Timing of successful settlement: demonstration of a recruitment window in the barnacle Semibalanus balanoides

Recruitment is a key factor in benthic population dynamics, and spatial and temporal processes that affect settlement may determine recruitment; however, temporal processes are not well understood. We tested whether the date that recruits settle is a random sample within the settlement season by measuring daily settlement of the barnacle Semibalanus balanoides throughout the entire settlement season. A total of 2721 barnacle larvae settled during 89 d on 12 quadrats. Individual settlers were tracked to reproductive age (11 mo after settlement); only 8 survived to reproduction. Survivors settled within a narrow 21 d recruitment window, a period shorter than expected by chance. The concept of a recruitment window has broad implications in studying benthic recruitment and population dynamics. Focus on the recruitment window when it is narrow could simplify the study of recruitment, since fewer factors would have to be considered.