Abstract: We conducted a survey to study the diversity index and seasonal fluctuation of benthic algal community in the intertidal zones of Gouqi island of Zhejiang Province in 2011. Results showed that 65 species were identified belonging to 4 phylums， among which 42 species belong to Rhodophyta， 11 species belong to Phaeophyta， 11 species belong to Chlorophyta， and 1 species belongs to Cyanophyta. The seasonal alternation of benthic algae species was obvious that spring had the largest number， followed by winter， then autumn， and summer had the least. The seasonal variation of biomass of the community declined as spring> autumn >summer>winter. Dominant species of algal community in Gouqi island were Sargassum horneri， Corallina sessilis， Sargassum thunbergii， Scytosiphon lomentarius， Ulva pertusa， Undaria pinnatifida， Chondria crassicaulis， Gelidium divaricatum and Sargassum fusiforme. The seasonal variation of the index of diversity can be described as spring > autumn > summer > winter. The results suggested that the community structure of benthic macro-algae in Gouqi island is relatively stable.

Key words: Gouqi island, benthic macro-algae, biomass, dominant species, seasonal variation, diversity index