Impact of marine heatwave on microbiome of mediterranean gorgonians

In this study, we sampled two gorgonian species (P.clavata and C.rubrum) with different visual health states (0% and 90% of tissue loss) during the record-breaking heatwave of 2022. This is the first time that gorgonians with obvious signs of tissue damage have been sampled to investigate changes in their bacterial communities. The gorgonians were collected in two protected areas (the Calanques National Park in France, and the Portofino Marine Park in Italy) that experienced different MHW intensities, with measurements reaching 27C and 26C at depths of 15 m and 30 m, respectively in the Calanques National Park and 19.8C at 35m depths in Portofino. The sampling sites are suited to study the impact of the 2022 MHW because they are located in protected areas with no anthropogenic threats other than seawater warming. The main objective of this study was to characterize the species-specific composition of bacterial communities associated with emblematic gorgonians from the Mediterranean Sea, in relation to their physiological conditions and collection sites. To this end, we analyzed a total of 96 samples from 7 collection sites and 2 species by amplicon sequencing of the 16S rRNA gene. This study provides important information on how gorgonian-associated microbiomes respond to thermal stress and will enable a better conservation and protection of Mediterranean MAFs.