Stream Macroalgae of the Hawaiian Islands: a Preliminary Study

Abstract

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 uS cm-l). Mean species number per stream segment was 3.4 and ranged from one to seven. Macroalgal cover varied considerably from < 1 to > 76% (mean, ca. 27%) of the stream bed. In the 114 populations of stream macroalgae collected, 34 species were found: 16 Chlorophyta, 11 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 < 1% 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.