Beschreibung:
<jats:title>Summary</jats:title><jats:p>We investigated bacterial assemblages associated with corals displaying symptoms of the ‘White Syndrome’ (WS), a general term used for indicating the appearance of bands, spots or patches of tissue loss, which is devastating wide areas of tropical ecosystems worldwide. We collected WS‐diseased (<jats:italic>n</jats:italic> = 15) and healthy (<jats:italic>n</jats:italic> = 15) corals from the natural reef (Indonesia, Indian Ocean) and from four large public aquaria. By using culture‐dependent and culture‐independent techniques, we found that a large fraction (73%) of the investigated WS events was associated with the presence of a high bacterial abundance and, specifically, of <jats:italic>Vibrio</jats:italic> spp. <jats:italic>Vibrio harveyi</jats:italic>, a pathogen of many marine organisms and recently involved in coral Yellow Band disease, was the most represented species, being recovered from five out of 15 diseased corals. In experimental infection assays, two <jats:italic>V. harveyi</jats:italic> strains, isolated from diseased corals, were inoculated on a total of 62 healthy colonies of <jats:italic>Pocillopora damicornis</jats:italic>. WS signs appeared in 57 corals, confirming the ability of <jats:italic>V. harveyi</jats:italic> strains to induce the disease. We conclude that <jats:italic>V. harveyi</jats:italic> is one of the coral pathogens involved in the appearance of WS. However, not all of the investigated WSs were associated to <jats:italic>V. harveyi</jats:italic> detection, nor to other <jats:italic>Vibrio</jats:italic> species (such as <jats:italic>V. coralliilyticus</jats:italic>), which supports the hypothesis that WS is not caused exclusively by <jats:italic>Vibrio</jats:italic> spp., but rather can have a multifactorial aetiology, or can represent a group of diseases caused by a variety of agents. Further investigations to identify specific virulence traits will contribute to the understanding of the role of <jats:italic>V. harveyi</jats:italic> in WS pathogenesis.</jats:p>