Abstract: Since the foundation of the Biologische Anstalt Helgoland in 1892, the macroalgal flora of Helgoland was intensively investigated. The 100-year-old herbarium, field-notes and published literature generated valuable though discontinuous and qualitative information about the change of the flora and littoral communities. In total, 274 macroalgal species were recorded between 1845 and 2002. Between 1845-1939 and 1959-1998 a shift in species composition was observed. After 1959 seventeen species (mostly spring to summer annuals) were not recorded at all or became very rare, while the records of perennial species were stable. Some species reappeared in the late 1990s after several decades. The spread of invasive or introduced species (Bonnemaisonia hamifera, Codium fragile, Mastocarpus stellatus, Sargassum muticum) around the island was qualitatively observed. Within the framework of GBIF Germany (BMBF; Förderkennzeichen UF-UFLI01097902-01LI0203) the herbarium at Helgoland will be digitised. This will enable a better analysis of hidden data like phenology and local distribution of macroalgae over the past 100 years.As only qualitative data were existent, a mapping survey of the littoral biotopes was initiated in 1999 to generate spatial and quantitative information. Twenty of the 57 eulittoral rocky shore biotopes and 4 of the 26 sub-biotopes classified for Britain and Ireland have been recorded on Helgoland in this baseline study. Only 4 out of the 24 biotopes and sub-biotopes are characterised by the visual dominance of faunal species, the others are macroalgal dominated. Comparison with past descriptions suggests continuing presence of most of the autochthonous biotopes over the past 80 years but also considerable change due to the recent invasion of the macroalgae Mastocarpus stellatus and Sargassum muticum during the past 20 years. One previously recorded cave biotope and a sublittoral seagrass biotope became extinct due to habitat loss, while other biotopes probably have extended their range due to habitat increase.Investigations of the rocky intertidal macrofaunal communities also showed changes in species composition over the past 20 years. Conspicuous differences were ascertained between semi-quantitative surveys in 1984 and 2002. In 2002, twenty-nine species were recorded that had not been observed in 1984 and 46 species of the 1984 study were not recorded any more in 2002. This change was especially obvious in species of hydrozoans, polychaetes, prosobranchs and opisthobranchs. As both studies may just reflect seasonal snap shots, they will be supplemented by regular and quantitative invertebrate sampling of the rocky intertidal in the future.The general lack of quantitative and spatial past information on benthic eulittoral communities for Helgoland only allows a descriptive account of the changes that have taken place, and underlines the need for quantitative research in the future. As part of this, research is undertaken to prove whether airborne methods may partly replace ground mapping in future (cooperation with DLR, Oberpfaffenhofen) and regular transects will be established by the LANU Schleswig-Holstein.