Main conclusion: Tight regulation of intra-thallus metabolite distribution in Fucus vesiculosus in late summer reveals the complex biochemical processes complying with reproduction and the preparation to the dark season. We used inductively coupled plasma atomic emission spectroscopy to study the tissue-specific elemental composition, and gas chromatography coupled to mass spectrometry to study the distribution of small-molecular weight primary and secondary metabolites of the brown alga Fucus vesiculosus thalli in the reproductive phase. Beyond general physiological requirements, the observed distribution of the analysed nutrients was also found to depend on characteristics related to the season of harvesting, i.e., the reproductive period. However, a particular curious result was the high metabolic activity found in the stipe of the plant. In conclusion, our data not only provide valuable information for industrial use of fucoids targeting specific algal ingredients, but also give highly interesting insights in the multifaceted system of intra-thallus biochemical interactions during reproduction of the brown algae.