The researchers adapted an existing technique called solid-phase adsorption toxin tracking, or SPATT. In plain terms, this means suspending porous resin beads in mesh rings in the ocean, where they continuously absorb dissolved compounds from the water over days or weeks.

The team deployed these passive samplers at the Santa Cruz Municipal Wharf, a recognized hot spot for toxic bloom activity in Monterey Bay. The samplers reliably captured copepodamide concentrations, and those measurements correlated directly with zooplankton counts taken with nets.

How much warning does the method provide?

The results represent a substantial improvement over current practice:

• Copepodamide tracking predicted blooms of Pseudo-nitzschia six weeks in advance with high statistical accuracy.
• For predicting domoic acid contamination in sentinel mussels above safety thresholds, the method delivered a seven-week lead time.
• Conventional models tracking domoic acid directly achieved peak accuracy at only one week.

The technique also reduced false negatives — the most dangerous failure mode in seafood safety, where contamination goes undetected before toxic shellfish reach the market. The new models successfully alerted managers to 22% of high-toxin events seven weeks in advance. Standard toxin tracking flagged only 14% of events, and just one week ahead.

"By capturing the chemical signals of biological predators, we've opened up a vital top-down window into ecosystem dynamics," said Kudela, a distinguished professor of ocean sciences at UC Santa Cruz. "By 'listening' to chemical interactions between marine grazers and algae, we can add a new and reliable monitoring technique to our early-warning toolbox."

Why does the early warning matter?

For decades, forecast models have relied almost exclusively on "bottom-up" physical drivers such as ocean currents, water temperature and nutrient upwelling. Current public health monitoring depends on measuring toxins in seawater or shellfish tissue, often giving coastal managers only days to a week of notice before they must close harvests.

The stakes are high. Domoic acid bioaccumulates up the food chain — first in filter-feeding shellfish, anchovies and sardines, then in the predators that eat them. In marine mammals and seabirds, the toxin causes severe neurological damage, disorientation, seizures and death. Over the past two decades, toxic blooms in Monterey Bay and along the Pacific coast have caused widespread strandings and deaths among California sea lions, sea otters, brown pelicans and humpback whales.

When toxin levels exceed the federal safety threshold of 20 micrograms of domoic acid per gram of tissue, agencies must impose immediate harvesting bans to prevent amnesic shellfish poisoning in humans. These shutdowns have repeatedly closed Dungeness crab, rock crab, razor clam, sardine and anchovy fisheries, costing California coastal communities tens of millions of dollars in lost revenue and disrupting tribal subsistence harvests and tourism.

What comes next?

The findings carry practical weight because SPATT samplers are already deployed routinely by monitoring networks along the Pacific coast and globally.

"By simply analyzing those existing resin samplers for grazer chemical signals alongside target toxins, coastal agencies can plug top-down information directly into our current warning networks without needing expensive new infrastructure," Kudela said.

The researchers' next goal, he said, is to adapt the passive sampling technology for autonomous underwater vehicles and gliders that would deliver real-time, high-resolution predictive risk maps across the entire California Current System.

The study comes with the usual caveats that accompany preliminary modeling work: the data derive from a single long-term monitoring site in Monterey Bay, and the statistical predictions flag only a fraction of high-toxin events weeks in advance. Still, the approach demonstrates that biological interactions between predators and algae — long invisible to monitoring programs — can be converted into actionable forecasts using tools that are already in the water.