The Effects of Salinity Changes on Coastal Bacterial Communities in Experimental Microcosms

Bacterial communities are important in coastal environments, but how these communities are affected by changes in salinity is understudied. We used an experimental microcosm approach to examine how short-term changes in salinity affect coastal bacterial community structure, diversity, and activity. Seawater in microcosms was amended with different treatments to decrease salinity or artificial seawater to raise it. Bacterial community structure and diversity were assessed over five days through 16S rRNA gene sequencing and the activity of microbial enzymes related to organic carbon, nitrogen, and phosphorus mineralization determined. While salinity treatments significantly affected bacterial community composition, there were few consistent patterns and time within the experiment was a more significant factor impacting bacterial communities. Highlights included a decline in the proportion of Cyanobacteriota, coupled with increases in heterotrophic taxa such as Campylobacteriota, although the latter did not occur under elevated salinity. β-glucosidase, a carbon-acquiring enzyme, showed lower activity in a decreased salinity treatment compared to controls, despite all treatments showing an initial burst in activity of this enzyme. While seawater bacterial communities did change following short-term changes in salinity, such changes were difficult to separate from those caused by experimental conditions, making predictions about natural systems an ongoing challenge.