We identified the oceanographic causes and transport routes for the harmful alga Pseudo-nitzschia in the offshore waters of the Pacific Northwest and improved predictability of the arrival of harmful algal blooms (HABs) on Washington and Oregon beaches from known HAB hot spots. The study area includes the Columbia River plume and potential HAB source regions off both Oregon (Heceta Bank) and Washington (Juan de Fuca Eddy).
Why We Care
Pseudo-nitzschia produces domoic acid, a toxin which accumulates in edible shellfish causing the human health syndrome Amnesic Shellfish Poisoning. Pseudo-nitzschia blooms and shellfish contamination (especially commercial razor clams) are a recurrent problem along the entire Pacific Northwest coast, especially Washington. Paralytic Shellfish Poisoning (PSP), attributed to the dinoflagellate Alexandrium catenella, caused over 100 human poisonings in central California in the late 1920s. The first incidences of PSP in Washington State were documented in the Strait of Juan de Fuca in 1942 when Native American children died after eating shellfish. Both organisms can cause devastating losses to commercial, recreational and tribal shellfisheries, commercial net-pen fish farms, and potentially wild fish harvests.
What We Are Doing
Our primary objective is to improve predictability of HAB events on Pacific Northwest coastal beaches by advancing our understanding of HAB development, dissipation, transport, and mixing processes using existing data in parallel with the latest physical and bio-physical models. The models include, for the first time, both the Columbia River plume and potential HAB source regions off both Oregon and Washington.
This project builds on the wealth of complementary information and enhanced knowledge generated from results of previous NCCOS-supported and other regional Pacific Northwest projects studying the transport and mitigation of HABs to the Washington coast from both northern and southern sources (e.g., RISE, ORHAB) and species analyses other than Pseudo-nitzschia (e.g., Alexandrium). The overriding conclusion from these studies is that lack of understanding of the effect of the Columbia River plume on cross-shelf and along-shelf transport and mixing is the greatest impediment to understanding how phytoplankton, in particular, HABs, arrive on coastal beaches.
- the Columbia River plume is a bioreactor for growth but not for toxin production,
- during downwelling winds, the Columbia River plume inhibits shoreward transport of toxic blooms,
- during upwelling winds, the Columbia River plume enhances cross-shelf transport of toxic blooms below the surface layer, and
- the Columbia River plume enhances northward transport of toxic blooms along the coast.
The project uses the Northwest Association of Networked Ocean Observing Systems (NANOOS) for model verification and also model improvement.
What We Found
The project model results demonstrate how plankton blooms develop seasonally in the two HAB hot spots and how winds move blooms to coastal beaches. In 2005, for example, model tracking from the two known HAB hotspots, one north (Juan de Fuca Eddy) and one south (Heceta Bank) off the central Washington coast, successfully hindcast observed HAB landfalls on Washington clamming beaches for that year. Model runs that include the Columbia River freshwater plume vividly illustrate how the plume location plays a vital role in determining whether or not a toxic bloom will be transported to coastal beaches or transported offshore where it can do no harm. The model now includes Puget Sound, coastal estuaries and river plumes, and extends north to central British Columbia and south to the California border. Recent model results show how upwelling intensity, or lack thereof, impedes or enhances HAB transport to the coast. Recent project findings incorporate upwelling into the model, showing how the strength of upwelling influences the transport direction of Pseudo-nitzschia.
Benefits of Our Work
This work increases our understanding of HABs and improves our ability to forecast HABs, which directly benefits a large group of government and tribal bodies with interests in coastal shellfish resources. New information on Alexandrium allows managers to shorten annual PSP beach closures. The biological model uses a new approach based on measured biological rates, providing a ten-fold improvement in forecasting skill over most existing models. The project model results encourage managers to not only factor the location of the Columbia River plume into predictions of potential HAB landfalls, but also the strength of upwelling prior to opening beaches for harvesting of razor clams.
This project is led by the University of Washington School of Oceanography in partnership with the University of California at Santa Cruz Ocean Sciences Department. The project team includes additional researchers from Fisheries and Oceans Canada’s Institute of Ocean Sciences, and from the University of Washington School of Oceanography. The project is part of the NCCOS Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) program.