Northwest Fisheries Science Center

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West Coast HAB species

SEM image.On the West Coast of the United States, at least 5 HAB organisms are found and will be discussed here.

Pseudo-nitzschia spp.

Domoic acid is produced by diatoms in the genus Pseudo-nitzschia. Pseudo-nitzschia are long needle-like cells that form chains by overlapping the tips of their cells. At the present time it is the only diatom that has been identified that produces a marine biotoxin. What complicates this picture is that not all Pseudo-nitzschia species produce domoic acid.

Pseudo-nitzschia chain Pseudo-nitzschia

Since 1991, domoic acid, produced by diatoms of the genus Pseudo-nitzschia, has been a problem for both recreational and commercial fishers along the west coast of the United States. Initially, it had been thought that either P. multiseries or P. australis were responsible for the domoic acid contaminating razor clams, Dungeness crabs, and other fishery species. Work in our laboratory indicates that the diatom P. pungens and P. Psedudodelicatissima are also capable of domoic acid production.

In both 1997 and 1998, our team participated in a cruise off the Washington coast and found large patches or blooms of Pseudo-nitzschia diatoms. Examination of samples taken during that cruise indicated that these blooms were composed almost entirely of P. Pseudodelicatissima. Furthermore, direct analysis of water samples by a sensitive receptor binding assay indicated moderate levels of domoic acid produced by these cells.

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Alexandrium catenella

Chain of Alexandrium catenella Chain of Alexandrium

The PSP suite of marine biotoxins are produced by the dinoflagellate Alexandrium catenella and some other members of this genus. Shellfish are filter feeders, meaning that they pump seawater and concentrate phytoplankton for their food. As they take in the Alexandrium cells, they break the cells and digest the cellular material releasing the toxin into their digestive system. The toxin is then distributed to various parts of the shellfish. In some species of shellfish, the toxin is associated more strongly with the siphon, e.g., butter clams (Saxidomus giganteus), while in others it can be associated with the viscera (like the gut) or distributed throughout the clam's body tissue. Recently, it has been shown that PSP toxins can also be found in crabs and lobsters. However, in crustaceans the toxin appears most strongly associated within the viscera, primarily the hepatopancreas (the crustacean equivalent of the liver). As Alexandrium disappears from the water, mollusks and crabs eventually lose the accumulated toxins and can become safe to eat. However, fishers should always check with local health authorities as to the safety of shellfish from any particular beach.

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Heterosigma

Heterosigma akashiwo
In addition to marine toxins, the salmon aquaculture industry in Washington State has suffered large losses due to Heterosigma. The golden-brown alga Heterosigma akashiwo (Raphidophyceae) is a bloom forming organism that has been associated with massive finfish mortalities in temperate waters world wide. In the northeast Pacific both the United States and Canadian aquaculturists and researchers have sustained both economic and environmental losses. Heterosigma has been identified in these waters since monitoring programs first began in the 1960's and the first recorded fish losses in the region were from a bloom at Lummi Island in 1976. It wasn't until 1986 that $2.5 million of salmon (about 1/3 the population) were lost in Sechelt Inlet BC and in 1989 a bloom covering >7,000 km2 caused the loss of another $4 million in caged fish in BC and another $4 million off of Cypress Island WA. A 1990 bloom in central Puget Sound killed 1.3 million fish (85-100% losses in each pen) valued at $5 million as well as the endangered species white river spring chinook brood stock. Recently (1994) wild salmon have also been killed in Heterosigma blooms. In 1997 central Puget Sound experienced a massive Heterosigma bloom that resulted in over $2 million in losses for commercial salmon aqauculturists.

Diarrhetic Shellfish Poison (DSP)

As the name implies, these intoxications are relatively mild and only become serious for those with impaired health status. The toxins, called collectively the dinophysistoxins, after the causative organism Dinophysis spp. This syndrome has been reported mostly in Europe; however the organism is quite cosmopolitan and found in a variety of locations in and around North America. Monitoring and surveillance for the toxins has been difficult, but some newer methods show promise for quick tests. Because the symptoms are mild, victims rarely seek medical help and so it is difficult to assess the true incidence of this particular syndrome. What surveys that have been done on shellfish indicate that the incidence of DSP toxins is very low. Most risk management plans for DSP rely heavily on monitoring the water column for the presence of the Dinophysis cells. They are relatively easy to distinguish from other phytoplankton in the water.

Ciguatera Poisoning

Ciguatera Poisoning, also known as Tropical Fish Poisoning, does occur in the tropical waters of the Pacific Region and the Caribbean. In the Pacific, it occurs in Hawaii and the U.S. Territories (American Samoa and Guam). In some Pacific regions, Tahiti for example, the toxin levels appear to be quite high and have resulted in several deaths over the past decades. For a long time, the mortality levels for ciguatera were about 5-10% but with better medical care this value is probably dropping. Another factor that is helping to drop mortalities is that we better understand the origins and etiology of the syndrome. The toxin (ciguatoxin or CTX) is produced by the benthic dinoflagellate Gambierdiscus toxicus found on coral reefs and hard surfaces on tropical reefs. The toxin, while known for some years, was structurally characterized only within the last 20 years. The toxin has a high molecular weight and is a fat-soluble toxin. Its high molecular weight have made methods for its chemical detection and monitoring very difficult. Risk management of the toxin is therefore limited. For many in tropical areas where people depend on reef fish for subsistence, managing the risk is limited to avoiding eating the viscera and fatty tissues of the fish and relying on local knowledge concerning safe fishing areas. However, even with these precautions, incidences of ciguatera are not uncommon in tropical areas.