On this typical sunny morning on this southeastern Florida beach, holidaymakers loll on their blankets and splash in the waves. Walking among them are two rather atypical beachcombers: Robert Higgins, 62 years old, dressed in a T-shirt and shorts and a floppy hat that covers his close- cropped hair; and Marie Wallace, a dark-eyed woman in her mid-forties in similar garb. They carry with them a shovel, buckets, plastic bottles, a fine-mesh screen, and a supply of freshwater--all the tools they’ll need for today’s scientific expedition.
Although the other people on the beach are completely unaware of it, beneath their feet, in the seemingly sterile sand, there exists a microscopic jungle of surreal animals waiting to be discovered. Some of these minuscule invertebrates spend their lives slithering between the sand grains. Others flutter along by whirling hairlike propellers on their heads. Still others, as waves crash over them, hold tight to the sand grains with tiny claws, as if clinging desperately to giant beach balls. Some of these tiny creatures graze on algae. Some of the grazers are themselves food for predators who insert lancelike tubes through their bodies and suck out their innards.
The dynamic, abrasive environment of a sandy beach might seem an impossibly inhospitable place to call home. Yet some of the greatest diversity of life on Earth hides here, on and between the grains of sand. It’s even richer, in taxonomy’s broadest terms, than the Amazon rain forest, says Higgins, one of the world’s experts on this hidden ecology. Those broad terms he is referring to are phyla--the 40 major groups into which all animals are divided. Humans, for example, belong to the phylum Chordata, which comprises all the animals that have backbones and thus includes birds, reptiles, fish, and lampreys. To fall into another phylum, you’ve got to be a radically different beast, yet so far 22 phyla of animals have been discovered living in sand.
Higgins has searched far and wide for such life, from the frigid beaches of Greenland to the rugged coast of southern Chile. But this tame Florida shore is prime hunting ground. The animals he has his eye out for are known collectively as meiofauna. The word means lesser animals, which is not a slight to the animals but a reference to the tools that zoologists use to collect them. Meiofauna describes animals that fall between two sizes of collecting screens, Higgins explains. The larger screens are made with 1-millimeter mesh, and scientists use them to winnow out big sand dwellers such as sea urchins and sea anemones. Meiofauna readily pass through such sieves, but scientists can gather them by using the 42- micrometer (.042 mm) screen--a mesh finer than a silk stocking. (Those who want to catch smaller game such as bacteria use an even finer mesh, with just 2-micrometer openings.)
Despite their small size, meiofauna are far from insignificant: they are as common and abundant as the grains of sand they call home. One study calculated that a single handful of wet sand contains 10,000 of these animals. Yet although meiofauna inhabit every seashore, as well as the sands and gravel far out at sea, they remain virtually unknown and poorly understood. Only within the past decade have ecologists begun to realize the important role they play in the health of the marine ecosystem, consuming detritus and pollutants that filter into the sands and serving as the primary food source for shrimp and bottom-feeding fish.
