Since 2011, fatal shark attacks occurred in Reunion Island and led to the "shark crisis", raising up different issues for humanities and social sciences. One of them consists in the links between science and society and particularly the issue related to the legitimacy of the scientific expertise evolving in a context of institutional crisis. From the communication sciences point of view, the evolution of the experts' legitimacy has never been analysed in the local media discourses. We built a corpus of 1600 articles from the local media LINFO.RE about the theme of shark risk, from 2011 to 2017. We studied this corpus qualitatively through an analysis grid made from argumentation and controversy theories. In addition, we led a quantative analysis in order to establish the frequency of appearance of discourses about science in relation to the total number of publications about the shark risk. An evolution of the legitimacy of scientific experts has been demonstrated with different turning points of qualifications / disqualifications according to the dynamics of the social context, the actors involved, and their arguments. The number of articles written about the shark risk showed peaks of publications in often following shark attack events. The frequency of appearance of discourses about science showed a variation in the media coverage according to the arrival of new disqualifying arguments, the publication of expertise reports, or a shark attack occurrence. Our study explores how the scientific discourses circulate in the social field and how they can be transformed and reappropriated by the different actors involved in a socio-scientific controversy. The case of media coverage of "shark crisis" in Reunion Island allows us to discuss the dynamics of the scientific e​x​p​e​