Free-living amoebae (FLA) are protozoa that are widely distributed in nature. They are important in the cycling of nutrients in aquatic food chains, but their distribution in natural aquatic environments is not well known. We conducted a survey to determine the presence and distribution of FLA and their relation to some physicochemical parameters in streams of the Mexico Basin in Central Mexico. Thirty-two sites from 18 streams were sampled. Samples were centrifuged and cultured onto NNA-media to isolate amoebae. Identifications were based on morphology. The pathogenicity of Acanthamoeba isolates was tested. Oxygen saturation, temperature, pH, specific conductance, water flow, dissolved reactive phosphorus, nitrites, nitrates, ammonia, dissolved inorganic nitrogen and coliforms were determined. One hundred-and-twenty FLA representing 18 genera were identified. The most frequent genera were Vannella, Rosculus and Acanthamoeba. The frequency of potentially pathogenic FLA was low and only 3 Acanthamoeba isolates were invasive in mice. The highest species richness of FLA was found in streams located into agriculture activity areas and those close to small villages that discharge wastewater into them. Water temperatures were always below 17°C. Oxygen saturation and pH were within the limits for the growth of most FLA. The presence of Acanthamoeba and Naegleria was low; nevertheless, they include potentially pathogenic species and can act as vectors and reservoirs for microbial pathogens and can produce human infections.

Background: In Mexico, species of four families of free-living calanoid copepods have been recorded as inhabitants of several freshwater systems. These families are Centropagidae, Temoridae, Pseudodiaptomidae and Diaptomidae. The generaLeptodiaptomusandMastigodiaptomusare the most speciose diaptomid genera in Mexico, and they inhabit natural and artificial lakes, ephemeral ponds, springs, and caverns.Leptodiaptomusis considered as an endemic Nearctic genus, whereasMastigodiaptomusis a widely distributed Neotropical genus in the southern USA, Mexico, the Caribbean Islands and Central America. Based on new and recent evidence,Mastigodiaptomusdiversity has been underestimated: six species of the genus were known before 2000. In this work three newMastigodiaptomusspecies have been described from different regions of Mexico by using integrative taxonomy. We also gave amended diagnosis ofM. nesusBowman (1986) andM. patzcuarensiss. str. (Kiefer, 1938).Methods: In this work, the taxonomic status of the species was clarified using modern, integrative method based on the COI gene as a DNA marker, plus micro-structural analysis (based on SEM and ligth microscopy).Results: Three new species ofMastigodiaptomuswere described based on genetic and morphological analyses:M. alexeisp. n.,M. hasp. n. andM. cihuatlansp. n. Also amended description ofM. nesus, morphological variation ofM. patzcuarensiss. str., and a comparison of them with all known sequences within the genus are provided. These new findings show that inMastigodiaptomusdifferences in several cuticular microstructures of several appendages (such as the antennules, the fifth legs, or the urosomites of these copepods) agree with the interspecific genetic divergence >3% observed in sequences of the COI gene, and the integration of this information is a powerful tool in species delineation.

The present long-term (1993–2013) study was aimed at identifying the effects of global change on the environmental characteristics and the plankton community of the tropical, high-altitude Lake Alchichica, Puebla, Mexico. We found no statistically significant increasing trend in air temperature, but an increase from 2002 to 2013, and interannual variability in the meteorological variables. Accordingly, the water temperature rose from 1993 to 2003 and remained similar until 2013. Nonetheless, on a longer-term (1966-2018), longer than the period considered in the present study, air and water temperatures showed an increasing trend in the range considered indicative of climate change. The lake displayed a characteristic warm monomictic thermal pattern but exhibited interannual variability. The planktonic community composition and structure remained similar. The small chlorophytes (e.g., Monoraphidium minutum) dominated the phytoplankton abundance, while the large diatom Cyclotella alchichicana dominated the biomass. The calanoid copepod Leptodiaptomus garciai dominated both the zooplankton abundance and biomass. However, as the temperature increased the large-size phytoplankton (i.e., C. alchichicana) abundance and biomass increased, but the small-size phytoplankton abundance and biomass, as well as the adult copepod abundance and biomass, decreased. The increase in temperature could have favoured the large-size over the small-size phytoplankton. In addition, the temperature increase could have negatively affected the calanoid copepods in two different ways—direct association with the negative effects of higher temperatures on the physiology of the copepods, or indirect association with the negative effects of higher temperatures on the small-size phytoplankton, which diminish the copepods’ food resource.

Due to their dimensions, small and shallow water bodies are more sensitive to changes in nutrient load, water flow, and human management. The four water bodies studied are small (area <0.01 km²), constantly supplied by a non-anthropogenic source of nutrients, and these water bodies present different trophic states: mesotrophic, eutrophic, and hyper-eutrophic. The objective of this study was to identify the key environmental factors that created differences in the trophic state of these adjacent shallow urban lakes by modeling chlorophyll-a (Chl a) through the application of the Partial Least Squares Regression (PLSR). The models (n = 36) explain 45.8–60.6% (R²), and predicts 39–52.9% (Q²) of the variance. Environmental variables were identified in the water bodies as critical factors of trophic state determination, water residence time (WRT), ions (e.g., Ca²⁺), and minerals as hydroxyapatite (HAP). These variables were related to processes that could improve trophic conditions, such as flushing and phosphorous precipitation. Conversely, N-NH₃ concentration was associated with nutrient recycling, and found to be able to promote eutrophication.

Daphnia (Ctenodaphnia) magna, a species widely used for ecotoxicological tests, was recorded for the first time in waterbodies of the Mexican protected area and RAMSAR site Ciénegas del Lerma. The identity of the species was confirmed using morphological traits and cytochrome oxidase I as a molecular marker. Haplotypes were 100% identical to cultures used in laboratory bioassays in México and Canada. Individuals analyzed are related to strains from Europe, and their sequences differed from natural populations reported from the United States of America and Canada. This Mexican wetland supports a rich community of migratory waterfowl; therefore, D. magna could quickly spread to other waterbodies and cause potential adverse effects on local Daphnia species. The utilization of non-native species in ecotoxicological tests must be undertaken with great care, to ensure escape to natural waters is prevented.

(1993). Littoral chironomids of a Mexican Plateau athalassohaline lake. SIL Proceedings, 1922-2010: Vol. 25, No. 1, pp. 444-447.