Rich diversity and active spatial–temporal dynamics of Thalassiosira species revealed by time-series metabarcoding analysis

Thalassiosira is a species-rich genus in Bacillariophyta that not only contributes positively as primary producer, but also poses negative impacts on ecosystems by causing harmful algal blooms (HABs). Although taxonomical studies have identified a large number of Thalassiosira species, however, the composition of Thalassiosira species and their geographical distribution in marine ecosystems were not well understood due primarily to the lack of resolution of morphology-based approaches used previously in ecological expeditions. In this study, we systematically analyzed the composition and spatial–temporal dynamic distributions of Thalassiosira in the model marine ecosystem Jiaozhou Bay by applying metabarcoding analysis. Through analyzing samples collected monthly from 12 sampling sites, 14 Thalassiosira species were identified, including five species that were not previously reported in Jiaozhou Bay, demonstrating the resolution and effectiveness of metabarcoding analysis in ecological research. Many Thalassiosira species showed prominent temporal preferences in Jiaozhou Bay, with some displaying spring–winter preference represented by T. tenera, while others displaying summer-autumn preference represented by T. lundiana and T. minuscula, indicating that the temperature as an important driving factor in the temporal dynamics. The application of metabarcoding analysis, equipped with appropriate molecular markers with high resolution and high specificity and databases of reference molecular marker sequences for potential all Thalassiosira species, will revolutionize ecological research of Thalassiosira species in Jiaozhou Bay and other marine ecosystems.