Fig 6. A constrained principal coordinates analysis (CAP) of 16S rRNA bacterial microbiome data collected from the mussel species Cyclonaias asperata, Fusconaia cerina, Lampsilis ornata, and Obovaria unicolor as well as seston from the Sipsey River, AL, USA.

Bray-Curtis dissimilarity was used to separate samples by site differences in physicochemical parameters. Three measurements of each environmental parameter were recorded between June 9 and September 28, 2016. CAP identified surface water ammonium, porewater ammonium, surface phosphate, pore phosphate, and surface nitrite as the most critical factors of all the measured parameters and those factors were retained in a reduced model. Surface measurements were collected from the flowing water body and pore measurements were taken from pore water. A. Within the mussel gut samples, these physicochemical parameters explained very little variability, combining 7.9% across each of the first two axes. B. Within the seston samples, environmental chemistry explained 44.5% of bacterial compositional differences across the two axes.