Pathogen surveillance of Haplosporidium pinnae by eDNA monitoring: a non-invasive approach to manage Pinna nobilis

Pinna nobilis is a species classified as “critically endangered” by the IUCN Red list of Threatened Species, it is necessary to periodically conduct monitoring campaigns to evaluate the state of the populations and the possible presence of new individuals. The main cause of the mass die-off that hit Pinna nobilis, is a protozoan, called Haplosporidium pinnae, that is part of the order Haplosporida, an order which includes other species previously responsible for deaths of bivalve molluscs. This outbreak began in Spain in 2016 and then spread to the entire Mediterranean Sea in a rather short period of time, reaching the upper Adriatic in 2019. Identify this pathogen is difficult because the affected organism dies within a short time and symptoms are only detectable once the infection is advanced. However, it is important to monitor the annual periods of presence to understand which environmental factors its presence may be linked to. To identify this pathogen, it is necessary to use non-invasive techniques to avoid causing further stress to living organisms. The technique that allows this consists in the analysis and extraction of environmental DNA. By sampling the organism's faeces, it is possible to detect the presence of the pathogen, after extracting the DNA from the sample, using specific primers and by subjecting the samples to real time PCR. The study included seasonal monitoring campaigns and the collection of faecal and tissue samples from live and deceased individuals at several locations in the Gulf of Trieste, including Grado lagoon and Miramare Marine Protected Area. The results showed the presence of H. pinnae mainly in the summer months (July and August 2024) and suggested a correlation with seasonal variations in water temperature. Furthermore, the activities highlighted the fragility of the remaining populations and the urgency of preventive actions, given the limited recovery capacity of the species.