Tuesday November 2, 2021, 1 pm GMT+1

Donald M. ANDERSON¹, Evangeline FACHON¹, Robert S. PICKART², Peigen LIN², Alexis D. FISCHER¹, Mindy L. RICHLEN¹, Victoria UVA¹, Michael BROSNAHAN¹, Leah MCRAVEN², Frank BAHR², Kathi LEFEBVRE³, Jacqueline M. GREBMEIER⁴, Seth DANIELSON⁵, Yihua LYU⁶, Yuri FUKAI⁷

Evidence for massive and recurrent toxic blooms of Alexandrium catenella in the Alaskan Arctic

¹ Biology Department, Woods Hole Oceanographic Institution, Woods Hole MA 02543, USA
² Physical Oceanography Department, Woods Hole Oceanographic Institution, Woods Hole MA 02543, USA
³ Environmental and Fisheries Sciences Division, Northwest Fisheries Science Center, National Marine Fisheries Service, NOAA, 2725 Montlake Blvd. East, Seattle, WA 98112, USA
⁴ University of Maryland Center for Environmental Sciences, Chesapeake Biological Laboratory, Solomons, MD 20688, USA
⁵ College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks AK 99775, USA,
⁶ South China Sea Environmental Monitoring Center, State Oceanic Administration, Guangzhou 510300, P.R. China
⁷ Graduate School of Environmental Science, Hokkaido University, North 10 West 5, Kita-ku, Sapporo, Hokkaido, 060-0810, Japan

Among the organisms that spread into and flourish in Arctic waters with rising temperatures and sea ice loss are toxic algae, a group of harmful algal bloom (HAB) species that produce potent biotoxins. Alexandrium catenella, a cyst-forming dinoflagellate that causes paralytic shellfish poisoning (PSP) throughout the world, has been observed in Alaskan waters for decades and is known to be transported into Arctic regions in waters transiting northward through Bering Strait, yet there is little recognition of this organism as a human health concern north of the Strait. Here we describe an exceptionally large A. catenella benthic cyst bed and hydrographic conditions across the Chukchi Sea that support germination and development of recurrent, self-initiating, and self-seeding blooms. Two prominent cyst accumulation zones result from deposition promoted by weak circulation. Cyst concentrations are among the highest reported globally for this species and the cyst bed is at least 6X larger in area than any other. These extraordinary accumulations are attributed to repeated inputs from advected southern blooms and to localized cyst formation and deposition. Over the last two decades, warming has likely increased the magnitude of the germination flux two-fold and advanced the timing of cell inoculation into the euphotic zone by 20 days. Conditions are also now favorable for bloom development in surface waters. The region is poised to support annually recurrent A. catenella blooms that are unprecedented in scale, posing a significant and worrisome threat to public and ecosystem health in Alaskan Arctic communities where economies are subsistence based.