Mass Mortality Events and Threats

Since 2016, a destructive and geographically widespread mass mortality event has been affecting Pinna populations across the Mediterranean basin. Prior to the outbreak, the species was widespread and locally abundant in some areas. The mortality events were triggered by a pathogen called Haplosporidium pinnae, a virus-like protozoan, and the associated deaths rapidly spread within less than three years from the western Mediterranean (starting in Spain) to the Eastern Mediterranean. Subsequent studies also reported that Mycobacterium and Vibriosis species contributed to the mortality events.

Currently, mortality rates across most of the Mediterranean, including areas with long-term Pinna monitoring programs, have reached 80-100%. There are only a few populations known to be free of the pathogen, and these are located in geographically isolated areas characterized by very specific environmental conditions.

The Sea of Marmara is home to the last remaining living and high-density individuals of Pinna nobilis in the Mediterranean.

The presence of the pathogen is extremely concerning, as it affects both juveniles and adults, hindering potential population recovery. Initially, threats were mostly local, such as illegal fishing, habitat loss, boat anchoring, and invasive species. However, more recently, climate change has been largely blamed for the spread of the pathogen and mass mortality events. Over the past decade, population sizes have declined by more than 80%.

While climate change is the trigger for mass mortality, numerous deliberate or accidental human activities continue to threaten Pinna stocks. Researchers attribute the deaths of live stocks in the Sea of Marmara largely to human activities.

Due to mass mortality events and the drastic decline in population size, the species has been assessed as Critically Endangered by the International Union for Conservation of Nature (IUCN).