Influence of Didymosphenia geminata on fisheries resources in the Black Hills, SD

Daniel A. James

Abstract – Didymosphenia geminata (didymo) is a diatom that historically occurred in low productivity streams and lakes at northern latitudes, but has recently expanded its geographic range and in many cases, has exhibited characteristics of an invasive species. The spread of didymo has prompted global concern among biologists because the stalks of didymo form dense, mucilaginous mats that cover the stream bottom, didymo can be easily spread across watersheds, and the establishment of didymo has been associated with significant changes in stream ecosystems. In 2002, didymo was reported from the Rapid Creek drainage in the Black Hills of South Dakota. Following its establishment, brown trout biomass decreased 60%. The purpose of this study is to quantify the impacts of didymo on brown trout and invertebrate resources in Rapid Creek. In addition, an adaptive management approach is presented that evaluates biological responses to nutrient enrichment in an experimental reach of Rapid Creek. Factors affecting the distribution and abundance of didymo and its associated impacts on fisheries resources will be conducted by measuring the water quality, physical attributes, and invertebrate composition and abundance in four streams of the Black Hills. An attempt to improve trout and invertebrate resources in a didymo-impacted area of Rapid Creek will be conducted using nutrient subsidies. After adding phosphorous to the stream, water quality, didymo biovolume, periphyton composition and abundance, invertebrate composition and abundance, and brown trout biomass will be measured to evaluate the effects of nutrient addition. Data will be collected to quantify prey availability in relation to brown trout growth potential in didymo impacted and non-impacted areas. Invertebrates will be sampled in drift nets and a bioenergetics model will be used to estimate growth for different sized trout.

References

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Spaulding, S., and L. Elwell.  2007.  Increase in nuisance blooms and geographic expansion of the freshwater diatom Didymosphenia geminata: recommendations for response.  Environmental Protection Agency, Denver, Colorado and Federation of Flyfishers, Livingston, Montana.