Pseudo-nitzschia is among a genus of phytoplankton known to produce toxins that negatively impact a wide range of organisms, including mankind. These blooms occur worldwide, particularly in the coastal regions of the Western United States. Recent evidence suggests that domoic acid, the neurotoxin produced by Pseudo-nitzschia, can be rapidly transported to the seafloor trapped within sinking particles. The goal of this thesis is to investigate the in situ behavior of DA as it sinks through the water column using a combination of monthly water column sampling coupled with moored sediment traps deployed at 150 and 540 m, respectively, in the Santa Barbara Basin. Results suggest that while sediment traps are an effective tool for the measurement of sinking particle flux, they underestimate DA fluxes by as much as 90% due to DA degradation within the sediment trap as a function of the poison used, and sample processing.

Measurements of upper water column Pseudo-nitzschia and DA abundance suggests that DA is produced throughout the upper 150 m and that most of the particulate DA is rapidly lost to the dissolved phase. Comparison of water column particulate DA inventories and those collected within the 150 and 540 m sediment traps (uncorrected for sediment trap loss) suggests that ∼5% of surface derived DA reaches the seafloor. These results suggest that the extremely high DA concentrations previously measured within deep moored sediment traps are substantially underestimated. Therefore, the impact of DA contamination in benthic food webs needs to be much more fully investigated in order to understand the potential long-term impacts of DA poisoning long after a Pseudo-nitzschia bloom may have occurred.