Effects of Current and Conditions Simulating Autogenically Changing Microhabitats on Benthic Diatom Immigration

Diatom immigration rates were affected by changes in current patterns similar to those found around substrates in streams and were increased by changes in microhabitat characteristics similar to those autogenically generated during diatom community development. Diatom abundances on tiles exposed for 24 h, i.e., diatom immigration rates, ranged from 30 t 1500 cells .cm—2.d—1. Immigration rates in areas sheltered from the 27 cm/s currents of two Michigan streams were greater than in areas exposed to the current. Diatom immigration rates increased by a factor of 6 when microhabitat conditions were altered by interrupting currents near the substrate surface, and by a factor of 2 when substrates wee coated with agar. These two microhabitat conditions, respectively, simulated changes in current patterns near the substrate, and in adsorptive characteristics of the substrate that could occur autogenically as diatoms accumulate on substrates. Species—specific effects of current velocity and microhabitat conditions were related to size and growth habits of cells.