Minnesota Profile - Diatoms (Bacillariophyta)

Unseen but ubiquitous

Diatoms are microscopic single-celled algae. They inhabit nearly every wet environment that receives sunlight and has the silica they need to make their cell walls. These abundant and diverse photosynthetic creatures, neither animal nor plant, can be found at varying temperatures (about 20 F to 100 F), salinities (nearly pure to more than twice as salty as seawater), and pHs (less than 3 to more than 9). Globally, diatoms produce more than 20 percent of the oxygen made through photosynthesis.

Appearance

Diatoms range from about 10 micrometers (1/100 of a millimeter) to, rarely, a millimeter in maximum dimension. They form brownish films on submerged surfaces, such as rocks and logs, and sometimes impart a golden brown tinge to water. Their most distinctive feature is the siliceous covering, literally a glass shell. Scientists use the various shapes and ornamentations of this shell to identify species. These nearly insoluble cases make them excellent microfossils. Sediments of lakes are often analyzed for diatom remains.

Habitats

Most diatoms float in the water or live on submerged surfaces. No one species is characteristic of Minnesota's waters. Some live in specific habitats. For example, Lemnicola hungarica typically attaches to roots of common duckweed.

Biological nuances

Diatoms reproduce asexually by dividing in half. When a diatom divides, each new cell keeps a half shell and develops a new, smaller inner half shell. As a result, each generation is usually smaller than the last. At some point, a population regenerates normal cell size, usually through a sexual cycle. This combination of asexual and sexual reproduction presumably favors change in the species. Thus, estimates of more than 1 million species might not be far-fetched, although described species currently number in the tens of thousands.

Role in ecosystems

Diatoms are the preferred food of most aquatic organisms. They produce omega-3 fatty acids, which are essential to neurological development of many vertebrates, especially humans.

Management

Most diatoms benefit ecosystems, although some impart a "fishy" taste or odor to water supplies, or produce slimes that may foul intake pipes or sand filters. Biological controls that don't harm other organisms are being investigated.

Dave Czarnecki
Loras College Freshwater Diatom Culture Collection