Temporal and spatial patterns in waterborne bacterial communities of an island reef system

The bacterial 16S rRNA gene diversity of waterborne bacterial (WBB) communities was assessed using PCR/denaturing gradient gel electrophoresis (DGGE) techniques, along with sequence analysis of selected bands. 16S rRNA gene diversity varied between seasons, and significant differences were recorded between night and day. However, there were no significant differences detected between low, ebb, flood and high tides when the water body sampled would have originated from completely different areas including those off-reef. These results suggest that changes in productivity and/or vertical diurnal migrations of plankton may have greater effects than large-scale water movements effected by tidal flows. These results do not demonstrate a strong link between WBB communities and their underlying benthos. This either suggests a lack of coupling between the benthos and the water column (benthic-pelagic coupling) or that the processes are extremely rapid and efficient with strong mixing. Previous studies at this site have shown cycling between coral reef and lagoon sediments via coral mucus release and tidal transport, supporting the latter. We found a strong seasonality in the abundance and composition of WBB communities, with Alphaproteobacteria being more prevalent during winter and Gammaproteobacteria during summer, but quantitative PCR (qPCR) showed no significant differences in vibrios between seasons.