DISTRIBUTION OF STREAM MACROALGAE IN THE EASTERN ATLANTIC RAIN-FORESTOF SAO-PAULO STATE, SOUTHEASTERN BRAZIL

Fifty-two stream segments were sampled from 16 August to 13 September in 1993 in the eastern Atlantic Rainforest of Sao Paulo State, southea stern Brazil (22 degrees 55'-25 degrees 00'S, 44 degrees 48'-48 degree s 03'W). Forty-two macroalgal subgeneric taxa were found and the most widespread species were Audouinella pygmaea (21% of sites), Compsopogo n leptoclados and Microcoleus subtorulosus (19%). Macroalgal species n umber per sampling site ranged from 0 to six (2.6 +/- 1.7) and was pos itively correlated to species abundance, whereas species cover ranged from 0 to 70% of the stream bed (15.5 +/- 20.8%). No significant corre lation was found among macroalgal species number and abundance with an y physical or chemical variable analyzed. Most sites were dominated by one or few macroalgal species, mainly, Audouinella macrospora, C. lep toclados and M. subtorulosus. No significant difference was found betw een the frequency distribution of variables measured for streams and f or total macroalgae but the most widespread species (A. pygmaea) diffe red significantly for current velocity, specific conductance, turbidit y and pH. Overall means for macroalgal occurrence include the followin g values: temperature ((X) over bar = 19.9 degrees C), current velocit y ((X) over bar = 45 cm s(-1)), oxygen saturation ((X) over bar = 66%) , specific conductance ((X) over bar = 59.6 mu S cm(-1)), turbidity (( X) over bar = 5 NTU) and pH ((X) over bar = 7.1). This pattern of patc hy distribution and dominance by few species has been suggested as typ ical of stream macroalgal communities and has been ascribed to the rap id fluctuation of physical and chemical conditions. Total macroalgal s pecies richness as well as mean species number per sampling site were considerably lower than found in similar studies of other regions. The Intermediate Disturbance Hypothesis was applied to explain these resu lts: the same factor (high precipitation) responsible for the maintain ance of the high species diversity in the surrounding forest can be, p aradoxically, a constraint to the development of a more diverse macroa lgal flora in streams.