Spatio-temporal variation in the prevalence of trematodes in the bivalve Perumytilus purpuratus

Perumytilus purpuratus is an abundant bivalve located in the intertidal rocky zone of South America that has been considered as a key species of the ecosystem. There are few studies of the host-parasite relationship of this bivalve; thus, this research aims to analyse the spatial and temporal variation in the prevalence of trematodes in P. purpuratus. Bivalves were collected from three localities (El Tabo, Las Cruces and Montemar) of central Chile (33A degrees S, 71A degrees W) during different seasons of 2010. The bivalves were also collected every metre, from the lowest to the highest level of the intertidal rocky zone, to determine the parasite distribution within the localities. Three species of trematodes as sporocyst stages were found: Prosorhynchoides carvajali, Proctoeces sp. and an undetermined fellodistomid species. Of the 37,692 bivalve specimens collected, 2.68% were parasitised. The undetermined fellodistomid species was the most prevalent parasite observed (1.69%). There were little detected differences in the prevalence of some trematode species between seasons. The prevalence of P. carvajali varied between localities, being most prevalent at Montemar. The distribution of trematodes along the rocky zone within the localities was variable, with P. carvajali being more prevalent in the mid-lowest level of the intertidal zone and the undetermined fellodistomid species being more prevalent in the mid-highest level. Both the abundance of definitive hosts and the environmental conditions likely result in different levels of infection by trematodes in P. purpuratus between and within the localities.