There is an article about Antarctic diatoms in the March issue of Natural History magazine. I suspect that diatoms are not familiar to most people, but that doesn’t mean they are not important. And they are also an interesting group of organisms.
Diatoms are single celled, or perhaps colonial algae. They are widespread in both marine and freshwater systems and are among the most important algae in aquatic food chains. The oxygen given off by diatoms as a byproduct of photosynthesis constitutes around one-half of the oxygen we breath. Diatoms can also serve as important indicators of water quality. Species differ in their tolerance to various aspects of the aquatic environment (e.g. dissolved oxygen). The diatom community of a stream that could support trout for example, will be quite different from, say, a stream where bullheads and carp would dominate.
It is interesting to note that the cell walls of diatoms are not made of cellulose. They are made of silica, opaline silica to be more precise. But in more relatable terms, diatoms live in glass houses. And these silica cell walls have small pores that allow materials in and out of the cell. Under an electron microscope the patterning of these pores is amazing.
As you might assume, the cell walls of diatoms do not decompose. As a result, when the diatoms die, they sink to the bottom of the body of water. Over geological time those silica cell walls may accumulate to form deposits several hundred feet. Some of those deposits are now mined and processed into a fine, white, rather gritty powder called diatomaceous earth. Diatomaceous earth has a variety of uses, including various filtering processes. A former student brought me a sample from what was used in the filtering system of a municipal swimming pool. Diatomaceous earth is also the gritty material in some silver polishes. And if you shake a white powder on your garden vegetable plants to kill those pesky chewing insects, the principle ingredient may be diatomaceous earth.
By the way, if you have slipped on the brown slippery coating of a rock while wading in a stream or lake, you can probably blame it on diatoms. Diatoms are important and intriguing organisms, but unfortunately not well known. Head to this website to learn a little more about diatoms — it has everything you want to know about them and more, including some amazing electron micrographs.
-Chuck Lura
