Variability and distribution of parasites, pathologies and their effect on wild mussels (Mytilus sp) in different environments along a wide latitudinal span in the Northern Atlantic and Arctic Oceans.

Histopathological examination in mussels can provide useful information for the diagnosis of ecosystem health status. The distribution of parasites in mussels can be conditioned by several environmental factors, including mussels collecting sites or the presence/absence of other species necessary to complete the complex life cycle of certain parasites. Thus, these variables could not only govern the parasitic burden of mussels but also the presence of pathologies associated to parasitism. The aim of this study was to identify the histopathological alterations which could be indicative of a health status distress along a wide latitudinal span in the Northern Atlantic and Arctic Oceans in mussels of two size-classes sampled in clean and impacted sites. A latitudinal gradient is clearly observed in gamete developmental stages as northern and southern mussels presented different conditions at the same period. Furthermore, mussels of the same size in different latitudes presented differences in the reproductive cycle and the appearance of related pathologies, which probably meant the age of individuals was different. In addition, specific parasitic profiles ruled by latitudinal conditions and the settlement of mussels in the shore (horizontal/vertical) have been demonstrated to be significantly influential in the health condition of mussels. Furthermore, the present work provides the first histological description of Gymnophallus cf. bursicola parasite causing a considerable host response in Tromsø and Iceland plus the report of grave histopathological status that included high prevalence of granulocytomas in Scotland and Germany.