Distribution and Prevalence of Harmful Algal Blooms in Arctic Waters

Principal Investigator: Donald Anderson, Woods Hole Oceanographic Institution

Project Summary

Many organisms may spread into and flourish in Arctic waters as a result of climate change, but few present such significant threats to human and ecosystem health as harmful algal bloom (HAB) taxa. Of particular concern are the toxic dinoflagellate Alexandrium catenella, the organism responsible for paralytic shellfish poisoning (PSP), as well as toxic diatoms in the genus Pseudo-nitzschia which cause amnesic shellfish poisoning (ASP). Recent measurements have provided irrefutable evidence that these HABs occur in the Chukchi Sea and adjacent waters, and that the potent toxins they produce are already impacting marine mammals, seabirds, and other resources that are critical to subsistence harvesters. These taxa have all been documented in recent plankton samples from the Chukchi Sea, and extraordinarily large concentrations of dormant A. catenella cysts have been measured in the sediments on the Chukchi shelf, representing a seedbed that can support recurrent blooms and further species dispersal into the Arctic. Germination of these cysts is temperature dependent, and warming temperatures will significantly increase the spatial and temporal window during which these blooms can initiate and persist. In light of recent HAB events and climate trends, there is an urgent need to expand our understanding of HABs in the Alaskan Arctic.

The goal of this project is to examine the distribution and prevalence of HAB species in Arctic waters. Sediment and water samples collected during two expeditions in 2018 aboard the US Coast Guard Cutter Healy (HLY1801, August; HLY1803, October-November) revealed a large- scale seedbed of A. catenella cysts located in the Chukchi Sea, as well as a bloom of A. catenella vegetative cells in August 2018. Both toxic and non-toxic diatoms in the genus Pseudo-nitzschia were detected, including species or strains that have yet to be characterized. Over this reporting period, sampling was repeated during the Distributed Biological Observatory (DBO) cruise (HLY1901, July-August 2019). Major findings of this expedition include the observation of an A. catenella bloom concurrent with a bird mortality event, as well as the identification of a secondary cyst seedbed near Barrow Canyon. We are using this information to develop conceptual models of the origin and transport of these organisms in the Chukchi Sea, which will inform assessment of the implications of future warming of Arctic waters, and how this may impact the risk from toxic algae to humans and wildlife in this region.