Changes in the bacterial community in port waters during ship’s ballast water discharge

Ballast water-mediated bioinvasion is a major threat to the health of aquatic ecosystems. Port environments are hotspots for marine bioinvasion due to ballast water uptake and discharge activities. As the first of its kind pilot study in a tropical ecosystem, we investigated short-term changes in the bacterial community at a port during ballast water discharge (BWD). Total bacterial count and total viable bacteria varied significantly in the port, which can be attributed to BWD. While Vibrio alginolyticus numbers increased, V. parahaemolyticus decreased during BWD, whereas total coliforms were reduced over time. Before BWD, Actinobacteria, β- and γ-proteobacteria were dominant at the port. However, Bacteroidetes and γ-proteobacteria were abundant after BWD, which may have been inoculated in the port through ballast water. Such a shift in bacterial diversity can alter the functional characteristics of the port and is a cause for concern. Investigating the long-term changes due to repeated inoculations will help in developing appropriate environmental management practices.