Stream Macroalgae Research Articles

Climate warming effects on photosynthetic responses of tropical stream macroalgae

Climate warming effects on photosynthetic responses of tropical stream macroalgae

Local spatial distribution of stream macroalgae – does gastropod activity matters?

Local spatial distribution of stream macroalgae – does gastropod activity matters?

Friends or foes? The ecological relationships between micro- and macroalgae in low-order tropical streams

Streambeds are abundantly colonized by benthic algal assemblages. Environmental factors are the most assessed to find out predictable correlations between algal presence and habitat conditions, but biological interactions can also be important determinant of species composition in stream algae communities. Although there is plenty of information about algal ecology, the mechanisms leading their spatial distribution remain insufficiently clarified. Herein, we contribute to a better understanding regarding this latter issue, carrying out an experimental study to assess possible interactions between micro- and macroalgae during a successional process (75 days) in nine streams, using artificial substrates. The experimental analyses revealed the following main results: (i) streams with higher abundance of macroalgae also registered higher microalgal densities; (ii) the relative interaction index showed values greater than zero for all sampling dates, suggesting positive interaction between micro- and macroalgae during colonization process; and (iii) the multiple partial regression analyses (redundancy, pRDA) showed that environmental variables and microalgae density together explained 25% of macroalgal variation. These results indicate that interactions between stream micro- and macroalgae may contribute to shape the community structure during the successional process on the streambed. As observed previously, microalgae are early successional settlers and macroalgae are late successors, but both community components, besides their inherent competition, seem to cooperate in order to keep their coexistence. Based on this perspective, some typical ecological concepts related to the stream macroalgae, specially from tropical regions, may be expanded. For instance, studies have reported that the highest richness and abundance of lotic macroalgae in tropical/subtropical streams are determined basically by variation in climatic and environmental factors. Our results showed that, in addition to climatic and environmental factors, the increase in richness and abundance of stream macroalgae may also be affected by biotic interactions. In this context, our results suggest that the higher abundance of microalgae on the streambed seems to allow a better development of the benthic algal community, reaching to the later successional stages, in which the relative occurrence of larger and more complex algae (i.e., macroalgae) become more evident.

Modeling the species richness and abundance of lotic macroalgae based on habitat characteristics by artificial neural networks: a potentially useful tool for stream biomonitoring programs

One of the major challenges in stream ecology is the development of computational models that can predict aspects of the community structure of organisms from these ecosystems when they are subject to natural or artificial environmental fluctuations. To contribute towards this aim, we conducted a study whose main goal was to evaluate the efficiency and accuracy of different architectures of multilayer artificial neural networks (ANNs) in predicting the species richness and abundance of macroalgae based on environmental variables of tropical streams. We used data from 82 streams located in southern Brazil, where species richness, macroalgal abundance, and environmental parameters were measured. A set of 20 environmental parameters measured directly in the stream was used as explanatory variables. The performance of the ANN architectures was assessed using two different pieces of software (random combinatorial and exhaustive) and the coefficient of determination (R 2) and mean-squared error (MSE). For both species richness and macroalgal abundance, the best ANN architectures were obtained using random combination software and the performance parameters showed a combination of high R 2 and very low MSE. Our results suggest that computational models that are constructed based on ANN frameworks can be efficient and accurate in predicting the species richness and abundance of stream macroalgae from environmental data. Therefore, considering that models based on linear relationships have often failed, we recommend the application of ANNs as a tool to estimate species richness and abundance of lotic macroalgae from environmental data, in the management, conservation, and biomonitoring programs of tropical stream ecosystems.

The influence of habitat structure, at different spatial scales, on the ecological distribution of macroalgal communities in streams

Habitat heterogeneity influences the composition and structure of macroalgal communities in lotic environments. However, depending on the spatial scale, different environmental characteristics may exert more or less influence. This study aimed to evaluate, at different spatial scales of observation, the influences of local and regional environmental variables on ecological distribution of macroalgae in stream ecosystems. The field work was conducted during the months of June and July 2007 in streams of two river basins located in southern Brazil. The spatial scales used were drainage basin, shading, mesohabitat, and microhabitat. According to the results, there are few differences regarding abiotic variables between spatial scales, however, suggesting that sunlight and, consequently, the shading scale have a strong impact on the distribution pattern of stream macroalgae. The mesohabitat scale at the current velocity proved to be an important factor in structuring communities of macroalgae. Finally, microenvironmental factors (e.g., substrate, current velocity, and light availability) appear to exert their direct influence on the spatial distribution of stream macroalgae, generating particular features in each spatial scale of observation, although regional abiotic parameters (e.g., temperature, pH, and conductivity) should also be considered for the structural characterization of these organisms.

