Molecular Detection and First Report of Gyrodinium jinhaense (Dinophyceae, Alveolata) in a Tropical River-estuary System

Gyrodinium jinhaense is a recently described unarmored heterotrophic dinoflagellate species based on samples collected from southern Korea. It was later reported to occur in other temperate environments. However, its biogeographic and ecological distribution remains to be fully characterized. In this paper, we report the finding that this species occurs in tropical waters, in particular in a riverine-estuarine environment in the Philippines. The finding was based on an analysis of environmental metabarcoding data obtained via sequencing of the full-length 18S rDNA marker using the PacBio platform. The samples were obtained from sites in the Pampanga River and its estuary in Manila Bay, which represent different salinity environments. Sequence analysis revealed the presence of full-length rDNA sequences from different collection sites or seasons that clustered distinctly to previously reported Gyrodinium jinhaense 18S rDNA sequences. This is the first report of Gyrodinium jinhaense in tropical waters and in the Philippines, as well as in brackish and freshwater environments. These findings provide insights into the biology and ecology of this species, in particular, to its potential tolerance to a wide range of salinity and temperature. Furthermore, multiple haplotypes of the Gyrodinium jinhaense 18S rDNA were observed, highlighting the potential diversity of the species in a single riverine system. Additionally, sequences that could represent undescribed Gyrodinium species were also discovered hinting at the taxonomic diversity of this genus that remains to be characterized.