Scripps Researchers Identify Neurotoxin
In San Diego Seawater For The First Time
Domoic acid, known to
animal species, found in seawater samples
By Mario Aguilera
Scripps Institution of Oceanography at the University of California,
San Diego, have documented for the first time in San Diego seawater
the presence of a neurotoxin that has been known to poison marine
mammals, birds and human consumers of shellfish.
the past few years, an increasing number of sea lions have been
found sick or dead on San Diego beaches. Many have been poisoned
by domoic acid, a neurotoxin produced by a common marine phytoplankton.
Until now, however, confirmation of domoic acid production has
occurred only further north.
Lilian Busse and Elizabeth Venrick reported that there were
moderate levels of domoic acid in the phytoplankton contained
in seawater samples collected on Feb. 18 and Feb. 25 off Scripps
Pier. The toxin is produced by a genus of diatoms called Pseudonitzschia.
Its presence coincided with a late February bloom of the species
Pseudonitzschia australis and may be related to several reports
of sea lion strandings from Malibu Beach to San Diego made during
that same time period.
the finding, researchers stressed that the risk to public health
in San Diego is low. In complementary samples of mussel tissues,
the California Department of Health Services detected six parts
per million of domoic acid. That concentration is well within
state safety guidelines. A reading of 20 parts per million would
trigger an alert from the agency to issue a public advisory.
There is no set standard for safe domoic acid levels in seawater.
"It is of great
scientific interest but is not a cause for public alarm,"
said Venrick, co-chair of the Integrative Oceanography Division
Busse agreed, adding,
"It's not that domoic acid hasn't been out there before
but it's the first time it's been tested for and detected in
seawater off San Diego."
Coincident with the
elevated domoic acid levels off San Diego, Busse identified
elevated levels at Newport Beach and San Clemente, although
these concentrations, like San Diego, appear to have been short-lived.
research team is participating in a multi-institutional monitoring
project that includes weekly samplings of local water and mussels.
Regular testing off San Diego began in October 2003. The purpose
of the endeavor is to characterize large aggregations, or blooms,
of Pseudonitzschia and another type of phytoplankton, the dinoflagellate
Alexandrium, which produces a potentially hazardous substance
take place periodically on the West Coast of North America and
elsewhere and the genus is found in most coastal marine environments.
The production of domoic acid by several species of Pseudonitzschia
is thought to be triggered by a combination of environmental
influences. It may be related to the diatom's interaction with
trace metals such as iron and copper, which occur naturally
in marine environments. The domoic acid is transferred to seabirds
and marine mammals by small prey fish, such as anchovies, which
themselves may be unaffected by the toxin. It can also be concentrated
in shellfish, including mussels and oysters.
Domoic acid was first
recognized in California after a dramatic seabird kill in 1991.
It also is known to contaminate mussels and may be transmitted
to humans with symptoms that include vomiting, diarrhea and
confusion, but have only rarely led to death.
In September 1991,
the deaths of more than 100 brown pelicans and cormorants in
Monterey Bay was linked to domoic acid poisoning. Since then,
the toxin has been associated with other deaths of marine mammals
and seabirds in Monterey and the Santa Barbara Channel.
Though this is the
first time domoic acid has been found in San Diego seawater,
the Department of Health Services has detected low concentrations
of domoic acid in the tissue of mussels on previous occasions
dating back to 1992.
The two-year project
is funded by the University of California Marine Council. In
all, researchers are monitoring more than 500 miles of California
coastline for the project. Busse said the study, which also
includes investigators from UC campuses in Santa Barbara and
Santa Cruz, will illustrate the amount of coherence among toxic
blooms along the California coast, helping determine whether
they are local occurrences or large-scale events. The study
could also establish connections between the blooms and environmental
conditions in coastal waters as well as dolphin and whale beachings.
Laura Mydlarz, a graduate
student at UC Santa Barbara, performed the chemical analysis
that led to the recent confirmation of domoic acid.
"It is not known
if the production of domoic acid is intensified or if the toxin
is spreading south from the central coast," said Busse.
"The increased frequency of reports along the coast, and
now off San Diego, may be the result of increased awareness
and better detection techniques."
This study could also
indicate whether such blooms have been on the increase in recent
years. Another component of the project is an analysis of seawater
samples collected in California waters from previous decades.
Busse said that she has found that specimens of the diatoms
that produce domoic acid have been in San Diego waters in high
abundance dating back to 1918.
Media Contacts: Mario Aguilera or Cindy Clark