Nuisance Algae: Didymosphenia geminata (“Didymo”)
Didymosphenia geminata, an algal species historically inhabiting clear, low-nutrient streams, appears to be expanding its geographic range and broadening its environmental tolerances. This diatom , commonly known as “Didymo,” was recently identified as an invasive species in New Zealand - the first confirmed record in the southern hemisphere. In the United States, nuisance blooms of Didymosphenia geminata are increasingly reported by the public and media. Nuisance blooms have been observed in Rapid Creek since May 2002 with the greatest mat densities observed near Johnson Siding (Figure 1).
A stream assessment was conducted to determine the impact of D. geminata blooms on the benthic organisms in Rapid Creek. Biological and water quality samples were collected monthly from May through October 2005 and 2006 at five monitoring sites located between Pactola Reservoir and Canyon Lake (Figure 2). Monitoring is also being conducted in May, August, and October 2007 and is scheduled to resume again in May 2008 (Figure 3).
A DENR bioassessment report entitled “Relationships between nuisance blooms of Didymosphenia geminata and measures of aquatic community composition in Rapid Creek, South Dakota” discusses results and analysis of the water quality and biological monitoring conducted in 2005 and 2006. This report indicates that nuisance blooms of D. geminata have likely altered the taxonomic composition of benthic macroinvertebrate and algal communities in Rapid Creek (Figures 4 and 5). |
||
Click on photos to enlarge |
||
Figure 1. Nuisance blooms of D. geminata found in Rapid Creek near the community of Hisega, SD.
|
||
Figure 2. Map of Rapid Creek drainage area, showing the location of monitoring sites between Pactola Reservoir and Canyon Lake. |
||
|
Figure 3. Collecting a macroinvertebrate sample in Rapid Creek near Pactola Reservoir.
|
|
|
Figure 4. Scatterplot showing a decrease in EPT taxa with increasing areal D. geminata coverage. EPT are a group of macroinvertebrates considered indicators of a healthy waterbody. |
|
|
Figure 5. Boxplot showing a fewer invertebrate predator species at sites impacted by D. geminata blooms. This functional feeding group may suffer in the presence of dense algal mats, where their mobility, or the mobility of their prey, might be reduced. |
|
Additional Resources
U.S. Environmental Protection Agency and Federation of Fly Fishers
EPA Region 8 - Water Quality Monitoring: Didymosphenia in Western Streams
Federation of Fly Fishers Didymo Website
Increase in nuisance blooms and geographic expansion of the freshwater diatom: Didymospenia geminata
Didymo: a nuisance and invasive freshwater alga
"Stop the Spread" information card
Biosecurity New Zealand
|
||
Top of page
