Large-scale disease outbreaks in Paramuricea clavata and other gorgonian species have recently occurred in the northwestern Mediterranean. The environmental driver of these events was an increase in seawater temperature during climatic anomalies in summer. From diseased P. clavata colonies, we previously isolated a Vibrio strain that showed thermodependent virulence, demonstrating that pathogenic microbes are associated to gorgonian mortalities. The composition and dynamics of the natural microbial communities living in association with P. clavata are unknown. The aim of the present study is to establish a baseline for diversity and abundance of associated bacteria. These data will be used to investigate changes in the normal microbiota at elevated temperature and to test specific hypothesis about factors leading to pathogen development and disease during anomalies. Preliminary data obtained by culture-independent techniques indicate that bacterial communities from geographically remote populations of P. clavata are similar, while observed seasonal changes in bacterial assemblages suggest that environmental factors could influence their composition. As part of the multidisciplinary Medchange program, this work will contribute to provide a better understanding of marine ecological responses to climate change.