Pseudonitzschia species found in digestive tracts of northern anchovies [Engraulis mordax)

The diatom species Pseudonitzschia australis Frenguelli has been implicated as the source of the domoic acid that contaminated anchovy species in Monterey Bay, California, during 1991. In other geographic areas, as well as in laboratory cultures of isolates obtained from various geographic areas, other Pseudonitzschia species have been shown to produce domoic acid. The stomach contents of anchovies caught in Monterey Bay during the following summer were analyzed to identify and determine the abundance of each of the Pseudonitzschia species present. Pseudonitzschia species present in net-tow samples taken at the same time from Monterey Bay were also recorded. In the stomach samples, nine different Pseudonitzschia species were found, including four that have produced domoic acid either under natural or laboratory conditions. These findings illustrate the risk of possible neurotoxin accumulation inherent in the diets of the anchovies studied. The planktophagous diet of the anchovies reflected the plankton composition of the surrounding water and also demonstrates the anchovies' ability to filter pennate diatoms from the near-surface seawater.

SEM observations of bloom-forming toxic diatoms from Monterey Bay, California

In the late summer of 1991, large numbers of seabirds in northern Monterey Bay, California died after showing unusual neurological symptoms. The first suspects were dinoflagellates, planktonic algae known to produce the toxins responsible for paralytic shellfish poisoning (PSP). Although toxic dinoflagellates were found, no evidence for PSP was present. Subsequent chemical analysis of tissue and stomach contents from affected birds and from locally collected northern anchovy showed high concentrations of domoic acid. During the seabird kill in Monterey Bay, the plankton was dominated by Pseudonitzschia australis (=Nitzschia pseudoseriata) a diatom not previously known to produce domoic acid.