Reproduction and Settlement of the Barnacle Semibalanus balanoides (L.) in Galway Bay

The onset and duration of brooding, fecundity, and the timing of larval release and settlement were investigated for the common intertidal barnacle, Semibalanus balanoides (L.), at two sheltered rocky shores (Ballyloughaun and Grattan Road) in Galway Bay over the period 1987-92. Throughout the investigation, brooding began within one or two days of 23 October. A significant correlation between brood number and aperture length was established for barnacles from Ballyloughaun. At Grattan Road in 1989-90, however, the relationship was not significant. Naupliar release began during the period mid-February to mid-March and ended in late March/early April, depending on year and location. Settlement times for the cyprids varied from year to year and was complete by early May. Maximum numbers of cyprids were observed 9-17 days after the beginning of settlement. The pattern observed in Galway Bay is broadly similar to that seen in other European locations but with some differences in timing. The infection rate of brooding S. balanoides by the isopod parasite Hemioniscus balani averaged 7%.