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

Abstract

A population of Littorina littorea on the north shore of Southampton Water, UK, has been examined for the occurrence of epifauna. Epifaunal cover was not affected by shore level below MTL but was greatest on larger shells, which were commoner on the lower shore close to MLWS. Epifaunal components included barnacles, serpulids. and bryozoans. The polychaete Polydora ciliata occurred most frequently on the lower shore where it excavates galleries in periwinkle shells. Heaviest infestations were found in larger shells. R. ciliata settles preferentially in or beside irregularities on the shell surface. Settlement of barnacles close to the shell aperture, where new shell growth takes place, produces shell distortion which creates sites for settlement of P. ciliata. The angle between serpulid tubes and the shell surface also attracts R ciliata. It is suggested that colonisation by barnacles and serpulids facilitates settlement by R. ciliata, and that the latter decreases survival of the host by progressively destroying the shell.