Habitat preferences in freshwater benthic macroinvertebrates: Algae as substratum and food resource in high mountain rivers from Mexico

The diversity of benthic macroinvertebrates in lotic systems is closely related to the availability and heterogeneity of habitats. These habitats may be of inorganic origin, such as the rocky substratum associated with the river bed, or organic such as macroscopic algae. The objective of this study was to determinate the importance of five species of algae that differ in their morphological type as a substratum and food resource regarding the associated establishment of macroinvertebrate assemblages taking account the climatic seasonality (warm dry, cool dry and rainy). We then evaluate the differences in macroinvertebrates assemblages with respect to the inorganic substratum by sampling high mountain rivers in central Mexico. The mucilaginous colonies of Nostoc parmelioides and Placoma regulare, the pseudoparenchymatous bambusiform thallus of Paralemanea mexicana and the laminate thallus of Prasiola mexicana had the highest densities of macroinvertebrates, represented by the genera Cricotopus, Paramerina, Simulium and Tanytarsini tribe. The relationship between algal morphological type and the richness and diversity of macroinvertebrates was positively related to specific conductivity, total dissolved solids and discharge variables. The dominant taxa associated with the inorganic substratum belonged mainly to the Trichoptera, Diptera and Ephemeroptera orders. Water temperature, discharge and concentration of orthophosphates were the main environmental variables able to explain the diversity of macroinvertebrates on this substratum. The dominance of detritivorous macroinvertebrates in these mountain rivers suggests the contribution of allochthonous organic matter possibly of anthropogenic origin. The assemblages of macroinvertebrates on inorganic substratum did not significantly differ among sites or climatic seasons.