Current climate trends resulting in rapid declines in sea ice and increasing water temperatures are likely to expand the northern geographic range and duration of favorable conditions for harmful algal blooms (HABs), making algal toxins a growing concern in Alaskan marine food webs. Two of the most common HAB toxins along the west coast of North America are the neurotoxins domoic acid (DA) and saxitoxin (STX). Over the last 20 years, DA toxicosis has caused significant illness and mortality in marine mammals along the west coast of the USA, but has not been reported to impact marine mammals foraging in Alaskan waters. Saxitoxin, the most potent of the paralytic shellfish poisoning toxins, has been well-documented in shellfish in the Aleutians and Gulf of Alaska for decades and associated with human illnesses and deaths due to consumption of toxic clams. There is little information regarding exposure of Alaskan marine mammals. Here, the spatial patterns and prevalence of DA and STX exposure in Alaskan marine mammals are documented in order to assess health risks to northern populations including those species that are important to the nutritional, cultural, and economic well-being of Alaskan coastal communities. In this study, 905 marine mammals from 13 species were sampled including; humpback whales, bowhead whales, beluga whales, harbor porpoises, northern fur seals, Steller sea lions, harbor seals, ringed seals, bearded seals, spotted seals, ribbon seals, Pacific walruses, and northern sea otters. Domoic acid was detected in all 13 species examined and had the greatest prevalence in bowhead whales (68%) and harbor seals (67%). Saxitoxin was detected in 10 of the 13 species, with the highest prevalence in humpback whales (50%) and bowhead whales (32%). Pacific walruses contained the highest concentrations of both STX and DA, with DA concentrations similar to those detected in California sea lions exhibiting clinical signs of DA toxicosis (seizures) off the coast of Central California, USA. Forty-six individual marine mammals contained detectable concentrations of both toxins emphasizing the potential for combined exposure risks. Additionally, fetuses from a beluga whale, a harbor porpoise and a Steller sea lion contained detectable concentrations of DA documenting maternal toxin transfer in these species. These results provide evidence that HAB toxins are present throughout Alaska waters at levels high enough to be detected in marine mammals and have the potential to impact marine mammal health in the Arctic marine environment.

[1] A four-box model of planktonic nutrient cycling was coupled to a high-resolution hindcast circulation model of the Oregon-Washington coast to assess the role of the Columbia River plume in shaping regional-scale patterns of phytoplankton biomass and productivity. The ecosystem model tracks nitrogen in four phases: dissolved nutrients, phytoplankton biomass, zooplankton biomass, and detritus. Model parameters were chosen using biological observations and shipboard process studies from two cruises in 2004 and 2005 conducted as part of the River Influences on Shelf Ecosystems program. In particular, community growth and grazing rates from 26 microzooplankton dilution experiments were used, in conjunction with analytical equilibrium solutions to the model equations, to diagnose key model rate parameters. The result is a simple model that reproduces both stocks (of nutrients, phytoplankton, and zooplankton) and rates (of phytoplankton growth and microzooplankton grazing) simultaneously. Transient plume circulation processes are found to modulate the Washington-Oregon upwelling ecosystem in two ways. First, the presence of the plume shifts primary production to deeper water: under weak or variable upwelling winds, 20% less primary production is seen on the inner shelf, and 10-20% more is seen past the 100 m isobath. River effects are smaller when upwelling is strong and sustained. Second, increased retention in the along-coast direction (i.e., episodic interruption of equatorward transport) causes a net shift toward older communities and increased micrograzer impact on both the Oregon and Washington shelves from the midshelf seaward.

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