Freshwater mussels and host fish gut microbe community composition shifts after agricultural contaminant exposure

AIMS: We examined the effects of a mixture of contaminants found in agricultural watersheds on the gut microbiota and physiology of both the freshwater mussel Lampsilis cardium, and L. cardium host fish Micropterus salmoides. METHODS AND RESULTS: Lampsilis cardium and M. salmoides were exposed to three concentrations of agricultural contaminants for 60 days (observing behaviour daily) before being sampled for gut microbiota analyses. DNA was extracted from the gut samples, amplified via PCR, and sequenced using the Illumina Mi‐Seq platform. Only L. cardium guts had differing microbiota across treatments, with an increase in potentially pathogenic Aeromonas. We also provide novel evidence of a core microbiota within L. cardium and M. salmoides. In terms of physiology, female L. cardium exhibited a decrease in movement and marsupial gill display in contaminant exposures. CONCLUSIONS: Exposure to contaminants from agricultural watersheds may affect population recruitment within freshwater mussel communities over time. Specifically, increased pathogenic micro‐organisms and altered behaviour can reduce the likelihood of glochidia dispersal. SIGNIFICANCE AND IMPACT OF THE STUDY: This study supports emerging research that contaminants found in agricultural watersheds may be a factor in freshwater mussel population declines. It also provides novel evidence that unionids have a core gut microbiota.