The Chroococcales is one of the least studied cyanobacterial orders comprising the non-baeocyte-producing coccoids cyanobacteria with stacked and fasciculated thylakoids. During a survey of aquatic biodiversity in Caohai Lake in Guizhou Province, China, a coccoid-like cyanobacterium was isolated. It was characterized using a polyphasic approach, based on morphology, electron microscopy, and molecular phylogenetic analyses. This species’ colonies exhibited morphological similarity to those of Microcystis species but differed in their larger colony sizes and widely oval cells. The 16S rRNA gene sequence of this species had the maximum homology, corresponding to 93.10%, to that of the genus Microcystis. The results of 16S rRNA gene threshold value and 16S rRNA phylogenetic analyses confirmed that the studied species belongs to the family Microcystaceae but is phylogenetically distinct from the other species of Microcystaceae. Furthermore, The D1–D1′, Box–B helix, and V3 helix of the 16S–23S ITS region were also different from those previously described in Microcystaceae taxa. Combining the morphological, ecological, and molecular features of the coccoid-like cyanobacterium, we here propose the establishment of the Cyanodorina gen. nov. and the Cyanodorina ovale sp. nov.

Water quality is directly linked to drinking water safety for millions of people receiving the water. The Danjiangkou Reservoir is the main water source for the Middle Route of the South-to-North Water Diversion Project (MR-SNWDP), located in the vicinity of Henan and Hubei provinces in China. Aquatic microorganisms are key indicators of biologically assessing and monitoring the water quality of the reservoir as they are sensitive to environmental and water quality changes. This study aimed to investigate the spatiotemporal variations in bacterioplankton communities during wet (April) and dry (October) seasons at eight monitoring points in Hanku reservoir and five monitoring points in Danku reservoir. Each time point had three replicates, labeled as wet season Hanku (WH), wet season Danku (WD), dry season Hanku (DH), and dry season Danku (DD) of Danjiangkou Reservoir in 2021. High-throughput sequencing (Illumina PE250) of the 16S rRNA gene was performed, and alpha (ACE and Shannon) and beta (PCoA and NDMS) diversity indices were analyzed. The results showed that the dry season (DH and DD) had more diverse bacterioplankton communities compared to the wet season (WH and WD). Proteobacteria, Actinobacteria, and Firmicutes were the most abundant phyla, and Acinetobacter, Exiguobacterium, and Planomicrobium were abundant in the wet season, while polynucleobacter was abundant in the dry season. The functional prediction of metabolic pathways revealed six major functions including carbohydrate metabolism, membrane transport, amino acid metabolism, signal transduction, and energy metabolism. Redundancy analysis showed that environmental parameters greatly affected bacterioplankton diversity during the dry season compared to the wet season. The findings suggest that seasonality has a significant impact on bacterioplankton communities, and the dry season has more diverse communities influenced by environmental parameters. Further, the relatively high abundance of certain bacteria such as Acinetobacter deteriorated the water quality during the wet season compared to the dry season. Our findings have significant implications for water resource management in China, and other countries facing similar challenges. However, further investigations are required to elucidate the role of environmental parameters in influencing bacterioplankton diversity in order to devise potential strategies for improving water quality management in the reservoir.

A new freshwater diatom species, Achnanthes licunese sp. nov., was found on pebble samples collected from Licun River in Shandong Province, China. The various taxonomic characteristics of Achnanthes licunese sp. nov. is observed under light and scanning electron microscope. The living cells of A. licunese sp. nov. possesses two chloroplasts. Its valves exhibit a linear to linear-lanceolate outline, slightly constricted in the middle part, with uniseriate striae. The central area of the raphid valves is expanded into a linear and thickened stauros, and the raphe is filiform. On the araphid valves, there is no central area, and the axial area (sternum) is located in the valve margin. The valve of the A. licunese sp. nov. possesses the marginal spines, but no marginal ridge and terminal orbiculi. By comparing the new species with similar Achnanthes species, A. licunese sp. nov. was confirmed to be sufficiently different regarding valve size, striae density, and the presence of marginal spines. The discovery of this species increases the diversity of freshwater diatoms.

The Danjiangkou Reservoir (DJKR) serves as the water source for the Middle Route of the South-to-North Water Diversion Project (MR-SNWDP), yet comprehensive understanding of its ecosystem structure and function remains limited. This study addressed this knowledge limitation by developing an Ecopath model with 22 functional groups, parameterized using field survey data from 2022 to 2023. Our findings revealed a trophic structure spanning levels 1 to 3.59, with the highest level occupied by piscivorous mandarin fish (Siniperca spp.). Energy flowed through two dominant pathways, with the grazing food chain demonstrating higher transfer efficiency compared to the detrital pathway. Mixed trophic impact analysis identified the introduced icefish (Neosalanx taihuensis) as exerting substantial negative impacts on most functional groups. Key ecosystem indices, including the total primary production to total respiration ratio (TPP/TR, 1.99), connectance index (CI, 0.248), and system omnivory index (SOI, 0.113), collectively indicated an ecosystem of moderate maturity and stability. Persistent challenges include the proliferation of N. taihuensis, suboptimal energy transfer between trophic levels III and IV, and inefficient utilization of primary productivity. To enhance ecosystem resilience and maintain water quality, we recommend the targeted removal of icefish and strategic management of zooplanktivorous fish populations.

It is imperative that freshwater fish biodiversity research incorporates diverse components, encompassing taxonomy, phylogeny and function, alongside multifaceted facets, including richness, divergence and regularity. This comprehensive approach is essential to facilitate a more profound comprehension of freshwater ecosystem functions, to elucidate the mechanisms underpinning fish community assembly, and to accurately assess the impacts of anthropogenic disturbance. Consequently, this scientific understanding can inform the development of effective fish conservation and ecosystem management strategies. This study utilized environmental DNA metabarcoding to assess the diversity of fish across the entire Yangtze River, encompassing the upper reach (Upper), the Three Gorges Reservoir area (RES_SX), and the downstream reach (Down). The results indicated that 150 distinct fish species were detected, with the RES_SX area exhibiting a significantly lower taxonomic diversity and fish detection rate in comparison to the other two regions. Conversely, phylogenetic and functional diversity exhibited stability post-normalization by taxonomic richness. Furthermore, investigation of the divergence facet of alpha-diversity demonstrated a reduction in clustering and an improvement of overdispersion on the phylogenetic and functional diversity, respectively, in the RES_SX and Down regions. Beta-diversity analysis further revealed lower taxonomic beta-diversity but higher phylogenetic and functional beta-diversity in the RES_SX area. A substantial degree of geographic distance-dependent similarity was identified for all three components of beta-diversity in the Upper Reach. Conversely, these components were found to be disrupted in the Down Reach. Finally, an analysis of the assembly mechanism revealed stochastic processes, dispersal limitation and drift as the dominant factors shaping the fish communities, with reduced dispersal limitation in the RES_SX area. This study provides novel insights into the multidimensional diversity of fish populations in response to dam construction, emphasizing the necessity of integrating multiple facets of diversity for accurate impact assessment and supporting evidence-based conservation of fish species in the Yangtze River.