Diatoms

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THOSE MARVELOUS, MYRIAD DIATOMS ARTICLE AND PHOTOGRAPHS BY RICHARD B. HOOVER Such perfect architects, these diatoms. They spin themselves intricate houses of opal in the sea. Glittering pinwheels, spirals, stars and chandeliers! More than twenty-five thousand species of diatoms, and no shell the same. Each a living jewel. My microscope becomes a kaleidoscope. Diatoms are soexquisite it is hard to believe they are also enormously important. They are, one could argue, the most vital plans on earth. They bob, drift, and sometimes glide through most of the waters of the world in incredible numbers. Just one liter of seawater may contain as many as ten million of these onecelled specks of algae-the primary foodstuff of the sea. Even land-dwelling creatures, including man, arein their debt, for diatoms that teem in the upper few meters of the oceans produce, through photosynthesis, much of the oxygen we breathe. By profession I explore the universe as an X-ray astronomer. About a decade ago I discovered a collection of these brilliant little plants my bride-to-be had inherited from her great-grandfather, an early diatomist named Cornelius Onderdonk. Now my off-hoursbelong to diatoms. They enchant and intrigue me. I have photographed thousands of them, and I travel the world to collect new specimens. These golden-brown algae thrive wherever there is light, water, carbon dioxide, and the necessary nutrients. I find them in cold Rocky Mountain streams, in thermal springs in Arkansas, in polluted pools and roadside ditches. Marine species often form a brown coatingon Arctic ice floes. Not all diatoms are aquatic. Under moist conditions, some live in topsoil, or attached to moss, tree trunks, or even brick walls. Diatoms can endure lengthy droughts. Recently, while studying the famous Van Heurck diatom collection in Antwerp, Belgium, I added water to diatoms that had been dried on paper in 1834. I was astounded when they began to swim - revived after nearly150 years in slumber. Diatoms vary widely in size, but the very largest measure only a millimeter across. To the naked eye, their appearance is usually unimpressive. In the Australian desert I once spotted a brownish layer of diatoms floating in a salty pool. "Are you sure they're diatoms and not just something left behind by a passing emu?" chuckled my naturalist friend John Ison. I scooped up asample, and later at John's bungalow my microscope convinced him. Hundreds of graceful S-shaped Pleurosigma glided past slender rods of Synedra. Diatoms are the most abundant kind of phytoplankton, and colder oceans support the greatest numbers. Some dwell near the seabed, and will even burrow into the mud. Most float near the surface, however, to absorb sunlight. One Species Has Built-in TidalClock Photographing diatoms, I soon learned to distinguish two basic forms. One group is often called the Centrales. They have markings - rows of pores or spines - that radiate with perfect symmetry. Most Centrales are oceangoing and are commonly wheel-shaped. They are typically bobbers, drifting near the surface, basking in sunlight and letting nutrients come to them. [Caption for photograph]Diatom graveyard gives man agents that filter, polish, insulate - and even help save his life by supplying the reflective sparkle in roadway-lane striping. They do all this through trillions of their lifeless shells, called diatomaceous earth. Kelly Phelps holds 25 pounds mined at Lompoc, California. Then there are the Pennales. These tend to be elongated, their markings in bilateral rows. Most livein freshwater streams, swamps, or ditches, or on the bottoms of shallow regions of oceans and estuaries. Many Pennales can move about by themselves. On tidal sand flats of Cape Cod, a species called Hantzschia

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virgata demonstrates their locomotion elegantly. When the tide is in, the Hantzchia lie buried in the sand. Marine biologist John Palmer has found that just after...