The data were accumulated during seasonal long-term (1999-2011) monitoring of infection of Littorina spp. and Hydrobia spp. snails with intramolluscan stages of 16 trematode species in intertidal sites in the Chupa Inlet of the White Sea. Singular Spectrum Analysis used in the study allowed identification of the trends in the long-term dynamics of prevalence of trematode parthenitae and larvae in the snails. These trends were mostly determined by the long-term dynamics of abundance of the final hosts (birds and fish of the coastal complex). The prevalence trends turned out to be connected with both the large-scale events (in the Chupa Inlet) and the local factors at the scale of the intertidal site. In addition, the long-term dynamics of trematode prevalence in intertidal snails was closely associated with the life cycle type (one-, two- or three-host). It was suggested that the main factors determining the long-term dynamics of the component communities of trematodes associated with intertidal snails in the