Spatial and temporal distribution of stream macroalgae in a tropical river basin

Spatial and temporal distribution of stream macroalgae in streams from southeastern Brazil were assessed for one year. The fluctuations in macroalgal species composition and environmental factors were monitored monthly. The region exhibit a tropical climate, with defined rainy and dry seasons. Nineteen species were found, with a predominance of Chlorophyta (52.7% of the species), followed by Cyanobacteria (26.3%), Ochrophyta and Rhodophyta (10.5% each). Scytonema arcangeli had the highest number of records (63.6%), while Mougeotia capucina occurred in all sampling sites. Community structure had low similarity (20-26%) and the environmental factors showed a weak contribution to the distribution pattern observed. Despite this, the light availability at the stream-bed seems to be a major influence on the macroalgal seasonal dynamics. We suggest that macroalgae communities are predominantly composed of rare species, and this could explain the lack of a clear spatial and temporal variation pattern of these organisms.

The relationship between macroalgal morphological complexity and hydraulic conditions in stream habitats

The effects of habitat complexity have been considered important factors for the evolution of morphological complexity in organisms. We assessed the possible relationship between hydraulic niche conditions and the morphological complexity of algal filaments by sampling four species of macroalgae inhabiting different hydraulic niches in two freshwater streams. These algal species exhibit different fractal dimensions, which were measured by applying a grid method. The results showed that morphological differences are a function of hydraulic niche for stream macroalgae. Algae with complex shape (Nitella wrightii and Batrachosperum puiggarianum) were established in slower flows, while algae with simpler filament shape (Vaucheria sp. and Oedogonium sp.) were more likely to occur in faster water currents. The sites where the species occurred are a reflection of their ability to hold position, which is ultimately driven by their morphology. The influence of flow in stream habitats is an important factor for lotic macroalgae settlement and its effects can be related to evolutionary adjustment of body shape in these environments. We suggest that the morphological structure (here as fractal dimension) of freshwater macroalgae can be considered an adaptation to the costs and benefits exhibited by different hydraulic niches.

Effects of crevice size on the establishment of macroalgae in subtropical streams.

Considering that in previous studies, the surface roughness (micrometric dimension) showed a weak effect on the colonization of stream macroalgae, we investigated the effects of different crevice sizes (milimetric dimension, a scale slightly higher than previous investigations) on the macroalgal abundance in three streams exposed to full sunlight in southern Brazil. We used smooth sterile glass plates with different shapes: P - plane surface without crevices; S - sinuous surface (depth of crevices with 0.159 mm ± 0.03); N - non-unifom surface (0.498 mm ± 0.09); C - surfaces with convex structures (1.190 mm ± 0.12); and three additional surface types with different patterns of heterogeneity with combinations of glass pieces: P + S (H1); P + S + N (H2) and P + S + N + C (H3). The plates were placed into the streams and after 105 days the percent cover of macroalgal community was measured. No significant differences among treatments were recorded. However, we observed a trend of macroalgae occurs within the crevices in all treatments and this suggests that, for stream macroalgae, the crevice sizes used in this study was still not enough to provide an expressive algal growth, even in the treatment with bigger crevices.

Influence of physical characteristics of environment (light and current velocity) on the substrate occupation by Spirogyra sp. in stream ecosystems

Among the various factors that influence the distribution of macroalgae in stream ecosystems, physical environmental characteristics are those which promote faster changes in the structure and composition of these organisms. Using a study on the macroalgae Spirogyra sp. as an example, this work aimed to evaluate the influence of physical habitat characteristics (substrate size, shading, mesohabitat, and time) on this alga’s colonization process. Field studies were carried out from October 29, 2012 to February 2, 2013 in a stream located in southern Brazil. The results showed that there was a weak relationship between substrate size and abundance of Spirogyra sp. The development of macroalgae occurred mainly in open and riffle environments, emphasizing the importance of light and flowing water (probably due to the higher nutrient content and oxygenation of the water) in the occupation of the substrate. When the time is considered, the observed colonization period of Spirogyra sp. was similar to those already described for communities of stream macroalgae, and it presented a final successional pattern that is characteristic of a climax species.

