Forecasting Harmful Algal Blooms

Harmful algal blooms (HABs) are a common occurrence on the Washington coast and of major concern to tribes, agencies, and recreational and commercial harvesters. Shellfish harvests of clams and oysters represent $50 million annually to the economy of the state, and closures of coastal beaches are more frequent. Most species of algae or phytoplankton are not harmful and are an important part of the food web. However, certain species, such as the diatom Pseudo-nitzschia spp., which produces the neurotoxin domoic acid and can cause amnesiac shellfish poisoning, and Alexandrium spp., which is known to cause paralytic shellfish poisoning, can be deadly. The processes that trigger these HAB events and govern their dispersal are not well known.

The Olympic Region Harmful Algal Bloom (ORHAB) project, sponsored by the National Oceanic and Atmospheric Administration (NOAA) and led by the National Marine Fisheries Service Northwest Fisheries Science Center, was started in July 2000 to investigate the mechanisms driving blooms of biotoxin-producing algae, and to examine the timing and location of events along the Washington coast. The ORHAB partnership includes federal, state, and local agencies, coastal tribes, marine resource-based businesses, public interest groups, and academic institutions.

Figure 1. SeaWiFS Ocean Color Image, August 9, 2001, Showing Enhanced Biological Production During Upwelling.

Figure 2. AVHRR Image of Sea Surface Temperature, August 9, 2001. Inset is 5-Night Composite Image for August 5-9, 2001. Juan de Fuca Eddy Shown in Red Box.

Researchers have identified an ocean feature, the Juan de Fuca eddy, as a potential initiation site of Pseudo-nitzschia spp. blooms. In the summer, wind-driven upwelling of nutrients is correlated with increased biological productivity and frequently higher levels of domoic acid. It is thought that in some years, the eddy moves onshore, carrying the domoic acid to shellfish beds.

As part of the ORHAB project, Battelle scientists are using two different satellites to track the extent and movement of the Juan de Fuca eddy: the NASA/OrbImage SeaWiFS (Figure 1) provides ocean color imagery, and the NOAA AVHRR (Figure 2) provides sea surface temperatures. Battelle is also looking at historical data to identify relationships between satellite imagery and chlorophyll concentrations, Pseudo-nitzschia spp. cell numbers, and measured toxin levels. These data, combined with modeling conducted by other ORHAB partners, are being used to determine the scenarios that result in transport of Pseudo-nitzschia spp. cells to the Washington coast.

As part of the ORHAB monitoring program, seven locations are being routinely sampled for phytoplankton cell numbers and tested for levels of domoic acid, chlorophyll, and nutrients. A series of moored buoys with sensors for temperature, salinity, and chlorophyll are deployed during the summer months to provide an accurate, ongoing record of environmental conditions.

Through the ORHAB monitoring program, a better understanding of where and when a bloom occurs is being acquired. This information, coupled with satellite imagery of sea surface temperature and chlorophyll concentrations, may allow the tracking of features leading up to a bloom event. The long-term goal is development of a forecasting tool or product that can be used as an advisory or bulletin of HAB events for coastal resource managers and tribes.

For more information contact Dr. Dana Woodruff at 360-681-3608, Dana.Woodruff@pnl.gov.