Predator chemical cues give weeks of warning before toxic algal blooms

Predator chemical cues give weeks of warning before toxic algal blooms

Passive resin samplers that pick up compounds released by grazing zooplankton have forecast harmful algal blooms up to seven weeks in advance in Monterey Bay.

Monitoring chemical signals from microscopic grazers could give shellfish managers up to seven weeks’ notice of harmful algal blooms (HABs) – far longer than the week or so typically offered by tracking toxins directly.

Researchers at the University of California, Santa Cruz (UC Santa Cruz), working with Northwest Indian College and Lund University, describe the approach in the Proceedings of the National Academy of Sciences (PNAS).

The method targets copepodamides, a group of polar lipids released by copepods as they graze on phytoplankton. Diatoms of the genus Pseudo-nitzschia, the main cause of HABs in the California Current System, sense these compounds and respond by increasing production of the neurotoxin domoic acid.

Copepodamides are dilute in seawater and degrade quickly, which has made them difficult to measure. The team therefore adapted Solid-Phase Adsorption Toxin Tracking (SPATT), in which porous resin beads held in mesh rings absorb dissolved compounds from the water over days or weeks.

During a 28-month campaign at the Santa Cruz Municipal Wharf, SPATT samplers captured copepodamide concentrations that correlated with zooplankton net counts. In laboratory tests, exposing local Pseudo-nitzschia strains to copepodamides produced a tenfold increase in cellular toxin production.

Statistical models built on the copepodamide data predicted Pseudo-nitzschia blooms six weeks in advance. For domoic acid in sentinel mussels above safety thresholds, the lead time was seven weeks. Models based on domoic acid itself performed best at one week.

The copepodamide models also reduced false negatives – the most hazardous failure in seafood-safety management. They flagged 22 per cent of high-toxin events seven weeks out, compared with 14 per cent flagged one week out by conventional toxin tracking.

When domoic acid exceeds the federal threshold of 20 micrograms per gram of tissue, harvesting must stop to prevent amnesic shellfish poisoning in humans. Closures affect Dungeness crab, rock crab, razor clam, sardine and anchovy fisheries. The toxin has also been linked to strandings and deaths of sea lions, sea otters, brown pelicans and humpback whales along the Pacific coast.

Because SPATT samplers are already deployed routinely by monitoring networks, the technique could be added to existing programmes. Senior author Professor Raphael Kudela said: “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.”

The team next aims to adapt the samplers for autonomous underwater vehicles and gliders to produce real-time risk maps across the California Current System. The work was funded by the National Oceanic and Atmospheric Administration (NOAA).

Read more: http://dx.doi.org/10.1073/pnas.2604233123