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

Summary 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. 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. 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. 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. 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. Habitat complexity and hydraulic conditions play an important role in the establishment of macroalgae in streams and could explain their naturally patchy distribution.

Estrutura das comunidades de macroalgas da bacia de drenagem do rio Cascavel, Estado do Paraná, Brasil

A bacia de drenagem do rio Cascavel encontra-se quase que inteiramente dentro do perímetro urbano do município de Guarapuava, Estado do Paraná, Brasil. Foram amostrados sete segmentos de riachos em duas estações do ano (verão e inverno). Foram encontrados 12 táxons de macroalgas com dominância de Chlorophyta (sete táxons) seguido de Cyanophyta (três táxons), Heterokontophyta e Rhodophyta (um táxon cada). Riqueza, índice de diversidade e equidade foram mais elevados durante o período de inverno enquanto a abundância e dominância foram mais elevadas no verão. Entre as características microambientais, a velocidade da correnteza foi a única que diferiu significativamente entre os períodos climáticos. A Análise de Regressão revelou que a riqueza do substrato foi responsável pela variação de riqueza, diversidade, equidade e dominância de espécies durante o período de verão. Durante o inverno, a velocidade da correnteza foi responsável pela variação da diversidade de espécies. A análise de agrupamento das comunidades de macroalgas não reuniu pontos do mesmo período temporal. A Análise de Correspondência Canônica (CCA) mostrou que os segmentos aproximaram-se devido à ocorrência de uma ou poucas espécies em comum. Os padrões de distribuição espacial e temporal de macroalgas lóticas parecem fortemente influenciados por características de microhabitat em diferentes escalas, porém apoiadas em variáveis mais regionais.

Determination of effects of environmental factors on stream macroalgae in Xin'an Spring by grey correlation analysis.

Determination of effects of environmental factors on stream macroalgae in Xin'an Spring by grey correlation analysis.

Effect of environmental factors on distribution of stream macroalgae in Niangziguan Spring in Shanxi Province, North China

A survey of the spatial and temporal distribution of macroalgae in a stream system in Shanxi Province, North China, was undertaken from March, 2006 to January, 2007. The percent cover, biomass of macroalgae and several environmental factors were monitored along a 20 m stretch at each of seven sites, every 2 months during 1 year. All the measured environmental factors had seasonal fluctuations in different extent, but only air temperature and P 3+ showed significant seasonality. In terms of temporal characterization of environmental factors, they also showed some differences among different sampling sites. Seventy-nine (79) species of macroalgae were found, with a predominance of Chlorophyta (38 species, 48.10%). Bacillariophyta and Charophyta represented the smallest proportion (3 species, 3.80% and 2 species, 2.53%, respectively). Three macoralgae species were the most widespread, occurring in all seven sampling sites. Thirty-five (35) species were found at only one site each. In terms of seasonality, 17 species occurred throughout the year, whereas 27 species were found in only one season each. The most key factor that affected the stream macroalgae was current velocity. We calculated Sorensen similarity indices to compare our study with other continent-wide surveys of stream macroalgae, but the similarity indices were all very low. This study also showed that macroalgae in different locations had significant reproductive isolation. Key words: China, distribution, environmental factors, spatial, temporal, stream macroalgae.

Effects of irradiance and spectral composition on the establishment of macroalgae in streams in southern Brazil

The relative effects of irradiance and spectral composition on the colonization and development of macroalgal communities were examined in four streams exposed to full sunlight in southern Brazil. A set of solar filters surrounded the artificial substrata to provide various quantitative and qualitative light conditions. In addition to the control, the conditions were full sunlight attenuated by 50, 70 and 90%, blue light (filter transmitting 430-500 nm), green light (500-600 nm) and red light (> 600 nm). Macroalgal percent cover was determined three times during the colonization period (15, 39 and 70 days). Significant differences occurred in the mean values for macroalgal community percent cover between treatments at 15 and 39 days, suggesting that early and intermediate stages of the colonization were directly influenced by irradiance. There was an almost complete absence of macroalgae with 90% attentuation, but progressive increases with 70 and 50% attenuation. However, the mean values for macroalgal community percent cover did not differ significantly between color treatments, suggesting that the effects of irradiance on macroalgal colonization were stronger than those of spectral composition at similar intensity. The quantitative responses differed among the taxa.

