The role of barnacles in the recruitment and subsequent survival of the brown alga, Fucus gardneri (Silva)

Abstract

Barnacles enhance recruitment of fucoid algae by reducing either herbivore pressure or desiccation stress, but no study has evaluated subsequent survival of algae recruiting onto barnacles. This study examined the substratum use patterns of small (< 2 cm), medium (2–10 cm), and large (> 10 cm) Fucus gardneri (Silva) plants in Prince William Sound, Alaska. Germlings were found growing on barnacles in either equal or greater proportions than the abundance of barnacles suggests. Plants large enough to be reproductive, however, were found almost exclusively in crevices or on smooth rock substrata. The effects of tidal level and wave exposure on the habitat use by Fucus were relatively minor compared to the effect of plant size. Fucus plants recruiting onto barnacles suffer higher mortality compared to those on rock. Marked young plants on barnacles had about 20% lower survival compared to similar sized plants growing on rock surfaces over one summer. In addition, the breaking strength of plants growing on rocks was about three times greater compared to plants growing on barnacles. Despite the initial positive effects of barnacles on fucoid recruitment, germlings growing on barnacles have a high probability of dislodgement before reaching reproductive age.