Long-lasting extraordinary spring bloom of Amphidomataceae (Dinophyceae) and AZA-2 in the Argentine Sea

GUINDER, VALERIA A.; TILLMANN, URBAN; RAMÍREZ, FERNANDO J.; FERRONATO, CAROLA; RIVAROSSA, MARTÍN; KROCK, BERND

Congreso; 20th International Conference on Harmful Algae (ICHA); 2023

During two research expeditions along the Patagonian shelf in the SW South Atlantic, amixed, high abundance bloom of Amphidomataceans was caught in the mid shelf (45.5-46°S,62-61°W) in spring 2021. Water discoloration was observed in the bloom area. The earlierstage of the bloom was sampled on 16th November with up to 32 million cells/L. Twelve dayslater in the second cruise the bloom was still in high abundance: 14 million cells/L, at astation ~50 km distant from the first sampled location. The magnitude of this bloom is aglobal record for these dinoflagellates so far reported in the literature. Amphidomataceaespecies represented the 98-99% of the total phytoplankton abundance. Azadinium spinosumand A. dalianense were the most represented (96%), other species identified by SEM were A.dexteroporum, Amphidoma parvula and A. languida. The companion protists in thecommunity were other dinoflagellates and ciliates. In both stages of the bloom AZA-2 wasdetected in net tows and in bottle samples, with values up to xx pg/L. The bloom wasassociated with strong water column stratification, deep mixed layer depth and highchlorophyll concentration in the surface and in the subsurface maximum depth. Retentionmechanisms may favor the development and persistence of the bloom in the outer shelf wherefrontal systems develop. High abundance of Amphidomataceaens has been documented inother areas of the Argentine shelf in spring, but further research is needed to understand theenvironmental drivers of the blooms and their impacts on the marine food webs.