On the central California coast, toxigenic populations of Pseudo-nitzschia sp. cause near annual harmful algal blooms (HABs) related to upwelling-favorable winds in the spring and summer. This leads to ecological and economic losses from domoic acid toxin. Between bloom events, sentinel mussels at the Santa Cruz Municipal Wharf (SCW) show continuous low-level contamination with domoic acid. Chronic, low dose domoic acid exposure is difficult to regulate and is an emerging health risk for coastal communities. Here we investigate two potential contributing sources to background domoic acid in mussels. The first is the accumulation of dissolved domoic acid. Due to its chemical stability, domoic acid has been shown to persist in marine environments long after causative blooms dissipate. In addition, sampling for dissolved domoic acid via solid phase adsorption toxin tracking (SPATT) from SCW suggest bloom de-coupled toxin events and rising concentrations of dissolved domoic acid in recent years. We use experiments with dissolved domoic acid and California mussels to elucidate dissolved toxin accumulation from the water. The second potential source is slow depuration by mussels after consuming toxic cells. We fit 1-box exponential models to timeseries data from the SCW, tracking depuration months after a bloom event. Results suggest that slow depuration is a good fit for data at this site, although slight uptake of dissolved domoic acid and transient Pseudo-nitzschia populations may also bolster background levels between large bloom events.
Trapp et al. (Fri,) studied this question.