CPR Australia heatwave. undefined

The Great Barrier Reef (GBR) is the world’s largest coral ecosystem under the threat of climate change. The 2016 Marine Heatwave (MHW) resulted in massive coral bleaching and death across GBR and despite major ecological changes linked to this unprecedented event have been assessed for marine biota (e.g. corals, algae, fishes and mobile invertebrates) little is known on its impact on the marine microbial communities. In this study, the impact of 2016 MHW in the spread of potential pathogenic Vibrio communities was investigated at an unprecedented spatial scale along a ca. 800Km transect in GBR. To this end, retrospective molecular microbiological analysis of archived plankton samples collected by the Australian Continuous Plankton Recorder (CPR) survey before, during and after the MHW was applied and ca 25,000 L of sea surface water were analysed. 16S rRNA metabarcoding analysis of CPR samples showed a dramatic large-scale shift in the associated bacterial community structure during the heatwave with changes that persisted four months later the event, despite a significant drop in sea surface temperature corresponding to austral winter in the region. Notably, a significant increase in the relative abundance of bacteria belonging to the genus Vibrio in CPR samples collected during and after the MHV was apparent. Droplet Digital PCR and targeted metagenomic analysis applied on samples collected when pre-heatwave conditions were partially recovered revealed the presence of several potential pathogenic Vibrio species previously associated to diseases in aquatic animals including the coral pathogen V. coralliilyticus. Overall, large-scale microbiological data generated in this study support a role played by 2016 MHW to foster the spread of thermotolerant potential pathogenic Vibrio species across GBR possibly by providing a selective advantage over species with lower thermal sensitivity thus representing an additional threat for marine biodiversity following the heatwave.