The effect of nuisance diatom growth on benthic macroinvertebrate communities

Didymosphenia geminata is a freshwater benthic diatom found in cold, mountain streams. In the past ten years it has become a nuisance species, producing a persistent stalk material that alters the benthic environment. Little is known about the extent to which these diatoms impact benthic macroinvertebrates. The goal of this study is to determine if the presence or absence of D. geminata affects macroinvertebrate community composition. Four sites along Boulder Creek, below Barker Reservoir Colorado, were chosen for this study. Periphyton was sampled every week from May 30th to August 2nd 2008. Additionally, macroinvertebrate samples were taken every other week from approximately the same location as the periphyton. The periphyton samples will be used to estimate the D. geminata cell and stalk contribution relative to other species of diatoms in each microhabitat. The macroinvertebrates will be identified by family and functional feeding group. It is predicted that the D. geminata will alter the benthic environment by creating a depositional habitat and preventing the colonization of other algal species. Further predictions are; due to increased organic matter within the stalk matrix, detritivores will dominate the benthic macroinvertebrate community, followed by herbivores preying on D. geminata.