The small island of Helgoland with its red sandstone cliffs and wave-eroded foreshore is the only rocky outcrop on the continental side of the southern North Sea and is of considerable conservation importance. Helgoland lies in a biogeographical region of the North Atlantic where canopy-forming fucoids and kelps are principal features. Plant and animal characterised biotopes have been identified using the British and Irish classification, and a recent baseline study recorded 19 intertidal biotopes, 5 biotope variants and one sublittoral fringe biotope. For mapping, the approach had to be broadened to include the often extensive mixtures of biotopes, and successional or seasonal variants. These species assemblages have been largely confirmed by numerical analysis of field data. Comparison of past descriptive accounts of intertidal communities with recent survey data suggests stability of fucoid, laminarian and other biotopes. Change, with implications for local biodiversity and conservation, has occurred through the loss of natural (caves, sea-grass) and the creation of new habitats, and the spread of non-native species. An Ascophyllum nodosum biotope is now present in sheltered harbours while the accidental introduction of Mastocarpus stellatus and invasion of Sargassum muticum has altered foreshore community structure.