Interactions between canopy forming algae in the eulittoral zone of sheltered rocky shores on the Isle of Man

The distribution and abundance of Ascophyllum nodosum, Fucus serratus and F: vesiculosus were described at four sheltered, rocky shores in the south of the Isle of Man. Canopy removal experiments were performed at mid tide level of one sheltered, canopy dominated shore to investigate the interactions between the dominant canopy alga, Ascophyllum nodosum and the competitively inferior canopy species of Fucus serratus and F. vesiculosus. Ascophyllum was removed from replicated plots, 2x2m in size, in both winter and summer; the early growth and survival of fucoids in the presence and absence of the Ascophyllum canopy were monitored and the eventual development of a new canopy described. Juveniles of F. serratus originally present beneath the undisturbed canopy of Ascophyllum died following canopy removal but new recruitment resulted in some canopy development, principally in the winter experiment. Fucus vesiculosus, despite being completely excluded from the Ascophyllum zone of all four shores described, dominated the canopy removal plots of both winter and summer experiments. The Ascophyllum canopy did not recover over a five year period of observation, although a considerable increase in the abundance of Ascophyllum juveniles occurred.