Biotic and abiotic drivers affect parasite richness, prevalence and abundance in Mytilus galloprovincialis along the Northern Adriatic Sea

Although it is generally known that a combination of abiotic and biotic drivers shapes the distribution and abundance of parasites, our understanding of the interplay of these factors remains to be assessed for most marine host species. The present field survey investigated spatial patterns of richness, prevalence and abundance of parasites in Mytilus galloprovincialis along the coast of the northern Adriatic Sea. Herein, the relationships between biotic (host size, density and local parasite richness of mussel population) and abiotic (eutrophication and salinity) drivers and parasite richness of mussel individuals, prevalence and abundance were analysed. Local parasite richness was the most relevant factor driving parasite species richness in mussel individuals. Prevalence was mainly driven by eutrophication levels in 3 out of 4 parasite species analysed. Similarly, abundance was driven mainly by eutrophication in two parasite species. Mussel size, density and salinity had only minor contributions to the best fitting models. This study highlights that the influence of abiotic and biotic drivers on parasite infections in mussels can be differentially conveyed, depending on the infection measure applied, i.e., parasite richness, prevalence or abundance. Furthermore, it stresses the importance of eutrophication as a major factor influencing parasite prevalence and abundance in mussels in the Adriatic Sea.