New insights on the identity of the naked dinoflagellates that formed an unprecedented bloom in the western Antarctic Peninsula

MASCIONI, M.; CUSICK, ALLISON; ALMANDOZ G. O.; SANCHEZ-PUERTA, M. VIRGINIA; VERNET, M

Christchuch

Simposio; XIII SCAR Biology Symposium; 2023

SCIENTIFIC COMMITTEE ON ANTARCTIC RESEARCH

The coastal areas along the western Antarctic Peninsula are characterized by the occurrence ofimportant phytoplankton blooms during summer. Large blooms of diatoms, cryptophytes,primnesiophytes, and prasinophytes have been recurrently recorded in these waters reaching highcell abundance. By contrast, the first massive bloom of small (~15 µm) naked dinoflagellates wasrecorded near Danco Island, in the Errera Channel (64°42′58.79′′S, 62°35′18.85′′O), on December18 th , 2016. The bloom reached an abundance of 9.5 x 10 6 cells L −1 and a carbon biomass of 1,597 μgC L -1 , and the blooming dinoflagellates represented around 90% of the total phytoplankton cell abundance and 97% of the total phytoplankton carbon biomass of the water sample. Naked dinoflagellates in Antarctic waters are an understudied group; their fragility makes them difficult to identify under the light microscope and find diagnostic characteristics for their classification. Despite umerous efforts, the blooming organisms could not be identified with light and scanning electron microscopy. In order to try to identify the organisms using molecular tools, we performed next-generation sequencing analysis on the bloom samples to obtain genetic information (e.g., 18S and 16S primers). In addition, we performed sequencing using dinoflagellate-specific primers (D1-D3 and ITS). Sequences suggest that these organisms are related to naked dinoflagellates of the genus Lepidodinium within the Gymnodiniaceae family. Species of this genus are known to have green kleptoplastidic plastids with prasinophyte’s origin and to form important blooms in other coastal areas around the world, in some cases leading to fish mortalities. This work provides important insights into the possible identity of these bloom-forming dinoflagellates and contributes to a better understanding of the diversity of these small organisms in Antarctic nearshore waters.