"Rock Snot" aka Didymo

OVERVIEW

Didymosphenia geminata, also known as Didymo or Rock Snot, is a diatom (a single celled algae) that can be found within many freshwater streams and lakes. Current research is indicating it is most likely native to parts of North America. When Didymo blooms in late summer, it covers the substrate of streams in large mats.

HABITAT

Didymo is commonly found in streams and rivers, but it can occur in lakes and ponds. It thrives in the following conditions: low, stable, flowing waters; waters three inches to six feet deep; with moderate to high current; below outlets of lakes or reservoirs; or, in sunny, open streams exposed to high intensity light to partial shade. The limiting factors seem to be light, dissolved oxygen, and pH (Didymo has been found in streams with a pH of 7 or higher). It is suggested that Didymo occurs more frequently in areas where temperature and flow have been regulated by dams, or areas in which riparian corridors have been disturbed. Current research is showing that Didymo will bloom inresponce to low dissolved phosphorus. This is the opposite of other forms of algae who will bloom inresponce to increased nutrients.

IMPACT

Didymo blooms in streams and rivers can clog up canals, hydropower generators, and water intakes. The blooms that extend 1 km may affect tourism that relies on the stream for recreation such as fly-fishing, aesthetics, or paddling. Fishermen have difficulty casting their lines in the thick blooms. Didymo blooms may also have a negative impact on local fish populations by smothering possible breeding substrate and removing important food sources by forming a barrier to caddis, mayflies, and stoneflies. Studies are underway to determine if fish populations are impacted.

PATHWAY

Cells can survive up to 40 days in a cool, damp, dark location. As Didymo is now considered a native, but very rare species to North America, previous thoughts on spread are no longer valid.

“Rough field guide”

Didymo can be distinguished from other species of algae by:

Color- beige/ brown/ white olive green, “NOT bright green”
Touch- feels like wet wool, “NOT slimy”
Strength- securely attaches to stones and “DOES NOT” fall apart when rubbed between fingers.

Didymo begins as small round brown spots on rocks like cotton balls. As the stalks lengthen and the ends fray, Didymo can develop into thick brown or beige mats that resemble wet toilet paper. It may look slimy, but when felt, it resembles wet wool. A microscope is needed to confirm the identification of Didymo.