Low salinity significantly alters the bacterial community of the marine foundation speciesSaccharina latissima(sugar kelp)

Abstract

As climate change progresses, the intensity and variability of freshwater outflow into the ocean is predicted to increase. The resulting increase in low salinity events will be a source of stress forSaccharina latissima(sugar kelp) and potentiallySaccharina’sassociated bacterial community. Bacteria are important to the health of their host because host-associated bacteria can facilitate or hinder host survival in stressful abiotic conditions. Therefore, understanding how bacteria change under abiotic stress is critical to our understanding of how host physiology will be affected by abiotic stress. In this study, sampled the bacterial community associated withSaccharinaand the surrounding environment across two years of field sampling at four sites with contrasting salinity profiles around Vancouver, Canada during the 2021 and 2022 spring freshet (562 samples) coupled with salinity manipulation experiments in the lab repeated eight times in 2022, concurrently with field sampling (269 samples). Our illumina data show that salinity is a significant factor in shaping the overall bacterial community ofSaccharina. We find significant increases in bacterial community diversity and paired with a significant reduction in the relative abundance of core bacteria in low salinity across lab and field data. Our findings suggest that host-filtering is significantly impaired in low salinity, raising questions surrounding how resilient some existingSaccharinapopulations may be to more intense and more variable freshwater influx.