Diversity and seasonal occurrence of haptophyta in northern South China Sea through size-fractionated metabarcoding

Haptophyta plays a key role in marine pico-nanoeukaryote communities but information on their diversity and ecology is extremely limited. A total of 103 water samples were collected in northern South China Sea to assess the diversity of haptophyta through metabarcoding targeting 18S V4 rDNA. Furthermore, we investigated the potential genetic differentiation among seasonal occurring Phaeocystis globosa using the high resolution molecular marker pgcp1. 18S V4 rDNA metabarcoding dataset revealed 41 species of haptophytes, with 16 of them as the first record in this region. Notably, six harmful species were detected, including Chrysochromulina leadbeateri, Phaeocystis globosa, and Prymnesium parvum. The pgcp1 marker revealed two clades of Phaeocystis globosa and both of them were present around the year. Clade I was found to predominate in warm season, while Clade III tended to bloom in cold waters. Our results highlight the risk potential of harmful haptophytes in the northern South China Sea.