Dinoflagellate Tripos species composition and seasonal dynamics in Jiaozhou Bay revealed through 18S rDNA V4-based metabarcoding analysis

Tripos is one of the largest dinoflagellate genera with ~800 reported taxa widely distributed in global marine ecosystems. These diverse Tripos species are ecologically important as critical primary producers and some Tripos species are also harmful algal bloom (HAB) species that may pose significant negative impact on marine ecosystems. However, due to the high morphological intraspecific variability and plasticity of numerous Tripos species, morphology-based identification and tracking of their dynamic changes have been both technically challenging and inconclusive. In this project, we carried out metabarcoding analysis of Tripos species in Jiaozhou Bay (JZB) through amplifying and sequencing of the common molecular marker 18S rDNA V4. The analysis identified five Tripos species (T. furca, T. fusus, T. eugrammus, T. falcatus and T. massiliensis), including two (T. eugrammus and T. falcatus) identified for the first time in JZB, demonstrating the competitive strength of metabarcoding analysis. This analysis of time-series samples collected in JZB revealed interesting seasonal dynamic changes of Tripos species, with different species demonstrating differential seasonal preferences. This analysis also suggested the possible existence of 11 additional Tripos species in JZB. The inconclusive identification of these 11 potential Tripos species indicated that the resolution of the common molecular marker 18S rDNA V4 applied in this study is inadequate and that the molecular reference data for Tripos is still limited. Selection of molecular markers with higher resolution (such as 28S rDNA D1-6) and the completion of reference sequences of Tripos species may facilitate more accurate identification of and tracking of their dynamic changes.