BIOGEOGRAPHY OF STREAM MACROALGAE IN NORTH-AMERICA

In a survey of 1000 20-m long stream segments in North America from 73-degrees-N to 10-degrees-N, 259 infrageneric taxa were identified, composed of 35% Chlorophyta, 24% Cyanophyta 21% Chrysophyta, 20% Rhodophyta, and one species of Phaeophyta. The most common morphological forms were mats (42%), gelatinous colonies (23%), and gelatinous filaments (13%); the majority of taxa were vegetative (78%). The frequency of reproductive states varied among the biomes examined, with the highest values observed as follows: vegetative (85%) in the tundra, sexual (35%) in the deciduous forest, and asexual (21%) in the tropical rainforest. In terms of total species, the tundra had the lowest number (54), the boreal forest had the greatest number (100), and other well-sampled biomes had 84 to 87. The Chlorophyta had the greatest species numbers in all biomes, and the relative contribution of this division did not vary significantly throughout the continent. With regard to similarity of species composition, the two closest associations were the boreal forest with the western coniferous forest and the eastern hemlock-hardwood forest with the deciduous forest. Species numbers per stream segment ranged from 0 to 11 (XBAR = 3.1), cover ranged from 0 to 100% (XBAR = 15%), and there was no significant difference in these values among the biomes. The cyanophyte Phormidium retzii (C. Ag.) Gom. was the most widespread species (in 172 segments and all biomes). The majority of species were found in moderate current velocities (XBAR = 40 cm.s-1), neutral to slightly alkaline pH (XBAR = 7.5), and moderately low ion waters (XBAR = 261-mu-S.cm-1). On both tropical and Arctic islands, there was no significant increase in total species or species numbers per stream segment with increasing surface area.