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Origins of Harmful Alga Scourge in Pacific Northwest Confirmed

Researchers have identified the oceanographic causes and routes for the harmful alga Pseudo-nitzschia in offshore waters of the Pacific Northwest. The team’s validated model shows that toxic Pseudo-nitzschia cells arrive at the coast, not from a single source (as previously thought), but from two sources, one north and one south of Washington’s beaches.

The northern source (Juan de Fuca region) occurs in late summer and fall with seasonal southward currents. The southern source (Heceta Bank) occurs in late winter and spring with seasonal northward currents. The model also confirms that the Columbia River can both inhibit shoreward harmful algal bloom transport and enhance harmful algal bloom transport along the coast. This regional model is based on extensive sampling cruises, satellite imagery, and observations from arrays and surface drifters.

Pseudo-nitzschia produces domoic acid, a toxin that accumulates in edible shellfish and can cause Amnesic Shellfish Poisoning in people who consume contaminated shellfish.

This NCCOS-funded research, also supported by the National Science Foundation, is published in the Journal of Geophysical Research: Oceans.

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