Occurrence of epifaunshers on the periwinkle,Littorina littorea (L.), and interactions with the the polychaete Polydora ciliata (Johnston)

A population of Littorina littorea on the northshore of Southampton Water, UK, has been examined forthe occurrence of epifauna. Epifaunal cover was notaffected by shore level below MTL but was greatest onlarger shells, which were commoner on the lower shoreclose to MLWS. Epifaunal components includedbarnacles, serpulids and bryozoans. The polychaetePolydora ciliata occurred most frequently on thelower shore where it excavates galleries in periwinkleshells. Heaviest infestations were found in largershells. P. ciliata settles preferentially in orbeside irregularities on the shell surface. Settlementof barnacles close to the shell aperture, where newshell growth takes place, produces shell distortionwhich creates sites for settlement of P. ciliata. Theangle between serpulid tubes and theshell surface also attracts P. ciliata. It issuggested that colonisation by barnacles and serpulidsfacilitates settlement by P. ciliata, and thatthe latter decreases survival of the host byprogressively destroying the shell.