Marine botanical research at Helgoland systematically took place since 1892 with a focus on taxonomy, life cycle studies, seasonality and relative distribution of species. Thus we have a good qualitative knowledge about macroalgal taxa present but very few quantitative data about abundance, density or biomass of species/communities in space and time from the last century. The best form of qualitative data is inherited in the reference herbarium located at Helgoland and comprising approx. 7000 herbarium sheets and approx 5000 permanent slides the latter being in a state urgently to be restored. There are 274 macroalgal species recorded for Helgoland; approx. 45% of total species and 60% of total genera are found in the herbarium. At the moment a database is build up and will be searchable via a GBIF portal (prototype version: http://ww2.biocase.org/abcdSimple/default.jsp).Considerable habitat change, eutrophication, invaders and probably also temperature change contributed to the change in species diversity at Helgoland. After 1959 seventeen species, mostly with heteromorphic life cylcles (spring to summer annuals), became seldom or were not re-collected. The perennial flora was rather stabile over the last 100 years, but 4 species are definitely lost. Four neophytes arrived (Codium fragile, Bonnemaisonia hamifera, Mastocarpus stellatus, Sargassum muticum) and some species showed discontinuous occurrence (e.g. Dictyota dichotoma, Leathesia difformis).Recent investigations of the intertidal macroalgal flora since 1999 provide approx. 2000 georeferenced point data with qualtitative (presence, absence) and quantitative cover values as well as a spatial georeferenced biotope map and a community map derived from hyperspectral remote sensing flights generating a baseline for future investigations.