Evaluation of seasonal dynamics and bioindication potential of macroalgal communities in a polluted tropical stream

Macroalgal communities and environmental variables were analyzed seasonally along a polluted tropical stream in São Paulo State, Brazil, We aimed to improve the knowledge of tropical macroalgal communities, to study the longitudinal and seasonal dynamics of these communities in influenced environments, to evaluate the relationship of algal frequency and abundance with selected environmental variables, and to look for potential macroalgal species indicators. The seasonal abundance pattern was similar to natural or low influenced systems and was mainly determined by rainfall regime. However, community composition was closely related to some chemical water pollution indicators, such as phosphorus and nitrogen compounds. Some species are suggested as potential indicators of organic pollution (e.g. Oscillatoria ornata, Stigeoclonium helveticum and Schizomeris leibleinii), but more detailed studies have to be developed to determine the tolerance limits of these species. on the basis of our results and literature data, the use of occurrence of Oscillatoriales in relation to other orders of Cyanoprokaryota is suggested to be a good indicator of organic pollution in tropical lotic ecosystems.

Distribution of stream macroalgae in three tropical drainage basins of southeastern Brazil

Three drainage basins belonging to different drainage systems, but in close proximity, were evaluated to compare the distribution of macroalgal communities in the northwest region of São Paulo State, southeastern Brazil. Monthly samplings were carried out from September 1992 through September 1993 in three sites along the main river of each basin. 10 m length cross segments were evaluated for species per cent cover and richness, on both the population and community levels. Selected stream variables were measured: specific conductance, temperature, turbidity, mean cross-sectional area of the reach, current velocity, pH, and oxygen saturation (%). Principal Coordinate Analysis (PCO), chi-square good-of-fitness, and Pearson Product-Moment correlation coefficient were applied to evaluate the distribution of the macroalgal species. The survey resulted in 36 taxa of macroalgae, of which Cyanophyta was the dominant group (17 taxa or 41.7% of the total), followed by Chlorophyta (15 taxa or 41.7%), Rhodophyta (3 taxa or 8.3%) and Chrysophyta (1 taxon or 2.8%). Stigeoclonium helveticum, 'Chantransia' stage of Batrachospermum spp., and B. delicatulum were the most widespread and frequent macroalgae throughout the basins. The analyses showed that conductance and current velocity were the factors most closely related to the distribution of the macroalgal species. Positive correlation between richness and percent cover was determined, which reinforces the patchiness of stream macroalgal distribution.

Temporal dynamics of two species of Chaetophoraceae (Chlorophyta) in tropical streams of São Paulo State, Southeastern Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Microhabitat and morphometric variation of two chaetophoracean (chaetophorales, chlorophyta) species in tropical streams of southeastern Brazil

Two populations of Chaetophora elegans (Roth) C. Agardh and two of Stigeoclonium helveticum Vischer were investigated for microhabitat characteristics and morphological variation in streams of Sao Paulo State, southeastern Brazil. Different patterns of microhabitat distribution were found between species investigated. Populations of C. elegans were distributed under relatively narrow microhabitat conditions (high irradiance, low depth, moderate to high current velocity, rocky substrata and lower values of niche width) and showing little morphometric variation (colony diameter, main axis cell size, and apical branch number). Stigeoclonium helveticum occurred under more diverse microhabitat conditions, revealed by lack of significant difference between sampling units with and without the alga and wider niche width, but also exhibited relatively narrow morphometric variation (plant length, main axis cell and lateral branch cell sizes). The narrow microhabitat conditions and smaller niche width of C. elegans can explain its low abundance (percentage cover) in streams from the area studied as well as in other regions of Sao Paulo State. In contrast, the wider variation of microhabitat conditions and the higher niche widths of S. helveticum suggest that this green alga is able to grow in a high number of stream ecosystems in the region investigated, ranging from undisturbed to highly disturbed habitats. Thus, the results suggest that S. helveticum is a generalist species.

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 and 1993 in the northwest region of São Paulo State, southeastern Brazil (19 degrees 45'-21 degrees 25'S, 49 degrees 05'-51 degrees 30'S). Thirty-six macroalgal subgeneric taxa were found and Chlorophyta was the dominant algal group (47% species), followed by Cyanophyta (33.5%), Rhodophyta (14%) and Chrysophyta (5.5%). The most widespread species were Stigeoclonium helveticum (25% sites), Batrachospermum delicatulum and Compsopogon coeruleus (20.5%). Distribution was patchy, with species number per sampling site ranging from 0 to six (3.1 +/- 1.7) and correlated positively with species abundance. Species cover ranged from 0 to 61% of the stream bottom (19.1 +/- 19.7%). Most sites (57%) were dominated by one or two macroalgae species. No significant difference was found between the frequency distribution of variables measured for streams and for total macroalgae, but the most widespread species differed for most parameters and occurred over wider ranges of environmental conditions. Mean species number and abundance were close to values found in distinct regions or biomes of North America. Higher conductance and lower oxygen values, as well as rocky substrata, generally constituted the most favourable combination of conditions for the development of macroalgae in the region. The pattern of strong dominance of few species was considered to be typical for stream macroalgal communities in general.