Summer 2021

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)


Moss Landing Marine Laboratories


Given the effects of harmful algal blooms (HABs) on human and wildlife health, understanding how domoic acid (DA) is accumulated and transferred through food webs is critical for recognizing the most affected marine communities and predicting ecosystem effects. This study combines stable isotopes of carbon (δ13C) and nitrogen (δ15N) from bulk muscle tissue with DA measurements from viscera to identify the foraging strategies of important DA vectors and predators in Monterey Bay, CA. Tissue samples were collected from 23 species across three habitats in the summer of 2018 and 2019 (time periods without prominent HABs), with a focus on California sea lions, as the primary predator affected by DA, their prey (anchovies, sardines, squid, krill, juvenile rockfish), and other key sentinel species (e.g., mussels). My results highlight 13C enrichment in krill and elevated DA concentrations ([DA]; ppm) in anchovies collected inside Monterey Bay, indicating inshore-offshore differences in coastal productivity and DA accumulation. The narrow, overlapping isotopic niches between anchovies and sardines and striking differences in [DA], suggests these common prey species exhibit dietary specialization and resource partitioning, potentially based on prey size. In contrast, krill, market squid, and juvenile rockfish accumulated minimal DA during 2018/19 and thus have a lower capacity to serve as DA vectors during years of low HAB activity. Low [DA] in the livers of stranded sea lions along with their large isotopic niche may indicate that individuals have different diets or feed in isotopically distinct locations limiting the ability to use sea lions as sentinels for DA outbreaks in a specific geographic area. Collectively, my results show that DA was produced a few kilometers from the coastline and that anchovies were the most powerful DA vector in coastal-pelagic zones (potentially associated with their feeding specialization and high mobility), while mussels did not contain detectable DA in the years of sampling (despite their status as the key indicator of DA in coastal systems) and only reflect in situ DA, δ13C, and δ15N values. In comparison, anchovy DA loads in this study consistently exceeded FDA regulatory limits for human consumption. The findings demonstrate the efficacy of combining multiple biogeochemical tracers to improve HAB monitoring efforts and identifying routes of DA transfer across habitats and trophic levels.