Biodiversity exploration in autumn using environmental DNA in the South China sea

Deep-sea caridean shrimps collected from the South China Sea with emphasizing their phylogenetic relationships

Despite the high biological and ecological diversity of the South China Sea, limited research has been conducted on the deep-sea species diversity of caridean shrimps. Based on the collections from three scientific expeditions conducted in the South China Sea, 31 caridean species, belonging to nine families, were reported, including the identification of two species not previously documented in this region, namely Janicella spinicauda (A. Milne-Edwards, 1883) and Systellaspis curvispina Crosnier, 1988. In addition to morphological features, the COI and 16S gene sequences of these species were analyzed to assess their evolutionary relationships within each family. Phylogenetic analyses, with highest species coverage to date, indicated that similarity in morphological characteristics does not always lead to closer phylogenetic relationships and some defining characteristics for specific taxa are not always synapomorphies but may be the result of convergent evolution. Our results establish reliable evolutionary relationships within specific taxa and highlight the necessity for further taxonomic revisions within these taxa.

Environmental DNA metabarcoding reveals the effect of environmental selection on phytoplankton community structure along a subtropical river

The Dongjiang River, a major tributary of the Pearl River system that supplies water to more than 40 million people in Guangdong Province and neighboring regions of China, harbors rich biodiversity, including many endemic and endangered species. However, human activities such as urbanization, agriculture, and industrialization have posed serious threats to its water quality and biodiversity. To assess the status and drivers of phytoplankton diversity, which is a key indicator of aquatic ecosystem health, this study used Environmental DNA (eDNA) metabarcoding combined with machine learning methods to explore spatial variations in the composition and structure of phytoplankton communities along the Dongjiang River, including its estuary. The results showed that phytoplankton diversity exhibited spatial distribution patterns, with higher community structure similarity and lower network complexity in the upstream than in the downstream regions. Environmental selection was the main mechanism shaping phytoplankton community composition, with natural factors driving the dominance of Pyrrophyta, Ochrophyta, and Cryptophyta in the upstream regions and estuaries. In contrast, the downstream regions was influenced by high concentrations of pollutants, resulting in increased abundance of Cryptophyta. The random forest model identified temperature, dissolved oxygen, chlorophyll a, NO2-, and NH4+ as the main factors influencing the primary phytoplankton communities and could be used to predict changes during wet periods. This study provides valuable insights into the factors influencing phytoplankton diversity and community composition in the Dongjiang River, and demonstrates the application value of eDNA metabarcoding technique in large-scale, long-distance river biodiversity monitoring.

Three new species of Paratanaoidea (Crustacea, Tanaidacea) from the South China Sea

Three new crustacean species of the order Tanaidacea are described from the South China Sea. Alloleptochelia falciformes sp. nov. (Family Leptocheliidae) can be distinguished from the most similar species, A. evansi (Edgar, 2012), by the much stouter body, and fewer articles on the antennule flagellum and relatively longer pereopods 46 dactylus of the male. Kalloleptochelia multiarticulata sp. nov. (Family Leptocheliidae) can be easily differentiated from its congeners by the male having significantly more antennule flagellum articles, a two-articled uropod exopod, one additional dorsal seta on the pereopods 23 merus, and one additional spiniform seta on the pereopod-6 carpus. Paranesotanais incisus sp. nov. (Family Nototanaidae) differs from its only congener, P. longicephalus Larsen & Shimomura, 2008, by the female having one robust inner seta on the palm of the cheliped propodus, and the male having one long and conspicuous notch extending from the outer surface to the ventrodistal corner on the cheliped carpus. Morphological keys and comparison tables of all known species of the genera Alloleptochelia and Kalloleptochelia, as well as a key of the genus Paranesotanais, are provided.