The fan mussel Pinna nobilis, is the largest endemic bivalve in the Mediterranean Sea, which has been worryingly impacted by a mass mortality over hundreds of kilometers of coast in the Western Mediterranean Sea. A haplosporidian parasite has been reported as the likely cause of the fan mussel mass mortality.

This study provides morphological and molecular characterization of a new species, Haplosporidium pinnae, very likely responsible for the mass mortality of P. nobilis in the Western Mediterranean Sea. This parasite was found in dead or moribund P. nobilis but did not occur in healthy fan mussels from locations that were not affected by the abnormal mortality.

The authors suggest that the scarce variability of the small subunit ribosomal DNA sequence of H. pinnae could suggest a recent arrival of this parasite in the Spanish Mediterranean coast, which would be consistent with the unprecedented recent mass mortality. However, it is stated that it is unknown how the parasite is transported, but, according to the spatial and temporal mortality data of P. nobilis observed along the Southern coasts of Spain, the outbreak spread following the direction of the summer marine currents.

It is concluded that, being the parasite now identified, a thorough study of epizootic dynamics and the complete life cycle of H. pinnae is needed to find ways to mitigate disease and limit spread of the pathogen, and to reverse the critically endangered status of P. nobilis in the Spanish Mediterranean coast.

Catanese G et al. (2018) Haplosporidium pinnae sp. nov., a haplosporidian parasite associated with mass mortalities of the fan mussel, Pinna nobilis, in the Western Mediterranean Sea. Journal of Invertebrate Pathology 157:9-24.