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.

Eutrophication presents a significant challenge for water quality management, as it threatens both the availability of freshwater and the integrity of aquatic ecosystems. Here, we integrally assessed the trophic state of ten reservoirs and lakes in Central Mexico that differ in trophic level. Environmental variables, Carlson Trophic State Index (TSI), trophic state indices for zooplankton abundances (TSI _ROT and TSI _CR ), and modified guild ratio (GR′) were analyzed. We also compared these indices with diversity indices (species richness, abundance, Hill numbers, and Shannon index). Sites with low Carlson TSI values exhibit reduced species richness, abundance, and diversity, while highly eutrophic and macrophyte-influenced sites display elevated diversity indicators. The modified guild ratio indicates a dominance of raptorial rotifers in reservoirs and lakes with low trophic levels, whereas microphagous species primarily dominate eutrophic ecosystems. The zooplankton indices (TSI _ROT and TSI _CR ) overestimate the trophic status when it is low and underestimate it when trophic conditions are high compared with Carlson’s trophic indices. Canonical correspondence analysis shows that Asplanchna priodonta , Synchaeta spp., and Daphnia spp. are associated with more transparent, less nutrient-rich waters, while brachionids, Filinia longiseta , and Diaphanosoma spp. thrive in eutrophic conditions like those in Xochimilco and La Estanzuela wetlands. This study confirms that zooplankton can be a good indicator of the trophic conditions of water bodies in high-altitude tropical regions, but the indices need to be adjusted to improve their accuracy.

Eutrophication, a growing environmental concern, exacerbates algal blooms and alters the physical and chemical properties of water, thereby diminishing biodiversity, water quality, and ecosystem services. While various control strategies have been developed, most are designed for temperate regions and may not be applicable to tropical systems, which differ ecologically and climatically. This study reviewed 84 articles published between 2000 and 2024, focusing on eutrophication management in tropical and subtropical lakes. The studies were categorized into physical (8), chemical (17), and biological (59) approaches. Over time, research activity has increased, with Asia leading in publication output. Among biological strategies, biomanipulation—especially the use of macrophytes—emerged as the most common and effective strategy. Macrophytes are preferred due to their strong antagonistic interaction with algae, ease of implementation, cost-effectiveness, and minimal ecological risks. While the review also addresses the limitations of each method, it concludes that macrophyte-based biomanipulation remains a promising tool for mitigating eutrophication in tropical and subtropical freshwater ecosystems. In this context, effective lake restoration requires balancing ecological goals with human needs, supported by stakeholder engagement, community education, and multi-sectoral governance.

Macrophytes and cladocerans represent the main antagonistic groups that regulate phytoplankton biomass; however, the mechanism behind this interaction is unclear. In laboratory conditions, we separately evaluated the effects of three submerged macrophytes (Ceratophyllum demersum, Myriophyllum aquaticum, and Stuckenia pectinata), as well as their exudates, and plant-associated microbiota (POM < 25 µm) + exudates on the population growth of Daphnia cf. pulex and Simocephalus cf. mixtus. Living Ceratophyllum, exudates, and POM < 25 µm + exudates exhibited the most robust positive effects on Simocephalus density and the rate of population increase (r). Subsequently, we examined the effects of Ceratophyllum on the filtration and feeding rates of Simocephalus and Daphnia, revealing significant (p < 0.001) promotion of filtration and feeding in Simocephalus but not in Daphnia. To elucidate the specific effects of this macrophyte on Simocephalus demography, we assessed selected life table variables across the same treatments. The treatments involving exudates and living Ceratophyllum resulted in approximately 40% longer survivorship and significantly (p < 0.01) enhanced fecundity. Our findings indicate that exudates from submerged macrophytes positively influence Simocephalus demography by increasing filtration rates, survivorship, and fecundity. This synergy suggests a substantial impact on phytoplankton abundance.