheatham with an intricate maze of tunnels. The ghost shrimp uses paddlelike appendages to create water currents through their burrows in order to bring food in and clean out shell fragments and fecal digesting bacteria in its pellets (hence, the tiny guts, somewhat like a sprinkles). termite. On a related note,

But if you’ve been the tiny, pin-sized holes keeping a diligent eye found below high tide out during your morning A ghost crab hole on the beach (top); Multiple holes created lines are also ghost beach walks, you already know that holes aren’t by a sponge that chemically drills into shell surfaces for anchorage (above). shrimp air holes. Air replaces water between solely found in shells or sand grains when the wood – they’re also found in the shore itself. So what tide recedes, and hollow spaces are left behind as the created those holes in the sand? sand dries. When the tide comes back in, bubbles emerge

The most obvious holes found between the low tide from the holes as those underground spaces fill up again line and the dune line are dug by ghost crabs. These large with sand and water. tunnels go into the sand at 45-dgree angles, and they end Whether on land or at sea, animals can’t help but in relatively spacious turn-around chambers. The reason leave behind numerous traces of their presence and for this is that ghost crabs have gills which need to stay behaviors (which goes for humans, too!) – so armed moist, so they burrow into damp sand during high tides with a little bit of knowledge, you can become a beach – reserving most of their aboveground excursions for detective who solves the “hole” story of the sea…while nightly low tides when they can best scavenge for food. also making your own mark in the sand.