Sanctuaries are not inviolable: Haplosporidium pinnae as responsible for the collapse of the Pinna nobilis population in Lake Faro (central Mediterranean).

The rapid spread of the protozoan Haplosporidium pinnae is having a strong negative effect on Pinna nobilis populations. A case study on a residual population in Lake Faro (Sicily, Central Mediterranean), whose long-term monitoring has revealed a dramatic decline following the 2018-2020 mass mortality event, is presented. In the framework of such monitoring, we performed tissue sampling on nine living P. nobilis, detecting the pathogen in seven of them. In contrast, other pathogens associated with P. nobilis disease in other areas, i.e., Mycobacterium spp. and Vibrio mediterranei, were not recorded. The surviving individuals (approximately twenty) showed that brackish areas only weakly mitigate the effects of H. pinnae disease and might not be resolutive. Nevertheless, the results show that Lake Faro may constitute one of the last Mediterranean P. nobilis sanctuaries.