The amazing sands of life

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 is not just tiny grains and salty water, he told her. It is 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. They are all denizens of a world where licking one's dinner off a sand grain is common practice.

Of all the strange worlds that summer brings us close to, few are as strange or as close as the one beneath. There, between the grains, is a microscopic ecosystem populated by sand-lickers, sticky-toed worms and four-legged "water bears". It is a world that remains largely unexplored, despite being near enough to touch.

Different rules

"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.

The animals living in the sand are often less than a millimetre long and sometimes as small as one-20th of a millimetre. They make up for the size with numbers: Scientists estimate that a bucket of sand might hold thousands of these tiny creatures; in a few square yards of beach, there might be millions.

This world plays by rules different from ours, researchers say. And the first rule is: grab hold of something. For such 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 itself kicked," said Hall, the Delaware educator. "Unlike humans, most of these small animals have enough sense to stay out of the surf." Sometimes, 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 either on or between the grains. "They are boulders," said Seth Tyler, a professor at the University of Maine, one of the few scientists who study this world.

The sand is a buffet as well as a shelter. 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 called copepods. "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. "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.

Because these creatures are so hard to see, they have been studied for only 100 years or so. One expert estimated that perhaps only 25 per cent of them have been identified. Even now, relatively few researchers focus on this inner life of the beach, though there are centres of scholarship, including the University of South Carolina.

"Literally, every time we go out, we see something new," said Hochberg, who alone has described 20 new animals or groups of animals. Because these creatures are so little understood, scientists are just beginning to explore what they can tell us about pollution or climate change.

In other places around the world, sand creatures have been shown to be sensitive to contamination. But there have been few case studies in the mid-Atlantic. Even though they have just begun to map the world of the sand dwellers, 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.

"If the people appreciate the shorebirds," said Don Boesch, president of the University of Maryland Center for Environmental Science, they should understand that the birds are alive because of "all of these little organisms that are living between the sand grains."