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The rocky intertidal biotopes of Helgoland: present and past

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Abstract: Nineteen of the 57 littoral rocky shore biotopes and 4 of the 26 variants as well as 1 sublittoral fringe biotope classified for Britain and Ireland have been recorded on Helgoland in this baseline study. Most of the wave-cut platform is at sublittoral and lower littoral levels and most high eulittoral biotopes are confined to narrow zones on seawalls. Large areas of gently sloping lower eulittoral and also boulder areas adjacent to seawalls are characterised by a mixture of two or more biotopes. Only 4 of the 23 littoral biotopes and variants are characterised by faunal species. Comparison with past descriptions of intertidal communities suggests continuing presence of most of the autochthonous biotopes over the past 80 years but also change due to the invasion of the macroalgae Mastocarpus stellatus and Sargassum muticum over the past 20 years. One previously recorded cave biotope and a sublittoral seagrass site have become extinct due to habitat loss while other biotopes probably have extended their range due to habitat increase. The presence of 4 intertidal biotopes (20%) considered rare or scarce in Britain supports the recognition of Helgoland as a site of special conservation in a regional and international context.

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