Benthic cyanobacterial mats are complex microbial ecosystems in which cyanobacteria coexist with diverse associated microorganisms that contribute biogeochemical cycles and the production of secondary metabolites. This study aimed to identify the foundation cyanobacteria and associated bacterial communities of benthic mats and to evaluate the effects of environmental and biotic factors on potential toxin production in tropical mountain rivers of siliceous and calcareous basins. We integrated morphological characterization, 16S rRNA gene amplicon sequencing, cyanotoxin-related molecular analyses, high-performance liquid chromatography (HPLC)-based toxin detection, and environmental profiling of the study sites. We identified the foundation cyanobacteria as Tychonema sp., Compactonostoc sp., Albertania sp., and Chamaesiphon mexicanus in siliceous basins, and Oxynema sp. and Ancylothrix sp. in calcareous basins. Associated bacterial communities were dominated by Pseudomonadota and Bacillota, although their composition varied substantially among mats. Nitrogen availability was associated with differences in bacterial community composition, whereas temperature, pH, and conductivity were associated with patterns of alpha diversity. Cyanotoxin-related analyses revealed both potentially toxigenic and HPLC-confirmed toxigenic mats, including the detection of microcystins in mats associated with Microcoleus sp. and Planktothrix agardhii. Bacterial community composition did not differ significantly between potentially toxigenic and HPLC-confirmed toxigenic mats, although community dispersion differed between groups. Overall, the results demonstrate substantial environmental and microbial heterogeneity among benthic cyanobacterial mats and document the occurrence of cyanotoxins in tropical mountain rivers, providing a basis for a more detailed assessment of ecological and environmental factors, as well as mutualistic relationships, associated with the support and metabolic stratification of toxin-producing cyanospheres.
Deforestation and monoculture expansion in tropical watersheds represent important pressures on aquatic ecosystems, yet their associations with zooplankton communities in Neotropical reservoirs remain poorly understood. We evaluated how land use and land cover are associated with the distribution, diversity, composition, and structure of zooplankton communities in six tropical reservoirs with contrasting landscape configurations and trophic conditions. Samples were collected at 12 points per reservoir during dry and rainy periods by filtering 100 L of water. A total of 112 zooplankton species were recorded, comprising 60 Rotifera, 41 Cladocera, and 11 Copepoda, with the highest species richness occurring in the oligotrophic Siriji reservoir. Zooplankton diversity varied among reservoirs, while abundance-weighted diversity showed no consistent pattern between oligotrophic and hypereutrophic conditions. Rotifers, particularly representatives of Brachionidae, showed greater numerical dominance in hypereutrophic reservoirs. A total of 28 indicator species were identified (IndVal > 70
The ecological impacts of non-native species are a primary cause of global biodiversity loss, yet in complex, multi-invader systems, the role of individual species can be masked. In tropical Lake Ziway, Ethiopia, the fishery historically dominated by the native Nile tilapia (Oreochromis niloticus) has shifted markedly over the past 3 decades toward dominance by non-native species. Here, we investigated the trophic role of the Japanese gengorobuna (Carassius cuvieri), a non-native fish species whose presence for decades was undocumented because of its persistent misidentification as crucian carp (Carassius carassius). Using stable isotope analysis (δ13C and δ15N), we tested the hypothesis that this long-overlooked herbivorous fish would primarily compete with other functionally similar native and non-native species. Our results revealed an interesting and more concerning interaction. While C. cuvieri exhibited moderate niche overlap with common carp (Cyprinus carpio) and African catfish (Clarias gariepinus), its isotopic niche showed high and significant overlap with the native Nile tilapia (71.8
In lake ecosystems, different dominant primary producers may exert distinct effects on methane (CH4) emissions. As key secondary producers and the principal grazers of phytoplankton and bacteria, zooplankton could modulate CH4 cycling. However, comparative studies are currently lacking that evaluate the impacts of zooplankton on ecosystem CH4 flux, and whether these impacts vary among systems containing different dominant primary-producer species. We posit that the influence of zooplankton on CH4 emissions is modulated by the functional and structural attributes of the dominant primary producers. In this study, we conducted a mesocosm experiment to examine the individual and combined effects of three dominant primary-producer species (macrophyte-dominated: Hydrilla verticillata, Vallisneria natans; phytoplankton-dominated: Chlorella pyrenoidosa) and zooplankton addition on ecosystem CH4 emissions. In treatments without zooplankton addition, H. verticillata mesocosms exhibited significantly higher CH4 fluxes across the water–air interface (104.7 ± 50.5 μmol m−2 day−1) than those of V. natans mesocosms (78.2 ± 43.4 μmol m−2 day−1). C. pyrenoidosa mesocosms exhibited intermediate CH4 fluxes, with no significant differences compared with either macrophyte treatment. Zooplankton addition was associated with higher CH4 flux in the H. verticillata treatment (160.8 ± 126.5 μmol m−2 day−1), whereas no significant effect was detected in the V. natans or C. pyrenoidosa treatments. Correlation analyses revealed weak but significant positive relationships between CH4 flux and both zooplankton biomass and H. verticillata biomass. Our findings suggest that lake CH4 flux responses to zooplankton addition are influenced by the identity and associated traits of the dominant primary producer.
Cryptobenthic fishes (CF) are cryptic species that exhibit mimicry with their benthic environment and can be either detritivorous or zoobenthivorous. Few studies have examined the influence of epibenthic macrofauna on CF diversity. This study analyzed the colonization and spatiotemporal succession of CF and macrofauna in fish-specific autonomous reef monitoring structures (FARMS) at Paranaguá Estuarine Complex (Brazil). Five FARMS were installed in localities in São Miguel, Amparo and Nova Brasília, which represented an estuarine gradient. Sampling was conducted every 2 months from October 2023 to August 2024; 303 individuals belonging to seven species associated with the FARMS were recorded, five of which were classified as CF. Bathygobius soporator was the dominant species in all of the sampled areas. To identify the epibenthic macrofauna, scrapings were performed every 2 months over the 10-month experiment from the FARMS installed in Nova Brasília and São Miguel. A dominance pattern of crustaceans, annelids and gastropods species was observed in Nova Brasília. In São Miguel, the macrofauna was dominated by annelids, bivalves, crustaceans, and ascidians. Individual FARMS were used as sampling replicates to evaluate spatial and temporal variation in fish assemblages. Fish community structure differed among areas, with a significant area × sampling event interaction indicating area-specific temporal trajectories, whereas no common temporal effect was detected. Macrofaunal assemblages differed between Nova Brasília and São Miguel, but no significant overall effect of fouling time was detected. Fish and macrofaunal community configurations were significantly concordant (procrustean randomization test, r = 0.636, P = 0.0348). These results indicate that cryptobenthic fish assemblages are spatially structured and that their temporal variation is associated with local changes in fouling communities, although the observational design did not demonstrate direct causal effects of macrofauna on fishes.
