The last fortress fell: mass mortality of Pinna nobilis in the Sea of Marmara

Abstract

A spring 2021 cruise to the south Marmara Islands revealed a mass mortality event of Pinna nobilis, which had been reported to be healthy just seven months ago. The cause of death might be associated with an epidemic disease or a catastrophic mucilage event seen after November 2020 in the Sea of Marmara. A total of 191 Pinna nobilis individuals were found at seven stations, of which 88% were dead. The population density (including dead and alive individuals) of P. nobilis was found to be between 0.3 ind.100 m-2 and 12 ind.100 m-2 in the area. A total of three live and four dead juvenile individuals were observed in the area, indicating low recent recruitment. The largest number of dead Pinna nobilis individuals was encountered in shallow waters (0-4 m depth). A total of 34 species, belonging to six taxonomic groups (Sipuncula, Oligochaeta, Polychaeta, Crustacea, Mollusca and Pisces), were found within the dead shells of four P. nobilis individuals. The mass mortality of Pinna nobilis in the Sea of Marmara, the last remaining disease-free sea, indicates the necessity of establishing and implementing emergency action plans for this species, including ex-situ conservation.