How thermal tolerance is inherited is still largely unknown in kelps and macroalgae. We investigated the thermal tolerance of juvenile Laminaria digitata sporophytes in the light of geographic origin of their female and male gametophyte parents. For this, we used unilinear gametophyte cultures isolated from Helgoland and Spitsbergen L. digitata, which are expected to differ slightly in their thermal characteristics. The first objective of this study was to identify potential genetically fixed differences in physiological and regulatory response to heat among sporophytes obtained from Helgoland and Spitsbergen gametophyte cultures. In a second step, we investigated potential effects of introgression of geographically distant genetic material on the regulation of metabolic pathways of reciprocal outcrosses among Helgoland and Spitsbergen populations.