Copulation by the barnacle Tetraclita japonica under natural conditions

Moulting and copulation by the barnacle Tetraclita japonica attached to an intertidal concrete pier were observed continuously with a video camera hou sed in a plastic case in summer 1996 and 1997. In a total of 779 individual -day observations, 10 individuals became sexually receptive as functional f emales and 14 moulted. Copulation occurred not only immediately after, but also before moulting. Duration of receptivity varied from 2 min to nearly 1 2 h, during which functional females accepted between two to 582 penis inse rtions by between one to 11 surrounding males. Each insertion time was shor t, ranging from 0.6 to 42 s, with a median of 2.4 s. Sex role changes were observed between two animals located close to each other, the shortest inte rval for which was 3.3 h. No significant size differences were detected bet ween functional males and females. A temporal pattern of copulation, with a high frequency of penis insertions of short durations, is discussed in rel ation to natural habitat conditions.