MEPS 579:227-231 (2017)  -  DOI: https://doi.org/10.3354/meps12277

ABSTRACT: The common periwinkle Littorina littorea is recognized as a keystone species in coastal habitats of the North Atlantic, and hence, interactions among factors influencing these snails’ population dynamics are of ecological interest. Here, I address the relationship between 2 regulating forces, parasitism and epibiosis, in a Danish population of periwinkles serving as host to trematode parasites (Himasthla elongata and Renicola roscovita) as well as substrate for encrusting fucoids (Ralfsia sp.). Results show a strong positive relationship between shell size (i.e. snail age) and epibiont coverage, but also a significant positive link between parasitism and epibiosis after statistical correction for shell size. Because epibiosis of periwinkles is controlled solely by mutual shell grazing, the relationship between parasitism and epigrowth likely stems from reduced grazing of infected snails’ shells by conspecifics that are known to avoid parasitized individuals. Trematode parasitism may thus indirectly facilitate the community of epibionts and in turn reinforce fouling as a regulator of periwinkle populations.

KEY WORDS: Littorina littorea · Trematode infection · Fouling · Epiphyte · Facilitation