Effects of artificial substratum types and exposure time on macroalgal colonization in a tropical stream

This study examines the development of the macroalgal community in a tropical stream on different artificial substrata (material and surface texture) and over varying periods of time. Our study indicated that the physical structure of the substratum did not affect species richness, but did alter the abundance of the macroalgal community. In addition, our results suggested that the amount of surface roughness could be an important factor driving the development of the macroalgal communities. The presence of a mucilaginous matrix with many diatoms and algal propagules on the surface of the substrata may have accelerated the colonization process. Macroalgal abundance peaked after 21 days of exposure. Generally, macroalgal species richness increased during the study period, however, a reduction in species richness was observed after 105 days of exposure, probably, as a result of competitive interactions.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Distribuição ambiental e temporal das comunidades de macroalgas de riachos da Serra da Prata, Estado do Paraná, Sul do Brasil

Considerando a carência de estudos enfocando comunidades de macroalgas de ambientes lóticos em regiões subtropicais, o presente estudo foi conduzido com o objetivo de investigar o padrão de distribuição destas comunidades em uma região de floresta ombrófila densa bem preservada. Oito pontos de amostragem foram amostrados em duas estações contrastantes (inverno e verão) na Serra da Prata (Parque Nacional Saint-Hilaire/Lange), localizada na porção leste do Estado do Paraná, Sul do Brasil. A Análise dos Componentes Principais (PCA) mostrou que as variáveis ambientais dos riachos analisados tiveram um padrão temporal claro, com uma distinção evidente entre inverno e verão. de modo contrário, a Análise de Correspondência Destendenciada (DCA), baseada na presença/ausência de espécies, não revelou nenhum padrão temporal ou diferenças entre a composição florística do inverno e do verão. Um padrão mostrado na DCA foi a separação dos pontos de amostragem pela intensidade do sombreamento da vegetação ripária. de maneira geral, a região estudada apresentou baixos valores de riqueza e abundância, e a maioria dos táxons foi restrita a um único ponto ou época de amostragem. Deste modo, os resultados sugerem que a estruturação das comunidades de macroalgas estudadas parecem responder à combinação das variáveis ambientais que se alteram continuamente no tempo e no espaço, enfatizando, entre outras, a importância das variações em pequena escala (microhabitat). Por outro lado, os resultados também indicaram que, em escala global, a distribuição das macroalgas dos ambientes lóticos da região de estudo, aparentemente, pode ser limitada pelo grau de sombreamento imposto pela vegetação marginal.Considering the scarcity of studies focusing on stream macroalgal communities in subtropical regions, the present study was conducted to investigate the environmental and temporal distribution patterns of these communities in a well-preserved region of ombrophilous dense forest. Eight samplings sites were sampled twice (Summer and Winter) in the Serra da Prata (Saint-Hilaire/Lange National Park), located in eastern portion of the Parana State, southern Brazil. The Principal Components Analysis (PCA) showed that the environmental variables of the investigated streams had a clear temporal pattern, with an evident distinction between winter and summer conditions. In contrast, the Detrended Correspondence Analysis (DCA), based on the presence/absence of macroalgae, did not reveal any temporal pattern, without evident differences between winter and summer floristic compositions. One pattern showed by the DCA was the separation of sampling sites by the intensity of riparian vegetation shading. Overall, the study region showed low values of richness and abundance, and the occurrence of majority of taxa were restricted to a single sampling site. Thus, the results suggested that the structure of the macroalgal communities studied seem to respond to a combination of environmental variables that change continuously in time and space, emphasizing the importance, among others, of variations on a small scale (microhabitat). Moreover, the results also showed that, on a global scale, the distribution of lotic macroalgae in the study region can, apparently, be limited by the degree of shading imposed by riparian vegetation.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

The influence of landscape on the spatial and temporal distribution of stream macroalgal communities of two types of subtropical biomes

