Both abiotic and biotic factors, such as desiccation and competition, respectively, impact the spatial distribution of marine intertidal organisms. In order to deal with these variable factors intertidal species have developed adaptations to live in a specific part of the shore and their distribution can change over relatively small scale (e.g. five meters). But sometimes intertidal organisms, such as marine snails, see their behaviour and physiology disrupted by trematode parasites. These changes induced in marine gastropods usually benefit the parasites at the expense of the host. Here, we investigated four rocky shores of Galway Bay, experiencing different levels of trematode parasite infection prevalence. We wanted to examine if Littorina saxatilis, Littorina obtusata and Nucella lapillus had an altered distribution, physiology and behaviour due to trematode infection. We observed that highly infected snails had a specific spatial distribution and they were more inclined to have a reduced reproduction capacity. This study provides a recent insight of the possible effect of trematode infection in intertidal marine gastropods. It also underlines the importance of parasitism in controlling marine snail populations and thus, shaping the intertidal ecosystems.
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