Beneath the towel, the beach is alive

CAPE HENLOPEN, Del. — Michelle Clark, 13, was lying on the beach — or, rather, in the beach, since a couple of giggling friends had buried her up to her belly — when Bill Hall walked over with an unwelcome lesson about sand.

It's not just tiny grains and salty water, he told her. It's alive.

The damp pile covering her legs was teeming with microscopic creatures, from tiny plants to wiggling worms, said Hall, a University of Delaware staff member who teaches classes about the ocean. The creatures are all denizens of a world where licking one's dinner off a sand grain is common practice.

"So I'm laying in them right now?" Michelle asked.

She was, Hall said.

"Awesome!" Michelle said, in a tone that indicated it was not.

Among the grains of sand is a microscopic ecosystem populated by sand-lickers, sticky-toed worms and four-legged "water bears."

It's a world that remains largely unexplored, despite being near enough to touch.

"I always tell people: If they only knew what they had their toes stuck into," said Linda Schaffner, a professor at the Virginia Institute of Marine Science in Gloucester Point, Va.

The animals living in the sand are often less than a millimeter long and sometimes as small as one-20th of a millimeter.

They make up for size with numbers: Scientists estimate a bucket of sand might hold thousands of these tiny creatures; in a few square yards of beach, there might be millions.

Holding on for dear life

The first rule in this undetectable world: Grab hold of something.

For these creatures, even the smallest wave breaks with tsunami force.

If a wave washed them into open water, the creatures could become food for small fish, mole crabs or other predators.

"Anything that lives in the surf gets its butt kicked," said Hall, the Delaware educator.

Every creature manages to hold on in its own way.

Animals called water bears, which have the puffed-up bodies and stubby limbs of a parade balloon animal, use tiny claws or suction cups.

Worms called gastrotrichs have bodies covered with tiny tubes that secrete a cement.

Other animals use spikes, which jam them into place, or toes that produce sticky glue.

In many cases, the animals anchor themselves using sand grains. In their world, these grains are large objects, less likely than a tiny animal to be swept out to sea. The animals live on or between the grains.

"[The grains] are boulders," said Seth Tyler, a professor at the University of Maine, one of the few scientists who study this world.

The sand is also a buffet.

Scientists say the grains are often covered in bacteria or tiny plants called diatoms.

Enough sunlight penetrates the sand that these plants can survive even an inch under the surface.

This food is licked off by worms that crawl over the surface of a grain or is munched on by tiny shrimplike creatures with waving legs.

An animal called Tetranchyroderma looks like a flying carpet with a mouth, propelling itself with a bellyful of hairs and vacuuming up bacteria.

Some worms called polychaetes simply eat the sand whole and let their digestive systems clean it off. Out the back end, eventually, comes a trail of clean sand.

"It really is a different kind of existence, the interstitial environment," said Douglas Miller, a professor at the University of Delaware.

Scientists call these creatures "interstitial" because they live in the interstices, or empty spaces, between grains.

Life in this world is short: Most creatures live only a few weeks.

That means they need to be ready for reproduction quickly, often a few days after birth. Some creatures have both male and female organs, although they don't usually fertilize themselves.

"Some animals can actually switch back and forth" between being male and female again and again, said Rick Hochberg, a professor at the University of Massachusetts at Lowell.

"Kind of makes some people jealous, I think."

Because these creatures are so hard to see, they've been studied for only 100 years or so. One expert estimated that perhaps only 25 percent have been identified.

A perk of studying sand dwellers is the discoveries. Scientists in other fields spend their whole careers trying to discover a new species. In this one, you'd have to try NOT to.

"Literally, every time we go out, we see something new," Hochberg said.

Earnhardt creature

As it turns out, finding new names is a regular problem because new species turn up so often. Tyler, at the University of Maine, said his group once named a particularly fast-moving species after NASCAR driver Dale Earnhardt.

"They get named after mother-in-laws and old girlfriends," Tyler said. It's considered bad form to name one after yourself.

Because these creatures are so little understood, scientists are just beginning to explore what they can tell us about pollution or climate change Sand creatures have been shown to be sensitive to contamination.

Even though they have just begun to map this world, scientists are sure of one thing: We should be glad these creatures are there.

They don't seem to cause any human diseases. In fact, they seem to act as the beach's unseen cleaning crew, eating the bacteria left behind by our discarded fries and uncurbed dogs.

And these creatures sit at the bottom of key food chains. They feed baby fish and small crabs and clams, which become food for larger creatures. Some important animals eat beach life directly, such as the piping plover, a threatened bird species.