Landscape properties must be considered in the interpretation of ecological patterns of stream macroalgal communities. In this study, we sampled streams with different types of riparian cover from two biomes (highland grassland, HG, and seasonal semideciduous forest, SSF) for a period of one year. Each stream was visited four times, once in each season, during which we observed the algal growth and recorded measurements of a set of physical and chemical properties. Nineteen macroalgal taxa were recorded for HG, while 21 were recorded for SSF, but only three species were common to both biomes. Student's t-test results showed that significant differences existed between HG and SSF only for stream depth for abiotic variables and for abundance for biotic variables, while the results of a detrended correspondence analysis (DCA) revealed that the taxonomic compositions were sharply different at the landscape level. In addition, the DCA results showed that when each landscape was considered individually, the HG macroalgal communities had a clear spatial structure, while for SSF macroalgal communities no spatial structure was detected. These results suggest that although the taxonomic richness of HG and SSF are relatively similar, the landscape conditions of each biome, mainly riparian cover types, could be relevant in the determination of quantitative and qualitative differences in the stream macroalgal communities both between and within biomes.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

The effects of habitat complexity and hydraulic conditions on the establishment of benthic stream macroalgae

1. Habitat complexity is thought to play an important role in various ecological communities, but its role under variable natural conditions is not well understood, particularly in lotic habitats where the complexity of the substratum influences the diversity and abundance of the benthic community.2. We investigated the effects of the habitat complexity of the substratum, as represented by fractal structure, on the establishment of stream macroalgae. We also analysed the influence of hydraulic conditions associated with variations in the fractal dimension of the substratum. We hypothesised that habitats with higher surface complexity would have higher macroalgal abundance and that hydraulic conditions would affect macroalgal establishment differently on surfaces of differing complexity.3. We designed a field experiment to elucidate the role of habitat complexity (represented by the fractal dimension and density of roughness elements) and consequent hydraulic conditions (assessed by the Reynolds number and drag forces) on algal growth. Sterile artificial substrata with five levels of complexity were placed in four unshaded streams. After 60 days of complete submergence, the substrata were removed from the streams, and the per cent cover of macroalgae was measured.4. We used a principal components analysis (PCA) to reduce the dimensionality and collinearity among our variables (fractal dimension, density of roughness elements, Reynolds number and drag force) and summarise them adequately. Axis 1 (PC1) values were used in a linear model to assess the relationship between the variables and macroalgal cover.5. PC1 explained 82.2% of the variability in substratum complexity and hydraulic condition. The fractal dimension and density of the roughness elements were negatively related with PC1, whereas the Reynolds number and drag force were related positively. Hydraulic conditions differed among each level of complexity, with the Reynolds number and drag force decreasing with increasing complexity. Macroalgal cover increased on surfaces with lower turbulence and drag force, indicating that less aggressive conditions are suitable for macroalgal colonisation. Additionally, the establishment of macroalgae was greatest on the leading edge of flat-top ridges, where the water velocity slows and the current changes direction.6. Habitat complexity and hydraulic conditions play an important role in the establishment of macroalgae in streams and could explain their naturally patchy distribution.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

The roles of environmental conditions and spatial factors in controlling stream macroalgal communities

In the last three decades, several studies have suggested that the structure of stream macroalgal communities is shaped by local environmental variables, but some recent papers have shown that the relevance of the environment on these communities may be overestimated. Using Partial Redundancy Analysis (pRDA), we analyzed macroalgal communities (considering all macroalgae and Phyla Chlorophyta, Cyanobacteria, and Rhodophyta individually) from 105 streams in southern Brazil to test the hypothesis that the relative contributions of the environment and space on the taxonomic composition of these communities is mainly determined by the biological traits and dispersal mechanisms typical for each group. The pRDA showed that the taxonomic composition of the entire community and green algae were explained by both space and environment, whereas for cyanobacteria, only the environment was significant, and for red algae, only space was significant. These divergences in the relative contribution among algal phyla were consistent with our initial hypothesis and can be ascribed to the differences in the ecological features of each group. Our results also support the idea that the community structure of organisms with low dispersal is influenced more significantly by spatial processes, whereas for organisms with high dispersal the local environmental variables are more influential.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq