Stream Macroalgae of the Hawaiian Islands: A Preliminary Study!

Thirty-four stream segments sampled on the four largest Hawaiian Islands had water temperatures ranging from 20 to 27°C, neutral to alkaline pH (6.7-8.0), and relatively low ion content (30-360 JlS cm-l). Mean species number per stream segment was 3.4 and ranged from one to seven. Macroalgal cover varied considerably from < I to > 76% (mean, ca. 27%) of the stream bed. In the 114 populations of stream macroalgae collected, 34 species were found: 16 Chlorophyta, II Cyanophyta, five Rhodophyta, and two Chrysophyta, of which 25 are new records for Hawai'i; the morphological forms were 16 mats, eight free filaments, seven tufts, one colony, one crust, and one gelatinous filament. The most widespread species was the cyanophyte Phormidium retzii (C.Ag.) Gom., occurring in 18 stream segments. In terms of reproductive status of the populations sampled, 75% were vegetative, 25% were asexual, and < I % was sexual. Only one new species was collected, the rhodophyte Batrachospermum spermatiophorum, belonging to the Section Contorta and having unique colorless spermatiophores and large whorls, carposporophytes, and carposporangia. OCEANIC ISLANDS HAVE biotas that have never been physically part of a larger, continental community, but consist of immigrants and their descendants (Pielou 1979). They tend to have fewer species than comparable continental regions (Schoener 1988). For freshwater organisms, intolerant of high salinities, immigration most likely occurs by jump-dispersal (Pielou 1979), either by migrating birds or by wind currents (Johansson 1976). Although certain freshwater algal taxa have been collected on oceanic islands, there are few whole 1 This research was supported by NSERC grant OGP 0105629 to R.G.S., NSERC grant 0645 to K.M.C., and NSERC grant OGP 2016 to Charles C. Davis. Manuscript accepted 2 July 1993. 2 Department of Biology, Memorial University of Newfoundland, St. John's, Newfoundland, AlB 3X9, Canada. 3 U.S. Geological Survey, Water Resources Division, Ohio District, 975 West Third Avenue, Columbus, Ohio 43212. 4 Department of Botany, University of British Columbia, British Columbia, V6T IZ4, Canada. 'To whom correspondence should be sent. floristic studies of macroscopic algae, particularly those inhabiting flowing waters. Examples of such studies include Tilden (1902) and MacCaughey (1917, 1918a,b) for the Hawaiian Islands, Starmach (1975) for the Seychelles, Johansson (1976) for the Azores, and Lobban et al. (1990) for Yap. However, in all of these reports, stream macroalgae represent only a fraction of the collection. The Hawaiian Islands provide an interesting location for study because they are ca. 3700 km from the nearest continental land mass and they have been only partially examined for the freshwater biota (Maciolek 1969). Most watersheds are typically small, with steep stream channels in the headwaters, little storage capacity, and a tendency for flash flooding at times of heavy rain (Department of Geography, University of Hawaii 1983). The water tends to be low in ions and slightly turbid. Many streams have been modified by diversion for irrigation purposes. Because of the paucity of information on the stream macroalgae from these Islands, this preliminary survey was initiated.