The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

Alexandrium species are of great concerns because most of them could synthesize toxins such as paralytic shellfish poisoning (PSP), posing severely negative impact on human health and marine ecosystems. Due to the limited differences in morphologies of different Alexandrium species, it is challenging to distinguish Alexandrium species by morphological identification in ecological investigations. Molecular technologies including metabarcoding analysis have greatly improved the accuracy of species identification, and have been widely used in the study of Alexandrium. In this study, the common molecular marker 18S rDNA V4-based metabarcoding analysis was applied to analyze species composition and spatial-temporal distributions of Alexandrium species in China seas. First, the completeness of the 18S rDNA V4 reference sequences in the PR² database was evaluated and revised. Through NCBI NT database searches and phylogenetic analysis, reference sequences of 24 Alexandrium species were identified, including sequences for three Alexandrium species (A. limi, A. ogatae and A. fragae) that were not included in the PR² database. Metabarcoding analysis of 7916 samples collected in different regions of China seas, ranging from the Bohai Sea to the South China Sea, identified 12 known Alexandrium species (A. affine, A. andersonii, A. catenella, A. fragae, A. fraterculus, A. leei, A. minutum, A. ogatae, A. ostenfeldii, A. pohangense, A.satoaum and A. tamiyavanichii) and five Alexandrium species that could not be determined with certainty because their 18S rDNA V4 sequences were identical. Six Alexandrium species (A. andersonii, A. fragae, A. ogatae, A. pohangense, A.satoaum and A. tamiyavanichii) were first reported in ecological expeditions in China seas. Most Alexandrium species showed broad geographical distribution, showing minor differences in coefficient of community (C). However, some Alexandrium species showed different spatial distribution patterns in China seas. For example, A. catenella was found only in northern regions, while A. tamiyavanichii was found mainly in southern sea areas as reported previously. Similarly, some Alexandrium species showed differential seasonal distribution patterns. While A. catenella was found primarily in spring, A. affine had higher relative abundance in summer. In this project, we also evaluated how Alexandrium species correlated with other phytoplankton species, and the composition and distribution of Alexandrium species were affected by environmental factors. The results of this study indicated that metabarcoding analysis could be used to identify the species diversity and spatial-temporal distribution of Alexandrium, and that the selection of molecular markers with higher resolution and the improvement of molecular marker databases may further improve Alexandrium biodiversity.

metabarcoding analysis, China sea area, Alexandrium, spatial-temporal distribution