Watershed-Scale Comparisons of Algal Biodiversity in High-Quality Proximate Hawaiian Stream Ecosystems!

The stream macroalgal floras of two proximate, high-quality stream valleys (Hanakapl'ai and Limahuli) located on the northern quadrant of the Hawaiian island of Kaua'i were inventoried and compared on a watershed scale, providing interesting insight into Hawai'i's potential taxonomic diversity and the influential role played by physical factors in shaping community characteristics. A total of 26 species of macroalgae (five Cyanophyta, 18 Chlorophyta, one Rhodophyta, and two Chromophyta) was identified, of which only eight were common to both streams. Chlorophyta composed the majority of macroalgal taxa identified (63.2% in Hanakapl'ai Stream and 66.7% in Limahuli Stream). Three macroalgal species are new records for Hawai'i and one (Chamaesiphon curvatus var. elongatum Nordst.) is a Hawaiian endemic. Significant differences in the macroalgal densities between HanakapI'ai and Limahuli Streams (Chlorophyta versus Chromophyta, respectively) were attributed to measured differences in riparian canopy cover (34.8% versus 70.0% closed, respectively). Significantly lower densities of macroalgal species in rime-run habitats in HanakapI'ai as compared with Limahuli Stream were potentially explainable by "top-down" control by robust populations of native herbivorous fish species. THE STREAM MACROALGAE of Hawai'i are poorly studied, yet they playa key ecological role as the dominant autotrophic component supporting stream food webs (Kido 1997a). Cladophora sp. (Chlorophyta) and various blue-green algae (Cyanophyta), for example, were found to be primary foods of the native gobiid fishes (Perciformes: Gobioidei: Gobiidae) Awaous guamensis Valenciennes and Sicyopterus stimpsoni Gill, respectively, which 1 This research was supported by the Hawai'i Division of Aquatic Resources (Hawai'i Department of Land and Natural Resources), Limahuli Garden (The National Tropical Botanical Garden), and the Natural Sciences and Engineering Research Council of Canada (NSERC). Manuscript accepted 28 January 2002. 2 Department of Botany, 3190 Maile Way, University of Hawai'i at Manoa, Honolulu, Hawai'i 96822 (E-mail: [email protected]). 3 The Hawai'i Stream Research Center-Center for Conservation Research and Training, 7370A Kuamo'o Road, Kapa'a, Hawai'i 96746 (E-mail: mkido@hawaii.