Background:

Several studies of lotic ecosystems have provided important ecological information on the influence of environmental heterogeneity on macroscopic algae composition.

Hypothesis:

The highest species diversity will occur during the cold-dry season, correlated to low temperature and oligothrophic water, while the distribution of each species will be related to heterogeneity of habitat and its dispersal strategies.

Studied species:

Twenty-two species of macroscopic algae of different Phyla (Chlorophyta, Cyanobacteria, Heterokontophyta and Rhodophyta).

Study site:

The macroscopic algae composition was described for 35 permanent mountain streams in the Basin of Mexico from 2012 to 2015.

Methods:

Algae species, physico-chemical water conditions and microhabitat factors were recorded in situ at each contrasting season. The relationship between diversity and the environmental factors was statistically evaluated by Canonical Correspondence Analysis and a Spearman test.

Results:

Macroscopic algae recorded had biological features and environmental abilities that separated them into two groups. The first included the most frequent and abundant species: Nostoc parmelioides, Placoma regularis, Prasiola mexicana and Vaucheria bursata. The second included species restricted to certain habitats: Draparnaldia mutabilis, Tetraspora gelatinosa, Batrachospermum gelatinosum and Paralemanea mexicana. Each Phyla responds differentially to the spatial heterogeneity of the streams, but the species does not change between contrasting seasons.

Conclusions:

Local and spatial environmental variables explain differences in richness and distribution of species on the studied area; however, species composition does not vary widely among sampling sites. Cyanobacteria and Chlorophyta are more affected by local environmental variables, whereas Rhodophyta is more influenced by spatial variables.

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