Response of macroinvertebrates to blooms of iron-depositing bacteria

Macroinvertebrate communities in six streams were exposed to high levels if iron, manganese, and concurrent blooms of Leptothrix ochracea, an Fe-depositing bacteria. Organisms in five streams were depauerate inside blooms, due to direct toxic effects, inability to consume bacteria as food, or behavioral avoidance of bacterial-coated substrates. Three mayfly species demonstrated increased mortality when caged inside blooms. The different responses of other species tested are reported.