Factors influencing trematode parasite burdens in mussels (Mytilus spp) from the north Atlantic ocean across to the north Pacific

The level and incidence of infection of blue mussels (Mytilus spp) by the trematode parasites Himasthla, Renicola and Gymnophallus were studied at 22 sites from north Atlantic waters (Ireland, Iceland, Norway) and across the Arctic Ocean to the Sea of Ohktosk in the north Pacific. Only at one site (Pechora Sea) were no parasites at all recorded. Infestation levels ranged up to 100% of individuals sampled.Data were analysed with the PRIMER-E package BEST routine. The analysis indicated a considerable influence of geographic location, with closely-connected sites also grouped together on the basis of their parasite communities. The BEST routine suggested that the major influence on infestation was bird (final host) numbers, but that exposure was also a strong factor. The implications of these findings in relation to human exploitation of mussels, to bird conservation, and to the provision of ecosystem goods and services in general is discussed.