Influence of salinity stress on bacterial diversity from a marine bioinvasion perspective: Evaluation through microcosm experiments

Abstract

Mid-ocean ballast water exchange has been used since the past few years to control bioinvasion through ballast water (BW), which requires the ship to exchange part of its BW in the open ocean. The change in salinity is expected to be detrimental to coastal species. This study evaluates the changes in bacterial diversity with respect to salinity stress when translocated into an environment with non-ambient salinity. Surface water samples from three coastal ports, namely hypersaline Kandla port in Gujarat, saline Paradip port in Odisha, and freshwater Kolkata port in West Bengal, India were collected and aged in dark for 30 days to mimic BW tank conditions. The aged water samples were translocated into water collected from the estuarine mouth (Dona Paula), midestuary (Cortalim) and upstream location (Sanvordem) of Zuari Estuary, Goa and incubated in the laboratory. Quantitative polymerase chain reaction technique was used to assess major bacterial phyla. Culturable marine bacteria and Vibrio spp., including gamma-proteobacteria preferred higher salinity, whereas culturable freshwater bacteria, including coliforms in conjunction with alpha-, beta-proteobacteria, Bacteroidetes and Firmicutes preferred lower salinity. The freshwater port bacteria could withstand salinity stress better than those from the hypersaline or saline ports. The species comprising these phyla could be regionand niche-specific. The invasive potential of these bacterial clades would depend on the environmental suitability of the recipient port. Studying the changes in the ecosystem of the port environment after BW discharge in real-time would provide meaningful insights into the invasive potential of these bacterial phyla.