Fucus specimens were collected at the island of Sylt (List, Germany) during low tide in April 2013. Each replicate consisted of four Fucus vesiculosus apical thallus parts comprising 4-6 tips; at the start of the experiment only a few tips per replicate were visually reproductive. The presented data are the increase of conceptacles per one randomly chosen receptacle per individual (= 4 receptacles per replicate) over a time period of 35 days. For details see material and methods in Graiff et al. 2017 (doi:10.1515/bot-2016-0081).