The development of hard bottom communities has been studied on test panels in Helgoland Harbour (German Bight) since 1977. Settlement and growth of epibenthic species was examined monthly. Natural variation in different seasons, years, and at three stations (the latter, only in 1981 and 1982) was investigated. At Station A (Binnenhafen), barnacles (Balanus crenatus ) and polychaetes (Polydora ciliata ) were always among the first settlers in spring. They were followed by other barnacles (Elminius modestus, Balanus improvisus ) and by colonical ascidians (Botryllus schlosseri ). The latter species often dominated from August to October, and tended to overgrow the barnacle populations.