Substrate characteristics affect colonization by the bloom-forming diatom Didymosphenia geminata

Abstract The long-stalked Didymosphenia is capa-ble of forming large blooms and is expanding its range. To better understand the colonization dynamics of this species, we investigated the role of substrate charac-teristics—rock roughness and biofilm condition—on Didymosphenia colonization in a montane Colorado stream. Rocks differing in roughness (shale and sandstone) were treated to manipulate the diatom-dominated biofilm by scrubbing or submersion in 30% hydrogen peroxide. Initial chlorophyll concentration differed among rock types (sandstone [ shale) and biofilm treatments (untreated [ scrubbed [ hydrogen peroxide-treated). Rocks were placed in a Didymo-sphenia bloom area for 8 days. More Didymosphenia colonized the rougher sandstone than the smoother shale, and more colonized stones with intact bio-films than stones with reduced biofilms (intact [ scrubbed [ hydrogen peroxide). These results suggest that rougher stones may be targeted for surveillance for new populations and that the colonization of intact biofilms is consistent with Didymosphenia’s habitat in regulated rivers, where biofilm-scouring spates may be suppressed