Miriam Bojorge-García

Temporal and spatial distribution of macroalgal communities of mountain streams in Valle de Bravo Basin, central Mexico

The stream macroalgal community is controlled by heterogeneous physical, chemical, and biological factors related with multiple spatial and temporal scales; however, the mechanisms that explain diversity and distribution are scarcely known. The present investigation was conducted to characterize the macroalgal community structure and spatial and temporal distribution and to recognize biogeographic affinities with mountain streams from other regions. Habitat characteristics, abundance, and diversity were investigated in four mountain streams of Valle de Bravo Basin, central Mexico, during two annual cycles. Sampling of visible benthic growths was collected in the most contrasting parts of the year. Physicochemical parameters were recorded in situ at each site and the main ions and nutriments were evaluated for every collection. Statistical analysis between dates was assessed with one-way analysis of variance (ANOVA) and Canonical Correspondence Analysis (CCA). Observed richness average was four species per site and the high abundance of Phormidium interruptum, Nostoc parmelioides, Paralemanea mexicana, Batrachospermum gelatinosum, Sirodotia suecica, Cladophora glomerata, and Prasiola mexicana correlated with cold dry season, high current velocity, and a major size substrate. Valle de Bravo streams can be viewed as a habitat subjected to moderated disturbance, mainly due to the effects of seasonal changes in rainfall contrary to torrents expected of tropical regions. The seasonal patterns of macroalgal communities in Valle de Bravo basin were typically characterized by two distinct periods essentially determined by the rainfall regime and related to temperature, and can be viewed as habitats subjected to moderate disturbance according to intermediate disturbance hypothesis. The distribution species pattern registered suggests a group of temperate species frequently found in mountain regions of the Mexican Volcanic Belt and temperate eastern region of North America and may indicate a possible biogeographic connection with the Neartic region with similar environmental requirements.

Species richness and diversity of benthic diatom communities in tropical mountain streams of Mexico

Abstract We examined community structure of benthic diatoms and their substratum preferences (epilithic vs. macroalgae) by season in 4 tropical mountain streams in central Mexico. Of the 74 species compiled, Cymbella silesiaca, Rhoicosphenia abbreviate, and Reimeria sinuata were the most abundant and frequent. About 14% of species were exclusively epilithic, 13% were associated with macroalgae, and 73% had no clear preference. Environmental factors most closely related to spatial and temporal distribution of epilithic diatoms were changes in stream discharge and water temperature. For diatoms associated with macroalgae, the most important factors were changes in current velocity and the coverage and richness of macroalgae. The similarities in species richness and diversity in the 4 study sites suggest that the diatom community develops under conditions of moderate disturbance. The few differences found in species richness between epilithic and macroalgae-associated diatoms suggest that these diatoms do not have substratum preferences. The abundance of macroalgae-associated diatoms in all sites suggests a positive effect (facilitation) of macroalgae on diatoms.

Phenology of Sirodotia suecica (Batrachospermaceae, Rhodophyta) in a high-altitude stream in central Mexico

The morphology and phenology of a monoecious population of Sirodotia suecica Kylin was evaluated seasonally in a central Mexican fifth‐order high‐altitude stream. Abundance of gametophytes is positively correlated with concentrations of total dissolved solids, specific conductivity and total ionic concentration; being present the whole dry season and disappearing in the rainy season. The gametophytes grew in eutrophic circumstances and particular microhabitat conditions: high current velocity (66–122 cm s−1), low irradiance (75–263 µmol photons m−2 s−1) and shallow depth (7–26 cm). Percent cover of gametophytes ranged from 5–90% and significant differences in abundance were not observed when alga was present. Some morphological and reproductive characteristics seem to be adaptations to high current velocity: abundant secondary branches, spermatangia and carpogonia. ‘Chantransia’ stage, microscopic creeping filaments associated with the base of the gametophyte, were not observed in natural conditions. In terms of reproductive success, the population studied can be regarded as highly efficient, considering the high fertilized carpogonia rate, similar to monoecious populations in lotic habitats. However S. suecica was not common in the study region because it was restricted to particular microhabitat conditions.

ESTUDIO DEL VALOR INDICADOR DE LAS COMUNIDADES DE ALGAS BENTÓNICAS: UNA PROPUESTA DE EVALUACIÓN Y APLICACIÓN EN EL RÍO MAGDALENA, CIUDAD DE MÉXICO

The application and development of environmental laws governing watershed management requires identification of biological indicators, parameters and measures to establish its ecological status, for which the present study aims to characterize the ecological indicator value of stream benthic algae in an urban area of Mexico City. Six sites of the Magdalena river were studied in the most contrasting seasons: dry-warm, rainy and dry-cold. At each site the physicochemical parameters of water were recorded and 10 samples were collected: Five with visible algal growths and five with diatoms. The environmental quality of each site was determined by the trophic status and its confirmation with the richness and benthic algal diversity, through a canonical correspondence analysis and the calculation of the indicator value of species (IndVal). According to the trophic status, three groups of sites were recognized. The first group (G1) was assessed as reference of the oligotrophic conditions and presented 11 species with the highest IndVal, protruding: Encyonema silesiacum, Gomphonema parvulum, Navicula cryptocephala, Planothidium lanceolatum, Vaucheria bursata, Placoma regulare and Nostoc parmelioides. A second group (G2) was associated with 15 species considered detectors, which were tolerant to increased nutrients in at least one season, such as Diatoma mesodon and Prasiola mexicana. The third group (G3) included sites with species that had a wide range of tolerance to pollution: Fistulifera saprophila , Nitzschia minuta , Nitzschia palea , Nitzschia recta and Phormidium autumnale. The species IndVal of Magdalena River has established reference sites of good environmental quality and those that are altered by human activities, therefore they are recommended as the first step in a methodological proposal for a long-term biomonitoring through a biological index.