Benthic macroinvertebrate community biodiversity of tropical lakes has been rarely addressed. The present study recognizes the taxonomic diversity of the deep benthic macroinvertebrate communities of 18 lakes of the Protected Natural Area "Lagunas de Montebello", Chiapas, Mexico. The lakes display different morphometric features and trophic states. Five sampling campaigns were carried out between 2013 and 2016. Forty-nine taxa (14 orders, 25 families, 40 identified genera, and 9 undetermined taxa) were recorded. Taxonomic richness varied between 0 and 19 taxa with a mean of 5 ± 6 taxa. The regional species richness was high compared to other tropical lakes in Mexico and worldwide; the richness per lake was similar to other tropical lakes. Chironomidae was the best-represented family with 17 genera. Even the studied lakes belong to the same lake district, low taxonomic similarity among them was found; 65.3% of genera were found in a single lake. Eutrophic shallow lakes had lower richness (2.5 ± 3.5, 0-5) compared to oligotrophic shallow lakes (5.0 ± 7.1, 0-10), and eutrophic deep lakes had lower richness (2.0 ± 1.8, 0-4) than oligotrophic deep lakes (7.0 ± 6.5, 0-19); nonetheless, we found no statistically significant differences. Eutrophication is reducing deep benthic community diversity, threatening these fragile ecosystems characterized by high taxonomic richness and singularity.

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A pesar del uso extendido de las comunidades de macroinvertebrados dulceacuícolas en estudios básicos y aplicados de ecología acuática, es poco lo que se conoce para la Isla de Providencia, más aun cuando la biota de las islas es de interés por sus posibles relaciones con el continente y con islas cercanas. El presente estudio caracterizó la composición y la estructura de las comunidades de macroinvertebrados dulceacuícolas de la Isla durante tres periodos de muestreo relacionados con el ciclo hidrológico e identificó las distribuciones geográficas de los elementos faunísticos encontrados. Se seleccionaron cinco sitios (Lazy Hill, Bailey, Fresh Water, El Pico y Old Town) en los cuales se midieron variables físicas y químicas y se recolectaron individuos en cada microhábitat disponible. Posteriormente se calcularon descriptores de la comunidad (riqueza específica y abundancia) e índices de diversidad (diversidad de Margalef, dominancia de Simpson y equidad de Shannon-Weiner) y se aplicaron pruebas de Kruskal Wallis para establecer las diferencias en las abundancias entre las épocas de muestreo y entre los sitios. Un ACC se realizó para establecer la asociación de los organismos con las variables físicas y químicas. Se encontró que los sitios de Lazy Hill y El Pico son los que representan mayor diversidad (DMg: 7.15 y 8.40, respectivamente) y pueden ser un refugio importante para las comunidades en la época de sequía. Las distribuciones geográficas no permitieron reconocer endemismos a nivel genérico, sino que las comunidades estudiadas son una combinación de elementos cosmopolitas centro y suramericanos principalmente. La estacionalidad tiene un efecto notable sobre la composición de las comunidades, siendo mayor en los cuerpos de agua con menos obras de intervención como Lazy Hill y El Pico.

Beta diversity is useful to explain community assembly across landscapes with spatial variation. Its turnover and nestedness components help explain how beta diversity is structured across environmental and spatial gradients. Assessing beta diversity in freshwater ecosystems is essential to conservation, as it reveals the mechanisms that maintain regional diversity. Nonetheless, so far, no studies have examined the beta diversity patterns of benthic macroinvertebrates in tropical lakes. We aimed to examine the beta diversity patterns and components of the deep benthic macroinvertebrate communities of tropical Lakes of Montebello, Mexico, along spatial and environmental gradients. We used presence/absence data of deep benthic macroinvertebrates from 13 lakes distributed along environmental and spatial gradients. We calculated beta diversity indices and correlated them to each lake’s environmental and spatial variables. The macroinvertebrate communities of the Lakes of Montebello showed high beta diversity driven by a turnover pattern that emphasises the importance of regional-scale conservation efforts. Short distances between lakes and high environmental heterogeneity promoted species turnover, resulting in a great singularity level among lakes. We did not find significant correlations between the beta diversity components and the environmental variables, suggesting a random distribution given by the species’ high dispersal capacity in a reduced spatial extent across the lake district.

Particulate organic carbon (POC) derived from inland water plays an important role in the global carbon (C) cycle; however, the POC dynamic in tropical rivers is poorly known. We assessed the POC concentration, flux, and sources in the Usumacinta, the largest tropical river in North America, to determine the controls on POC export to the Gulf of Mexico. We examined the Mexican middle and lower Usumacinta Basin during the 2017 dry (DS) and rainy (RS) seasons. The POC concentration ranged from 0.48 to 4.7 mg L−1 and was higher in the RS, though only in the middle basin, while remaining similar in both seasons in the lower basin. The POC was predominantly allochthonous (54.7 to 99.6%). However, autochthonous POC (phytoplankton) increased in the DS (from 5.1 to 17.7%) in both basins. The POC mass inflow–outflow balance suggested that floodplains supply (C source) autochthonous POC during the DS while retaining (C sink) allochthonous POC in the RS. Ranging between 109.1 (DS) and 926.1 t POC d−1 (RS), the Usumacinta River POC export to the Gulf of Mexico was similar to that of other tropical rivers with a comparable water discharge. The extensive floodplains and the “Pantanos de Centla” wetlands in the lowlands largely influenced the POC dynamics and export to the southern Gulf of Mexico.

In tropical first‐order streams, the availability of basal resources changes according to tropical seasonality, i.e., dry and rainy seasons, with consequences for the food web structure. However, the seasonal variation in autotrophic and detrital pathways remains unclear. In this study, we aimed to establish whether the dominant pathway of the benthic macroinvertebrate food web in two tropical first‐order streams in the Lacandona rainforest, Mexico, relies on autotrophic or detrital food resources. We evaluated the assimilation of autotrophic and detrital food resources through carbon and nitrogen stable isotope (δ13C and δ15N) analysis. We included the biomass of the macroinvertebrates sustained by the autotrophic and detrital pathways and the food web structure—trophic position, size structure, and degree of omnivory. The biomass sustained by the detrital pathway remained similar throughout the year in both streams. In contrast, the biomass sustained by the autotrophic pathway was higher in the dry season than in the rainy season. The benthic macroinvertebrate food web had four levels, a poorly developed size structure, and an important degree of omnivory in both streams and in both seasons. It is likely that omnivory was a response to high resource variability and a strategy to reduce intraguild competition. Autotrophs had a relatively higher importance than detritus since a much lower algae biomass sustained an equal or higher macroinvertebrate biomass, particularly in the dry season when the biomass of autotrophs increased. Seasonality influenced the macroinvertebrate food web by modifying the food resource availability and transference to higher trophic levels. However, the high frequency of omnivory reduced the seasonal changes in the food web structure. Our results suggest that the autotrophic pathway plays an important role in maintaining the benthic macroinvertebrate food web in tropical streams. The relative importance of autotrophs in the macroinvertebrate food web is associated with seasonality, the rainfall pattern, and its effect on the stream hydrology.

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