Corals are foundation species that form important ecosystems such as coral reefs or gardens. They rely on interactions with bacteria, fungi, virus, archaea, and dinoflagellates (the microbiome), which together with the coral colony, composes the coral holobiont. These microorganisms’ importance arises the questions «how» and «when» the coral obtains them and whether this depends on the reproductive strategy of the coral. Bacteria can be taken up by early life stages of tropical scleractinian corals vertically (from parental source), horizontally (from environmental source) or both in tropical corals, independent of their sexual reproductive strategy (brooder or broadcast spawner). Bacterial transmission in temperate octocorals, has not been studied. Here we investigate bacterial communities across early life stages of the temperate gorgonians Eunicella verrucosa, a broadcast spawner, and two morphotypes of Paramuricea cf. grayi, one spawner and the other brooder. We identified changes in bacterial community in E. verrucosa and in the brooding P. cf. grayi. Mixed transmission occurred in both reproductive modes. Vertical transmission occurred from adults to eggs, including clade BD17 bacteria, and horizontal transmission of bacteria, including Pseudoalteromonas. We also identified Pseudophaeobacter as a common genus of bacteria in larvae of different reproductive strategies, which could indicate importance in ontogeny.
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