Passive sampling for grazer cues incorporates top-down effects in harmful algal bloom monitoring and toxin prediction

Domoic acid (DA) produced by toxigenic species of the diatom genus Pseudo-nitzschia during harmful algal blooms (HABs) bioaccumulates in filter feeders, bait fish, and commercial seafood products, posing a threat to marine organisms and public health. Copepodamides, a group of polar lipids exuded by copepods, are known to induce DA production in multiple species of Pseudo-nitzschia . However, copepodamides are not currently considered in HAB monitoring and prediction, in part because of challenges associated with measuring ambient concentrations of dilute and labile compounds. Here we employ solid phase adsorption toxin tracking (SPATT) to measure natural concentrations of copepodamides over 28 mo in Monterey Bay, California, a known hotspot for HAB events. Copepodamides were significantly correlated to copepod biovolume, confirming utility as a zooplankton proxy. In generalized linear models, copepodamides from SPATT provided greater accuracy and lead time for predicting Pseudo-nitzschia abundance and DA concentration in sentinel mussels than DA from SPATT. Field experiments in the Northeast Atlantic assessed sampling methodology, and lab experiments demonstrated DA induction in Pseudo-nitzschia multiseries isolated from Monterey Bay. Results show potential for copepodamides to improve HAB predictions and encourage development of novel approaches to include top-down information in HAB monitoring systems.