Didymo "Rock Snot"
OVERVIEW
Didymosphenia geminata, also known as Didymo or Rock Snot, is a diatom (a single celled alga) that can be found within many cold-freshwater streams and lakes. Current research is indicating it is most likely native to parts of North America including the Northeast. 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 can occur in lakes and ponds. It thrives in 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 pH, sodium chlorides and phosphorus. 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 in response to low dissolved phosphorus. This is the opposite of other forms of algae who will bloom in response to increased nutrients.
IMPACT
When Didymo blooms in streams and rivers it can clog up canals, hydropower generators, and water intakes. The blooms that extend 1 km may impact tourism that relies on the stream for recreation such as fly-fishing, aesthetics, or paddling. Fishermen have difficulty casting their lines in the thick mats of algae. 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Didymo is now considered a native, but very rare species to North America, previous thoughts on spread prevention are no longer valid.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.
Lab Identification:
When looked at under a microscope Didymo looks like an old-fashioned coke bottle. An apical porefield is present at the footpole of the valve.
General cell Morphology: Cell Length 80-140 um, Cell Width 25-43 um, Striae number 8-10 in 10 um.
If you are concerned that you might have Didymo in your watershed, please contact the Winooski Natural Resources Conservation District to have a sample identified.
