Bivalve vulnerability is enhanced by parasites through the deficit of metallothionein synthesis:: A field monitoring on cockles (Cerastoderma edule)

The effect of the parasite Labratrema minimus (digenean trematode) on metallothionein (MTs) biosynthesis by the cockle Cerastoderma edule (bivalve) was investigated. An in situ monitoring allowed to describe and compare monthly variations of MTs concentrations in cockles with and without L. minimus in a site free of metal pollution (Banc d'Arguin, Arcachon Bay, France). These concentrations are correlated with the reproductive cycle of the bivalve: (1) in spent cockles, MTs concentrations are higher in infected cockles, probably due to host tissue lysis; (2) during maturation, MTs biosynthesis increases in all cockles. However, concentrations are lower in parasitized individuals in relation with castration by parasites. Therefore, parasite infection in cockles, which can affect 100% of individuals, may contribute to a higher vulnerability of organisms to metal contamination.