Ecological distribution of stream macroalgae in different spatial scales using taxonomic and morphological groups

We examined the ecological distribution of macroalgal communities in streams using species groups (taxonomic units = algal phyla, and morphological = morphological types) with similar structures and functions instead of the species themselves. The study was conducted from June to July/2007 in two drainage basins located in mid-southern region of Parana State , Brazil. Evaluations of macroalgal communities took into consideration the following spatial scales: the drainage basin (the Pedras river and Marrecas river basins), shading regime (open and shaded stream segments), mesohabitats (riffles and pools), and microhabitats (sampling units of 0.05m2). A total of 29 taxa (23 subgeneric, one generic, and five vegetative groups) were identified. On these, 12 taxa belong to Chlorophyta, 11 to Cyanobacteria, four to Heterokontophyta, and two to Rhodophyta. The proportions of morphological types were: 24% free filaments, 17.25% mats, tufts, gelatinous colonies, and gelatinous filaments, 7% crusts. In terms of spatial scales, we observed a predominance of Chlorophyta in open stream segments and Cyanobacteria in shaded stream segments, reflecting the loss of competitive advantage of green algae in sites with low energy availability. In the mesohabitats, the morphological types recorded in pools were predominantly poorly adapted to fast currents (free filaments), while those found in riffles (mats, tufts and gelatinous filaments) were highly resistant to fast water flows. As such, the use of species groupings based on algal taxonomy associated with morphological characteristics proved to be useful to understanding the distributions of these organisms in lotic environments.

Spatial variations at different observational scales and the seasonal distributions of stream macroalgae in a Brazilian subtropical region

We examined the relationships between environmental variations in lotic ecosystems with the seasonal dynamics of macroalgae communities at different spatial scales: drainage basin of two rivers (Rio das Pedras and Rio Marrecas), shading (open and shaded stream segments), mesohabitat (riffles and pools), and microhabitats. Data collections were made on a monthly basis between January and December/2007. A total of 16 taxa were encountered (13 species and 3 vegetative groups). All of the biotic parameters (richness, abundance, diversity, equitability, and dominance) were found to be highly variable at all of the spatial scales evaluated. On the other hand, abiotic variables demonstrated differences only at mesohabitat (in terms of current velocity) and shaded habitat (in terms of irradiance) scales. The seasonality of the macroalgae community structure was strongly influenced by microhabitat variables (current velocity, substrate H', and irradiance), demonstrating their importance over time and at different scales. Regional variables (temperature, oxygen saturation, specific conductance, pH, and turbidity) were found to have little influence on the temporal dynamics of the macroalgae communities evaluated.

Longitudinal distribution and seasonality of macroalgae in a subtropical stream impacted by organic pollution

AIM: This study was carried out to assess longitudinal and temporal distribution and the effects of organic pollution on macroalgal communities in a subtropical stream; METHODS: The occurrence and percent cover of stream macroalgae were investigated during seasonal period in four sampling sites along the course of the Cascavel Stream, in Paraná State, subtropical area of Brazil. Sampling sites were randomly chosen; however, their location in relation to urban organic pollution sources was taken into consideration. Besides, several stream variables usually related to organic pollution in aquatic ecosystems were measured; RESULTS: Eleven macroalgal taxa were found during the samplings. Chlorophyta was the prevailing division (4 species or 36.3% of the total richness), followed by Cyanophyta and Rhodophyta (3 or 27.3%) and Heterokontophyta (1 or 9.1%). Analysis of variance (ANOVA) showed no significant differences in species diversity, percent cover and diversity index among seasons or the sampling sites. In addition, species diversity was not correlated with any environmental variable in particular. On the other hand, the relative composition of the stream macroalgal communities showed wide spatial and temporal variation. Thus, Chlorophyta had higher values of richness and percent cover in sampling site with higher levels of organic pollution, while Rhodophyta was never found in this segment. Taking seasonality into consideration, Chlorophyta had higher values of percent cover in winter, but Rhodophyta and Cyanophyta in spring and fall, respectively; CONCLUSIONS: In general terms, in this study macroalgal community structures were slightly affected by organic pollution, mainly by increase in richness and percent cover of Chlorophyta associated with the absence of Rhodophyta in the most polluted sampling site. The analysis of the richness throughout the stretch of the stream showed that the highest values were found in the intermediate part, being partly in accordance with the RCC (River Continuum Concept).

