The Predation of Pinna nobilis (Mollusca) Juveniles by the Spiny Sea Star Marthasterias glacialis (Echinodermata) in the Sea of Marmara

Abstract

The critically endangered bivalve species, the pen shell Pinna nobilis, has been suffering from an epidemic disease in the Mediterranean Sea, and its populations have totally disappeared in many areas across the basin. The Sea of Marmara’s populations of the pen shell, which were previously assumed to have remained unaffected by the epidemic disease because of the special hydrographical condition of the sea (brackish water), have been devastated after the catastrophic mucilage event suddenly outburst in November 2020 in the region. The settlement of healthy juvenile specimens of the species was frequently observed in the area after the mucilage event. However, an unexpected predator of juvenile specimens of the pen shell, the spiny sea star Marthasterias glacialis, was encountered in the area in January 2023. Two cases were observed and the spiny sea star has a capability of crashing one valve of the sea-pen through which it consumes its flesh. This predation might have the potential to affect populations of P. nobilis, which has been struggling to survive in the region after its mass mortality due to the mucilage event. Such data are of utmost importance to imply effective conservation planning for the sustainability of the remaining populations of the pen shell in the region.