The US Geological Survey newsroom has just put out an advisory on the importance of washing your hands after playing in the sand on the beach:
By washing your hands after digging in beach sand, you could greatly reduce your risk of ingesting bacteria that could make you sick. In new research, scientists have determined that, although beach sand is a potential source of bacteria and viruses, hand rinsing may effectively reduce exposure to microbes that cause gastrointestinal illnesses.
Yes, indeed, my mother - and mothers in general - were right: "wash your hands!".
Beach pollution is a significant problem, but things could be a lot worse.
I learned many things in the course of writing the book, but perhaps the most extraordinary revelation was the staggering diversity of minute creatures that creatively and tenaciously make their livelihoods in the miniature worlds between the grains of sand on our beaches. The general term for this microscopic zoo is meiofauna, the "lesser animals." Representatives are shown in the image at the head of this post (photos by M.D. Hooge), and it is their world that Rachel Carson was referring to in The Edge of the Sea, when she wrote "Walking back across the flats of that Georgia beach, I was always aware that I was treading on the thin rooftops of an underground city." And the meiofauna do a heroic job of keeping our beaches clean. Here are a couple of extracts from Sand on the interstitial jungle:
In the great hierarchy of living things on our planet, it is generally accepted that, at the head, there are five kingdoms, one of which—animalia—contains all multicelled animals. Within each kingdom are a number of phyla: all mammals, birds, reptiles, amphibians, and fish belong to the phylum chordata. Depending on which biologist you speak to, between thirty-six and forty total phyla are recognized on our planet. Rainforests, our flagships of biodiversity, are known to contain sixteen phyla. The spaces in between sand grains are home to twenty-two.
The dark, watery world beneath the surface of the intertidal zone of most beaches is home to many kinds of bacteria—and a jungle of other minute creatures. Silica, or quartz-based sands, are the most hospitable, since the calcium carbonate in sands composed of shell fragments makes the water too alkaline for many creatures to flourish. Pick up a handful of wet quartz sand on the beach and you are holding a miniature zoo with thousands of inhabitants. Some of these were first observed by Antony van Leeuwenhoek as he peered down his microscope at sand grains and his animalcules, but we owe our understanding of the incredible diversity and importance of this community to the work of Robert Higgins, who since the 1960s has devoted his life to identifying and describing its members. Now retired from the Smithsonian Institution, Higgins is the pioneer of work on meiofauna (“lesser animals”), creatures whose giants are 1 millimeter long; he continues to contribute to the identification of new species, which crop up at the rate of a dozen or so every year. In a 2001 symposium that paid tribute to his discoveries, Higgins modestly described his work as “how the ‘lesser-knowns’ became better-known.”
Life between the sand grains is not an easy one. The grains move and settle under the pressure of the waves and the incessant flushing of the tides, water occasionally drains out completely, and the ecosystem contains a variety of predators. Life has had to adapt, and it has done so in strange and extraordinary ways that reflect an intimacy with the behavior of granular materials. Many of these creatures have armored or padded bodies designed to withstand abrasion by moving sand grains; their shape is often flat or elongated to enable squeezing between the grains; and they have developed a variety of ways of attaching themselves, using glue or suction, to individual sand grains, clinging on for dear life. Rotifers, nematodes, mystacocarids, tardigrades, gastrotrichs, turbellarians, and kinorhynchs—it’s tempting to view these little animals as rejoicing in their exotic names. Tardigrades, which live in both marine water and freshwater, can’t swim, so hanging on to a sand grain is vital; some use mechanical suction toes, some claws, some both. A gastrotrich can glue and unglue itself in an instant. A kinorhynch is ungainly, described by Higgins as an umbrella in a canister, but it moves effectively, if slowly, exploring one sand grain at a time. Rotifers, so named because they look like rotating hairy wheels, are represented by 2,500 different species, most of which are freshwater dwellers. Tardigrades have the remarkable ability to suspend operations if the water disappears, remaining dormant and dehydrated for a hundred years, only to spring back to life when rewetted. They seem to do this by replacing the water in their cells with sugar, which renders them immune to freezing and radiation, a talent that is of considerable interest in the worlds of medicine and extraterrestrial biology.
In the entire living world, only three new phyla were identified in the twentieth century, and one of them came from the strange world of meiofauna. In the 1970s, Reinhardt Kristensen, a professor at the University of Copenhagen and an old student of Higgins, showed him a collection of creatures from the coast of Brittany that he could not identify. “Oh,” responded Higgins, “I have one of those too.” The animals fit with no known group of living things, and it took several years of meticulous collaborative work to define the character of the creature as a new phylum. It looks rather like a classical amphora with snakes emerging from it, and they named it loricifera, “corset-bearing,” reflecting the appearance of the rings that sheathe the animal. More than seventy species have now been identified, but we know next to nothing about their behavior, since, sadly, they die before reaching the laboratory. One remarkable thing we do know is that loricifera have the smallest cells of any known animal.
Inevitably, the community of organisms growing on or living in sand has its own name: psammon. Among the psammon are psammophiles (or arenophiles, if you prefer Latin to Greek), psammobionts, and psammoxenes. The names are weighty, but the members of the community are not; what they are is wondrous. Most of us don’t know they exist, but we should be grateful for them. Without meiofauna, the sands of our beaches and lakeshores would be stinking, toxic places, with organic debris rotting unconsumed and dangerous bacteria rampant. The microscopic creatures of the meiofauna feed off this debris: they keep our beaches clean.
[for more information on these fascinating creatures, see the site of the network of 94 European marine institutes, http://www.marbef.org/wiki/Meiofauna_of_Sandy_Beaches, the International Association of Meiobenthologists at http://www.meiofauna.org/, http://discovermagazine.com/1995/apr/lifeonagrainofsa491, and http://whyfiles.org/022critters/meiofauna.html, the latter particularly on Higgins.]