Different facets of alpha and beta diversity of benthic diatoms along stream watercourse in a large near-natural catchment.

Understanding the processes and mechanisms that shape the distribution patterns and variations of biodiversity along spatial gradients continues to be a priority for ecological research. We focused on the biodiversity of benthic diatom communities within a large near-natural watershed. The objectives are: (1) to explore the overall spatial patterns of benthic diatom biodiversity; (2) to investigate the effects associated with watercourse position and environmental variables, as well as both common and rare species on two facets (i.e., taxonomic and functional) of alpha and beta diversity; and (3) to unveil the mechanisms underlying their spatial variations. Alpha diversity indices along the stream watercourse showed a clear increasing trend from upstream to downstream sites. Results of random forest regression identified conductivity as the primary factor influencing functional alpha diversity, while elevation emerged as the predominant factor for taxonomic alpha diversity. Beta diversity partitioning revealed that taxonomic beta diversity generally exceeded functional beta diversity. These diversity measures exhibited different patterns along the watercourse position: taxonomic beta diversity remained relatively consistent along the watercourse, whereas functional total beta diversity and its two components of middle stream sites were lower than those of upstream and downstream sites. Functional beta diversity was sustained by dominant and common species, while rare species made significant contributions to taxonomic beta diversity. Both taxonomic and functional beta diversity and its components displayed a stronger influence from spatial factors than from local environmental, geo-climatic, and nutrient variables. Collectively, taxonomic and functional alpha and beta diversity demonstrated distinct responses to the main environmental gradients and spatial factors within our catchment, highlighting their different insights into diatom diversity. Furthermore, research is required to assess the generalizability of our findings to similar ecosystems. In addition, this study presents opportunities for expansion to include other taxa (e.g., macroinvertebrates and fish) to gain a comprehensive understanding of the driving mechanisms behind stream biodiversity.

Complete mitochondrial genome identification of Niwaella nigrolinea (Cypriniformes: Cobitidae).

In this study, the complete mitochondrial genome of Niwaella nigrolinea (Cypriniformes: Cobitidae) from Zhejiang, China, was determined for the first time. We found that the sequenced length of the complete mitochondrial genome of N. nigrolinea was 16,565 bp. The genome contained 13 protein-coding genes, 22 transfer RNAs, two ribosomal RNAs, and two non-coding regions, identical to most other vertebrates. Our phylogenetic analysis results confirmed that N. nigrolinea was close to an unclassified Cobitis sp. and the fishes of the genus Cobitis. These data would contribute to the genetic conservation genetics and stock evaluation of N. nigrolinea.

The mitochondrial genome of Sinobdella sinensis (Synbranchiformes: Mastacembelidae) from China's Qiantang River.

This study determined the mitochondrial genome of Sinobdella sinensis (Synbranchiformes: Mastacembelidae) from China's Qiantang River for the first time. The mitochondrial genome of S. sinensis was sequenced to be 16,543 bp in length, larger than S. sinensis from China's Yangtze River. The genome contains 13 protein-coding genes, 22 transfer RNAs, two ribosomal RNAs, two central non-coding regions (the control region and the origin of light strand replication), identical to most other vertebrates. Phylogenetic analysis highly supported that S. sinensis from China's Qiantang River was different from other Mastacembelus fish. However, it showed a close relationship with Macrognathus aculeatus. These data would explain the evolutionary mechanisms and biogeography of the family Mastacembelidae and is helpful for the conservation of genetics and stock evaluation for S. sinensis.

The complete mitochondrial genome of Formosania galericula (Cypriniformes: Gastromyzontidae).

This study determined the complete mitochondrial genome of Formosania galericula (Cypriniformes: Gastromyzontidae) from Zhejiang, China, for the first time. The complete mitochondrial genome of F. galericula was sequenced to be 16,555 bp in length. The genome contained 13 protein-coding genes, 22 transfer RNAs, two ribosomal RNAs, two central non-coding regions (the control region and the origin of light strand replication), identical to most other vertebrates. Phylogenetic analysis highly supported that F. galericula was close to Crossostoma lacustre and the genus Vanmanenia fish. However, F. galericula was not firstly clustered with Formosania chenyiyui but after the genus Vanmanenia fish. These data would explain the evolutionary mechanisms and biogeography of the family Gastromyzontidae and is helpful for the conservation of genetics and stock evaluation for F. galericula.

Variability of polychaete secondary production in intertidal creek networks along a stream-order gradient.

Dendritic tidal creek networks are important habitats for sustaining biodiversity and ecosystem functioning in salt marsh wetlands. To evaluate the importance of creek heterogeneity in supporting benthic secondary production, we assess the spatial distribution and secondary production of a representative polychaete species (Dentinephtys glabra) in creek networks along a stream-order gradient in a Yangtze River estuarine marsh. Density, biomass, and secondary production of polychaetes were found to be highest in intermediate order creeks. In high order (3rd and 4th) creeks, the density and biomass of D. glabra were higher in creek edge sites than in creek bottom sites, whereas the reverse was true for low order (1st and 2nd) creeks. Secondary production was highest in 2nd order creeks (559.7 mg AFDM m-2 year-1) and was ca. 2 folds higher than in 1st and 4th order creeks. Top fitting AIC models indicated that the secondary production of D. glabra was mainly associated with geomorphological characters including cross-sectional area and bank slope. This suggests that hydrodynamic forces are essential factors influencing secondary production of macrobenthos in salt marshes. This study emphasizes the importance of microhabitat variability when evaluating secondary production and ecosystem functions.