Branch formation in Pulvinularia suecica (Nostocales, Cyanoprokaryota) and considerations on the classification of dichotomously and pseudodichotomously branched genera

During a study on stream macroalgae from highland areas of southeastern Brazil (Serra do Cipo, Minas Gerais State), populations of Pulvinularia suecica were found. Study of the specimens provided a detailed description of the pseudodichotomous branch formation, in which the bifurcation is originated by one cell that remains at the basis of the branch and does not integrate any of the branch arms. The taxonomical position of Pulvinularia has been debated since the genus was firstly described. During the course of identification and branch formation studies, it became clear that organisms with dichotomous or pseudodichotomous branching type should be placed under the same family. Thus, it is proposed to adopt Capsosiraceae (sensu Bourrely) to group the genera Capsosira, Colteronema, Desmosiphon, Geitleria, Hyphomorpha, Letestuinema, Loriella, Pulvinularia and Stauromatonema. Additional taxonomical and ecological information on the populations are presented.

Longitudinal distribution and seasonality of macroalgae in a subtropical stream impacted by organic pollution

AIM: This study was carried out to assess longitudinal and temporal distribution and the effects of organic pollution on macroalgal communities in a subtropical stream; METHODS: The occurrence and percent cover of stream macroalgae were investigated during seasonal period in four sampling sites along the course of the Cascavel Stream, in Parana State, subtropical area of Brazil. Sampling sites were randomly chosen; however, their location in relation to urban organic pollution sources was taken into consideration. Besides, several stream variables usually related to organic pollution in aquatic ecosystems were measured; RESULTS: Eleven macroalgal taxa were found during the samplings. Chlorophyta was the prevailing division (4 species or 36.3% of the total richness), followed by Cyanophyta and Rhodophyta (3 or 27.3%) and Heterokontophyta (1 or 9.1%). Analysis of variance (ANOVA) showed no significant differences in species diversity, percent cover and diversity index among seasons or the sampling sites. In addition, species diversity was not correlated with any environmental variable in particular. On the other hand, the relative composition of the stream macroalgal communities showed wide spatial and temporal variation. Thus, Chlorophyta had higher values of richness and percent cover in sampling site with higher levels of organic pollution, while Rhodophyta was never found in this segment. Taking seasonality into consideration, Chlorophyta had higher values of percent cover in winter, but Rhodophyta and Cyanophyta in spring and fall, respectively; CONCLUSIONS: In general terms, in this study macroalgal community structures were slightly affected by organic pollution, mainly by increase in richness and percent cover of Chlorophyta associated with the absence of Rhodophyta in the most polluted sampling site. The analysis of the richness throughout the stretch of the stream showed that the highest values were found in the intermediate part, being partly in accordance with the RCC (River Continuum Concept).

Diatoms: unicellular surrogates for macroalgal community structure in streams?

As wholesale biodiversity assessment is often impractical, the use of surrogates that reflect the assemblage structure and diversity of other taxa has attracted increased attention. We sampled 47 boreal streams for diatoms and macroalgae and examined their assemblage patterns along major environmental gradients. Our main intention was to examine whether diatoms might be useful surrogates for macroalgae in boreal streams. We also assessed whether taxon richness and community composition provided similar insights into the patterns of cross-taxon concordance. According to canonical correspondence analysis, diatom distribution was most strongly related to water pH, conductivity, latitude and longitude, and macroalgal distribution to water pH and iron content, latitude and bed instability. In Mantel’s test, diatoms and macroalgae showed significant cross-taxon concordance. However, there was no significant correlation between taxon richness of the two algal groups, likely reflecting their differing responses to environmental variables. We found evidence that although diatoms and macroalgae are partly controlled by different environmental factors, they are segregated rather similarly along latitude and a few environmental gradients such as water pH and iron content. We conclude that, at least at broad geographical extents and in small streams, diatoms reflect the structure of the macroalgal community and are therefore useful surrogates for cost-effective biomonitoring of algal communities in streams.