The Hawaiian Islands are located 3700 km from the nearest continental land mass and as such provide an interesting research opportunity to study freshwater organisms intolerant of seawater. The freshwater biota have been only partially studied with little research on the stream macroalgae. The only previous study to focus solely on stream macroalgae, reported 25 new species to the Hawaiian Islands from 34 stream segments sampled. The purpose of our study was to expand the sampling of streams to better determine macroalgal distributions and species richness. Twenty-three additional stream segments (7 on Oahu, 8 on Kauai and 8 on Hawaii) were sampled for macroalgae. The physical and chemical parameters of each stream were measured. Stream segments ranged greatly in size from 1.2 m to 40 m in width. Water temperature was relatively uniform (ca. 21°C) but other chemical parameters differed from site to site (pH 5.5-8.9, specific conductance 20-200mS/cm). Mean species richness per stream segment was 3.9 with one to eight species collected per segment. Ninety populations of 44 infrageneric taxa were identified from the Cyanobacteria (20), Chlorophyta (18), Rhodophyta (3) and Chrysophyta (3). The most abundant taxa were Spirogyra sp. 2, Audouinella pygmaea and Phormidium retzii. All three of these species are cosmopolitan. Twenty-two of the taxa are new records for streams in the Hawaiian Islands. The large percentage (50%) of new taxa suggests that more research is needed to fully catalog the Hawaiian stream macroalgal diversity.

Key words: Hawaiian Islands, macroalgae, survey