Pseudo-nitzschia species (Bacillariophyceae) and the domoic acid concentration in Pseudo-nitzschia cultures and bivalves from the northwestern Sea of Japan, Russia

This is the first detailed investigation of domoic acid (DA). a potent neurotoxin causing Amnesic Shellfish Poisoning. in Pseudo-nitzschia cultures and bivalves from the northwestern Pacific. The DA analysis covered a total of 9 strains of Pseudo-nitzschia and 96 samples of commercially valuable bivalves, collected during 2007-2013 in the northwestern Sea of Japan. A light and electron microscopy examination of 161 field-collected phytoplankton samples revealed six species of the genus Pseudo-nitzschia. Among them, P. pungens var. pungens, P. delicatissima, P. calliantha, and P. multistriata are bloom-forming species that can reach a high percentage of occurrence (6-21%) and a high density (>10(4) cells.L-1) in the phytoplankton. The DA toxicity of P. multistriata, P. calliantha, P. delicatissima, and P pungens var. pungens has been confirmed for the first time based on laboratory cultures isolated from the northwestern Pacific. The highest cellular DA concentration was found in cultures of P. multistriata and P. calliantha (up to 0.57 and 0.44 pg . cell(-1), respectively) isolated during their bloom events. Despite the domoic acid concentration in bivalves tissues was low and ranged from 0.01 to 0.3 mg . kg(-1) the increase of DA concentration in the mussel digestive gland samples during fall and early winter coincided with blooms caused by P. multistriata and P. calliantha. The Pearson coefficient of correlation between P. calliantha density and DA concentration in the samples of bivalve digestive glands was found to be high (r = 0.7). The correlation between the high DA concentration in the samples of bivalve digestive glands and the increase of Pseudo-nitzschia spp. density in plankton during bloom events was also confirmed using the methods of statistical hypothesis testing. The obtained results indicate a potential risk of seafood contamination in fall, which can be related with the recurrent blooms of toxic P. calliantha and P. multistriata in the study area.