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In our recent investigations of diatom diversity, we studied three species, namely, Skeletonema costatum, Skeletonema subsalsum, and Skeletonema potamos. Although they have been found frequently in Changjiang (Yangtze) River Basin, their morphological and molecular identification is difficult in taxonomy. Therefore, to integrate morphological and molecular biological approaches, we compared systematically their morphological characters and performed phylogenetic analysis. Twelve strains of Skeletonema were collected and isolated from Shanghai and Jiangsu, China, and their morphological characteristics were examined by light microscopy (LM) and the scanning electron microscopy (SEM). Based on morphological comparison, we determined that S. potamos is easy to distinguish from the other two species. The heavily silicified areolae, undulated or cleft distal ends of terminal fultoportula processes (TFPPs), absence of basal pores of fultoportula processes (FPPs), the root-like protrusions of FPPs, and no interlocking connection are the stable characteristics that can be used to identify S. potamos. However, there are only two features that can distinguish S. costatum from S. subsalsum, namely the location of terminal rimoportulae (TRPs) and the distal shape of TFPPs. In addition, we amplified and sequenced nine common genetic markers from the strains, from which 101 sequences were obtained, constructed phylogenetic trees based on the nine genes and evaluated that seven genes can be used to identify S. potamos, and revealed that S. subsalsum is the closest known relative of S. costatum, and only ATP synthetase beta-subunit gene (atpB) is able to distinguish them from each other, which strongly support that it is an effective molecular marker for Skeletonema. This work provided a theoretical basis for the taxonomic study of Skeletonema. [ABSTRACT FROM AUTHOR]

Based on a combination of morphology and molecular data of ribosomal DNA genes, a new diatom genus Lineaperpetua gen. nov. Yu, You, Kociolek & Wang is described. The features that help define Lineaperpetua at the level of genus include: a tangentially undulated valve face; continuous cribra areolae on the valve interior consisting of pores arranged as strips; single rimoportula located inside the ring of marginal fultoportulae. Additionally, phylogenetic analysis based on nuclear small subunit (SSU) rDNA sequences and nuclear large subunit (LSU) rDNA gene placed the three strains of L. lacustris in a single, monophyletic clade at a considerable sequence distance from the other genera (Thalassiosira, Conticribra, Planktoniella, Shinodiscus, and other genera) belonging to Thalassiosirales. Despite the similarities with some species of Thalassiosira, Conticribra, and Spicaticribra, the suite of features found in Lineaperpetua differentiate it from these other genera. These molecular data and morphological characters suggest an affinity of the new genus to the Thalassiosiraceae. [ABSTRACT FROM AUTHOR]

Tourism remains one of the top threats in nature reserves worldwide. In this study, we first used both a field survey and in situ nutrient enrichment experiments to assess the effects of tourisms on aquatic ecosystems in a World Natural Heritage site that includes lakes, streams, shoals, and waterfalls. The results showed that phosphorus (P) enrichment altered benthic algal assemblage composition and the color of bryophyte-dominated benthic substrates in a shoal. Epilithic diatoms and their responses to the nutrient addition were significantly different between the control and test sites on a lake, which had contrasting tourist impacts in a lake. Second, we assessed the resilience of a lake heavily visited in the reserve by comparing phytoplankton density before and after a 2-year reserve closure due to an earthquake. Our study confirmed the hypotheses: (1) the perceived color change in Jiuzhaigou Natural Reserve waters was caused by nutrient enrichment in relation to tourist activities and was closely associated with a shift in algal composition; and (2) the changes to the fluvial and lake systems are still at their early stages and could be recovered by reducing tourism pressure. Our findings provide managers of protected karstic nature reserves with critical information for identifying causes of reserve degradation, estimating the carrying capacity for tourism and establishing limits of acceptable ecosystem changes. Guiping Deng (deceased) [query] [ABSTRACT FROM AUTHOR]

Melosira is one of the most common diatom genera found in freshwater ecosystems. There are many freshwater species of Melosira, of which M. varians is the most common. In our investigation of periphytic diatoms in the Jinsha River, China, a new species, M. capsularum sp. nov, was characterized in combined morphological and molecular approaches. M. varians was also analyzed using molecular data. The new species is similar to M. varians, M. moniliformis, M. nummuloides, and M. lineata in morphology. The cells are capsular and join to filaments by mucilage pads that are secreted on the valve face and united into pairs by their cingula. The valve face is domed and covered with small granules, and the valve mantle edge has a milled appearance. The two strains of M. capsularum are in a single clade obviously away from other Melosira species, as determined in phylogenetic analysis based on nuclear small subunit (SSU) rDNA sequences and the chloroplast-encoded rbcL gene. Thus, the results of morphological comparisons and phylogenetic analysis based on molecular data provide strong evidence that M. capsularum is a new species, thereby increasing the total number of recognized freshwater diatom species in China. In addition, we have systematically reclassified the freshwater Melosira that have been recorded in China. [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]

Ecological community assembly has been one of the central issues in ecology. In this study, twenty sites were selected in a shallow man-made lake and its surrounding canals in Shanghai, China. We examined monthly phytoplankton assemblages during 2010-2012, with the use of cluster and ordination analysis, to identify phytoplankton assemblages patterns. Our results indicated that phytoplankton assemblages varied along a gradient of turbidity and nutrients. The large canal with ample nutrients and high turbidity was dominated by diatoms (e.g., Navicula cryptocephala). Flagellates (e.g., Cryptomonas erosa, Chlamydomonas globosa and Euglena oxyuris) dominated in the canals with the decreased nutrient and turbidity. Dinoflagellates (e.g., Gymnodinium sp.) were abundant in the lake. The lake experienced drastic changes in physico-chemical conditions since its creation in 2003, such as desalination and nutrient enrichment. Phytoplankton assemblages trajectories followed environmental changes closely. A relatively stable seasonal cyclic character in the phytoplankton development was observed in lake during 2010-2012. These results suggested that local environmental constraints can be strong enough to structure local phytoplankton assemblages in this highly interconnected system. [ABSTRACT FROM AUTHOR]