EPILITHIC BACTERIAL AND ALGAL COLONIZATION IN A STREAM RUN, RIFFLE, AND POOL - A TEST OF BIOMASS COVARIATION

Epilithic bacterial and algal biomass were compared among a run, riffl e, and pool along an open-canopy section of a third-order, temperate s tream. Epilithic biofilms were sampled after 3, 7, 14, 21, 28, and 35 days colonization on unglazed ceramic tiles that were attached to plas tic trays (n=3) placed across each of the three habitats (i.e., run, r iffle, pool). The diverse habitats and sampling regime were selected t o provide a range in algal biomass so that potential covariation betwe en epilithic bacterial and algal biomass could be assessed. There were significant differences among habitats and among trays within each ha bitat for both chlorophyll a and AFDM. Chlorophyll a and AFDM increase d in the run and pool throughout the colonization period. In the riffl e, chlorophyll a and AFDM increased rapidly early in colonization, the n decreased. Epilithic bacterial biomass increased rapidly with no sig nificant differences among the three habitats throughout colonization. Further, bacterial biomass did not correlate with either chlorophyll a or AFDM in any of the three habitats or on any of the sampling days. These results suggest that epilithic algal and bacterial biomass may be regulated by independent controls in some stream environments.