Inventory of the distribution of Haplosporidium pinnae, a parasite of Pinna nobilis, in other molluscs along the rocky coast of the Albères and in the Salses-Leucate pond

In March 2020, the French Office for Biodiversity and the Gulf of Lion Marine Natural Park launched a call for projects on 4 themes, including naturalist inventories, data acquisition on coastal and marine biodiversity issues. The project proposed by MarePolis and CRIOBE was one of the winners. Since 2016, the populations of the large mother-of-pearl, Pinna nobilis, in the western Mediterranean have experienced massive mortalities and those in Languedoc-Roussillon have not been spared. This outbreak is caused by the parasitic protozoan species Haplosporidium pinnae. Initial aquarium experiments have shown that, even in the absence of natural populations of P. nobilis on the Albera coast, the parasite remains present and active if P. nobilis is transplanted. It is therefore likely that another species of mollusk acts as a “healthy” carrier. The objective of the project was therefore to test the presence of H. pinnae in bivalve species colonizing the same habitats as P. nobilis in order to determine if any of them were likely to serve as a reservoir for the parasite and maintain it in the environment. To do this, 15 species of bivalves were collected from various sites in the Gulf of Lion Marine Natural Park. The presence of H. pinnae in the latter was investigated by amplification and sequencing of specific DNA. The results showed that none of the 15 species carried H. pinnae. On the other hand, they were carriers of the Minchinia tapetis parasite, but the latter is not involved in the epidemic that P. nobilis is experiencing. It is therefore necessary to continue research on H. pinnae in order to identify which other mechanisms (e.g. other types of organisms, dormant forms of the parasite in sediments or the water column) may be responsible for the maintenance of this parasite in the environment.