Influence of a tributary stream on benthic communities in a Didymosphenia geminata impacted stream in the Sierra Nevada, USA

Abstract

The freshwater stalked diatom Didymosphenia geminata can alter benthic community structure. However, the numbers of D. geminata that must be present to do this is not clear. Is it possible that benthic communities in streams with D. geminata are not altered? A comparison of benthic communities in two similar, adjacent streams (one with and one without D. geminata) was conducted to identify the effects of D. geminata presence on benthic community structure. An additional comparison was made below the confluence of the two streams to determine the influence of an unregulated tributary stream on the temporal and spatial patterns of potential impacts of D. geminata on benthic communities. Benthic algal biomass (chlorophyll a and ash-free dry weight) in the D. geminata stream (dominated by D. geminata and Achnanthidium spp. throughout study period) was an order of magnitude higher. High D. geminata growth altered the physical environment of the stream benthos resulting in fewer grazing invertebrates and greater densities of burrowing invertebrates such as Chironomidae and Oligochaeta. Below the confluence, benthic community structure became more similar to the non-D. geminata stream. Results show that extensive growth of D. geminata can alter benthic communities, however, an unregulated non-D. geminata tributary stream can assuage impacts and establish benthic community structure resembling the non-D. geminata tributary stream over a relatively short distance. This study provides insight into the extent and mechanisms by which growth of D. geminata affects benthic communities and helps determine the influence of tributary stream on D. geminata growth and patterns in benthic communities.

Keywords:

• Didymosphenia geminata
• stalk diatoms
• benthic macroinvertebrate
• stream ecology

Acknowledgements

We acknowledge the institutional support of the Desert Research Institute and the Hydrological Sciences program at The University of Nevada, Reno and the financial support from the Aileen and Maki Fellowship. We would also like to acknowledge the Systems Microbial Ecology Laboratory at the Desert Research Institute for assistance with data collection and analysis. Also we would like thank the anonymous reviewers for the helpful edits and contributions.