Algal toxins in Alaskan seabirds: Evaluating the role of saxitoxin and domoic acid in a large-scale die-off of Common Murres

Abstract

Elevated seawater temperatures are linked to the development of harmful algal blooms (HABs), which pose a growing threat to marine birds and other wildlife. During late 2015 and early 2016, a massive die-off of Common Murres (Uria algae; hereafter, murres) was observed in the Gulf of Alaska coincident with a strong marine heat wave. Previous studies have documented illness and death among seabirds resulting from exposure to the HAB neurotoxins saxitoxin (STX) and domoic acid (DA). Given the unusual mortality event, corresponding warm water anomalies, and recent detection of STX and DA throughout coastal Alaskan waters, HABs were identified as a possible factor of concern. To evaluate whether algal toxins may have contributed to murre deaths, we tested for STX and DA in a suite of tissues obtained from beach-cast murre carcasses associated with the die-off as well as from apparently healthy murres and Black-legged Kittiwakes (Rissa tridactyla; hereafter, kittiwakes) in the preceding and following summers. We also tested forage fish and marine invertebrates collected in the Gulf of Alaska in 2015–2017 to evaluate potential sources of HAB toxin exposure for seabirds. Saxitoxin was present in multiple tissue types of both die-off (36.4%) and healthy (41.7%) murres and healthy kittiwakes (54.2%). Among birds, we detected the highest concentrations of STX in liver tissues (range 1.4 –10.8 µg 100 g-1) of die-off murres. Saxitoxin was relatively common in forage fish (20.3%) and marine invertebrates (53.8%). No established toxicity limits currently exist for seabirds, but concentrations of STX in birds and forage fish in our study were lower than values reported from most other bird die-offs in which STX intoxication was causally linked. We detected low concentrations of DA in a single bird sample and in 33.3% of marine invertebrates and 4.0% of forage fish samples. Although these results do not support the hypothesis that acute exposure to STX or DA was a primary factor in the 2015–2016 die-off event, additional information about the sensitivity of murres to these toxins is needed before we can discount their potential role in the die-off. The widespread occurrence of STX in seabirds, forage fish, and marine invertebrates in the Gulf of Alaska indicates that algal toxins should be considered in future assessments of seabird health, especially given the potential for greater occurrence of HABs in the future.