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Toxicity, morphology and distribution patterns of three bloom-forming species of the diatom genus Pseudo-nitzschia (potential producers of the neurotoxin domoic acid and causative organisms of amnesic shellfish poisoning) from Peter the Great Bay in the northwestern Sea of Japan are presented. Pseudo-nitzschia calliantha, P. multistriata and P. multiseries bloomed in Peter the Great Bay in the fall, with abundances exceeding 106 cells l-1. This is the first report of toxicity in P. multiseries from Russian waters. Domoic acid was found in stationary-phase (days 20–35) cultures of P. multiseries isolated from Peter the Great Bay at concentrations varying between 180 and 5390 ng ml-1 or 2 to 21 pg cell-1, which is in the range reported for other isolates of P. multiseries. The Russian isolate had an increasing ability to produce domoic acid over time in culture rather than the usual trend of decreasing toxicity. No domoic acid was detected (<2 ng ml-1) in cultures of P. calliantha and P. multistriata from the same locality. The Russian isolate of P. multiseries produced gametes when mated with the Canadian strains of the opposite mating type, but they never developed into zygotes, auxospores or large initial cells. This suggests that there might be “cryptic” species within P. multiseries. However, a comparison of molecular and morphometric data between the Russian and Canadian strains showed that they indeed belong to the same species.

The lipid and fatty acid compositions of the marine diatom Chaetoceros salsugineus were investigated during the life cycle, including the vegetative and resting stages. The relative proportion of the lipid classes and their fatty acid composition varied during the life cycle. The amount of polar lipids, structural components of the cell membranes, increased rapidly in the period of the resting cell formation. Individual lipid classes were found to have a characteristic fatty acid composition. Changes in the proportion of polar lipids contributed to a difference in the total fatty acids. In polar lipids, polyunsaturated fatty acids, predominantly 16:3(n-4) and 20:5(n-3), composed up to 59 % of the total fatty acids, peaking during resting cell formation. The results suggest that in resting cells the structural components of photosynthetic and cellular membranes accumulate, thus ensuring the immediate growth and development of cells upon the return of favourable environmental conditions.

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