Stream Macroalgae of the Fiji Islands: A Preliminary Study

Abstract

Twenty-seven stream segments sampled in August 1994 on the three largest Fiji Islands ranged considerably in channel size (maximum width 1-20 m, maximum depth 20->100 cm) and mean current velocity (1-118 cm sec-1 ). Water temperatures tended to be warm (23-30°C), pH was neutral to slightly alkaline (7.2-8.6), and specific conductance was quite variable (40-510 mS cm-1 ). Mean number of species per stream segment was 2.6 and ranged from one to five. In the 71 populations of stream macroa1gae sampled, only 15 species were identified: seven Cyanophyta, six Chlorophyta, and two Rhodophyta. All of these species represent new records for the freshwater algal flora of Fiji. Macroalgal cover ranged from <1 to >76% (mean ca. 36%) of the stream bottom and was positively correlated to maximum depth and mean current velocity. The most widespread species that occurred on all three islands were the cyanophytes Phormidium retzii (C.Ag.) Gom. and P. subfuscum Klitz. and the chlorophyte Spirogyra sp. 2 (17, 9, and 19 segments, respectively). Morphological forms included nine mats, three free filaments, and one each of gelatinous colonies, crusts, and tufts. Eleven of the 15 species were in the vegetative state. There were nine species of stream macroalgae on Vitu Levu and eight each on Vanua Levu and Taveuni. The Sorenson's similarity index was highest for the last two islands and lowest for the first two islands.