Since autumn of 2016, the cryptogenic parasite Haplosporidium pinnae has caused an unprecedented mass mortality event of the protected endemic Mediterranean bivalve Pinna nobilis in the western Mediterranean Sea.

This study confirms the spread of the parasite in the eastern Mediterranean and provides the direct evidence on the collapse of the P. nobilis populations in the coastal waters of Lesvos Island (Aegean Sea, Greece). The presence of the parasite was confirmed through histopathological and molecular methods.

While the infection caused >93% of mortality in most sites, the authors highlight that in a single site (among 13 surveyed sites) mortality was relatively low and the parasite was not detected. It is underpinned that this observation stresses the importance of possible parasite-free refugia sites.

In front of the worrying spread of this infection, the authors call for continuous monitoring of the spread of the parasite and its impacts, and for urgent targeted research and actions to identify the factors affecting the parasite’s virulence, investigate biotic and abiotic conditions that characterize refugia sites, and strictly protect the remaining P. nobilis populations to increase the chance for the survival of the species.

Katsanevakis et al. (2019) The cryptogenic parasite Haplosporidium pinnae invades the Aegean Sea and causes the collapse of Pinna nobilis populations. Aquatic Invasions 14.