Diatoms Speak Volumes

Diatoms, single-celled algae about a thousand times smaller than a pinhead, are being used to monitor everything from water quality to global climate change.

Slurping up lake mud with a turkey baster is one way to collect diatoms. Scraping algal slime from the surfaces of rocks and pulling a fine mesh net through water are two other methods Academy Research Scientist Sarah Spaulding uses to collect these microscopic organisms.

Scanning electron microscope (SEM) image of a new species of diatom of the genus Gomphonema from a lake in Tasmania, the large island off the southern coast of Australia. It is surrounded by many other, smaller species of diatom, all of them are found together in a benthic (bottom water) habitat. Photo: Sarah Spaulding

Diatoms grow nearly everywhere on Earth, from the equator to the poles, and form the basis of aquatic food webs in both marine and freshwater habitats. Giving off oxygen as a by-product of photosynthesis, they produce close to 40 percent of atmospheric oxygen, second only to tropical rainforests.

Eunotia serra (left), Stephanodiscus niagarae Photo: CAS Special Collections

Tetracyclus emarginatus Photo: CAS Special Collections

Dr. Sarah Spaulding at Praia Sambangombe, southwest São Tomé. Photo: Dong Lin

Spaulding is trying to pin down diatoms' historic and current distributions. Many species of diatoms are restricted to certain regions with specific pH, salinity, and nutrient levels. Knowing what species grow where, scientists can use them to monitor the health of streams and rivers and even determine the effects of acid rain.

Because the cell walls of diatoms are composed of silicon dioxide, they are preserved in lake and ocean sediments. Thus, their fossils can be used to reconstruct past environmental conditions, such as climatic records, over time.

SEM of a second new species of Gomphonema from a lake inTasmania. Detail of one end of the valve, called the footpole. This diatom has a porefield at the footpole. The porefield functions to secrete a mucilaginous stalk. The stalk allows the diatom to attach to aquatic plants or other surfaces. Photo: Sarah Spaulding

Cymbella affinis Photo: CAS Special Collections