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Impact of Salmon Spawning on Microbial Communities in a Northern California River

ABSTRACT We studied microbial communities in the water column during the fall 2002 Chinook salmon (Oncorhynchus tshawytscha) run on the Feather River in northern California. We quantified culturable heterotrophic bacteria, live/dead bacteria, and Aeromonas spp. bacteria in the water column. Concentrations of each group peaked two weeks following the peak of new salmon carcasses in the river then declined. During the fall 2003 Chinook salmon spawning season we used fluorescent in situ hybridization with domain-specific DNA probes to characterize changes in epilithic biofilm communities. Eukarya counts were lower than Bacteria counts earlier in the salmon run; however, by the end of the salmon migration season, cell concentrations of Bacteria and Eukarya were approximately equal. Chlorophyll a concentrations from epilithic biofilm began to increase in parallel with the increase in Eukarya. Since the biofilms persisted through the spawning season, it is possible that these communities support a food chain that leads to insect populations which become nutrients for the newly hatched salmon fry in the winter and spring.