Rock Snot, NPS photoDidymo, NPS photoDidymo, NPS photo

Diatoms are one-celled, photosynthetic organisms that form the base of food webs in aquatic ecosystems throughout the Crown of the Continent. The biodiversity of diatoms in the Crown is high with estimates of well over 1000 diatom species—including 232 new species described since 2009.

Nearly all diatoms are microscopic. Although small individually, diatoms can form large colonies that are often visible as slick brown coatings found along the edges of lakeshores or on rocks in streams. Didymo (Didymosphenia germinata), a native diatom, is the only algae of concern in the Crown. Nuisance blooms of Didymo may negatively affect macroinvertebrate abundance, which could lead to a reduction in food and spawning habitat for fish.

Diatom species generally require very specific ranges and tolerances in the chemistry of the water in which they live. This allows scientists to study diatoms as environmental indicators. For example, some diatoms, like Didymo, thrive in warmer waters. New occurrences of Didymo in northern latitudes and higher elevations indicate warming water temperatures, which directly relates to warming climate trends. On the other hand, Distrionella incognita, a species found only in cold, mountainous, glaciated regions, could be expected to decline when glacial meltwaters no longer feed the lakes it inhabits.