The Infestation Of Mytilus Edulis Linnaeus By Polydora Ciliata (Johnston) In The Conwy Estuary, North Wales

Abstract

The incidence of the shell-boring parasite Polydora ciliata in Mytilus edulis from the Conwy estuary, North Wales is described. Amongst mussels >40 mm in shell length both the occurrence and abundance of P. ciliate increased steeply with host size. Infestation was highest amongst mussels near the mouth of the estuary where around 60–65% of the population was parasitized; no systematic relationship between the incidence of P. ciliata and tidal elevation was observed. Mussel condition was negatively correlated with the degree of infestation. Moderately and heavily infested mussels, however, never accounted for more than ca. 10% of this population and the overall detrimental effects of P. ciliata on growth and production is thus probably quite small. Whilst heavily infested mussels were evidently more vulnerable to predation, the shore crab, Carcinus maenas, selected smaller, non-infested mussels whenever these were available. No obvious relationships were found between the presence of P. ciliata and the incidence of either pearls or pea crabs.