A Marteilia parasite and digestive epithelial virosis lesions observed during a common edible cockle Cerastoderma edule mortality event in the Spanish Mediterranean coast

The presence of a Marteilia parasite, potentially M. refringens, was observed by histology and by 18S rDNA Marteilia genus specific in situ hybridisation on common edible cockles Cerastoderma edule growing at the Ebro Delta bays during a mortality event in 2008. Marteilia parasites, such as M. refringens, are marine invertebrate pathogens affecting commercial bivalve species such as the flat oyster Ostrea edulis and the mussels Mytilus edulis and M. galloprovincialis. However, occasionally, Marteilia parasites including M. refringens, have also been observed in other commercial bivalve species such as Chamalea gallina, Solen Marginatus and C. edule among others. In the case of the cockle C. edule, a single notification of the presence of Marteilia sp., in 1975, based on histological and ultrastructural studies, has been reported up to date. Parasite prevalence observed in the present study was not negligible (40%) and was potentially associated to the cockle mortality event. Parasite infection intensity was high and moderate, and, in general, developmental stages observed reminded M. refringens infecting flat oysters and mussels. Furthermore, lesions, similar to those produced by digestive epithelial virosis, were observed by first time in cockles. The viral lesions were observed in all the examined specimens in moderate and high intensity. The in situ hybridisation assay for detection of Marteilia sp. using an 18S rDNA probe (SMART2) showed the affinity of the cockle parasite to the Marteilia genus probe. This is the first report of a Marteilia parasite in cockles in Spain and the second report in the world. The potential impact, of both observed pathogens, on the cockle industry and shellfish aquaculture needs to be urgently addressed.

► The cause of a cockle C. edule mortality event in Spain was studied.
► It was observed an important prevalence (40%) of a Marteilia parasite.
► Digestive epithelial virosis lesions were also observed, by first time, in cockles.
► This is the first report of Marteilia in cockles in Spain and the second elsewhere.
► The impact of these pathogens on shellfish industry needs urgently to be addressed.