Fouling of gastropods: a role for parasites?

A sample of mud snails Hydrobia ulvae (Prosobranchia) from an intertidal po pulation revealed that the shells of trematode-infected specimens were espe cially likely to be fouled with epibionts. Experimentally trematode-infecte d Biomphalaria glabrata (Pulmonata) appeared to be especially prone to deve lop epigrowth in comparison with uninfected conspecifics as well. These fin dings suggest an interaction between trematode infections and epibiosis in aquatic gastropods. The two most likely explanations for this are (1) that trematode infections weakens the snails' natural defences against epibionts , or (2) that the defences against epibionts also are effective against inv ading trematodes, causing snail specimens with a particularly good fouling defence to be less likely to become infected.