On the West Coast of the United States, at least 5 HAB organisms
are found and will be discussed here.
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](pn/images/PseudoChain.jpg)
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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.
To read more about Pseudo-nitzschia, please use the navigation
bar to the right.
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.
To read more about Alexandrium catenella, please use the
navigation bar to the right.
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 km
2 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.
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, 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.