Recent morphological and genetic studies show that Fucus radicans is a separate species from the sympatric F. vesiculosus. Fucus radicans recently diverged from F. vesiculosus in the Baltic Sea where populations grow in mixed stands. Thus, strong reproductive barriers are expected to be in place to prevent introgression. The seasonal timing of reproduction of the two species in Estonia was shown to be different, likely forming an effective pre-zygotic reproductive barrier. In Sweden, however, no such temporal difference was found. We artificially crossed Swedish F. radicans and F. vesiculosus to identify other potential reproductive barriers. Fertilization success and survival was equally high within and between species in the artificial crossings, suggesting no early post-zygote barriers. Both species recruit new thalli both sexually and asexually, but F. radicans is generally more asexual than F. vesiculosus. By studying their reproductive efforts we found that Swedish F. radicans allocates more resources to adventitious branches than to gamete production compared to F. radicans in Estonia and F. vesiculosus in both Sweden and Estonia. This indicates that Swedish F. radicans has an asexual reproductive strategy while Estonian F. radicans and F. vesiculosus have sexual reproductive strategies.