High-resolution DNA metabarcoding of modern surface sediments uncovers a diverse assemblage of dinoflagellate cysts in the Pacific and Arctic Oceans.

Resting cysts of dinoflagellates can persist in sediments, seeding harmful algal blooms (HABs). A DNA metabarcoding approach was employed, targeting the large subunit ribosomal (LSU D1-D2) and the internal transcribed spacer (ITS1) to investigate the diversity and biogeography of dinoflagellate cysts from the South China Sea to the Chukchi Sea. The LSU and ITS1 datasets identified 196 and 118 species, respectively, with only 59 dinoflagellate cyst species revealed by both approaches. Eleven cyst species of potentially toxic dinoflagellates and 82 species previously unknown as cyst producers were detected. Cysts of Heterocapsa cf. horiguchii, Heterocapsa minima, Heterocapsa iwatakii, Heterocapsa rotundata, and Heterocapsa steinii were documented through germination for the first time, with the latter three species also detected via metabarcoding. This study provides critical insights into the diversity and biogeography of dinoflagellate cysts by highlighting the complementary detection capabilities of LSU and ITS1 molecular markers and their trans-latitudinal distribution patterns. The identification of potentially toxic cysts and their ecological distributions offers crucial information on the ecology of harmful dinoflagellates. These findings underscore the importance of molecular techniques in monitoring dinoflagellate cysts.