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Fifty samples of cyanobacteria were collected and characterized as part of the Hawaiian Freshwater Algal Biodiversity Survey. Fifty-two percent of the samples originated from Oahu, while the remainder were collected from Kauai (14%), Maui (20%) and Hawaii (14%). A diversity of habitats (e.g. streams, wet walls, taro fields, terrestrial areas and ditches) was represented by the collection sites, which is reflective of the abundance of suitable non-marine algal substrata in these isolated, humid, subtropical islands. Most samples were isolated and cultured for observation of morphological features, and all were sequenced for both the Universal Plastid Amplicon (UPA) marker (partial 23S rRNA) and 16S rRNA gene. Alignments of both markers (separately and concatenated) with additional GenBank sequences for phylogenetic representation were analyzed using Maximum Likelihood, Bayesian and Maximum Parsimony approaches. Nodal support was highest for the concatenated UPA+16S rRNA gene alignment, and phylogenetic analyses indicated a monophyletic Nostochophycidae, and monophyly, although with low support, for the Oscillatoriophycidae and Synechococcophycidae. A conservative estimate is that 11 of the taxa are putative endemics to the Hawaiian Islands, further highlighting the uniqueness of this isolated and understudied flora, and the potential for discovery of novel taxa through taxon-focused biodiversity surveys.

BackgroundA remarkable range of environmental conditions is present in the Hawaiian Islands due to their gradients of elevation, rainfall and island age. Despite being well known as a location for the study of evolutionary processes and island biogeography, little is known about the composition of the non-marine algal flora of the archipelago, its degree of endemism, or affinities with other floras. We conducted a biodiversity survey of the non-marine macroalgae of the six largest main Hawaiian Islands using molecular and microscopic assessment techniques. We aimed to evaluate whether endemism or cosmopolitanism better explain freshwater algal distribution patterns, and provide a baseline data set for monitoring future biodiversity changes in the Hawaiian Islands.Results1,786 aquatic and terrestrial habitats and 1,407 distinct collections of non-marine macroalgae were collected from the islands of Kauai, Oahu, Molokai, Maui, Lanai and Hawaii from the years 2009–2014. Targeted habitats included streams, wet walls, high elevation bogs, taro fields, ditches and flumes, lakes/reservoirs, cave walls and terrestrial areas. Sites that lacked freshwater macroalgae were typically terrestrial or wet wall habitats that were sampled for diatoms and other microalgae. Approximately 50% of the identifications were of green algae, with lesser proportions of diatoms, red algae, cyanobacteria, xanthophytes and euglenoids. 898 DNA sequences were generated representing eight different markers, which enabled an assessment of the number of taxonomic entities for genera collected as part of the survey. Forty-four well-characterized taxa were assessed for global distribution patterns. This analysis revealed no clear biogeographic affinities of the flora, with 27.3% characterized as “cosmopolitan”, 11.4% “endemic”, and 61.3% as intermediate.ConclusionsThe Hawaiian freshwater algal biodiversity survey represents the first comprehensive effort to characterize the non-marine algae of a tropical region in the world using both morphological and molecular tools. Survey data were entered in the Hawaiian Freshwater Algal Database, which serves as a digital repository of photographs and micrographs, georeferenced localities and DNA sequence data. These analyses yielded an updated checklist of the non-marine macroalgae of the Hawaiian Islands, and revealed varied biogeographic affinities of the flora that are likely a product of both natural and anthropogenic dispersal.