Trophic transfer of domoic acid: trophic niche proxies of the main vectors and predators affected in central California

Domoic acid (DA) is a harmful neurotoxin produced in specific types of harmful algal blooms (HABs) that when ingested by humans, causes amnesic shellfish poisoning, which is potentially life threatening. DA outbreaks in coastal communities have significant economic and ecological implications; they’re responsible for large scale fisheries closures and mass marine mammal mortalities. To develop monitoring and mitigation efforts, we need to understand locations prone to HABs and DA’s impact on local food webs. Unfortunately, such information remains unknown. This research constitutes the first study integrating carbon and nitrogen stable isotopes and DA concentrations to track the origin of toxic blooms, identify habitats sourcing DA and routes of phycotoxin transfer in Monterey Bay, California. Specifically, δ¹²C, δ¹⁵N and DA values were obtained from muscle and viscera of >200 individuals representing eight species collected in 2018. Bayesian models were used to estimate foraging habitats and isotopic niches of stranded sea lions (a top predator influenced by DA) and key small pelagic species, including anchovies, sardines and euphausiids. Mixing models incorporating information from sea lions were used to determine their primary prey and whether sea lions were exposed to DA inside Monterey Bay. In conjunction with GPS points of sampling sites, we determined that species in coastal and offshore regions of Monterey Bay occupy unique isospaces, potentially driven by distinct elemental cycling. Species also varied in their capacity to transfer phycotoxins to higher consumers. This comprehensive understanding of the geographic location (i.e. coastal or pelagic) fueling DA production and key vectors of trophic transfer in years without extreme events provides information critical to downstream users. It allows stakeholders to monitor high risk areas and forecast future events. Finally, it will support policies related to health, economic and ecological challenges associated with DA outbreaks and the health of fishing industries and its consumers.