LONGITUDINAL DISTRIBUTION OF MACROALGAE IN 2 TROPICAL LOTIC ECOSYSTEMS FROM SOUTHEASTERN BRAZIL

Macroalgal species richness and diversity were analysed along a longit udinal profile in small and large scales during Spring, Fall and Winte r, respectively in a small stream and a mid size river in the northwes t region of Sao Paulo State, southeastern Brazil (20 degrees 23'-20 de grees 49'S, 49 degrees 26'-51 degrees 19'W). Longitudinal variation in species richness and diversity in small scale was strongly associated with incident light. Microhabitat distribution (from data taken by qu adrat technique) revealed no significant correlations. Principal coord inates analysis (PCO) indicated no consistent groupings among sampling sites in distinct seasons (Spring, Fall and Winter). Longitudinal ana lysis in large scale revealed different patterns in the two seasons sa mpled (Spring and Winter), whereas species diversity presented a consi stent tl end: high upstream, low in mid reaches and higher downstream. It was associated with type of substratum in Spring, rocky substrata presenting the highest values for species richness and diversity. Weak correlations were observed in Winter. Microhabitat distribution showe d significant correlations between species abundance and the following variables: positive for rocky substrata and current velocity and nega tive for sandyclayish substratum and macrophyte-dominated substratum. PCO delineated only one consistent grouping formed by the two headwate r sites. Small scale macroalgal distribution corroborated the longitud inal pattern predicted by the River Continuum Concept, whereas the lar ge scale approach showed a distribution more associated with substratu m type than to light availability. These results showed an opposite tr end in relation to the expected distributional pattern. Longitudinal d istribution in macroalgal community structure has yet to be better doc umented, particularly for tropical streams and no generalization is po ssible at this stage.