Parasite communities in cockles (Cerastoderma edule) along a latitudinal gradient (North Africa to Scandinavia): pattern and processesX. de Montaudouin, M. Baudrimont, H. Bazairi, M. Cottet, L. Dabouineau, C. Desclaux, M. Gam, P. Gonzalez, K.T. Jensen, F. Jude, M. Krakau, G. Lassalle, N. Raymond, K. Reise, F. Russell-Pinto, D.W. Thieltges, C. PaillardCockles (Cerastoderma edule) are important shellfish resource in the northeast Atlantic shallow water ecosystems. Their population sizes are highly fluctuating between years, so the standing crop in Europe is estimated to vary from 30 to 90 000 mt per year (FAO, 2005). Among factors involved in the population dynamics of cockles, digenean parasites can play an important role. Cockles are infected by free-swimming propagules (miracidia or cercariae larvae) through the bivalve ventilation current. Infection success and kinetics are closely related to host dynamics (especially growth rates) and to environmental parameters (especially temperature). With respect to the wide latitudinal distribution of this bivalve, this parasite/host system is an excellent model for studying role of climatic factors in controlling spread of vector borne pathogenic organisms and for predicting future epizootics in marine organisms as a result of climate change.Cockle dynamics, parasite species richness, parasite infection kinetics and environmental parameters have been surveyed since March 2005, focusing on the same cockle cohort (2005). This monitoring is concomitantly performed in Moulay Bousselham (Morocco), Aveiro (Portugal), Arcachon (France), Saint-Brieuc (France), Sylt (Germany) and Skallingen (Denmark). Comparisons of the different parasite/host systems point out the best parasite strategies and assess the plasticity of these biotic interactions.