DISTRIBUTION OF STREAM MACROALGAE IN THE NORTHWEST REGION OF SAO-PAULO STATE, SOUTHEASTERN BRAZIL

Forty-four stream segments were sampled from May to October in 1992 an d 1993 in the northwest region of Sao Paulo State, southeastern Brazil (19 degrees 45'-21 degrees 25'S, 49 degrees 05'-51 degrees 30'S). Thi rty-six macroalgal subgeneric taxa were found and Chlorophyta was the dominant algal group (47% species), followed by Cyanophyta (33.5%), Rh odophyta (14%) and Chrysophyta (5.5%). The most widespread species wer e Stigeoclonium helveticum (25% sites), Batrachospermum delicatulum an d Compsopogon coeruleus (20.5%). Distribution was patchy, with species number per sampling site ranging from 0 to six (3.1 +/- 1.7) and corr elated positively with species abundance. Species cover ranged from 0 to 61% of the stream bottom (19.1 +/- 19.7%). Most sites (57%) were do minated by one or two macroalgae species. No significant difference wa s found between the frequency distribution of variables measured for s treams and for total macroalgae, but the most widespread species diffe red for most parameters and occurred over wider ranges of environmenta l conditions. Mean species number and abundance were close to values f ound in distinct regions or biomes of North America. Higher conductanc e and lower oxygen values, as well as rocky substrata, generally const ituted the most favourable combination of conditions for the developme nt of macroalgae in the region. The pattern of strong dominance of few species was considered to be typical for stream macroalgal communitie s in general.