Distribution of Fan Mussel (Pinna Nobilis) Population in the Sea of Marmara

Abstract

The fan mussel (Pinna nobilis Linnaeus, 1758), a species severely affected by mass mortality events caused by Haplosporidium pinnae since 2016 throughout the Mediterranean Sea, continues to survive in isolated areas. The Sea of Marmara (SoM) represents one of the largest areas where alive fan mussels persist in high density. This study addresses critical data gaps by investigating the spatial distribution patterns and ecological characteristics of fan mussels in the SoM, providing a foundation for long-term monitoring and conservation initiatives. The dataset was generated through underwater surveys conducted between June and September 2024, covering approximately 35,000 m(2) across 144 stations along 1300 km of coastline in the entire SoM. Using non-destructive observational methods, 4748 fan mussels were recorded, 90.5% of which were alive. Spatial distribution patterns revealed distinct clustering, with an average density of 12.1 ind/100 m(2) and a maximum density of 122.1 ind/100 m(2) in specific hotspot areas. A strong association with seagrass habitats was evident, with 84.4% of the population found in these areas. The population structure was predominantly adult, with similar to 70% of individuals exceeding 10 cm in shell length, while recruits smaller than 10 cm represented 9.2%. The findings highlight the high density, low mortality rate and strong recruitment capacity of fan mussel populations in the SoM. This study provides the first comprehensive underwater observation-based mapping of fan mussel populations across the entire SoM and identifies new areas critical to their conservation.