Abstract
Pseudo-nitzschia multiseries produces a high level of domoic acid (DA) in culture. Significant amount of DA is also detected in P. seriata and P. australis, the latter of which causes massive death of sea lions and sea birds. On the other hand, a small amount of DA is detected in various species of Pseudonitzschia including those observed in the Japanese coastal waters. A low level of DA is also reported in a benthic species Amphora coffeaeformis. Recently, we have confirmed a significant level of DA production in a benthic diatom, which was identified as a new species Nitzschia navis-varingica. These facts show that DA distributes widel both in planktonic and benthic diatoms, though the level is different among the species. DA production of P. multiseries has been pointed out to be much affected by environmental bacteria. No DA is detected in these bacteria, suggesting that they are not involved directly in DA production of P. mutiseries. In contrast, DA production of the species with low or medium productivity was not affected much by bacteria.
