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Skeletonema potamos is a freshwater diatom that has been widely distributed in North America, Europe, and Australia since the 1980s. However, there have been few previous reports of S. potamos in China. Only recently has S. potamos been frequently found in our extensive ecological surveys in China, and it has sometimes even been the dominant species. This study clarified the morphology, distribution, and origin of S. potamos, as well as the underlying mechanism contributing to its dominance. We examined the samples collected from the Changjiang River (Yangtze River) Basin during 2016–2022 and determined their geographical distribution. Genetic distance analysis indicated that S. potamos strains in China might have been transported by ships and ballast water from the USA or Japan through the East Sea into the Yangtze River Estuary. Cargo ships possibly contribute to its dispersal. An analysis of the ecological factors affecting the occurrence and distribution of S. potamos in China indicated that many waterbodies provide environments suitable for S. potamos. The suitable environment, small size, and rapid reproduction of S. potamos are the reasons for its dominance in the Yangtze River Basin. We predict that S. potamos is likely to form "blooms" in China in the future. [ABSTRACT FROM AUTHOR]

Three new species of Hannaea Patrick from the Hengduan Mountains in China are formally described herein, based on light and scanning electron microscope observations. Hannaea yalaensis sp. nov. has three continuous inflations along the ventral margin, resulting in an undulate outline compared to the outline of the most commonly reported Hannaea species. The valve of Hannaea hengduanensis sp. nov. is narrower, asymmetrical about the apical axis with capitate apices, dorsal and ventral sides almost parallel. On the ventral side of valve is an unornamented central area. The valve of Hannaea clavata sp. nov. is clavate. Valve margin is straight or slightly curved. The apices of the valve constrict sharply to form the capitate ends. In addition, we also briefly described other Hannaea from this region. Here, we document the morphologies of these new species and discuss the biogeographic distribution of the genus Hannaea in Asia. [ABSTRACT FROM AUTHOR]

Understanding how long-term environmental variation and biotic interaction determine biological assemblages is critical for evaluating the response of biological communities to anthropogenic and climate changes. We sampled plankton and water quality from a man-made lake monthly from 2006 to 2015 for the period from after creation to 13-year old of the lake. We used correlation, variation partitioning, multivariate autoregressive state-space models, and dynamic factor analyses to disentangle interactions of biotic and abiotic factors in regulating the dynamics of plankton size groups. We found that annual average total abundances decreased 86% for phytoplankton and 78% for zooplankton, while concentrations increased 1.8 times for total nitrogen and 2.7 times for total phosphorus during the study period. We concluded that the decline of plankton abundance was largely attributed to the predation of zooplankton on phytoplankton, fish predation on both phytoplankton and zooplankton, and linkages with the decline of water salinity, pH, and the increase of clarity. The decline of plankton abundance was apparently not resulted from long-term change in nutrient concentrations. These conclusions were further supported by that abundances of nano-phytoplankton and micro-phytoplankton oscillated in opposite direction with extremely low density of Cladocera (< 1 individual/L) during the study period. Our conclusions were also supported by the strong interactions between Rotifera and macro-phytoplankton and between nano-phytoplankton and Copepoda, as well as by the describability of the six plankton size groups in a shared trend that was opposite to the trends of water clarity and planktivorous fish stock density. [ABSTRACT FROM AUTHOR]

SUMMARY: Achnanthes maolanensis nov. sp. is a large diatom collected from subaerial, freshwater habitats in karst landforms in central‐south China. Living cells have two chloroplasts. Valves of this new species are panduriform in outline, slightly constricted in the middle part of the margins, with uniseriate areolae; the raphe is filiform, and there is a linear, thickened stauros in the central area of the RV. On the ARV, there is no central area, and as well there are no terminal orbiculi, marginal ridge, or terminal spine externally. The axial area (rapheless sternum) is located down the center, not offset from the center as in many other species of the genus and is narrow and almost straight. This suite of characters makes the new species easy to distinguish from other species in the genus. Its presence adds further documentation of the unique and diverse freshwater diatom flora from karst habitats in this region of China. [ABSTRACT FROM AUTHOR]

Periphytic diatoms play important functional roles in aquatic ecosystems. Their community compositions are widely used in water quality monitoring due to their wide distribution, short reproductive cycles, and sensitivity to environmental changes. In this study, 116 samples of periphytic diatom samples were collected from lakes in the lower reaches of the Yangtze River. The weighted average without tolerance down-weighting regression method was used to develop total phosphorus (r2 = 0.661), total nitrogen (r2 = 0.699), and chemical oxygen demand (r2 = 0.423) models, and the optimal and tolerance values of 78 periphytic species were calculated. Then, a new index, the comprehensive diatom index (CDI), was established on the basis of the optima and tolerances of these 78 species concerning the three environmental variables (TP, TN, and COD) to assess the water trophic status of the lakes in this region. According to the CDI, the trophic statuses of 8, 17, 23, 30, 22, and 14 sample sites were oligotrophic, mesotrophic, light eutrophication, moderate eutrophication, heavy eutrophication, and ultra-eutrophication, respectively. The CDI was more strongly correlated with the conductivity, pH, TP, TN, COD, and TDS than other diatom indices. These results demonstrate that the CDI is a useful metric for assessing the water trophic status of the lakes in the lower reaches of the Yangtze River. [ABSTRACT FROM AUTHOR]

Harmful cyanobacterial blooms are a widespread destruction to the processes and function of aquatic ecosystems. To study effects of cyanobacterial blooms on plankton diversity and composition, we analyzed data of cyanobacterial, eukaryotic phytoplankton, metazoan zooplankton, and physicochemical samples collected from 24 sites for four seasons in 2017 and 2018 from the large, shallow Lake Taihu. We found that cyanobacterial abundance significantly correlated with phytoplankton biomass, species richness, functional richness and evenness, and zooplankton biomass, Shannon's diversity, Simpson's evenness, and functional evenness and richness. High cyanobacterial abundance during summer did not result in low species and functional diversities for both phytoplankton and zooplankton compared with other seasons. Species and functional diversities of sites with high cyanobacteria abundance were not significantly lower than other sites with relatively low cyanobacteria abundance. Structure equation modeling indicated that cyanobacteria had direct influence on phytoplankton and zooplankton compositions. Physicochemical and temporal-spatial factors had direct influence on phytoplankton and zooplankton, and had indirect influence on phytoplankton and zooplankton through direct influence on cyanobacteria. Variance partitioning analysis quantified that cyanobacteria alone and interactions with physicochemical and spatial-temporal factors explained about 10% of phytoplankton variation and 26% of zooplankton variation. Our results indicate that cyanobacteria have substantial effects on phytoplankton and zooplankton biodiversity and community composition. Physicochemical and spatial-temporal factors could potentially obscure the detection of cyanobacterial effects on plankton in Lake Taihu that has cyanobacterial blooms in all seasons. Our findings may improve the understanding of dynamics and responses of plankton communities to environmental changes and cyanobacterial bloom disturbance and enhance the capability of assessing the effectiveness of eutrophication management and restoration of aquatic ecosystems., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2021 Elsevier B.V. All rights reserved.)