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29 July 2020

Pinna nobilis: species under threat


Pinna nobilis (Pinna) is the largest endemic bivalve in the Mediterranean Sea. Since 2016, its mortality has been affected throughout the Mediterranean because it is threatened by a pathogen, Haplosporidium pinnae (H.pinnae). Losses are now evident in both the Western and Eastern Mediterranean, causing 80-100% mortality rates.

In the past, the major threats to Pinna came from illegal fishing, the loss of marine habitats (Posidonia oceanicae meadows, Cymodocea nodosa), boat moorings, invasive species and, more recently, climate change. However, none of these threats had led to an extremely large but rapid decline in the species population. Currently, the most worrying and widespread threat to Pinna nobilis throughout the Mediterranean is the parasite Haplosporidium pinnae (H.pinnae), which has spread en masse throughout the Mediterranean Sea.

Regarding Greece, the mass mortality of Pinna began to be observed in the summer of 2018. In the areas of the North Aegean, more than 90% of the population has already disappeared, while there are many reports of mass mortality in several areas of Greece. So far there are healthy populations of the species in the northern Dodecanese. It has not been established how the parasite appeared. It is probable that the presence of an alien species transmitted the parasite to the water.

Haplosporidum pinnae. The parasite that threatens the Mediterranean Pinna
The parasite Haplosporidum pinnae reportedly first appeared in 2016 off the coast of Spain. Within a year of the outbreak, Pinna’s population off the Spanish coast dropped dramatically. Haplosporidum pinnae has already wiped out entire Pinnas populations in the western Mediterranean.
Although it has not yet been determined how Haplosporidum pinnae appeared, it is possible that the presence of an alien species may have transmitted the parasite to the water, while it is transported by sea currents.

According to studies that have been carried out and according to the recent Greek researches, the parasite infects the tissues, destroys the cells and creates an extensive inflammation, with the result that the pin can not be fed and dies.

It is a very specialized pest, as it has not been found to infect other species of Pinna, such as Pinna rudis which is a similar species in the Mediterranean. Using genetic and histological data, the researchers concluded that the cause of the mass killing was a protozoan, affecting only Pinna nobilis.

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