This research investigates the occurrence of Pinna nobilis (Linnaeus, 1758) in the Mediterranean Sea, where it is an endemic and the largest bivalve species. Such a species is protected under the European Council Directive 92/43/EEC since 1992, being exposed to anthropogenic impacts. The distribution of this species has been known, in the past, only from reports in scientific literature. Presently, the concerns, threats and risks for P. nobilis are increasing and a more detailed mapping of the actual distribution from a largest to a local spatial scale is essential for the implementation of monitoring, management and conservation actions. Here we provide a systematic review on the occurrence of P. nobilis, employing and combining different sources of information, such as scientific and grey literature, NATURA 2000 geodata and citizen science records. The methodological approach is a pilot test based on a scaling down of the geographical area of study, from the whole of the Mediterranean Sea to the Italian and Apulian coastline (South-East Italy); accordingly, the above mentioned sources of data have been gradually included. The results show that the combination of multiple sources of information provide a more exact determination of the species distribution at a local scale, identifying sites where in-depth actions are required to ensure the species conservation and restoration. Also, the IUCN has recently underlined that the conservation of P. nobilis has become a difficult challenge, so that each of the spatial scales for the investigation is crucial to enable a better preservation and conservation of the species in the Mediterranean Sea.
